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* From the Division of Trauma/Critical Care, Department of Surgery, Los Angeles County + University of Southern California Medical Center, Los Angeles, CA.
Correspondence to: Howard Belzberg, MD, FCCP, LAC + USC Medical Center, 1200 N State St, Room 9900, Los Angeles, CA 90033-4525; e-mail: belzberg{at}hsc.usc.edu
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Abstract |
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 TOP Abstract IntroductionScope of the Problem...Risk Factors for Cardiac...Preoperative Diagnostic Goal:...Therapeutic InterventionsReferences |
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Introduction |
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TOPAbstractIntroductionScope of the Problem...Risk Factors for Cardiac...Preoperative Diagnostic Goal:...Therapeutic InterventionsReferences |
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While the cardiac care units developed, there was a growing ability to maintain patients with general anesthesia during and after surgery. Ventilators and other life-support techniques used in the operating room made their way to the recovery room, which ultimately gave rise to the surgical ICU.
With the development of invasive hemodynamic monitoring and advanced imaging techniques, the ability to evaluate cardiac function has progressed significantly. We now can visualize the architecture of the chambers, valves, and arterial supply. More importantly, we can evaluate the function of the heart under circumstances of stress, variable volume, and demand.
We can now not only monitor and identify cardiac function and problems but also intervene to control cardiac function. Interventions for both short-term and long-term control of cardiac status are available in a wide variety of circumstances.
A cardiac tune-up of the preoperative patient is an attempt to reduce complications and improve outcome. It should bring to bear the diagnostic, monitoring, and therapeutic interventions available to reduce the risk of cardiac and extracardiac complications. These complications may arise from some combination of the surgical intervention, the surgical stress associated with the procedure, the anesthetic risk, and the recuperative period.
Estimation of the risk for a given patient in a specific clinical situation must be individualized. Despite extensive anecdotal reports and some significant efforts at prospective trials, the risks and benefits of preoperative management of cardiac function still must be determined on a case-by-case basis.
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Scope of the Problem (Epidemiology) |
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TOPAbstractIntroductionScope of the Problem...Risk Factors for Cardiac...Preoperative Diagnostic Goal:...Therapeutic InterventionsReferences |
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In addition to direct complications associated with coronary artery disease leading to myocardial infarction, a large number of extracardiac complications in the perioperative period can be due to cardiac dysfunction or can be minimized if cardiac function is managed aggressively. In the presence of active congestive heart failure, there is an increase in the incidence of perioperative cardiac and extracardiac morbidity.6 7
Organ systems that are subject to dysfunction if cardiac impairment occurs include renal,8 CNS, GI, and hepatic. For example, renal failure associated with surgical intervention is 80 to 90% due to acute tubular necrosis. While acute tubular necrosis has many causes and is almost always multifactorial, low flow to the renal system is frequently a major contributing factor. Low flow to the GI system has been associated with ischemia and necrosis of the small and large intestines. While large prospective studies of the impact of reversing cardiac dysfunction are limited, some studies of patients with carotid artery disease have shown reduced complication rates when coronary artery bypass grafts are performed preoperatively.9
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Risk Factors for Cardiac Complications Postoperatively |
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TOPAbstractIntroductionScope of the Problem...Risk Factors for Cardiac...Preoperative Diagnostic Goal:...Therapeutic InterventionsReferences |
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Patients with clinical symptoms of unstable angina are at increased risk of perioperative myocardial infarction, a 28% incidence, and acute congestive heart failure. The perioperative surge in catecholamines and changes in coagulation pattern13 increase the risk of acute myocardial infarction14 in the perioperative period.
Valvular Heart Disease: Patients with valvular heart disease require particular attention to the risk factors associated with both their anatomic abnormalities and their physiologic adaptation to their disease states.
Severe aortic stenosis carries the greatest risk for noncardiac surgery15 due to the high incidence of sudden death (15% in asymptomatic patients and 20% in patients with prior symptoms). Severe aortic stenosis leads to a 14-fold increase in sudden death16 due to the potential for severe decrease in cardiac output in patients with a fixed cross-sectional area of the valve < 1 cm2.17 18
Aortic insufficiency carries significant risk due to the potential left ventricular failure associated with severe volume overload. If the process is acute, the risk of left ventricular failure is high. In chronic cases, the patient usually tolerates the valvular failure well until symptoms appear, usually indicating the beginning of rapid deterioration.19
Mitral stenosis carries a significant risk in the perioperative period owing to the potential for severe pulmonary congestion if tachycardia induces a reduction in the diastolic filling time.20
Mitral regurgitation, which is commonly caused by papillary muscle dysfunction, is associated with increased perioperative risk largely due to increased regurgitant fraction in the event of abrupt volume shifts. Mitral valve prolapse, while usually asymptomatic, evolves in 10% of cases to mitral regurgitation.17 18
Prosthetic valves increase the risk of endocarditis and thromboembolic phenomena.21
Cardiomyopathy: Cardiomyopathies lead to increased risk for several reasons. The individual cause of the cardiomyopathy (infiltrative, toxic, alcoholic, etc) must be evaluated independently. In addition, the hemodynamics of cardiomyopathy may lead to increased venous capacitance, decreased ejection fraction, and potentially an outlet obstruction pattern. In particular, there is serious risk of cardiac morbidity (congestive heart failure) associated with septal hypertrophy, leading to severely reduced stroke volume in the event of volume contraction.22 23 24
Electrical Disturbances: Electric disturbances and arrhythmias place a patient at increased risk largely dependent on the underlying cause. In the absence of cardiac disease, ventricular arrhythmias, such as premature ventricular contractions, complex ectopic contractions, or nonsustained ventricular tachycardia, do not carry a significant increased risk.25 26 27
Atrial fibrillation carries increased risk of prolonged hospital stay,28 largely due to increased incidence of stroke29 30 31 32 and mortality.33 The management of anticoagulation is discussed below.
Supraventricular arrhythmias have been identified as independent risk factors.34 35 Their increased risk is most significant as a marker of underlying cardiac disease or extracardiac problems such as electrolyte disturbances, drug toxicity, or metabolic derangements. In addition, supraventricular arrhythmias may exacerbate underlying cardiac disease, as in cases in which rapid ventricular responses may increase myocardial oxygen demand in patients with fixed blood flow (oxygen supply) due to coronary artery disease. Certain supraventricular arrhythmias may trigger aberrant pathways and result in severe ventricular tachycardia, as in Wolff-Parkinson-White (WPW) syndrome. Sudden death may be the initial manifestation of WPW and other aberrant conduction diseases.36
High-grade conduction abnormalities such as complete heart block, trifascicular block, and bifascicular block carry significant mortalities. These blocks may lead to an actuarial 5-year mortality from bradycardia arrhythmia of 6%. Tachyrhythmia may account for as many as 42% of sudden deaths in patients with coronary artery disease and congestive heart failure that manifest these high-grade conduction disturbances.37 In less severe conduction disturbances, such as chronic bifascicular block or left bundle branch block, the risk of progression to complete heart block in the perioperative setting is rare.38
Congestive Heart Failure: The presence of congestive heart failure in the preoperative period had been associated consistently with increase morbidity and mortality in extracardiac surgery.34 39 40 The severity of the congestive heart failure, based on both functional and diagnostic evaluation, accounts for much of the increased mortality.39
Extracardiac Risks
Pulmonary diseases impose a significant risk of cardiac
complications in the perioperative period. The presence of hypoxemia is
a major risk for myocardial ischemia. In addition, those conditions
that lead to increased work of breathing will increase the demand for
cardiac output. As much as 25% of the oxygen delivered from the heart
is used for the work of breathing. In particular, pulmonary
hypertension, which may be secondary to a variety of causes, is a
significant risk factor for myocardial complications. Elevation of the
pulmonary vascular resistance was associated with an elevated gradient
between the pulmonary artery diastolic pressure and the pulmonary
capillary wedge pressure. When this gradient exceeded 5 mm Hg for
12 h, the mortality rate was 60%.41
Systemic hypertension has been studied extensively in both the general and surgical populations. While severe hypertension (diastolic BP > 110 mm Hg) may be associated with some increased risk,42 43 44 45 there is no evidence that mild-to-moderate hypertension independently increases perioperative risk.46 47 48 Of interest is one study that demonstrated that reduction of BP intraoperatively in previously hypertensive patients was associated with increased risk of perioperative ischemia.44
Diabetes mellitus, while a modest independent risk factor, is important because of the widespread incidence of the disease and the diagnostic difficulties it induces. There is a twofold increase in both early and late mortality among diabetic patients compared with nondiabetic patients.49 The diagnostic difficulties in diabetics are related to the high incidence of "silent myocardial infarctions," which may approach 25% in the diabetic population.
Vascular disease is very commonly associated with coronary artery disease and should be considered as a risk factor for perioperative cardiac complications. In a large review of the English-language literature, Hertzer50 found that one half of the perioperative mortality in vascular surgery was attributable to cardiac disease and that patients who met criteria for a coronary artery bypass graft had a 5-year mortality twice that of other patients.50
Age is widely recognized as a major risk factor for coronary artery disease.51 As a person ages, the response to perioperative stress is effected by a decrease in heart rate and increase in stroke volume for any given cardiac output,52 probably due to a decreased responsiveness to endogenous catecholamines. Also, the volumes of the heart chambers tend to enlarge, and this is true for both systole and diastole, leading to reduction in left ventricular ejection fraction, and thus a reduced stress response in elderly patients.
Obesity has been recognized as an independent risk factor for coronary artery disease. In addition, the Framingham study53 demonstrated that the risk associated with obesity was higher for women than for men.
Gender influences on the risk of coronary artery disease are currently under investigation. Although coronary artery disease is the major cause of death among women, the diagnosis and therapy of coronary artery disease are much less than in men. Whether this is due to sociologic or physiologic factor is currently under intense evaluation. It is critical to note that being female can be a significant risk for cardiac disease, and that women’s symptoms may be different than men’s symptoms.54 55
Lipid elevation of total and low-density lipoprotein levels has been confirmed as a risk factor for cardiac disease in both interpopulation and intrapopulation studies.56 Tobacco use is also a significant risk factor for coronary artery disease.51
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Preoperative Diagnostic Goal: Identify High-risk Patients |
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The preoperative evaluation should be targeted at the following: establishing a reasonable estimate of the risk of complication; identifying factors that can be modified to reduce risk; planning an operative approach and timing that will limit risk; and choosing an anesthetic most favorable for the specific patient and planned surgery.
These goals should then lead to a preoperative tune-up that can provide those diagnostic and therapeutic interventions that will provide maximal risk reduction to the patient with minimal imposed risk and at an acceptable cost.
Extensive study has been devoted to developing tools to quantify the potential risk of surgery in patients with underlying cardiac disease. The most well established of these systems are the risk categories developed by Goldman and colleagues34 60 and Detsky and colleagues.47 These tools are summarized in Table 1 .61
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Although risk prediction can be based on the references just mentioned, several points relating to risk are of major interest. The traditional concern regarding recent myocardial infarction as a risk for reinfarction in the perioperative period must be tempered by more recent observations. While early reports62 noted a dramatic rise in the risk of reinfarction until 3 and 6 months postinfarction, recent data do not support such a blanket statement. Current recommendations, supported by several authors,14 61 are that the risk of reinfarction is limited to those patients with myocardium at risk of ischemia due to coronary artery lesions, and most patients can be operated on safely with proper hemodynamic monitoring within 4 to 6 weeks of infarct.
Identification of factors that can be modified to reduce risk provides an opportunity for perioperative intervention that may improve outcome. Unfortunately, most of the risk factors enumerated above are not amenable to intervention in the preoperative period (eg, diabetes mellitus), or while important are not independent risk factors (eg, mild-to-moderate hypertension). Specific attention should be paid to optimal therapy of underlying pulmonary disease. Hypoxemia and hypercarbia as well as increased work of breathing may increase the risk of acute cardiac complications in the perioperative period. In addition, the exacerbation of pulmonary disease may lead to difficulty in discontinuing ventilator support, which in turn may complicate the patient’s cardiac condition. Hypoxemia, high intrathoracic pressures, and potential pulmonary infection can be reduced by adequate bronchodilator and antibiotic therapy. Active identification and treatment of pulmonary hypertension is indicated. Adequate control of reactive airway disease should be pursued. In addition, a recent multivariate analysis of postoperative pulmonary complications included nasogastric intubation, preoperative sputum production, and prolonged duration of anesthesia.63
Metabolic derangements can contribute to perioperative complications and should be diagnosed by routine blood tests, including electrolyte panels, renal panels, and liver function testing.
Although there are limited data referring to modifying the surgical approach in patients at risk of cardiac complications, there is ample evidence to support shorter anesthetic time.61 63 While there are serious hemodynamic consequences of laparoscopic surgery, some data suggest that these changes are very transient,64 and the reduced surgical stress associated with laparoscopic surgery may reduce the risk of cardiac complications.
Other factors such as the selection of the type or approach for vascular surgery do not appear to influence cardiac complications.65 66 However, some data suggest that increased volume of surgery for a given condition does reduce the rate of complications.67
Regarding the contribution of anesthetic technique, the most important factor appears to be the length of time the anesthetic is used rather than the route or type of agent. Studies comparing sevoflurane, isoflurane, halothane, and isoflurane with opiates all report complication rates of 18%.68 69 Regional anesthesia appears to have no cardiac benefit over general anesthesia.70 71 There are some specific circumstances in which regional anesthesia may have benefits that reduce extracardiac complications, such as the need for reoperation in peripheral vascular surgery,72 which should be considered in the choice of surgical technique.
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Therapeutic Interventions |
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Coronary Artery Disease/Coronary Reperfusion: Several large prospective and retrospective studies, including data extracted from the Coronary Artery Surgery Study, have demonstrated that when long-term and immediate benefit considered together, the decision to perform coronary artery bypass graft prior to a planned elective surgery is warranted.83 84 Unfortunately, the role of prophylactic coronary artery bypass graft procedures remains controversial, largely due to the absence of prospective randomized clinical trials.85 In addition, to further confound the issue of prophylactic reperfusion, the role of angioplasty procedures is an evolving question. A retrospective series from the Mayo Clinic reported a perioperative myocardial infarction rate of 5.6% and a mortality rate of 1.9% in high-risk patients who underwent angioplasty an average of 9 days prior to elective surgery.86 While there are insufficient data to form firm positions on the prophylactic use of angioplasty, guidelines are available87 that recommend the use of angioplasty in a fashion similar to that of coronary artery bypass graft. However, in the planning of elective surgery, it is necessary to consider the timing of angioplasty because of the following: the need for antiplatelet therapy postangioplasty; the risk of restenosis, which peaks in hours to days after the procedure; and the ongoing remodeling of coronary arteries, which continues for several weeks.61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
Medical therapy for coronary artery disease is frequently offered as an alternative to surgical revascularization. Several studies support the use of surgery in severe multivessel or critical lesion coronary artery disease, especially in patients with coexisting peripheral vascular disease.88 89 90 91 Nevertheless, the use of ß-blockers, calcium channel blockers, and nitrates plays a significant role in ensuring that the myocardial oxygen demand does not exceed the supply. Patients well compensated while receiving these agents should be continued on their therapy through the perioperative period.61 Special attention should be paid to avoiding excess catecholamine effects by the sudden withdrawal of ß-blocker therapy. At least one study supports the use of ß-blockade immediately prior to surgery: in 1988, Stone and colleagues42 gave oral ß-blockers 2 h prior to surgery and reported a decrease in frequency of ST segment depression from 28% among control patients to 2% in treated patients. Similarly, in 1987, Pasternack and colleagues92 reported a reduction from 18 to 3% incidence of acute perioperative myocardial infarction in patients treated with metoprolol immediately prior to and following surgery. More recently, Podesser and colleagues93 demonstrated in patients undergoing coronary artery bypass procedures that the combination of nifedipine and metoprolol was associated with a lower incidence of ischemic events than nifedipine alone. This lower incidence was related statistically to a reduced heart rate as compared with patients receiving nifedipine alone.93
Specific Interventions To Reduce Extracardiac Complications of
Cardiac Problems
Cerebrovascular: The risk of complications of
cerebrovascular disease in the perioperative period is relatively low.
However, it is associated with significant mortality and long-term
disability, especially in patients with underlying cardiac disease. In
1987, Brener and colleagues94
reported that the incidence
of transient ischemic attacks or cerebrovascular accident following
cardiac surgery was 1.9% in patients without carotid disease and 9.2%
in patients with carotid lesions. The factors that appear to increase
the risk of cerebrovascular complication are often cardiac in origin:
hypotension and thromboembolic events.95
Therefore, the
cardiac treatment of patients who are at risk of cerebrovascular
complications must include the avoidance of hypotension.96
Gastrointestinal: GI complications that result from cardiac causes are relatively rare: only 35 such complications occurred in a series of > 4,000 cardiopulmonary bypass surgical procedures. Of these 35 complications, 20 were GI bleeding and the remainder were intestinal infarction and acute pancreatitis.97 The mortality associated with either occlusive or nonocclusive complications affecting the superior mesenteric artery is 73 to 100%.98 99 Ischemic cardiac disease or arrhythmia was present in 83.8% of patients with GI complications. Most importantly, GI complications were associated with low cardiac output and the use of massive doses of vasopressors or intraaortic balloon pumping to support BP.100 Earlier identification and a high index of suspicion for GI complications may encourage the maintenance of higher cardiac output to reduce GI complications in patients at risk.
Renal: Renal failure in the postoperative period carries a very high risk of prolonged hospital stay, prolonged chronic incapacitation, and death.101 Factors associated with postoperative renal failure that are amenable to preoperative therapy that are associated with complications include congestive heart failure and elevated serum creatinine levels. In addition, the use of a variety of diagnostic and therapeutic agents in the preoperative period may predispose patients to renal complications; a high index of suspicion will lead the physician to utilize drugs less likely to induce renal failure.102 The risk of contrast-induced renal failure can be significantly reduced by adequate volume loading, usually requiring 1 to 2 L of crystalloid solution on the evening prior to contrast administration.103
A relatively rare cause of postoperative renal failure that may be associated with emboli or vascular complications is rhabdomyolysis.104 This form of renal failure has a relatively better prognosis and should be treated with aggressive hydration, mannitol-induced diuresis, and alkalinization of the urine.
Pulmonary: Pulmonary complications are among the most common encountered in patients with cardiac compromise. The interplay of pulmonary and cardiac functions frequently induces simultaneous complications. Preoperative therapy to reduce the pulmonary demands for increased oxygen consumption is indicated in patients with marginal cardiac output. Optimization of bronchodilator therapy and reduction in pulmonary infection may allow for more expedient ventilator weaning and reduced complications associated with prolonged intubation. Treatment of clinical or subclinical congestive heart failure will improve gas exchange and allow for more efficient breathing and more rapid extubation.61 Although there are limited data referring to the impact of pulmonary hypertension on noncardiac surgery, the high mortality associated with this problem in the ICU makes its treatment an important effort. Therapy with adequate oxygen, nitrate therapy, and, occasionally, morphine delivered through a pulmonary artery catheter should be optimized prior to surgery. This therapy should be continued through the postoperative period.
Interventions To Reduce Cardiac Complications and Their
Consequences
Hemodynamic Monitoring: There may be no more
controversial subject today than the roles of the pulmonary artery
catheter and hemodynamic monitoring.105
While the
controversy rages, a serious dilemma emerges: how can the diagnostic
tool be separated from the therapeutic interventions that it is
designed to direct? The more important question may be: can we separate
the value of making a diagnosis from the ability to impact that
diagnosis?106
107
The ability to use the pulmonary artery
catheter to diagnose subclinical pulmonary edema was initially reported
by Forrester and colleagues107
108
in 1973. Since the
initial descriptions and analysis of the pulmonary artery catheter, it
has been widely utilized for diagnosis, but the therapeutic maneuvers,
such as diuresis and inotropic support, remain controversial.
The general use of the pulmonary artery catheter was brought into question again recently by Connors and colleagues105 in a cohort study that attempted to develop a "propensity score" to match patients with and without pulmonary artery catheters and compare their outcomes. These authors concluded that there was an increased mortality in patients undergoing right heart catheterization. The propensity score on which these conclusions were based was determined retrospectively on data from chart abstraction, and did not account for the physician evaluation that prompted the placement of the catheter. In addition, the patient pairs used in the analysis were largely renal failure (46%) and multisystem organ failure (34%) patients. In summary, while this study was an important observation, the conclusions are not germane to the discussion of the preoperative management of high-risk patients.
In response to the study by Connors et al,105 the Society of Critical Care Medicine published a large review of the data regarding the use of the pulmonary artery catheter. In reference to the use of the catheter in preoperative management, Leibowitz and Beilin109 concluded there was insufficient randomized clinical trial data to support or refute the routine use of pulmonary artery catheters in preoperative care. We believe that the difficulty in making these decisions is due to the inconsistent and unclear management of the findings on pulmonary artery catheterization. In fact, the diagnostic value of right heart catheterization in the preoperative period is driven by the risk factors described above and the importance of identifying the presence of cardiac disease prior to the development of renal or multisystem organ failure.
In several studies and meta-analyses,110 111 112 113 114 the impact of hemodynamic variables on the outcome of surgical patients has been evaluated. While some controversy remains as to the benefit of increasing cardiac output and oxygen delivery, the preponderance of the evidence points to improved outcome in those patients who achieve a high output and high oxygen-delivery state. There is little doubt that when this state can be achieved with only volume and hemoglobin there is a positive impact,115 but the data regarding the use of inotropic support to achieve these end points are less clear.116 It is safe, however, to conclude that those patients who can spontaneously achieve a high oxygen delivery have an improved outcome.117 Although many of the studies utilize specific numeric targets as end points, the more physiologic approach of achieving a flow-independent state is most likely to be applicable to the individual patient.118 119 The flow-independent state is a state in which the oxygen consumption does not increase significantly as the oxygen delivery increases. It should be noted that there will be some increase in oxygen consumption as the delivery increases due to the increased cardiac work associated with the increase. When the oxygen consumption is plotted vs the oxygen delivery, a change in the slope can be appreciated and this change of slope can be considered the flow-independent level of oxygen delivery.
The diagnostic importance of the pulmonary artery catheter may be more significant than its role in the determination and direction of oxygen-delivery mechanics. The diagnostic sensitivity and specificity in determining filling pressures (volume status) and left ventricular performance (cardiac output) exceed the capacity of the physical examination and clinical history.120 121 122 The preoperative risk of patients with underlying cardiac disease is largely determined by the balance of congestive heart failure, adequacy of cardiac output, adequacy of coronary blood flow, and level of perfusion of vital organs, which is often influenced by the degree diuretic therapy.5 6 8 9
Preoperative optimization or "tune-up" should be considered in the light of the risk factors above, and in the context of the individual patient and planned procedure.
The volume status of the patient should be controlled to ensure adequate perfusion without evidence of clinical or subclinical pulmonary edema. If there is any doubt regarding the volume status of a patient with underlying cardiac disease, a pulmonary artery catheter will help direct the decision making. It is important to note that the ideal value of the pulmonary capillary wedge pressure must be individualized. Some patients will require a higher pressure to maintain adequate cardiac output and may tolerate relatively high pulmonary capillary wedge pressures without developing pulmonary edema.123 To determine the optimal pulmonary capillary wedge pressure, sequential fluid boluses may be administered with close observation of the cardiac output. If the pulmonary capillary wedge pressure exhibits a sustained (> 5 min) increase of more than 3 to 5 mm Hg with a moderate fluid challenge (200 to 500 mL), and the cardiac output remains the same or decreases, there is little advantage to further increase in the filling pressure. Similarly, if the initial pulmonary capillary wedge pressure is high (> 18 mm Hg), a gentle diuresis while observing the cardiac output is indicated.124 If there is a net loss of fluid without dramatic reduction in the pulmonary capillary wedge pressure, reduction in cardiac output, or increase in systemic vascular resistance, then diuresis should be continued until the pulmonary capillary wedge pressure is reduced to minimal levels necessary to maintain cardiac output without increase in heart rate or systemic vascular resistance.
The use of transfusion in the preoperative patient is a decision that should be evaluated carefully. While the risk of transmission of blood-borne pathogens is rare—for hepatitis 1 in 34,000 transfusions, for HIV 1 in 493,000 transfusions—the consequences can be catastrophic.125 126 Traditional or arbitrary values of hemoglobin or hematocrit prior to surgery should not be used routinely, and the need for transfusion should be based on the individual patient’s requirements. In general, hematocrits > 36% do not improve oxygen delivery due to rheologic influences that reduce blood flow at the capillary level.127 The traditional level of 10 g/dL of hemoglobin is no longer appropriate for maintaining a minimum hemoglobin concentration by transfusion. Recently, Weiskopf and colleagues128 demonstrated that in 32 healthy volunteers, acute reduction of hemoglobin to 5 g/dL did not result in detectable inadequate systemic oxygen delivery. However, this study did not address any increased demands associated with acute illness or surgical stress. In a large series of 8,787 patients undergoing surgery for hip fractures, Carson and colleagues129 showed that a hemoglobin level of 8 g/dL did not appear to influence mortality at 30 or 90 days postoperatively.
While currently available data do not provide a specific level of hemoglobin, the optimal preoperative hemoglobin and therefore transfusion requirement must be determined on an individual basis.130 Factors that should be considered include ability of the patient to increase cardiac output without inducing myocardial ischemia (cardiac reserve), ability of the patient to fully saturate hemoglobin (pulmonary reserve), and risk of ischemic events in vital organs (such as cerebrovascular events) in patients with arteriosclerotic disease. Those patients who are at risk of these events or unable to compensate adequately should be closely monitored and have transfusion as indicated by physiologic demands.131 Finally, in the decision to transfuse patients preoperatively, it should be noted that banked blood may be deficient in 2,3 diphosphoglycerate and therefore may not immediately provide full oxygen-carrying capacity.132
The use of inotropes in the preoperative patient has been studied prospectively in the context of increasing oxygen delivery and maximizing oxygen consumption. Studies using high doses of catecholamines to achieve uniform predetermined goals found increased mortality.133 Studies in which underlying cardiac problems were treated with combination therapy, including inotropes, found improved outcome and reduced complications.61 134 135 136 137
There are a variety of pharmacologic agents available and widely used as vasodilators, with or without additional cardiac effects. The most widely used of these agents are nitrates, calcium channel blockers, ß-blockers, and amiodarone. While in the preoperative phase, control of angina is indicated. The risks of continuing nitrate therapy intraoperatively must be considered. The vasodilators may mimic or increase the vasodilation associated with many anesthetic agents. In patients with reduced intravascular volume, the nitrates may induce serious hypotension.61 Several authors have found that the prophylactic or intraoperative use of nitrates does not reduce the risk of perioperative cardiac events.138 139 140 In some applications, intraoperative nitroglycerin has been beneficial: for example, in patients with segmental wall motion abnormality141 or cerebrovascular diseases undergoing carotid endarterectomy.142 Some data support the intraoperative use of nitroglycerin to improve hemodynamics and reduce the risk of postoperative complications.143
Calcium channel blockers and amiodarone are widely accepted for specific therapy in the preoperative period for control of angina, ischemia, and rhythm disturbances.144 Most authorities strongly recommend the continuation of therapy with these agents throughout the operative period.61 In addition, the treatment with ß-blockers and clonidine should be continued throughout the operative period to avoid potential rebound with tachycardia and hypertension.
Arrhythmia Control: The preoperative management of arrhythmias is an important component of the preparation of the patient for surgery. Most arrhythmias are secondary to metabolic derangements, particularly electrolyte abnormalities. The most common of these abnormalities are hypokalemia and hypomagnesemia, which should be corrected well before surgery as the urgent administration of electrolytes (especially potassium) may cause more problems than they solve.61 145 146
Bradycardic and serious conduction abnormalities not treated by reversal of electrolyte disturbance, ischemia, or hypoxemia should be treated with temporary or permanent pacemaker placement.61
Atrial fibrillation and other supraventricular arrhythmias should be treated preoperatively. Digitalis remains a treatment of choice for atrial fibrillation. It should be administered in a sufficient dose to reduce the ventricular response rate to < 100 beats/min. Calcium channel blockers or ß-blockers may be used for control of supraventricular tachycardias. While all these agents have the potential for depressing myocardial contractility, diltiazem has been shown to have minimal negative inotropic effect and good control of tachycardias, as well as cardioprotective effects against ischemia.147 148 In the relatively rare group of patients with arrhythmias secondary to accessory pathways, as in the WPW syndrome, surgical division or catheter ablation should be strongly considered prior to elective surgery.149 The risk of embolization in the presence of atrial fibrillation is approximately 5% per year.150 The optimum therapy remains warfarin, although in the perioperative period, warfarin therapy may be stopped and heparin may be used. Warfarin therapy can be discontinued briefly if necessary in the immediate preoperative period and resumed as soon as surgical bleeding is no longer a major risk.
Metabolic Control: The contribution to perioperative complications of diabetes is predominantly attributable to associated arterial disease. In a series of 192 procedures, Hood and colleagues151 report a death and complication rate of 10.2% for lower extremity procedures and 25.7% for aortic procedures. The incidence of complications and death was not predicted by preoperative history or noninvasive testing, supporting the view that all diabetics must be considered at high risk for perioperative complications. The treatment initiatives for diabetic patients in the perioperative period should be targeted at the avoidance of hyperglycemia sufficient to cause an osmotic diuresis and consequent hypovolemia, and the avoidance of hypoglycemia, which may go unrecognized during the anesthetic and postoperative period and lead to serious neurologic consequences. The use of a continuous IV insulin drip to control the serum glucose level in a range between 150 and 200 mg/dL is prudent. This approach avoids the potential risk of erratic absorption of subcutaneous insulin and accommodates the dietary variability associated with the perioperative period. Long-acting oral hypoglycemic agents should be avoided in the perioperative period.
The perioperative maintenance of normothermia in patients with risk factors for perioperative cardiac morbidity reduces the risk of cardiac complications, including ventricular tachycardia.152 Normothermia can be maintained by careful attention to environmental circumstances, such as the temperature of the operating room, warmed IV fluids, and the maintenance of dry and warm covering for the patient. Active warming with heating blankets, warm air devices, and heated humidified air through the ventilator should be utilized during the intraoperative and postoperative periods.
The renal risk factors and consequences are discussed above. The reduction of the risk of renal failure in the perioperative period is dependent on avoidance of nephrotoxic agents and ensuring adequate blood flow to the kidneys. The primary method to ensure adequate blood flow to the kidneys is to ensure adequate cardiac output by providing sufficient preload.103 123 In addition, the use of low-dose dopamine to improve renal perfusion has been advocated by many authors.153 154 While recently the use of low-dose dopamine has been brought into question due to lack of compelling evidence in small clinical trials,155 a more recent report by Hoogenberg and colleagues156 demonstrated in healthy volunteers a significant increase in renal blood flow with the use of low-dose dopamine despite the simultaneous infusion of norepinephrine. The positive impact of this observation is believed to be sufficient to warrant the use of low-dose dopamine in all critically ill patients.157
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TOPAbstractIntroductionScope of the Problem...Risk Factors for Cardiac...Preoperative Diagnostic Goal:...Therapeutic InterventionsReferences |
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