POSTOPERATIVE MANAGEMENT OF VASCULAR PATIENTS

Vascular surgery patients require special attention during the postoperative period because most cardiac complications occur postoperatively, and other problems may arise that require immediate attention. Conventional practice is to monitor all vascular surgery patients in an intensive care unit setting after surgery. Some centers have set up specialized vascular step-down units, where lower risk patients can be evaluated frequently by specialized nursing staff. There are, however, no clinical trials to support this practice, and most centers admit all vascular surgery patients to the intensive care unit postoperatively.

Myocardial ischemia and cardiac morbidity occur most frequently in the postoperative period. Patients should be carefully monitored for signs and symptoms of ischemia, but up to 90% of these episodes are asymptomatic.^{[84] [125] [129] [131] [715] [716]} The determinants of myocardial oxygen supply and demand should be optimized for all patients (see Fig. 52-5 ) to prevent ischemia before it develops. β-Blocker therapy should be continued throughout the postoperative period. Dysrhythmias may be secondary to ischemia or to sympathectomy associated with regional anesthesia.

Besides myocardial ischemia and cardiac morbidity, other problems include coagulopathy, from residual heparin or dilutional coagulopathy after massive transfusion. Even in the absence of coagulopathy, bleeding through fresh vascular anastomoses may occur when significant postoperative hypertension is untreated. Hypovolemia occurs after aortic surgery as a result of significant third-space fluid losses and bleeding. Hypovolemia may lead to hypotension and hypoperfusion of the coronary arteries or lower extremity vascular grafts. Graft occlusion in the lower extremities occurs in 3% to 10% of patients^{[79] [500] [501]} after lower extremity or aortic surgery and should be recognized immediately and surgically corrected. Lower extremity pulses should be checked at hourly intervals. Some patients require administration of heparin or dextran to prevent thrombosis when the surgical repair is questionable or when patients have diffuse atherosclerotic disease.

Figure 52-21 A, Incidence of postoperative cardiac morbidity for patients who were actively warmed with a forced-air system (i.e., normothermic group) and those who received no warming (i.e., hypothermic group). Morbid cardiac events (i.e., unstable angina, myocardial infarction, or cardiac arrest) occurred more frequently in the hypothermic patients (P = .03). Ventricular tachycardia and combined electrocardiographic or morbid events also occurred more frequently in the hypothermic patients (P = .04 and P = .001, respectively). B, Incidence of myocardial ischemia after lower extremity vascular surgery by core temperature on admission to the intensive care unit, anesthetic technique, and age. Patients with temperatures below 35°C had a twofold to threefold greater incidence of ischemia. Patients older than 65 years of age had a twofold greater incidence of ischemia. (A, Adapted from Frank SM, Fleisher LA, Breslow MJ, et al: Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events: A randomized clinical trial. JAMA 277:1127–1134, 1997; B, adapted from Frank SM, Beattie C, Christopherson H, et al: Unintentional hypothermia is associated with postoperative myocardial ischemia. The Perioperative Ischemia Randomized Anesthesia Trial Study Group. Anesthesiology 78:468–476, 1993.)

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Residual hypothermia in the early postoperative period is associated with an increased incidence of myocardial ischemia and cardiac morbidity; therefore, body temperature should be carefully monitored and controlled in all vascular surgery patients. In a prospective randomized trial, the relative risk of early postoperative cardiac morbidity was reduced by 55% when normothermia was maintained by use of a forced-air warming system^[310] ( Fig. 52-21 ). In the early postoperative period, vascular surgery patients have a twofold to threefold greater incidence of myocardial ischemia when core temperature is less than 35°C.^[311] Even mild hypothermia of approximately 35°C is associated with a 200% to 700% increase in norepinephrine levels,^{[308] [717]} generalized vasoconstriction,^[718] and increased blood pressure in postoperative patients.^[308] Shivering occurs, which increases total body oxygen consumption, but only by about 40% in the typical elderly vascular patient.^[307]

It is important to control the stress response in the postoperative period. This includes preventing the potential triggers for myocardial ischemia (pain, anemia, hypothermia, hemodynamic extremes, and ventilatory insufficiency). In mechanically ventilated patients, the weaning period is especially stressful, and myocardial ischemia occurs frequently during this time.^[719] Careful sedation and expeditious weaning are desirable. When possible, extubation in the operating room is less stressful and is preferable for carotid and lower extremity vascular surgery patients. For more invasive surgical procedures (TAA and abdominal aortic aneurysm), postoperative mechanical ventilation is usually necessary.

Vascular surgery continues to challenge the anesthesiologist, given the significant physiologic stress superimposed on a relatively elderly patient population with a high incidence of coexisting disease. Clinical studies provide insight into the preoperative assessment and optimization of cardiac risk, the implications of anesthetic technique, and the diagnosis, prevention, and treatment of myocardial ischemia in vascular surgery patients. These studies have improved our ability to care for the vascular surgery patient with reduced morbidity and better overall outcome.