What the Anesthesiologist Should Know before the Operative Procedure
Anesthesia for coronary artery bypass grafting (CABG surgery) is an extremely complex subject and overlaps most of the field of cardiac anesthesia. Extensive literature has been written on this subject. This clinical decision support will be an over view of the subject. Many areas covered are mired in controversies as to what is the best. I will briefly discuss the controversies then render my opinion when the evidence based literature is inconclusive. Most recent articles with the latest references are listed at the end to provide better insight on these areas. Many areas will not have references because only 10 references can be listed on a topic of this magnitude. Many procedure in CABG surgery are based on a “this works so we will do it this way” concept, such as adequate anticoagulation for cardiopulmonary bypass (CPB).
In my clinical experience of more than 30 years I have witnessed multiple attempts at “reinventing or redesigning the wheel” in anesthesia, with the same result. So a lot of what is recommended now was in and out of favor in the past. Most of my opinions reflect a common sense approach to a problem when the evidence-based literature is lacking. A lot of literature on CABG has been published, but many are merely pro-versus-con references. In this chapter, areas in which evidence-based literature are available are documented.
As anesthesiologists, we believe that we are the most valuable persons in the operating room; however, with CABG surgery, if you do not have a good surgeon, you will have a patient who will not do well despite all your efforts. I approach patients presenting with CABG surgery with the following insights. The outcome is extremely dependent on the surgeon’s ability to revascularize the heart. Thus, assuming a complete revascularization, the post -pump and ICU period should be the easiest part of the perioperative day. Thus, we must do our best to minimize any harm to the patient until revascularization can take place.
I divide the care of CABG patients into distinctive periods: (1) preoperative evaluation; (2) precardiopulmonary bypass period or also the pre-revascularization period for off-pump CABG (OPCABG); (3) the revascularization period for OPCABG or CPB period; and (4) the post-revascularization or post-CPB period, up to the time you leave the operating room; and, finally, (5) the ICU period.
CABG surgery can be done either via the use of CPB or without the use of cardiopulmonary bypass (OPCABG). As usual, controversy surrounds which technique is better. Clinicians believed that the problems with CPB could be avoided with the use of OPCABG surgery. These problems included renal and pulmonary dysfunction, as well as neuropsychological dysfunction. Potential issues with OPCABG include revascularization, which is not as good because it involves connecting grafts to a beating heart.
Studies have yielded mixed results with regard to one technique having fewer complications than the other. The role that I see for OPCABG surgery is that it is warranted for severe aortic disease (atheroma, porcelain aorta) and prevents cannulation of the ascending aorta, in turn, preventing the risk of arterial embolization.
In the prepump or prerevascularization period, your goals should be to optimize the patient’s hemodynamics, without making the myocardium work too difficult as to promote ischemia. This is the period when vein grafts, radial artery grafts, are obtained and the internal thoracic artery (IMA, internal mammary artery) is prepared for grafting – and in CPB cases, the cannulae are placed. In reoperations, it is also the period when the heart is dissected away from the scar tissue.
One caveat in this period is fluid management. Do you restrict fluid to prevent hemodilution and not increase pulmonary permeability? Or, are you more liberal in fluid management? There are arguments to both sides. My approach is to ensure adequate urine output and, via echocardiography, an adequate preload. Then if necessary, use a vasopressor to support the blood pressure. Another controversy is: do you use crystalloids or colloids as your primary fluid? My choice is crystalloids, but it’s a minority opinion. The data does not support one or the other.
Should you maintain a cardiac index at 2 L/min/m2 or greater in the prerevascularization period is another controversy. Use of an inotrope may aid in providing adequate organ perfusion; however, this technique could detrimental because it increases oxygen demand, leading to myocardial ischemia. Global oxygen consumption is reduced under general anesthesia, permitting a cardiac index of 2 L/min/m2 or less. A normal, measured, mixed-venous saturation will reflect adequate oxygen delivery in this situation.
Should an antifibrinolytics be used to reduce the amount of perioperative bleeding? There were three antifibrinolytics used to reduce perioperative bleeding in CABG patients. All three are lysine analogs that bind to plasminogen and plasmin and inhibit the binding of plasmin to fibrinogen. The concern was that the CPB circuit and the body’s reaction to CPB caused a low-grade disseminated intravascular coagulopathy (DIC); these drugs would prevent this, thus decreasing bleeding and, hopefully, blood product administration.
All three have confirmatory studies suggesting their efficacy. Aprotinin, probably the most effective agent, was withdrawn from the market over concerns of higher incidences of renal failure and graft occlusion with its use. Tranexamic acid and amicar (epsilon amino caproic acid) are also effective. Tranexamic acid is more frequently used in Europe and Canada, whereas amicar is used in the United States. Amicar is administered at a 50 mg/kg loading dose, followed by 25mg/kg/hr, which is started pre-CPB and continued in the intensive care unit. Tranexamic acid is administered at a loading dose of 10mg/kg, with an infusion of 1 mg/kg/hr thereafter. There is institutional variability in dosages with both drugs.
One challenge throughout this type of surgery is determining: What is an adequate blood pressure? How low would you allow the blood pressure to decrease for aortic cannulation while the patient is on CPB, especially since the patient has some form of arterial stenosis throughout his or her body?
The answers are very difficult; obviously, if you lower the blood pressure and see signs of inadequate organ perfusion, then allow the blood pressure to rise. Unfortunately, we often do not have immediate signs of inadequate perfusion. Then it becomes a risk/benefit issue. Low BP leads to bad organ perfusion versus high BP, which can lead to an aortic dissection or increased bleeding. This is where knowing and trusting your surgeon allows for better analysis of what to do. When in doubt, discuss with the surgeon and arrive at a joint consensus as to what is best for this particular patient, given the particular circumstances you are in at the time.
In the pre-bypass period, the patient’s blood sugar should be controlled to about a range of 150 mg/dL. This is another controversy in how “tight” blood sugars should be controlled perioperatively. Studies have shown poor neurological outcomes, wound healing, and increased infection rate when blood sugars are elevated. But how tight should control be? The tightness of control has to be balanced against the other potential, unrecognized hypoglycemia in an anesthetized patient, with resultant poor outcomes.
My approach is to try to keep the blood sugars in the 150 mg/dL range (not too tight control) and, hopefully, prevent extreme rises in blood sugars. I tend to start an insulin infusion pre-pump on diabetic patients, as CPB triggers extreme insulin resistance that is very difficult to treat even when the blood sugars are normal or only slightly elevated. In this situation, I will start an insulin drip at 1 unit per hour and will check frequent sugars. Most institutions have published guidelines on glucose levels versus insulin bolusing and infusion rates. Once on CPB, sugars rise quickly, but I believe having the insulin infusion already running decreases the peak values that would occur.
Regardless of whether the procedure is done with or without CPB, in most cases the patient will require a sternotomy. The surgeon will use a saw to open the sternum. This part of the procedure will cause a sympathetic response accompanied by hypertension and tachycardia. This can be treated with vasodilators, beta blockers, and/or deepening the anesthetic level. You can do any combination of these to control the hemodynamics. Soon after sternotomy, the surgeon will be opening the pericardium, another challenging time. Besides the hypertension and instead of tachycardia, the patient may have a reflex bradycardia. Again, treatment is tailored to the effect you want to achieve. The other type of off-pump CABG is PCABG, a MIDCABG where a double lumen tube and an anterior-lateral thoracotomy is done.
With either on-pump CABG or OPCABG, the patient is anticoagulated. This is an important step that requires (1) that you give an adequate dose of heparin and (2) that you make sure the heparin made it to the blood by aspirating back on the central venous line. You want to ensure adequate anticoagulation before CPB heparin binds with antithrombin III, and this complex counters the effects of thrombin, factor IX , X, and other proteins.
With the OPCABG procedure, the anticoagulation is to prevent graft clotting. The amount of anticoagulation needed for off-pump surgery is surgeon-dependent, and surgeons will suggest an initial dose of heparin, followed by where they would like the ACT (activated clotting time) to be. With the use of CPB, the initial dose of heparin is between 300 to 400 units per kg weight of the patient. Note that the clinical perfusionist also primes the pump with heparin. At our institution, 10,000 units are added for an adult pump. You can proceed with CPB when the ACT is 480 seconds or more. I use an initial dose of 400 units /kg, as each patient has a variable response to heparin, and I find that the higher dose more consistently allows for an ACT of more than 480 seconds.
What is so magical about an ACT of 480 seconds? This is based on a study that showed there was no micro-clot formation in the cardiopulmonary bypass circuits with an ACT higher than 480 seconds. If ACT is lower than 480 seconds, then you have a patient with heparin resistance. Heparin resistance is where, for a given dose of heparin, ACT does not rise to the expected level – thought to be due to a relative decrease in antithrombin III (ATIII), which binds heparin to create the anticoagulation effect. The clinical way to deal with heparin resistance is to redose with heparin to see if a response occurs; if not, then the clinician should provide AT III, either with fresh frozen plasma (source of ATIII) or with an antithrombin III concentrate.
There are many types of cannulation for CPB, but the basic type involves a cannula in a major artery and another in a central vein. The venous cannula withdraws blood from the patient, and then the blood is passed into the CPB machine where two events occur. First, blood can be heated or cooled and, second, blood is passed through a membrane where oxygen can be added and carbon dioxide removed. Inhaled anesthetic agents can also be delivered. Thus, the CPB machine provides ventilation of the patient, as well as flow to provide adequate organ perfusion.
Despite all the advances in the circuitry of the CPB machine, it is still a foreign surface and the patient’s blood will react to it. Over time, this will lead to blood and protein destruction. The clinical perfusionist adds mannitol to the pump prime to assist urine output and to attempt to decrease the incidence of renal failure while on the nonpulsatile flow of CPB. The surgeon will often arrest the heart to provide a quiet heart to operate on. The heart is typically arrested by the application of an aortic cross clamp on the aorta then is given an infusion of a cardioplegia(i.e., a mixture of blood ,electrolytes, and potassium [to arrest the heart]) solution. This solution is delivered via two mechanisms: antegrade in the aorta, whereby the solution then flows down the coronary arteries, and retrograde via the coronary sinus. The solution is infused via the coronary sinus, then it goes retrograde from the coronary veins to the distal coronary arteries. The retrograde cardioplegia provides additional myocardial protection to areas where the antegrade cardioplegia cannot get by the coronary artery blockage.
While on the nonpulsatile CPB, another area of concern arises: At what perfusion pressure and at what cardiac index should you flow? CPB is an artificial state and organ autoregulation is often impaired. So a higher perfusion pressure and higher flows may be warranted. But doing this may cause more bleeding, more trauma to the blood, and, possibly, intracranial bleeds. Therefore, discussion and compromise with the surgeon is often the rule. Various institutions have different protocols that they follow. Is one better than the other? This subject is controversial.
Weaning from CPB consists of adequate reperfusion time of the myocardium, which was chemically arrested so that the operation can be performed. This reperfusion period, typically 30 minutes, allows the cardioplegic solution, as well as the metabolites that have built up in the arrested heart, to be washed out. The amount of time for reperfusion is very surgeon-dependent; however, I believe 30 minutes is optimal.
The actual weaning process is much similar to performing an ACLS (advanced cardiac life support) protocol: A, B, and C. The most important thing that you can do is to ventilate the patient. Inflate the lungs manually to get a feel for lung compliance as well as to visually see the lungs inflate and eliminate any atelectasis. Then place the patient on the ventilator. The surgeon will often ask you to hold ventilation post pump in order to fix some bleeding since the patient’s inflated lung can interfere with the surgeon’s field. This is a time to be very diligent because failure to restart ventilation can be catastrophic. I keep one hand on the reservoir bag of the anesthesia machine and never let it go until mechanical ventilation is restarted. The other advice is to never silence the ventilator alarms for apnea. Diligence is imperative.
After ventilation, work with and check off a checklist: Are the electrolytes normal? Usually, ionized calcium is low and potassium from the cardioplegia is high. So you may see the consequences of electrolyte abnormalities on myocardial function as well as electrical activity. Next, look at the temperature and make sure that your patient is at least at 36.5 °C via a bladder temperature.
Is the hematocrit adequate? If the surgeon actively cooled the patient on CPB, then rewarmed for weaning from CPB, the patient may have temperature variations, depending on which organ group is being measured. I use bladder temperature because it is a more slowly reperfused and warmed area than the pulmonary artery catheter that measures blood temperature, which is quickly rewarmed. If the temperature is 36.5 °C, then most of the patient’s tissues have been rewarmed.
Last, the determinants of myocardial performance are looked at: contractility, heart rate, rhythm, preload, and afterload. I use direct visualization of the heart, transesophageal echocardiography, ECG, and pulmonary arterial pressure values to help guide my management. I use the upstroke of the arterial line waveform tracing as an indication of myocardial performance. A steep up-slope indicates a high dP/ dT, which indicates good ventricular function; if you get a poor upstroke, you will need to start an inotrope.
You can also look at the echo after the patient is off CPB for LV and RV function. Also, you can look into the surgical field and look at the RV free wall and the LV apical function. You can look at the ECG to see the heart rate and rhythm, which are often affected by the metabolic, surgical, and temperature derangements. A heart rate of 70 to 90 beats per minute with an atrial kick is recommended. Atrial kick can contribute 10% to 40% of the patient’s cardiac output.
Obtaining a correct heart rate and rhythm can be accomplished either by correcting the underlying problem or via A (atrial) or AV (atrial-ventricular) pacing. Often, the heart is in a junctional /slow rhythm from the potassium cardioplegia. In this situation, I will administer calcium chloride IV at up to 1 gram to reverse this effect on conduction. It is also an inotrope and will increase both left and right ventricular performance.
Calcium chloride was taken out of the ACLS protocols but can be very useful here. Calcium chloride does have side effects, so the decision is one of risk versus benefit. The surgeon can place pacing wires directly on the right atrium or right ventricle. Visualization of the surgical field, as well as TEE, can give an indication of preload and of whether there is a need to administer volume. Initially, this volume is administered from the CPB machine reservoir, then via fluid administration through IVs.
Afterload is simply the mean arterial pressure measurement if the patient has good LV function. If LV function is good and MAP is low, add a vasoconstrictor; if MAP is high and LV function is good, add a vasodilator. If the patient has bad LV function, first, improve it; then, look at the MAP and treat accordingly.
If you are doing an OPCABG, you will miss the experience of CPB and replace it with what I term a “roller coaster ride” of trying to keep the patient alive while the surgeon does the coronary bypasses on a beating heart. The surgeon typically approaches the bypasses by placing the first graft to the most important area of coronary insufficiency, which is usually the LAD territory. This area is also where the least manipulation of the heart is required when performing the distal anastomosis. The surgeon then has to position the heart for each of the subsequent bypasses by packing, pressing, or holding the heart in very unnatural positions.
To perform the grafts, the surgeon uses a variety of devices to assist him or her in positioning the heart. Often the heart is jacknifed so the apex sticks upward out of the chest, with the patient in a severe Trendelenberg position. As can be imagined, there will be significant hemodynamic compromise with this manipulation. The anesthesiologist’s goal during this period is to maintain adequate perfusion pressure, preload, and contractility. This goal is accomplished through the early use of vasopressors, such as norepinephrine, phenylepinephrine, or vasopressin, inotropes (epinephrine), and using intravenous nitroglycerin to provide coronary vasodilatation. Early and quick intervention is required to prevent cardiovascular collapse during these manipulations.
Once off CPB and while all the cannulae are in, you can give back the remaining volume in the pump. I use this time to establish a post-pump Frank-Starling curve. I administer the volume via the aortic cannula and watch to see if the MAP rises. If it does, then there is room on the Frank Starling curve; if it does not and the the patient’s blood pressure decreases, the patient can be placed in a reverse Trendelenburg position to decrease the preload. Either way, you can use the OR table on tilt reverse or Trendelenburg to get the pump volume into the patient and control the MAP. Once the venous cannula is removed and drained, this would be the last of the pump volume to be given back to the patient prior to aortic decannulation.
What if you cannot give back this volume due to poor ventricle function? In this situation, the remaining volume can be processed through a cell saver (remove excess volume), but give back red blood cells. Then, the protamine can be administered to reverse the heparin. Protamine binds to the heparin and inactivates it.
Do you start the protamine administration with the cannulas in or out? The risks of giving protamine with the cannulae in are clot formation and embolization to various organs, depending on which cannula has the clot. I have seen clot formation with as little of 10 mg of protamine administered (very rare). The surgeon weighs this risk versus a potential protamine reaction and the need to recannulate. Most surgeons I work with will give a test dose of protamine after the venous line is removed and then, in a minute, remove the aortic line before any clot can form. A few surgeons will remove all cannulae, then give the protamine test dose.
Post pump, the surgical goals are to control any bleeding as well as to insert chest tubes and close the sternum with wires. The anesthesiologist’s goal is to maintain hemodynamics, as mentioned above, as well as to reverse the heparin with protamine. Every institution has its own protamine reversal protocol, including the use of a heparin protamine titration curve, which looks at the heparin dosing versus the ACT, and plots the amount of protamine to be administered.
From a safety standpoint, protamine should be administered via an infusion of more than 20 minutes to avoid rare but potentially deadly side effects as a result of rapid administration. Using a heparin/protamine titration curve is probably the most effective method. Heparin has a half-life of around 1.5 hours, which is prolonged with hypothermia. Thus, some clinicians do manual calculations of the amount of heparin left and give 1 to 1.3 mg for every 100U of heparin remaining.
Clinically, if I cannot have a heparin titration curve done, then I start with an empiric dose of 250 mg of protamine and check an ACT. If it is close to the preheparin ACT, then there should be little heparin left. Surgeons frequently ask for another dose of protamine. Is this a problem? Too much protamine can cause bleeding (rarely) and there are side effects to protamine, including anaphylactoid/anaphylactic reactions, hypotension (most frequent), and pulmonary vasoconstriction. So I try to titrate to effect and will give an additional dose if requested: if the ACT decreases, then the decrease is a good development; if the ACT increases, then I worry about the anticoagulant effect of protamine or the patient going into DIC. These issues are all eliminated if the clinician uses heparin titration curves.
In the post-pump or post-revascularization period, frequent problems to watch for include compression of part of the heart or retraction of the heart by the surgeon while he or she looks for bleeding or places sutures to stop surgical bleeding. This will cause significant hemodynamic compromise, mainly hypotension during compression, then hypertension when the compression is released. More important for the anesthesiologist is the request to hold ventilation while the compression and surgical search and repair is going on. On rare occassions, the anesthesiologist may forget to restart ventilation, with resultant hypercarbic acidosis, leading to pulmonary hypertension, and, if prolonged, to apnea, hypoxia with brain injury, and cardiac arrest.
My approach is, when apneic, ALWAYS have one hand on the reservoir bag on the anesthesia machine and do not remove it until ventilation is reestablished. These periods of apnea can lead to microatelectasis, so remember to inflate the lungs fully and add PEEP (positive end-expiratory pressure) starting at 5 cm H2O. There also is controversy regarding the use of 100% oxygen or a lower concentration of oxygen during the procedure. Clinicians worry about absorption atelectasis and oxygen toxicity with high oxygen levels. Studies have been nonconclusive, so I use 100% oxygen that is decreased to 60% on arrival at the CVICU, depending on pulse oximeter readings. I do this to ensure safety while transferring the patient to the CVICU, when an ambu bag is frequently the transfer ventilation of choice.
In the post-revascularization period, it has been documented that with TEE, the pulmonary veins may have residual air in them. The air is thought to come from air migrating from the lungs to the pulmonary veins while on CPB. Up to 12 hours post bypass, this air may be released into the ascending aorta. The most frequent spot in which the air embolizes is down the right coronary artery (due to the supine position of the patient, the most superior artery). With this embolization, cardiovascular collapse can occur. Frequently, the clinician will see a slow sag in BP, unresponsive to fluids, then inferior wall ST segment changes, and then ventricular fibrillation or cardiac arrest. In this scenario, aggressive and early treatment with phenylephrine can override this by maintaining a coronary perfusion pressure. This treatment maintains the blood pressure while flushing the occluding air through the coronary circulation. This event occurs most frequently when the patient is being transferred from the operating room table to the transfer bed (it dislodges any residual air). This is the time when there is a lot of movement and little attention is paid to the patient’s blood pressure, the ventilator is disconnected, and transducers are being moved. Suddenly, you see that the patient’s blood pressure is low, and, with all the movement going on, wonder whether such is real or not. Treat aggressively, then find out.
Chest closure causes numerous hemodynamic changes with chest wall compression of the heart. This causes a change or a decrease in compliance, where higher filling pressures reflect lower intravascular volumes and a decrease in cardiac index; often, simple volume administration corrects the problem. If you are concerned about giving more volume, perform a simple test for volume responsiveness, which is a tilt test. Place the patient in Trendelenburg position and if the mean arterial pressure rises and cardiac index improves, the patient needs more volume. Besides the compliance, change chest closure can cause obstruction of one of the coronary grafts, especially with an inexperienced surgeon. You will see hemodynamic compromise, usually unresponsive or minimally responsive to vasopressors, inotropes, and volume. You may see ECG changes of ischemia and new regional wall motion abnormalities on TEE. Reopening the chest usually resolves this problem; the surgeon must reposition the graft before chest closure is reattempted.
ICU management will be briefly discussed later. ICU management is an extension of the operating room management.
1. What is the urgency of the surgery?
What is the risk of delay in order to obtain additional preoperative information?
Obviously, the risk of delaying surgery is death or a myocardial infarction with its associated consequences. Most patients with presumed coronary artery disease are worked up by cardiology and have cardiology interventions such as angioplasty, thrombolysis, and stent placement before surgery is considered. The patients that do not fit into the cardiology intervention categories, elect surgery over these interventions, or fail these interventions are referred to cardiac surgery. Medical therapy is also an option, but most patients elect to have the “plumbing fixed.” Patients that are unstable are urgently or emergently referred for surgery.
The timing of surgery is dependent on multiple factors, including type of disease – left main or left main equivalent – where an increase in occlusion or atheroma embolization can cause major areas of myocardial infarction or death. If the patient has unstable angina relieved by a nitroglycerin tablet, with a lesser myocardial area of risk, then he or she is in a lower risk category. In these cases, delaying surgery for several days for further work-up or simply scheduling the patient for the next available surgical time is possible. Whereas someone with a left main coronary artery lesion or left main equivalent should probably be operated on within 24 hours. Most of these decisions are usually made without the anesthesiologist becoming involved. Medical therapy, which can be effective, has much lower costs associated with it, especially in elderly patients.
Emergent: Emergent surgeries include surgeries involving the above-discussed left main or left main equivalent coronary artery disease that is not amenable to cardiology intervention; complications of a cardiology intervention as coronary artery dissection; iatrogenic occlusion; or coronary artery perforation, with or without pericardial tamponade. Remember: these patients will be coagulopathic, secondary to the use of thrombolytic agents, aspirin, and clopidogrel, or associated agents. In this situation, relieving the angina and maintaining hemodynamics until placement of CPB is important. Often, just the induction of general anesthesia will relieve the markers of myocardial ischemia, such as ECG changes in addition to beta blockers and nitroglycerin infusions. Evolving infarctions with possible signs and/or symptoms of congestive heart failure/pulmonary edema, ventricular septal defects, ruptured infarcted papillary muscles with mitral regurgitation, and intractable arrhythmias, with or without intra-aortic balloon pump placement, are a second group of emergent CABG patients. These patients are extremely unstable and often arrive in the operating room intubated. The anesthesiologist’s goal is to try to stabilize the patient with inotropes, vasopressors, and vasodilators to ensure adequate oxygen delivery to the patient until the patient is placed on cardiopulmonary bypass. Correction of the 3 Hs (hematocrit, hypoxia, and hypercarbia) often helps and often improves hemodynamics. CPB is your endpoint. Once the patient is on CPB, the surgeon has time to fix the problem that, regardless of anything else, will determine how the patient does. It allows the anesthesia team time to catch up and to optimize the patient for weaning from CPB.
Urgent: Urgent operations are often performed because of much less severe symptoms than emergent operations, but these must be done before the patient can be discharged from the hospital.
Elective: Elective cases are the easiest if the cardiac surgeon performs a complete revascularization. These patients can be operated on either via the off pump or on pump surgical technique. There is controversy about perioperative beta blockade and the government’s requiring documentation on every CABG patient receiving beta blockers. Quoting in favor of preoperative beta blockers: “[O]ver a 60% reduction in postoperative atrial fibrillation in 30 studies showing a benefit.” Other studies revealed no benefit. Because this is a government mandate for isolated CABG study, the use of perioperative beta blockers will continue.
2. Preoperative evaluation
I am most concerned about the patient’s airway. Why? Large numbers of cases of unexpected difficult airways are seen in cardiac operating rooms. Dr. Sergio Bustamante of our department has found that, currently, 5% of our patients have unexpected difficult airways; which is much higher than what has been reported in the literature. This high incidence of unexpectedly difficult airways has led me to alter my anesthetic induction technique, as I discuss later.
These patients are being operated on for coronary artery disease. Thus, knowing the extent of the disease, areas of myocardial risk, and whether there are distal areas in which to obtain an anastomosis will help clinicians successfully bypass a blockage and improve the patient’s overall ventricular function.
Has the CAD caused a myocardial infarction? If so, what is the ejection fraction? Has a major portion of the heart been infarcted? Has the infarct caused mitral regurgitation or a ventricular septal defect (VSD)? Are there stents in the coronary arteries? If so, are they bare metal or drug eluting? What anticoagulation is being provided for the stents and how should this medication be altered to provide anticoagulation without excessive perioperative bleeding? Is the patient on a long-acting platelet inhibitor? If so, which one and how long must the surgery be delayed to allow for an adequate perioperative bleeding risk. These are questions that must be answered preoperatively.
Hypertension is another common disease associated with patients with coronary artery disease. You need to look at the range of blood pressure readings that the patient has been recording, what antihypertensive medications they are taking, and whether they experience any side effects from the medications.
Check to see if the patient has left ventricular hypertrophy (LVH) from chronic hypertension. The LVH will affect your anesthetic management, owing to the alteration in the pressure-volume relationship. The pressure-volume relationship will be shifted upward and to the left. Thus, the patient will have elevated filling pressures but may be hypovolemic. The preoperative echocardiogram will not only identify whether the patient has LVH but also ventricular systolic/diastolic function and wall segment abnormalities. In addition, any other cardiac abnormalities or valve abnormalities can be identified by a preoperative echo. The preoperative echo will also assist in determining whether the patient has atheroma in the ascending or descending aorta, thus, influencing cannula placement for CPB, partial cross clamp placement for proximal vein anastomosis, and whether an intra-aortic balloon pump can be placed without dislodging an atheroma.
Chronic renal disease (CKD) is another preoperative issue that has major perioperative implications. CKD patients have a high incidence of CAD and frequently require CABG surgery. The nature of the CABG surgery, regardless of whether it is on pump or OPCABG, will in general worsen the renal function. Thus, for a dialysis patient, unless it is emergent surgery, the dialysis must be timed presurgery to coincide so that surgery occurs at an optimal time. Thus, the nephrologist, surgeon, and anesthesiologist must discuss and coordinate the timing to ensure the best possible patient outcome. Normalization of the patient’s volume status, acidosis, and hyperkalemia are the most frequent parameters to look for. A more challenging scenario involves a patient with CKD who does not require dialysis. In this situation, you will try to minimize any insult to the kidneys. There is nothing to offer the patient in terms of renal protection other than to maintain a preload and perfusion to the kidneys. Clinical perfusionists frequently add mannitol to the pump prime to promote urine output on the nonpulsatile CPB. Mannitol may have some renal protective effects, but, currently, there is nothing else that can provide renal protection.
Diabetes mellitus, especially type II, is one of the most common diseases affecting us today. Its relationship with renal disease, CAD, PVD, and hypertension is well established. Diabetes affects all the organ systems. Diabetes has a multitude of complications that can worsen with CABG surgery, including diabetic neuropathy, infection, and nephropathy. Perioperative control of blood sugars is important to reduce neuropsychological complications, infections, and poor wound healing.
Peripheral vascular disease (PVD) is another condition that coexists with the all these diseases affecting patients with CAD. It is important to know where there are associated lesions in the various arterial systems for two reasons: (1) to maintain adequate pressure and flow to the organ, passed the blockage, such as the brain or intestines; and (2) to identify sites where the surgeon and anesthesiologist should not cannulate. For the anesthesiologist, blockage in an axillary artery will lead to lower blood pressures in that arm if the arterial line is placed there. Problems that concern the surgeon were outlined under the atheroma section above.
Cigarette smoking with its associated chronic obstructive pulmonary disease/chronic bronchitis is associated frequently with CABG surgery. It is a causative factor in the development of CAD. Most patients that arrive in the operating rooms have this problem already maximally medically managed. The problem is that in these patients, CPB may initiate an inflammatory response that can trigger acute bronchospasm and, rarely, acute pulmonary hypertension post CPB. The combination of the surgery, which is quite extensive, and patient pulmonary reserve, which can be marginal, can lead to a long ICU stay. These patients often experience failure to wean from the ventilator, pulmonary atelectasis, and pulmonary infection despite aggressive respiratory therapy.
Obesity is another associated problem that is frequently encountered with CABG surgery. Obesity affects all organ systems in the body; thus, a thorough investigation is necessary. Special perioperative issues include possible airway issues, poor wound healing, pressure ulcers, poor respiratory mechanics (restrictive), delayed gastric emptying with reflux symptoms, and ambulation problems leading to deep vein thrombosis.
Iatrogenic anemia is a phrase that I use with regard to patients who have been admitted to the hospital for work-up of their CAD and have their CABG surgery during the same admission. The frequent blood draws plus the post-cardiac catheterization cause groin hematomas, sometimes leading to several units of blood loss, which may be reflected only by a slightly lower hematocrit. Hematocrit may be slightly lower because these patient, by the nature of their hospitalization, are often volume-depleted so that their hematocrit does not accurately reflect their true volume status. For example, on the day of surgery, their HCT may be 34 (39 a week ago), and after induction and some volume repletion of 800 cc, their next HCT could be 29. This HCT would reflect the true red blood cell volume in the patient.
Medically unstable conditions warranting further evaluation include the coexisting diseases listed above. Three problems that require immediate work-up and possible correction before elective surgery include (1) bleeding, most frequently from the gastrointestinal tract; (2) infections, as urinary tract infections; and (3) transient ischemic attacks or recent changes in mental status (strokes).
Delaying surgery may be indicated if any of these conditions exist, unless it is an emergent CABG, where the benefits outweigh the risks. These risks include (with regard to bleeding) worse bleeding intraoperatively since patients are anticoagulated; (with regard to the CNS) if a hemorrhagic CNS event is involved, then worsening of the CNS problem occurs. If a CNS ischemic event is involved, then perhaps worsening of this ischemic event will occur during the surgery. Infection is another risk-benefit issue, and often for UTIs, a 24-hour course of antibiotics is instituted before surgery, with a full course of antibiotics to continue.
3. What are the implications of co-existing disease on perioperative care?
This topic was discussed in earlier sections.
b. Cardiovascular system:
As previously discussed, patients for CABG surgery are probably the most evaluated patients, with regard to their cardiovascular status.
Very valuable information can be obtained from the patient’s history and physical (H and P). From the history, you can gain information on medications, used as well as their effects on the patients – for instance, the effects of beta blockers and sublingual nitroglycerin. The patient’s history of exercise tolerance is valuable not only for intraoperative but also for postoperative management. The patient’s level of exercise tolerance may influence the amount of physical and respiratory therapy that may be needed. With the physical exam, you will look at findings that may guide further testing, as well as obtain an overview for looking at potential arterial line, central line, and peripheral intravenous sites.
In addition to the information obtained from the 12 lead ECG and chest X-ray, there are numerous additional tests. Patients undergo stress testing (providing information on limits of tolerable heart rates and blood pressure); an echocardiogram revealing ventricular function, potential intra- and extracardiac problems, as well as valvular and aortic abnormalities; and cardiac catheterization, revealing again ventricular function and the extent and location of the coronary artery disease. If a patient presents urgently or emergently, he or she will have, at least, a cardiac catheterization, ECG, and chest X-ray for your evaluation. An intraoperative echocardiogram can be performed. The same is true for someone with hypertension, as discussed in detail earlier.
COPD and its association with smoking was discussed earlier. Again, a review of the patient’s previous health records is important, as well as information on whether the patient has quit smoking. If so, how long ago? Remember that it takes several weeks of smoking cessation before airway reactivity is decreased and 48 hours of cessation before carbon monoxide levels are normalized. The patient should be medically managed to the maximum. This can be delineated by a careful H and P. Usually, pulmonary function tests (PFTS) or bedside PFTs are not needed. I prefer bedside PFTs in patients who have marginal pulmonary reserve obtained from the H and P. These patients may be a difficult wean from the ICU ventilator, and the PFT values may be useful in their postoperative care.
Reactive airway disease (asthma)
In patients for CABG, asthma, not associated with smoking, is not very common, but the approach to these patients is the same as the approach for COPD. The patient may experience severe bronchospasm with light anesthesia, during placement of the endotracheal tube, and when emergencing from anesthesia. The other highest risk period for bronchospasm is while the patient is on CPB, with its proinflammatory effects. The first sign is hyperinflated lungs when ventilation is reestablished when the patient is weaned from CPB. This topic was discussed earlier.
In both of these conditions, I continue patient preop inhalers and medications up to the time of surgery, and, prior to induction, I will have the patient undergo an inhaler session.
Renal disease, especially CKD, was previously discussed. All patients for CABG surgery will have exposure to a contrast agent with cardiac catheterization and thus will have potential worsening of renal function; the same is true in patients with renal disease. As mentioned in the previous discussion, maintaining volume status is important. Thus, drinking fluids is encouraged in patients without congestive heart failure and oliguric renal failure. For dialysis patients, unless for emergent surgery, the dialysis must be timed presurgery to coincide so that surgery occurs at an optimal time.
The nephrologist, surgeon, and anesthesiologist must discuss and coordinate the timing of surgery to ensure the best possible patient outcome. Normalization of the patient’s volume status, acidosis, and hyperkalemia are the most frequent parameters to look for and correct prior to surgery. Frequently, patients undergo dialysis and are immediately brought to surgery. In these patients, the hyperkalemia and acidosis are corrected. The volume status is frequently hypovolemia and so care with the induction of anesthesia in a potentially hypovolemic patient is warranted.
A phenomenon of dialysis disequilibrium is occasionally encountered where the patient’s mental status is transiently altered post dialysis. If this occurs, surgery is delayed until the patient’s mental status returns to baseline. This syndrome must be differentiated from a stroke or TIA, as these patients frequently have generalized atherosclerosis and are at risk for ischemic insults. Perioperatively, potassium-containing solutions should be eliminated. Remember that the surgeon will use a potassium-based cardioplegia solution to arrest the heart, if the procedure is to be performed on CPB.
Hyperkalemia may be encountered post CPB. This condition can be treated temporarily with calcium, glucose-insulin, and bicarbonate administration. If necessary, dialysis on CPB can be performed. Thus, CKD with dialysis may be an indication for an off OPCABG.
Patients with CKD frequently have impaired platelet function, and post-bypass DDAVP (desmopressin) in doses of 0.3 mcg/kg can be administered to treat post-pump bleeding thought to be due to platelet dysfunction. CKD patients also have anemia, with hematocrits in the low 20s. There have been studies where patients were given erythropoietin preoperatively to increase the red blood cell mass; the CABG was then performed later. There are two problems with this approach: first is the cost of therapy (approximately $5000.00); perioperative administration of packed red cells is much less expensive but obviously has disadvantageous effects. Second, it delays surgery for 1 to 2 months and with it comes the associated risk of delayed surgery.
Esophageal reflux with its associated risk of aspiration on induction of anesthesia is probably the most frequently encountered GI issue.
Continuation of the antireflux medication, including the morning doses as well as NPO status after midnight, is warranted. Unless the patient has severe reflux with nausea, I usually do not prescribe bicitra orally due to the frequent nausea and possible vomiting that can accompany it. These symptoms may induce a myocardial ischemic episode in the patient.
CABG patients are frequently elderly and have peptic ulcer disease or various lower GI lesions that can bleed. Thus, looking for signs or symptoms or occult GI bleeding is important, as these patients are anticoagulated during surgery and an occult bleed can become major bleeding intraoperatively.
With the common use of transesophageal echocardiography (TEE) for CABG surgery, a history of dysphagia should be investigated for an esophageal pathology. Passage of the TEE probe is associated with esophageal injury perforation or bleeding. This risk could be increased in patients with esophageal strictures, masses, varicosities, etc. The use of TEE in CABG surgery is not a category I indication.
Neurological issues were briefly discussed earlier and are further discussed below.
Any acute CNS event first needs to be treated according to the acute stroke protocol to see if thrombolytic therapy is warranted. This evaluation by the stroke team will determine the type of stroke: embolic/ischemic versus hemorrhagic. The former is treated with thrombolytics; the latter is not. Either way, the CABG surgery will be postponed. Surgery is rescheduled for later, when the patient is stable. A more common decision scenario is when critical carotid and coronary disease present together, and a decision has to be made regarding which procedure should be done first. The feasibility of stenting the carotid and/or the coronary lesions depends on the capabilities of your institution. If this is not feasible, there have been many studies showing the efficacy of doing a combined procedure. In this scenario, the carotid lesion is done first, the incision is packed and covered, then the CABG is performed. After this procedure is done, the neck incision is closed. Obviously, during the carotid portion of surgery, maintaining cerebral perfusion pressure is important. Often, one procedure is chosen to be done, then the other procedure is performed at a separate surgery. Why? From an outcome standpoint, it has never been very clear to me. Correcting one lesion but leaving the other has potential serious consequences.
With any chronic CNS issue, it is important to determine that the process is stable and not an acute or chronic process. CABG surgery, whether on CPB or off, can worsen neuropsychological functions in patients and may worsen any chronic process. There is some controversy over the use of benzodiazepines in these patients: some studies have shown worst neuropsychological outcome in patients receiving these agents, whereas other studies have not. Personally, I use midazolam in this patient population for its amnesia and anxiolytic effects. If an individual has had a stroke, then monitoring neuromuscular blockade should be done on the normal functional side of the patient.
Diabetes mellitus was previously discussed.
Again, it is important to document the extent of the disease. Diabetes affects every organ system in the body. CABG surgery can lead to worsening of any organ function. Thus, the combination of the disease with surgery can be very harmful to the patient. Blood sugar control is important, as complications will rise with poorer chronic control of blood sugars.
The question is: When would you cancel surgery? Saya patient has blood sugars that are out of the norm for him or her. This elevated blood sugar needs to be investigated. One frequent cause would be an undiagnosed infection, such as a urinary tract infection, tooth abscesses, upper respiratory tract infection, infected skin ulcer or lesion, pneumonia, etc. Before an elective procedure, the infection should be completely treated and blood sugars returned to the patient’s normal level range. Obviously, diabetic ketoacidosis can occur in this situation.
Preoperatively, I continue the patient’s medications as prescribed, including continuing oral meds the morning of surgery. Metformin should be withheld, according to the package insert, because its continued use may cause iatrogenic lactic acidemia. This condition is rare, and a retrospective study at my institution showed no difference, whether it was held or not.
How you continue insulin therapy is usually institution-based, and as long as the glucose is controlled and atrogenic hypoglycemia is avoided, the method of administering insulin therapy does not matter. I usually try to avoid administering long-acting insulin preparations after midnight the night before surgery and use a sliding scale insulin until the patient arrives at the operating room area. At that time, an insulin infusion is started and titrated throughout the perioperative period. Once the patient is taking oral fluids in the ICU, the infusion is stopped as the endocrinologist restarts the patient’s usual diabetic therapy with breakthrough coverage.
The reason I avoid the long-acting insulin preparation, especially the day of surgery, is two-fold . First, the patient is NPO and with even a reduced dose of long-acting insulin can become hypoglycemic; second, the patient’s skin and subcutaneous area will have altered absorption while under anesthesia and experience peripheral cooling. This may result in erratic absorption during the case, potentially causing large fluctuations in blood sugars.
g. Additional systems/conditions that may be of concern in a patient undergoing this procedure and which are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
All systems/conditions were previously outlined and discussed.
4. What are the patient's medications and how should they be managed in the perioperative period?
Herbal medications should be stopped prior to surgery.
In general, most herbal medications cause an increase in bleeding, especially when taken with other anticlotting agents. Herbal medications that fall into this category include garlic, vitamin E, ginseng, ginkgo, and feverfew.
Ephedra can cause blood pressure elevations, along with ginseng, goldenseal, and licorice.
Valerian, St. John’s worts (unproven), and kava-kava may increase the effects of anesthetic agents.
Echinacea and kava-kava may cause liver injury.
h. Are there medications commonly seen in patients undergoing this procedure, and for which should there be greater concern?
Diuretics: In general, diuretics cause a chronic loss of potassium and a contraction alkalosis with chronic use. Thus, patients frequently present with low serum potassium but also low intracellular potassium. The low potassiums are responsible for perioperative arrhythmias. These diuretics also cause a chronic magnesium loss, which will compound the arrhythmia problems. Diuretics are withheld the morning of surgery.
Angiotensin inhibitors can cause profound intraoperative hypotension but also may have important anti-inflammatory effects and beneficial effects on endothelial function. I give it the morning of surgery, as there have been some case reports of a rebound phenomenon when the drug is withheld.
Clopidogrelis an antiplatelet drug that is used to prevent coronary stent thrombosis. It has a long half-life, and for regional anesthesia, the recommendation is to stop it 7 days before surgery. For emergent CABG surgery, the patient will have increased bleeding due to platelet inhibition.
Warfarin is frequently used if the patient has a mechanical prosthetic valve or is in chronic atrial fibrillation. Warfarin inhibits the vitamin K-dependent coagulation factors. It is long-acting; for elective cases, patients on warfarin will be admitted to the hospital, where warfarin will be stopped and intravenous heparin started. The reversal of the warfarin can be measured by measuring serial prothrombin times.
Glucophage, an oral antiglycemic drug, has been associated very rarely with unexplained lactic acidosis and recommendations are to withhold it for several half-lifes prior to anesthesia. A retrospective study showed no effect if taken the morning of surgery.
Beta blockers have a special place in CABG surgery. Studies (STS [Society of Thoracic Surgery] data base) have shown that CABG patients receiving beta blockers had lower 30-day mortality than patients that did not receive beta blockers. Thus, quality of care indicators now require all CABG-only patients to receive beta blockers – unless there is reason not to administer a beta blocker, such as bronchospastic disease and low ejection fraction, which must be documented. The irony is that the smallest dose of a beta blocker can be administered even if it does not have a clinical effect, and this indicates compliance.
i. What should be recommended with regard to continuation of medications taken chronically?
Cardiac: Withhold diuretics because they can be given intravenously in the operating room. Statins have been shown to be cardiac protective and anti-inflammatory and should be continued.
Pulmonary: Continue all medications, including inhalers.
Renal: Withhold diuretics.
Neurologic: Continue all chronic medications.
Antiplatelet: Clopidogrel and other similar agents should follow the recommendations noted above. With regard to aspirin, numerous studies have shown that low-dose aspirin used for CAD can be continued throughout the entire perioperative period. In fact, the benefit of prevention of graft and coronary thrombosis outweighs the risk of bleeding.
Psychiatric: Continue all medications. Care must be given to patients on MAO (monamine oxidase) inhibitors, as the use of indirect-acting adrenergic agents can cause an exaggerated response. In the past, it was thought that stopping the MAOI 14 days prior to anesthesia was necessary; however, recent studies have shown that patients can be safety anesthetized if smaller doses of direct-acting adrenergic agents are carefully titrated. Again, a risk-benefit ratio must be weighed: the risk of continuing MAOI versus stopping the MAOI and worsening the patient’s depression. MAOIs are often started after a patient has failed other antidepressive medications; they are the patient’s last hope.
j. How to modify care for patients with known allergies
First, you have to check if the condition is, indeed, a true allergy versus a side effect, such as nausea. Then, if it is an allergy, avoid the drug and substitute an appropriate agent. Most frequently, a patient will present with a penicillin allergy. A third-generation cephalosporin (cefuroximine 1.5 gram every 4 hours for 48 hours) is used as antibiotic prophylaxis for this procedure and there is a 20% cross reactivity in allergic response with patients allergic to penicillin, given a cephalosporin. You can either give the cephalosporin and see if you get a reaction or use vancomycin 1gram IV every 12 hours for 48 hours. Vancomycin, when levels are elevated, can cause renal dysfunction. Due to federal regulations defining quality care, antibiotics must be given within 1 hour prior to incision, and documented accordingly.
Heparin allergy or heparin-induced thrombocytopenia (HIT) was previously described, where heparin, usually due to its chronic administration, causes the development of an antibody to heparin. HIT develops in between 5% to 30 % of patients receiving heparin. The patient may experience a range of symptoms.
HIT 1, a mild disease, is just a mild decrease in platelet count ad is thought to be due to the proaggregatory effect on heparin in platelets. HIT 2 is more severe and antibody-mediated. When this disease is considered, a hematologist needs to be involved in performing various tests to confirm the diagnosis. Patients going to the operating room will require another type of anticoagulation, as direct thrombin inhibitors are used. (This subject matter is beyond the scope of this chapter.)
k. Latex allergy – If the patient has a sensitivity to latex (e.g., rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
Currently, most products used in the operating room are latex free. You should confirm this matter with in your institution. One item that is not latex free is the pulmonary artery catheter. The balloon contains latex; a special PAC with a latex-free balloon should be used. This catheter is stiffer and more difficult to pass. In the past, we had a latex-free cart that contained everything needed to manage a latex-allergic patient; now that cart does not exist. Remember that on multidose vials, the membrane that the needle punctures may be latex.
l. Does the patient have any antibiotic allergies
This topic was discussed in an earlier section.F.
m. Does the patient have a history of allergy to anesthesia?
Documented. You need to avoid all triggering agents, such as succinylcholine and inhalational agents, and make sure that the anesthesia machine has had the vaporizers removed from the machine and been vented so no residual agent is in the circuit; usually, 6 hours of high air flow (>6 liters/minute) will accomplish this.
Proposed general anesthetic plan: In this situation, a total intravenous technique can be used; make sure that the intravenous agents are delivered while on CPB.
Ensure the malignant hyperthermia cart is available. Everyone should be well-versed with the malignant hyperthermia protocol. Remember: It takes time to draw up dantrolene. A dedicated individual may have to be assigned to do this.
Family history or risk factors for MH: In this situation, since we can easily provide a total intravenous anesthetic, I would proceed as above with a patient with known MH.
Local anesthetics/muscle relaxants
With regard to local anesthetics, this is not an issue as regional anesthesia will not be used. If the patient has had a lidocaine allergy, then amiodarone can be used as an antidysrhythmic. With regard to allergy to muscle relaxants, there are two classes, depending on chemical structure. Depending on which relaxant caused the allergy, you can use the other class of agents or not use a muscle relaxant at all.
5. What laboratory tests should be obtained and has everything been reviewed?
Because of the comprehensive nature of the work-up in general for CABG surgery, patients undergo basic hematology, complete electrolyte panel, coagulation panel, and a complete metabolic panel. These panels are useful not only in identifying preoperative problems but also in providing a baseline in case of postoperative problems.
Age and gender do not affect which tests are obtained preoperatively other than documentation that a female patient is not pregnant. The same tests are obtained for every patient.
Hemoglobin levels: This is a procedure associated with a potential for large blood loss. It is routinely obtained along with a platelet and white blood cell count.
Electrolytes: A complete panel is obtained for all the prior discussed indications.
Coagulation panel: Normally a PT, PTT, and platelet count is obtained.
Imaging: These tests were previously discussed.
Other tests: Other tests are obtained, depending on the patient’s other associated diseases. For instance, a patient that is hypothyroid and on replacement therapy will get a thyroid panel.
Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
With regard to the type of anesthesia for CABG surgery, worldwide, 99.9% of these surgeries are performed under general anesthesia.
Regional anesthesia alone (thoracic epidural) has been successfully done and reported in several Eastern European studies as well as India.
More frequently used than regional anesthesia alone is general anesthesia combined with regional anesthesia (thoracic epidural or intrathecal narcotics).
The main problem with the use of a combined regional/general or regional technique is the potential for epidural hematomas, as these patients are fully heparinized. This disadvantage has not been proven, but in the United States, it equates to medical legal liability, whether it be true or not. Many anesthesiologists are unwilling to risk legal action to do a combined technique.
The other problem with a purely regional technique is that although it has been successfully done, it requires a T1-C7 upper level. Thus, adequate ventilation may be hard to obtain. In addition, a full sternotomy is performed, and one or both pleural spaces are entered in a spontaneously breathing patient. So the effect is a loss of negative pleural pressure. Then, while on CPB, depending on the sweep of the CPB machine (removes carbon dioxide), the patient can breathe while the heart is arrested and while the surgeon is trying to operate on a still surgical field. In the legal medical legal climate of the United States, despite the possibility of doing the anesthetic this way, I do not see this happening.
Most CABG surgeries are done in the supine position. One exception (the MID CABG) is using an anterior-lateral thoracotomy to do an off-pump LIMA to LAD graft. In this situation, a double lumen tube is used to isolate one lung. Care is taken in padding the arms; as in many institutions, both arms are tucked beside the patient’s body to allow better operating conditions. The most frequent peripheral nerve injury is an ulnar nerve injury. This can result from bad positioning but also from overzealous use of the IMA retractor and sternal retractors.
Other common nerve injuries may be due to injury to the phrenic nerve or recurrent laryngeal nerve by the surgeon, as both nerves are near the heart – outside or attached to the pericardium. Thus, if a patient has these injuries, it can be from something the anesthesiologist did, but, more likely, it is related to the surgery itself. It is often hard to differentiate the cause.
As stated above, I do not see a strict regional anesthetic routinely performed for CABG surgery. But I do see a combined regional-general anesthetic being used elsewhere throughout the world.
The major concern with a regional technique as a thoracic epidural is the potential for epidural hematoma with the full anticoagulation. But is there any benefit for doing this? Numerous articles showing a decreased incidence of atrial fibrillation, decreased pulmonary complications, and improved pain satisfaction scores have been published by Dr. Nick Scott of Glasgow, Scotland. Other investigators’ studies, such as those of Dr. Mark Chaney of Chicago, have shown no benefit. From a medical legal standpoint, I believe this technique will not catch on – not that the technique will not offer some advantages. I am most intrigued by the reduction of atrial fibrillation that has been reported with perioperative thoracic epidural use.
Other investigators have used lumbar spinals with intrathecal narcotics. They have used the much smaller spinal 25- or 26-gauge needles in the lumbar area (no spinal cord at this level, so if an epidural hematoma, it may not cause any neurological sequel) to improve the safety profile. Studies show excellent postoperative pain relief. But again, medical legal issues are probably the biggest barrier to growth of the combined technique.
Peripheral nerve block
Surgeons have done local infiltration of local anesthetics to decrease pain with success. The use of intercostal nerve blocks would require bilateral T1 to T12 blocks that would require toxic doses of local anesthetics.
General anesthesia is by far the most frequent technique for CABG surgery. Induction of anesthesia for a patient with CAD has always included the maintenance of hemodynamic stability with minimal fluctuations. Blood pressure must be in the patient’s normal range and heart rate must be keep low so that the myocardial oxygen supply versus demand remains balanced. Some studies have shown that the more episodes of myocardial ischemia perioperatively, the worse the outcomes.
In the past, most clinicians used a “high dose narcotic” technique. With this technique, 50 to 100 µg/kg of fentanyl with a muscle relaxant are administered to the patient. For maintenance, you would either give additional narcotics or add an inhalational agent. This provides excellent hemodynamic stability but at the cost of possible intraoperative awareness as well as a potential prolonged intubation.
With the advent of “fast track cardiac anesthesia,” and the drive to move patients quickly but safely through the perioperative period, the high dose technique fell out of favor. Short-acting induction agents and limiting the total amount of narcotics replaced the high dose technique. Thus, most clinicians today use a “poly-pharmacy” induction approach. An induction agent plus small doses of fentanyl, +/- lidocaine or benzodiazepines would be used.
This approach is what I used until we encountered a high and rising rate of difficult airways in our cardiac operating rooms over the past several years – now at 5%. The “poly-pharmacy” approach may make waking the patient up difficult in a cannot-intubate/cannot-ventilate scenario. It does provide fairly good hemodynamic control though. Use of esmolol to control tachycardia and intravenous boluses of nitroglycerin to control hypertension on induction have replaced the poly-pharmacy approach in my practice, as well as in awake fiber optic intubations.
Does it matter what agents you anesthetize a CABG patient with? No! If you know the pros and cons of the agents you use and can treat any of the con effects, then it does not matter.
In terms of both induction agents and muscle relaxants, what you use may depend on what is available. Currently, thiopental is unavailable in the United States. Over the past 2 years, propofol, succinylcholine, pancuronium, and thiopental all have been in short or no supply. Etomidate has been the drug of choice of everyone, except me, in my department. It provides very good cardiovascular stability in a poly-pharmacy approach. If used in a patient with normal ventricular function and without supplemental narcotics, you will see hypertension and tachycardia (unless beta blocked). Etomidate also can cause myoclonus, and for this reason, I do not use it. It also may cause adrenal suppression, even with a single dose.
If the patient has myoclonus and you cannot ventilate him, do you give a muscle relaxant? What if you do give the muscle relaxant and you still cannot ventilate the patient? Now you are in a scenario where – if you cannot intubate, then what? You have progressed well down the ASA’s difficult airway algorithm. This is a reason why I do not use etomidate.
Propofol and thiopental are excellent induction agents, with hypotension and decreased cardiac output as side effects. As long as you know this, you can give the patient a vasoconstrictor or inotropic agent as necessary.
Due to potential airway issues, I use succinylcholine in all my inductions, unless there is a contraindication. The reason for this is that I use a monotherapy induction agent, such as propofol, which is short-acting, then establish ventilation, and then use succinylcholine to facilitate intubation. If it is a difficult intubation and I need to wake the patient up, I can easily do so. I use vasopressors, dilators, and beta blockers as necessary to control the hemodynamics.
The important point is any induction technique is appropriate as long as you are aware of and can treat any untoward consequences.
With regard to maintenance of anesthesia, any technique can be used safely. There is a concept that exposure to inhaled anesthetic agents may protect the myocardium when exposed to an ischemic insult because of their ability to mimic ischemic preconditioning. All three inhaled agents have this property; desflurane has sympathetic-stimulating properties that make it harder to use. Intravenous infusions of propofol do not have this ischemic preconditioning property.
Currently, I use isoflurane as a maintenance agent because it is effective and inexpensive. From a historical perspective, just after isoflurane was released, there were a number of articles on isoflurane – that it could cause a coronary artery steal situation and should not be used in patients with coronary artery disease. Coronary steal is where its use would cause blood flow away from a myocardial ischemic area. Over time, this issue has been proven to be false.
Special monitoring for CABG surgery
In addition to the standard monitors, patients for CABG surgery need their blood pressure monitored constantly and during periods of nonpulsatile flow; thus, an arterial line (A line) is placed. Most institutions place the arterial line in one of the radial arteries. This works well except, occasionally, you may see inaccurate measurement after hypothermic CPB, where the radial A line is measuring blood pressure that is much lower than the central aortic pressure. This is thought to be due to a decrease in the forearm’s vascular resistance. This lasts for about 20 minutes to 1 hour post CPB. If this happens, temporary measurement of the aortic pressure can be done until the discrepancy is resolved. Other institutions will use femoral or brachial arterial lines to eliminate this potential problem. My institution uses brachial arterial lines.
The feared complication of brachial arterial lines is brachial thrombosis. Several studies have shown that this complication does not occur when the patient is placed on CPB and fully heparinized. With regard to femoral arterial lines, there is an issue with keeping the area around the A line clean in the groin area.
With the use of multiple infusions, including many that are vasoactive agents, a central venous line (CVP) is placed for these operations. It is also used for monitoring. Central venous pressures can be taken with a CVP or with a pulmonary artery catheter (PAC), with which you can monitor pulmonary artery pressures, pulmonary occlusion pressure, and cardiac output. The placement of the central lines is usually done after induction and intubation, unless the central line is needed for IV access or the patient is extremely ill; then, it will be used to guide a safe induction. With the use of transesophageal echocardiography (TEE) in these cases, a PAC is not needed for intraoperative management; however, it is useful for postoperative management. The use of PAC is a debated subject because, in general, its use has not been proven to alter outcomes; however, PAC availability does help in the making of many decisions in the ICU, especially at night.
There are many cerebral monitors on the commercial market; however, their efficacy has not been established.
6. What is the author's preferred method of anesthesia technique and why?
What prophylactic antibiotics should be administered?
A third-generation cephalosporin (cefuroximine 1.5 gram every 4 hours for up to 48 hours) is used as antibiotic prophylaxis for this procedure. SCIP measures state that the antibiotics should be continued for at least 3 doses after surgery. For cardiac surgery, it is extended to 48 hours postoperatively. If there is an allergy to the cephalosporins, then use vancomycin 1 gram IV every 12 hours for 48 hours. Vancomycin, when levels are elevated, can cause renal dysfunction. Due to federal regulations defining quality care, antibiotics must be given within 1 hour prior to incision and documented accordingly.
What do I need to know about the surgical technique to optimize my anesthetic care?
Most of this information is discussed in the first part of the chapter. The first item to be decided on is the procedure: an on-pump CABG or an OPCABG. If an OPCABG, then is it to be done through an anterior lateral thoracotomy with a double lumen tube or supine with a full sternotomy. If an anterior lateral thoractomy, will it be a robotic or nonrobotic procedure? Regardless of the approach, the procedure can be divided into three phases, discussed earlier in the chapter. The first phase is the pre-revascularization phase; the second is the revascularization phase, and the third is the post-revascularization phase. These phases were discussed earlier.
What can I do intraoperatively to assist the surgeon and optimize patient care?
Ways to intraoperatively assist the surgeon were discussed earlier: the anesthesiologist’s job is to keep the patient alive and the patient’s organs perfused while the surgeon performs the operation. This may sound trite, but every case is similar to doing CPR; it is resuscitation. The anesthesiologist monitors and supervises blood pressure and hemodynamic control, and ventilation control to allow an adequate surgical operating field. Control and correction of the electrolytes, blood sugars, coagulation and anticoagulation, and fluid and blood product administration also are the anesthesiologist’s responsibilities.
What are the most common intraoperative complications and how can they be avoided/treated?
Intraoperataive complications are all life-threatening.
Cardiac arrest: Every CABG surgery if on CPB case (weaning from CPB) involves the resuscitation of the heart. Remember what was previously discussed: (i) Airway: make sure the endotracheal tube is in the correct position and the ventilator is working. (ii) Make sure you are adequately ventilating the patient. (iii) Address the circulation with all the determinants of myocardial performance (preload, afterload, contractility, heart rate, and rhythm).
Bleeding: Bleeding can be multifactorial. It may be from a surgically correctable problem. It may be from the CPB, where platelets are destroyed and clotting factors are low. It may be from residual heparinization or, last, it can be a DIC (disseminated intravascular coagulopathy). Treatment is directed at the cause. Obtaining an ACT and clotting studies, as well as a TEG thromoelastograph, will help to determine the cause. Remember the 5 Ps of bleeding (prolene, platelets, plasma, protamine, and patience [pack the heart and remove the retractor and wait 15 minutes]). Packing/patience allow contact activation of the clotting factors to occur. Prolene refers to surgically correctable bleeding.
Low cardiac output: It can arise from many different causes, and the treatment is based on the cause. It can be mechanical from surgical manipulation or compression of the heart with chest closure. Other causes include a low preload state (hemorrhage), high afterload state, too slow or too fast heart rate, or dysrhythmias. It may be from intrinsic myocardial dysfunction, where an inotrope will be needed. No inotrope has been found to be better than the other. In choosing an inotrope, do a comparison of the effects of the drug versus the hemodynamic situation that you want to correct. In the open heart surgery arena at my institution, epinephrine is the primary iontrope used because of its combined beta and alpha effects. Milrinone is the second drug utilized. Milrinone has a different mechanism of action. It is a phosphodiesterase inhibitor that increases myocardial contractility and reduces afterload, both in systemic and pulmonary circulations. Norepinephrine (alpha with some B1 receptor activity) and vasopressin are my vasoconstrictors of choice. Dopamine and dobutamine cause more tachycardias and lead to a higher incidence of postoperative atrial fibrillation than epinephrine in this patient population and, thus, I do not use them .An intra-aortic balloon pump (IABP) can be used to reduce afterload while augmenting a coronary perfusion pressure. An IABP can generate about 1.9 L/min cardiac output. As a last resort, a ventricular assist device (VAD) or extra corporeal membrane oxygenation (ECMO) can be used.
Myocardial ischemia/infarction: Identifying the cause will direct the treatment modality. The ischemia can be from low blood pressure, with resultant low coronary perfusion pressure. The treatment for low coronary perfusion pressure involves raising the blood pressure via a vasoconstrictor. It may be from mechanical compression of the graft, which can be treated by relieving the compression. This may be as simple as allowing the graft to lie in a different position or regrafting the vessel. It may be from debris (atheroma) or intra-cardiac air going into a coronary artery or graft, and the treatment is to maintain the perfusion pressure with a vasoconstrictor. Tachycardia can be a cause, which can be treated with a short-acting beta blocker such as esmolol. Coronary vasospasm is another cause, which can be treated with nitroglycerin and calcium channel blockers. An intra-aortic balloon pump can also be utilized, as it mechanically maintains afterload while decreasing preload.
Arrhythmias: Again, the recurring theme is to identify the cause, then treat it. Causes may be ischemia, mechanical (air or debris down the conduction system artery), or electrolytes (low potassium, low magnesium acidosis). Treatment is according to the ACLS protocol.
Protamine reaction: Usually, administering protamine too rapidly can result in hypotension – such as with the administration of morphine. This can be treated with volume administration, ephedrine or phenylephrine, and stopping the protamine infusion. The next type of reaction can be anaphylactoid/anaphylactic. The treatment would be similar to that of any anaphylactic reaction: stop the drug, administer volume, treat with epinephrine and vasopressors. The last type of reaction is a severe pulmonary hypertensive crisis with right heart failure. When it fails, the right heart – which normally gets its perfusion in both systole and diastole – now receives it only in diastole like the left ventricle. So the goals for approaching
right heart failureare to maintain an adequate perfusion pressure, afterload reduction of the RV (vasodilate the pulmonary artery [avoid hypoxia, hypercarbia, and acidosis]), and inotropic support. Aggressive support is needed, as outlined above, with epinephrine and vasopressors, milrinone to support the right heart, and perhaps inhaled nitric oxide (pulmonary vasodilator). After the patient is stabilized, should the protamine be readministered in any of these reactions? I would not in the last two reactions; however, in the first, I would give the protamine slower, and watch. In the last two reactions, I would let the residual heparin wear off. The half-life of heparin is about 90 minutes under normothermic conditions.
One important point to remember in CABG surgery: You have the ultimate backup, CPB. If nothing is working, the patient can be placed on CPB until the problem is identified.
Cardiac complications: See earlier discussion.
Pulmonary: Bronchospasm and pulmonary edema (permeability type) can result from the patient’s being on CPB. The bronchospasm can be treated in the traditional ways: make sure the endotracheal tube is not on the carina or in a main stem bronchus; suction the lungs to remove any secretions, then use inhaled beta 2 agonist and inhaled anticholinergics; deepen the anesthesia; use IV epinephrine and steroids (6 hours to any effect). Again, you can return to or let the patient stay on CPB until the brochospasm is resolved. The pulmonary edema that can occur post pump is quite difficult to treat. While the patient is on CPB, you will see the endotracheal tube fill with pink frothy secretions. Make sure that this is not part of a transfusion reaction. After the initial suctioning to make sure there is no obstruction or thick secretions, continued suctioning is not useful. PEEP is added and titrated to try to minimize further pulmonary edema. Often, levels of 15 to 20 cm H20 are needed. Titrate the PEEP to “best PEEP,” which controls the pulmonary edema without compromising the hemodynamics. Unless the PEEP works or the edema spontaneously resolves, little can be done except to keep the patient alive until the pulmonary edema resolves. Steroids are used in this scenario, without any data to support their usefulness. Furosemide is often given for its diuretic effect. Remember that if both these conditions are unresolved, the patient cannot be adequately ventilated and oxygenated. Extracorporeal membrane oxygenation (ECMO) is the next alternative. ECMO may buy you time until the problem reverses itself.
Neurologic: The most serious complications are neuropsychological issues, embolic stoke, and diffuse cerebral encehalopathy. Perpheral neuropathies and phrenic nerve injuries were discussed earlier and are further discussed below.
One of the most frequent comments of families whose loved ones have undergone CPB is: “You know grandpa is not the same since his operation.” General anesthesia, longer anesthetic times, and patient age relate to the severity of neuropsychological changes. There is numerous research in the area but as yet, not on prevention or treatment strategies. Patients can recover, especially the younger ones. Patients for CABG have generalized atherosclerosis and all have some degree of aortic manipulation that can cause an embolic stroke. In addition, air can be entrained into the pulmonary veins from the lungs and pass into the systemic circulation while on CPB. This air can cause a stroke.
TEE and epiaortic scanning, done with chest open, have been very useful in identifying and determining the location of atheroma and air. Once the atheroma areas are identified, the surgeon can alter the surgical approach so as not to dislodge the plaques. In addition, CPB cannulae are modified and filters placed on the aortic cannula to prevent embolic events.
Diffuse cerebral encephalopathy is a grave diagnosis, which is usually diagnosed via CAT scan, when the patient fails to awaken from anesthesia. It is thought to be due to a myriad of issues, including prolonged poor CNS perfusion and diffuse shower of emboli. The outcome is poor when this diagnosis is made. In addition, patients may experience cerebral bleeds perioperatively from the heparinization, with associated berry aneurysms or weakened CNS vascular walls. Again, the outcome is poor.
b. If the patient is intubated, are there any special criteria for extubation?
With the advent of fast track cardiac anesthesia, there has been a push to extubate patients, either in the operating room or within 4 hours of arrival in the intensive care unit (ICU). The parameters used in the extubation of these patients are the same as those used in any general anesthesia case; however, you must also consider whether the patient is hypothermic, the amount of chest tube drainage, the hemodynamic stability, and any surgical concerns.
Whether to extubate in the operating room or in the ICU has been a concern that I still ponder. I believe that early ambulation and extubation are important, but reintubation to return to the operating room is also an issue. I favor transferring the patient, intubated, to the ICU and then, once everything is stable, proceeding with rapid weaning and extubation. If you take the patient to the ICU with this approach, please keep in mind the neuromuscular blockade status of the patient. Often, patients are transferred to the ICU paralyzed but not sedated. Sedation is withheld to early extubate the patient, but the status of the neuromuscular blockade is overlooked.
c. Postoperative management
All CABG patients go to the ICU postoperatively. Many hospitals have special units or sections of the ICU unit dedicated to “fast track” the patients. The typical stay for a uncomplicated CABG is 1 to 2 days. Once stable and the chest tubes are removed, the patients are transferred to the step-down unit. One of the most frequent causes for either readmittance to the ICU or delayed leavingfrom the ICU is postoperative atrial fibrillation(AF). AF can occur in 5% to 30% of post-op patients, and costs the health-care industry billions of dollars a year. There are many studies trying to find therapies to prevent the onset of AF. (A discussion on this subject is beyond the scope of this chapter.)
What analgesic modalities can I implement?
After uneventful general anesthesia, patients, once extubated, can use IV PCA (patient-controlled analgesia) and PRN narcotics. When patients start taking oral fluids, then their pain meds are switched to opioids with acetaminophen.
What are common postoperative complications, and what are some ways to prevent and treat them?
In addition to the above-mentioned intraoperative complications, which can occur postoperatively, cardiac tamponade is common in the first 24 hours. It often occurs in a scenario of declining urine output , low CO, low MAP, and increasing PA and CVP pressures despite increasing fluids and inotropic support. The diagnosis can be quickly made with echocardiography, either TEE or TTE. Postoperatively, the myocardial function, in general, declines due to edema and inflammatory reactions that occur during surgery, affecting the myocardium. The maximum effect occurs around 9 to 12 hours after CPB and can persist for a day or two. Often, the patient has good myocardial performance and then, overnight, will require inotropic support. (AF was discussed earlier.)
What's the Evidence?
Baba, T, Goto, T, Maekawa, K, Ito, A, Yoshitake, A, Koshiji, T. “Early neuropsychological dysfunction in elderly high-risk patients after on-pump and off-pump coronary bypass surgery”. J Anesth. vol. 21. 2007. pp. 452-8.
Gold, JP, Torres, KE, Maldarelli, W, Zhuravlev, I, Condit, D, Wasnick, J. “Improving outcomes in coronary surgery: the impact of echo-directed aortic cannulation and perioperative hemodynamic management in 500 patients”. Ann Thorac Surg. vol. 78. 2004. pp. 1579-85.
Knapik, P, Nadziakiewicz, P, Urbanska, E, Saucha, W, Herdynska, M, Zembala, M. “Cardiopulmonary bypass increases postoperative glycemia and insulin consumption after coronary surgery”. Ann Thorac Surg. vol. 87. 2009. pp. 1859-65.
Stadnicka, A, Marinovic, J, Ljubkovic, M, Bienengraeber, MW, Bosnjak, ZJ. “Volatile anesthetic-induced cardiac preconditioning”. J Anesth. vol. 21. 2007. pp. 212-19.
Hogue, CW, Palin, CA, Arrowsmith, JE. “Cardiopulmonary bypass management and neurologic outcomes: an evidence-based appraisal of current practices”. Anesth Analg. vol. 103. 2006. pp. 21-37.
Shroyer, AL, Grover, FL, Hattler, B, Collins, JF. “On-pump versus off-pump coronary-artery bypass surgery”. N Engl J Med. vol. 361. 2009. pp. 1827-00.
Scott, NB, Turfrey, DJ, Ray, DA, Nzewi, O. “A prospective randomized study of the potential benefits of thoracic epidural anesthesia and analgesia in patients undergoing coronary artery bypass grafting”. Anesth Analg. vol. 93. 2001. pp. 528-35.
Chassot, P-G, van der Linden, P, Zaugg, M, Mueller, XM, Spahn, DR. “Off-pump coronary artery bypass surgery: physiology and anaesthetic management”. Br J Anaesth. vol. 92. 2004. pp. 400-13.
Raghunathan, K, Connelly, NR, Kanter, GJ. “Epsilon-aminocaproic acid and clinical value in cardiac anesthesia”. J Cardiothor Vas An. vol. 25. 2011. pp. 16-19.
Mehta, Y, Kumar, S. “ICU care: new horizons for critical care in cardiac surgery”. Indian J Crit Care Med. vol. 8. 2004.
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- What the Anesthesiologist Should Know before the Operative Procedure
- 1. What is the urgency of the surgery?
- What is the risk of delay in order to obtain additional preoperative information?
- 2. Preoperative evaluation
- 3. What are the implications of co-existing disease on perioperative care?
- b. Cardiovascular system:
- c. Pulmonary:
- d. Renal-GI:
- e. Neurologic:
- f. Endocrine:
- g. Additional systems/conditions that may be of concern in a patient undergoing this procedure and which are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
- 4. What are the patient's medications and how should they be managed in the perioperative period?
- h. Are there medications commonly seen in patients undergoing this procedure, and for which should there be greater concern?
- i. What should be recommended with regard to continuation of medications taken chronically?
- j. How to modify care for patients with known allergies
- k. Latex allergy - If the patient has a sensitivity to latex (e.g., rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
- l. Does the patient have any antibiotic allergies
- m. Does the patient have a history of allergy to anesthesia?
- 5. What laboratory tests should be obtained and has everything been reviewed?
- Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
- 6. What is the author's preferred method of anesthesia technique and why?
- What prophylactic antibiotics should be administered?
- What do I need to know about the surgical technique to optimize my anesthetic care?
- What can I do intraoperatively to assist the surgeon and optimize patient care?
- What are the most common intraoperative complications and how can they be avoided/treated?
- What analgesic modalities can I implement?
- What are common postoperative complications, and what are some ways to prevent and treat them?