Perioperative Care of the Vascular Surgery Patient: The Perspective of the Internist ROSANNE GRANIERI, MD, DAVID S. MACPHERSON, MD ATHEROSCLEROTIC PERIPHERAL VASCULAR DISEASE is a
common problem in internal medicine. Although internists have an important role in the evaluation and medical management of these patients (see accompanying article), surgical intervention is often necessary. Frequently, the surgery required is stressful but necessary to save life or limb. Usually, the stress of extensive surgery is inflicted on a patient with extensive medical comorbidity. Over half of patients who undergo vascular surgery have coronary artery disease, and almost one-fifth have either diffuse inoperable coronary occlusions or three-vessel or left main coronary artery ("left main") disease) Unfortunately, the patient's history, physical examination, and resting electrocardiogram are not enough to exclude significant coronary artery disease. As many as two-thirds of vascular surgery patients without symptoms of coronary artery disease who have normal resting electrocardiograms have at least singlevessel coronary occlusion, and one fourth have threevessel or left main disease. 2 Furthermore, preoperative silent ischemia has been found in 18% of vascular surgery patients 3 and postoperative ischemia in 47%. 4 For this reason, the risk of serious perioperative medical complications, especially cardiac complications, must be considered to be high in the vascular surgery patient. These complications are serious, as up to 70% of surgical mortality in vascular surgery patients can be attributed to cardiac disease. ~, 5-~ Thus, the internist seeing the patient before vascular surgery cannot view this patient in the same way as the patient scheduled for nonvascular preoperative evaluation. In the past decade several new technologies have been developed to help physicians assess the risk of vascular surgery, and additional data have accumulated as to the magnitude of risk and the options to decrease risk. Some have called for additional programs to train internists with special expertise in vascular medicine, including the assessment of preoperative risk and the management of the medical complications of vascular surgery, s Received from the Department of Medicine, Division of General Internal Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania. Address correspondence to Dr. Macpherson: Pittsburgh Veterans Affairs Medical Center, 11A, University Drive C, Pittsburgh, PA 15240. Address reprint requests to Dr. Granieri: Department of Medicine, Division of General Internal Medicine, 167 Lothrop Hall, 190 Lothrop Street, Pittsburgh, PA 15261.
102
Although a comprehensive review of medical issues in surgical patients has been published in the Journal of General Internal Medicine? we offer the present review to assist internists in achieving the goals of perioperative consultative medicine involving the vascular surgical patient: 1) to estimate the risk of medical complications of surgery, 2) to reduce the risk of surgery by optimizing the patient's medical condition, and 3) to assist the surgeon in managing the medical aspects of patient care in the perioperative period. Although other medical complications are frequent in vascular surgerypatients, our discussion focuses on cardiac morbidity because of the limitations of space and the less complete literature regarding non-cardiac complications from vascular surgery. Furthermore, we confine our discussion to those patients undergoing peripheral vascular or aortic surgery, and have chosen not to review carotid procedures, as the need for this surgery is evolving.t°
METHODS We attempted to identify all relevant articles regarding vascular surgery and medical complications from 1975 through the present. The National Library of Medicine Medlars system was used to search the SDILINE, MEDLINE, and BACKFILE files. Key words used included vascular surgery, angioplasty (transluminal), heart catheterization, ventricular ejection fraction, dipyridamole, thallium, preoperative care, postoperative care, and postoperative complications. Additional citations were obtained from reference lists from the above retrieved articles and from major textbooks.
High-risk Nature of Vascular Surgery Despite a decreasing trend in overall surgical mortality rates, the patient about to undergo peripheral vascular surgery remains at high risk for both postoperative morbidity and mortality. Three factors contribute to the high morbidity and mortality of vascular surgery: the advanced age of the patient, the nature of the intended surgery, and the presence of generalized atherosclerosis, which is frequently occult.
Age. The incidence of symptomatic peripheral vascular disease increases sharply with age. Mean ages of patients undergoing vascular surgery range from 59 to 71 )1, 12 The mortality rate for patients more than 65 years of age undergoing major bypass surgery for pc-
JOURNALOFGENERALINTERNALMEDICINE, Volume 7 (January/February), 1992
ripheral vascular disease is 15%, c o m p a r e d with 5% for patients less than 65 years of age. 13 It is difficult to determine w h e t h e r age per se or the increase in comorbid conditions associated with age increases the risk for postoperative complications. However, Goldman's Multifactorial Risk Index 14 and a subsequent modification is have found age, after adjustment for medical comorbidity, to be an i n d e p e n d e n t predictor of cardiac morbidity and mortality in large series of patients undergoing both vascular and nonvascular surgery.
Nature of Surgery. Vascular surgery itself increases the risk of cardiac complications. The risk is increased even after taking into account the older age and higher comorbidity of vascular surgery patients. The increased risk has been found both for aortic surgery 14 and for other major vascular procedures. 16 Excess risk associated with aortic surgery may be due to adverse hemodynamic changes associated with aortic cross-clamping. Clinical reports describe increases in systemic vascular resistance, decreases in stroke volume, and decreases in cardiac o u t p u t with onset of infrarenal aortic cross-clamping. 17The adverse hemodynamic responses are more striking in patient w h o have underlying coronary artery disease. 17, is For example, c o m p a r e d with patients with no evidence of cardiac disease, patients w h o have coronary occlusions d e v e l o p e d increases in central venous pressure, pulmonary artery pressure, and p u l m o n a r y capillary w e d g e pressure with aortic cross-clamping. Afterload reduction with either intravenous nitroglycerin or nitroprusside has been advocated during cross-clamping in order to r e d u c e subendocardial i s c h e m i a ) 7, 19 In addition to aortic cross-clamping, traction on the mesentary can affect hemodynamics. Significant falls in systemic vascular resistance and mean arterial pressure with increases in heart rate, cardiac index, and p u l m o n a r y artery pressure have been reported with mesenteric traction. 2°, 21 The precise pathophysiology o f these hemodynamic changes is unknown; however, these changes may adversely affect the balance of myocardial demand and oxygen supply and therefore may lead to more cardiac complications. The Presence of Generalized Atherosclerosis. Peripheral vascular atherosclerotic disease does not exist in isolation but may serve as a marker of diffuse atherosclcrotic disease. The association of peripheral vascular disease with coronary artery disease is of param o u n t importance as it is the concomitant coronary artery disease that is the leading cause of both surgical and late mortality in these patients. Proportions of surgical mortality attributed to coronary artery disease range from 33% to 70% (Table 1).1, 6, 7, 22 From a study c o n d u c t e d at the Cleveland Clinic, w h e r e all vascular surgery patients (that is, patients both with and without signs of coronary artery disease)
103
TABLE 1 Prevalence of Coronary Artery Disease in Patients Evaluated for Vascular Surgery Percentage of Patients with
over 70% Stenosis of Vessel(s) Reference*
Single
Double
Triple or Left Main
Hertzel et al.1 Orrecia et al.Zt
27 31
19 12
13 32
* For complete reference citations, see the reference list. ?Percentages estimated from bar graph.
u n d e r w e n t coronary artery angiography prior to surgery, 13% of the 1,000 patients had three-vessel disease or left main disease and 6% had diffuse disease d e e m e d inoperable. 1 In addition, 57% had at least one-vessel disease, and only 8% had normal coronary arteries. The absence of clinical evidence of coronary artery disease (by symptoms or EKG) was not reassuring, as 15% of this group had coronary artery disease. A smaller series of patients undergoing " r o u t i n e " cardiac catheterization before aortic surgery corroborates the Cleveland Clinic experience. 2 However, in this series 64% of patients without a history of coronary artery disease or symptoms were found to have significant coronary occlusions. Thus, the presence of peripheral vascular or aortic disease that necessitates surgical intervention is a marker for coronary artery disease. Even those patients with no symptoms and a normal EKG have a significant f r e q u e n c y of hemodynamically important stenoses of their coronary arteries. Preoperative Cardiac Evaluation
A pertinent history and physical examination are mandatory in the preoperative evaluation o f the patient being considered for elective peripheral vascular surgery. The history should focus on angina, dysrhythmia, congestive heart failure, valvular heart disease, and prior myocardial infarction. The physical examination should include a detailed cardiopulmonary examination to elicit signs of congestive heart failure, aortic stenosis, or arrhythmia. An EKG is indicated. With this information, findings that place the patient at "prohibitive risk," for example, a myocardial infarction within the past three months, u n c o m p e n s a t e d congestive heart failure, or unstable angina, should p r o m p t l y be addressed prior to further consideration for elective surgery. In addition, with data available from the history and physical examination, and pertinent screening laboratory data, an estimate of the risk o f surgery can be determined using published clinical prediction rules.
Surgical Risk Indices and the Vascular Surgical Patient. Several clinical prediction rules have b e e n d e v e l o p e d over the past 15 years to aid physicians in
Granieri, Macpherson. VASCULARSURGERYPERIOPERATNECARE
104
estimating surgical risk. 6, t4, t~ The Multifactorial Cardiac Risk Index developed by Goldman et al. is one of the most popular prediction models, but it has limitations. Validation studies of the original index indicate that, although the index stratifies the risk of cardiac complications (that is, the risk of class 1 patients is lower than that of class 2 and so forth), the absolute percentage risk for vascular surgery patients is higher than that for nonvascular procedures. 23z5 Thus, the Muhifactorial Cardiac Risk Index underestimates the chances of cardiac complications in vascular surgery patients. For this reason, estimates of risk of cardiac complications predicted by the Multifactorial Cardiac Risk Index should be adjusted upward for the vascular surgical patient. A modification of the original index, by Detsky et al.,l~ is useful in this regard. To use this prediction rule, the pretest probability of disease (the overall risk of perioperative cardiac events in patients undergoing vascular surgery) is multiplied by a likelihood ratio (which is determined from the patient score from the modified index), resulting in a posttest probability that is the chance of a cardiac event (myocardial infarction, alveolar pulmonary edema, or death) for that patient. For physicians uncomfortable with the use of likelihood ratios, a simple nomogram is included in the article. The modified index has yet to be validated in a separate setting but is an important addition because it takes into account the higher overall risk of vascular surgery. The most recent study reporting use of the Multifactorial Cardiac Risk Index in vascular surgical patients N o found that the risk index stratified risk. 26 However, many patients who were judged class 1 in this report were found to have positive dipyridamolethallium-201 scintigraphy and underwent coronary revascularization prior to vascular surgery. Thus, the authors believe that had they not used the dipyridamole-thallium test, many more class 1 patients would have suffered perioperative cardiac events.
Despite the wide use of clinical prediction rules to help estimate surgical risk, clinicians should be aware of some of the problems of clinical prediction rules when used in practice. First, if the prediction rule is to be accurate in predicting cardiac periopertive events, the clinician must search for and define perioperative myocardial infarction in the same manner as the investigators who developed the clinical prediction rule. 27 Important differences can result if the clinician uses a different intensity of surveillance for perioperative myocardial infarction. It is also important to note that clinical prediction rules developed for the surgical patient have focused only on cardiac morbidity. When faced with estimating the risk of surgery for the individual patient, the clinician must ask what the chance of serious morbidity in any organ system is. Unfortunately, a multivariate study to aid the clinician in predicting overall poor outcome of surgery, other than mortality or cardiac morbidity, has not been conducted. Finally, as many know from experience, prediction for an individual patient is more uncertain than prediction for a group of patients. 2s Although clinical prediction rules have an important place in risk estimation for the vascular surgical patient, clinicians should be aware of their limitations and use them as an aid to clinical judgment, not a crutch upon which decisions are made.
Additional Cardiovascular Testing Prior to Vascular Surgery. Given the high morbidity and mortality of vascular surgery, the high frequency of asymptomatic coronary artery disease in this population, and the limitations in clinical prediction rules, physicians should consider additional cardiovascular testing prior to vascular surgery. Several noninvasive and invasive methods for further assessing significant cardiac disease are available to the consulting physician. These include exercise electrocardiography, techniques to estimate left ventricular function, ambulatory electrocardiographic monitoring, and dipyridamolethallium-201 scintigraphy, discussed below.
TABLE 2 Left Ventricular Function and Surgical Mortality of Vascular Surgery Patients
Reference* McEnroe et al.z6 Fletcher et al.34 Kazmers et al.~ Mosely et a l p Lazor et al.~ Pasternack et al?9
n 58 72 60 41 42 I O0
Definition of Abnormal Ejection Fraction (EF) Echo EF < MUGAt EF < MUGA EF < MUGA EF < MUGA EF < MUGA EF
common problem in internal medicine. Although internists have an important role in the evaluation and medical management of these patients (see accompanying article), surgical intervention is often necessary. Frequently, the surgery required is stressful but necessary to save life or limb. Usually, the stress of extensive surgery is inflicted on a patient with extensive medical comorbidity. Over half of patients who undergo vascular surgery have coronary artery disease, and almost one-fifth have either diffuse inoperable coronary occlusions or three-vessel or left main coronary artery ("left main") disease) Unfortunately, the patient's history, physical examination, and resting electrocardiogram are not enough to exclude significant coronary artery disease. As many as two-thirds of vascular surgery patients without symptoms of coronary artery disease who have normal resting electrocardiograms have at least singlevessel coronary occlusion, and one fourth have threevessel or left main disease. 2 Furthermore, preoperative silent ischemia has been found in 18% of vascular surgery patients 3 and postoperative ischemia in 47%. 4 For this reason, the risk of serious perioperative medical complications, especially cardiac complications, must be considered to be high in the vascular surgery patient. These complications are serious, as up to 70% of surgical mortality in vascular surgery patients can be attributed to cardiac disease. ~, 5-~ Thus, the internist seeing the patient before vascular surgery cannot view this patient in the same way as the patient scheduled for nonvascular preoperative evaluation. In the past decade several new technologies have been developed to help physicians assess the risk of vascular surgery, and additional data have accumulated as to the magnitude of risk and the options to decrease risk. Some have called for additional programs to train internists with special expertise in vascular medicine, including the assessment of preoperative risk and the management of the medical complications of vascular surgery, s Received from the Department of Medicine, Division of General Internal Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania. Address correspondence to Dr. Macpherson: Pittsburgh Veterans Affairs Medical Center, 11A, University Drive C, Pittsburgh, PA 15240. Address reprint requests to Dr. Granieri: Department of Medicine, Division of General Internal Medicine, 167 Lothrop Hall, 190 Lothrop Street, Pittsburgh, PA 15261.
102
Although a comprehensive review of medical issues in surgical patients has been published in the Journal of General Internal Medicine? we offer the present review to assist internists in achieving the goals of perioperative consultative medicine involving the vascular surgical patient: 1) to estimate the risk of medical complications of surgery, 2) to reduce the risk of surgery by optimizing the patient's medical condition, and 3) to assist the surgeon in managing the medical aspects of patient care in the perioperative period. Although other medical complications are frequent in vascular surgerypatients, our discussion focuses on cardiac morbidity because of the limitations of space and the less complete literature regarding non-cardiac complications from vascular surgery. Furthermore, we confine our discussion to those patients undergoing peripheral vascular or aortic surgery, and have chosen not to review carotid procedures, as the need for this surgery is evolving.t°
METHODS We attempted to identify all relevant articles regarding vascular surgery and medical complications from 1975 through the present. The National Library of Medicine Medlars system was used to search the SDILINE, MEDLINE, and BACKFILE files. Key words used included vascular surgery, angioplasty (transluminal), heart catheterization, ventricular ejection fraction, dipyridamole, thallium, preoperative care, postoperative care, and postoperative complications. Additional citations were obtained from reference lists from the above retrieved articles and from major textbooks.
High-risk Nature of Vascular Surgery Despite a decreasing trend in overall surgical mortality rates, the patient about to undergo peripheral vascular surgery remains at high risk for both postoperative morbidity and mortality. Three factors contribute to the high morbidity and mortality of vascular surgery: the advanced age of the patient, the nature of the intended surgery, and the presence of generalized atherosclerosis, which is frequently occult.
Age. The incidence of symptomatic peripheral vascular disease increases sharply with age. Mean ages of patients undergoing vascular surgery range from 59 to 71 )1, 12 The mortality rate for patients more than 65 years of age undergoing major bypass surgery for pc-
JOURNALOFGENERALINTERNALMEDICINE, Volume 7 (January/February), 1992
ripheral vascular disease is 15%, c o m p a r e d with 5% for patients less than 65 years of age. 13 It is difficult to determine w h e t h e r age per se or the increase in comorbid conditions associated with age increases the risk for postoperative complications. However, Goldman's Multifactorial Risk Index 14 and a subsequent modification is have found age, after adjustment for medical comorbidity, to be an i n d e p e n d e n t predictor of cardiac morbidity and mortality in large series of patients undergoing both vascular and nonvascular surgery.
Nature of Surgery. Vascular surgery itself increases the risk of cardiac complications. The risk is increased even after taking into account the older age and higher comorbidity of vascular surgery patients. The increased risk has been found both for aortic surgery 14 and for other major vascular procedures. 16 Excess risk associated with aortic surgery may be due to adverse hemodynamic changes associated with aortic cross-clamping. Clinical reports describe increases in systemic vascular resistance, decreases in stroke volume, and decreases in cardiac o u t p u t with onset of infrarenal aortic cross-clamping. 17The adverse hemodynamic responses are more striking in patient w h o have underlying coronary artery disease. 17, is For example, c o m p a r e d with patients with no evidence of cardiac disease, patients w h o have coronary occlusions d e v e l o p e d increases in central venous pressure, pulmonary artery pressure, and p u l m o n a r y capillary w e d g e pressure with aortic cross-clamping. Afterload reduction with either intravenous nitroglycerin or nitroprusside has been advocated during cross-clamping in order to r e d u c e subendocardial i s c h e m i a ) 7, 19 In addition to aortic cross-clamping, traction on the mesentary can affect hemodynamics. Significant falls in systemic vascular resistance and mean arterial pressure with increases in heart rate, cardiac index, and p u l m o n a r y artery pressure have been reported with mesenteric traction. 2°, 21 The precise pathophysiology o f these hemodynamic changes is unknown; however, these changes may adversely affect the balance of myocardial demand and oxygen supply and therefore may lead to more cardiac complications. The Presence of Generalized Atherosclerosis. Peripheral vascular atherosclerotic disease does not exist in isolation but may serve as a marker of diffuse atherosclcrotic disease. The association of peripheral vascular disease with coronary artery disease is of param o u n t importance as it is the concomitant coronary artery disease that is the leading cause of both surgical and late mortality in these patients. Proportions of surgical mortality attributed to coronary artery disease range from 33% to 70% (Table 1).1, 6, 7, 22 From a study c o n d u c t e d at the Cleveland Clinic, w h e r e all vascular surgery patients (that is, patients both with and without signs of coronary artery disease)
103
TABLE 1 Prevalence of Coronary Artery Disease in Patients Evaluated for Vascular Surgery Percentage of Patients with
over 70% Stenosis of Vessel(s) Reference*
Single
Double
Triple or Left Main
Hertzel et al.1 Orrecia et al.Zt
27 31
19 12
13 32
* For complete reference citations, see the reference list. ?Percentages estimated from bar graph.
u n d e r w e n t coronary artery angiography prior to surgery, 13% of the 1,000 patients had three-vessel disease or left main disease and 6% had diffuse disease d e e m e d inoperable. 1 In addition, 57% had at least one-vessel disease, and only 8% had normal coronary arteries. The absence of clinical evidence of coronary artery disease (by symptoms or EKG) was not reassuring, as 15% of this group had coronary artery disease. A smaller series of patients undergoing " r o u t i n e " cardiac catheterization before aortic surgery corroborates the Cleveland Clinic experience. 2 However, in this series 64% of patients without a history of coronary artery disease or symptoms were found to have significant coronary occlusions. Thus, the presence of peripheral vascular or aortic disease that necessitates surgical intervention is a marker for coronary artery disease. Even those patients with no symptoms and a normal EKG have a significant f r e q u e n c y of hemodynamically important stenoses of their coronary arteries. Preoperative Cardiac Evaluation
A pertinent history and physical examination are mandatory in the preoperative evaluation o f the patient being considered for elective peripheral vascular surgery. The history should focus on angina, dysrhythmia, congestive heart failure, valvular heart disease, and prior myocardial infarction. The physical examination should include a detailed cardiopulmonary examination to elicit signs of congestive heart failure, aortic stenosis, or arrhythmia. An EKG is indicated. With this information, findings that place the patient at "prohibitive risk," for example, a myocardial infarction within the past three months, u n c o m p e n s a t e d congestive heart failure, or unstable angina, should p r o m p t l y be addressed prior to further consideration for elective surgery. In addition, with data available from the history and physical examination, and pertinent screening laboratory data, an estimate of the risk o f surgery can be determined using published clinical prediction rules.
Surgical Risk Indices and the Vascular Surgical Patient. Several clinical prediction rules have b e e n d e v e l o p e d over the past 15 years to aid physicians in
Granieri, Macpherson. VASCULARSURGERYPERIOPERATNECARE
104
estimating surgical risk. 6, t4, t~ The Multifactorial Cardiac Risk Index developed by Goldman et al. is one of the most popular prediction models, but it has limitations. Validation studies of the original index indicate that, although the index stratifies the risk of cardiac complications (that is, the risk of class 1 patients is lower than that of class 2 and so forth), the absolute percentage risk for vascular surgery patients is higher than that for nonvascular procedures. 23z5 Thus, the Muhifactorial Cardiac Risk Index underestimates the chances of cardiac complications in vascular surgery patients. For this reason, estimates of risk of cardiac complications predicted by the Multifactorial Cardiac Risk Index should be adjusted upward for the vascular surgical patient. A modification of the original index, by Detsky et al.,l~ is useful in this regard. To use this prediction rule, the pretest probability of disease (the overall risk of perioperative cardiac events in patients undergoing vascular surgery) is multiplied by a likelihood ratio (which is determined from the patient score from the modified index), resulting in a posttest probability that is the chance of a cardiac event (myocardial infarction, alveolar pulmonary edema, or death) for that patient. For physicians uncomfortable with the use of likelihood ratios, a simple nomogram is included in the article. The modified index has yet to be validated in a separate setting but is an important addition because it takes into account the higher overall risk of vascular surgery. The most recent study reporting use of the Multifactorial Cardiac Risk Index in vascular surgical patients N o found that the risk index stratified risk. 26 However, many patients who were judged class 1 in this report were found to have positive dipyridamolethallium-201 scintigraphy and underwent coronary revascularization prior to vascular surgery. Thus, the authors believe that had they not used the dipyridamole-thallium test, many more class 1 patients would have suffered perioperative cardiac events.
Despite the wide use of clinical prediction rules to help estimate surgical risk, clinicians should be aware of some of the problems of clinical prediction rules when used in practice. First, if the prediction rule is to be accurate in predicting cardiac periopertive events, the clinician must search for and define perioperative myocardial infarction in the same manner as the investigators who developed the clinical prediction rule. 27 Important differences can result if the clinician uses a different intensity of surveillance for perioperative myocardial infarction. It is also important to note that clinical prediction rules developed for the surgical patient have focused only on cardiac morbidity. When faced with estimating the risk of surgery for the individual patient, the clinician must ask what the chance of serious morbidity in any organ system is. Unfortunately, a multivariate study to aid the clinician in predicting overall poor outcome of surgery, other than mortality or cardiac morbidity, has not been conducted. Finally, as many know from experience, prediction for an individual patient is more uncertain than prediction for a group of patients. 2s Although clinical prediction rules have an important place in risk estimation for the vascular surgical patient, clinicians should be aware of their limitations and use them as an aid to clinical judgment, not a crutch upon which decisions are made.
Additional Cardiovascular Testing Prior to Vascular Surgery. Given the high morbidity and mortality of vascular surgery, the high frequency of asymptomatic coronary artery disease in this population, and the limitations in clinical prediction rules, physicians should consider additional cardiovascular testing prior to vascular surgery. Several noninvasive and invasive methods for further assessing significant cardiac disease are available to the consulting physician. These include exercise electrocardiography, techniques to estimate left ventricular function, ambulatory electrocardiographic monitoring, and dipyridamolethallium-201 scintigraphy, discussed below.
TABLE 2 Left Ventricular Function and Surgical Mortality of Vascular Surgery Patients
Reference* McEnroe et al.z6 Fletcher et al.34 Kazmers et al.~ Mosely et a l p Lazor et al.~ Pasternack et al?9
n 58 72 60 41 42 I O0
Definition of Abnormal Ejection Fraction (EF) Echo EF < MUGAt EF < MUGA EF < MUGA EF < MUGA EF < MUGA EF
