Hemodynamic monitoring of patients undergoing abdominal aortic surgery

Invasive monitoring in patients with heart failure

The syndrome of heart failure is characterized by symptoms that are relatively insensitive and nonspecific. Physical diagnosis may be unreliable even in the hands of experienced clinicians, despite the presence of significantly elevated filling pressures or a significantly depressed cardiac output. Instrumentation and devices such as the insertion of a pulmonary artery catheter and the implantable hemodynamic monitor have a major role in the diagnosis and management of cardiovascular disease. They provide a means of measuring intracardiac pressures for point-in-time measurements (cardiac catheterization), short term in an acute situation (insertion of a pulmonary arterial catheter), and, more recently, a long-term assessment increasing our understanding of the nuances of the hemodynamic derangements associated with heart failure and other conditions. With improved ability to accurately assess and monitor filling pressures, clinicians can more precisely adjust therapy with the goal of improving patient symptoms and possibly outcomes.

Coronary artery disease in patients with peripheral vascular disease

For patients requiring peripheral vascular surgery, coronary artery disease is the major determinant of perioperative mortality and long-term survival. The management of coronary artery disease in these patients is controversial as no randomized blinded prospective studies have been conducted. Data on the prevalence, diagnosis and management are reviewed.

The role of a defined protocol for cardiac risk assessment in decreasing perioperative myocardial infarction in vascular surgery

Major elective peripheral vascular surgery has historically carried a significant risk of perioperative myocardial infarction; this risk has been quantified further by its association with proved reduction in cardiac reserve/presence of coronary artery disease by stress testing or invasive monitoring. Recognition of this risk logically should lead to protocols that delineate coronary artery disease/cardiac reserve before surgery and correct for observed abnormalities during surgery. This study sought to show that a coherent algorithm of preoperative cardiac assessment combined with aggressive perioperative management could indeed reduce perioperative myocardial infarction rates. Six hundred thirty consecutive elective vascular operations were performed by the author during 6 years. All patients were entered into a prospective protocol for preoperative cardiac risk assessment, which then determined the choice of operation, type of anesthesia, and level of hemodynamic monitoring. Sixty-eight percent of the patients demonstrated clinical coronary artery disease, 15% had previously undergone coronary catheterization or surgery, and 9% had ejection fractions less than 35%. All patients underwent baseline detailed cardiac histories, radionuclide cardioangiography, and electrocardiograms. Patients with significant historic coronary artery disease or ejection fraction less than 50% underwent stress thallium testing; patients with positive fixed or redistribution defects then underwent catheterization, constituting 7% of the series. Risk stratification by age and cardiac assessment then dictated the perioperative care. The overall perioperative myocardial infarction rate was 0.7% (5/628), ranging from 0% for 156 aortic operations and 114 carotid endarterectomies to 0.6% for 159 femoropopliteal and 3.3% for 90 femorotibial revascularizations.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation and management of patients with both peripheral vascular and coronary artery disease

The prevalence of serious angiographic coronary artery disease ranges from 37% to 78% in patients undergoing operation for peripheral vascular disease. Clinical studies have demonstrated that cardiac outcome after peripheral vascular surgery is not adequately predicted by the standard criteria of history, physical findings and rest electrocardiogram. An adequate exercise work load, left ventricular function and thallium redistribution have proved important in perioperative risk stratification. The choice of a perioperative functional cardiac test depends on patient-related factors and the nature of the peripheral vascular operation. Although procedures involving aortic cross-clamping exert a greater hemodynamic stress than do carotid endarterectomy and femoral popliteal surgery, late cardiac morbidity and mortality are significant in all patients with atherosclerotic disease. The decision to proceed with preoperative coronary angiography and myocardial revascularization should be based primarily on indications independent of the peripheral vascular procedure. However, peripheral vascular surgery may influence the timing of myocardial revascularization. Patients with high risk or unstable coronary artery disease may benefit from preoperative coronary revascularization, although this hypothesis remains unproved. In all patients, careful monitoring during and after operation is essential. All patients with peripheral vascular disease should be considered to be at lifelong risk for fatal and nonfatal cardiac events and should undergo appropriate clinical and laboratory evaluation and be treated accordingly.

Anaesthesia for abdominal aortic surgery--a review (Part II)

Patients presenting for abdominal aortic surgery have a high incidence of vascular disease elsewhere, manifested primarily by hypertension, coronary and cerebrovascular disease, as well as co-existing respiratory, renal and metabolic disorders. Routine clinical assessment, electrocardiogram, chest roentgenograms, resting and exercise radionuclide ventriculography and echocardiography, dipyrdiamole-thallium scanning are all designed to assess the functional status of the myocardium and to detect the presence of significant coronary artery disease. Patients with no abnormalities on physical examination, routine evaluation and no redistribution on dipyridamole-thallium scanning should proceed to surgery with the expectation of very low perioperative cardiac risk. Patients with evidence of coronary artery disease and significant redistribution on dipyridamole-thallium scan should undergo coronary angiography and possible myocardial revascularization before definitive aortic vascular surgery. For high cardiac risk patients with no bypassable lesions presenting for abdominal aortic aneurysm resection a conservative policy of serial three monthly ultrasound or CT assessment may be adopted, with selective resection for rapid aneurysm expansion or symptom development. A variety of extra-anatomical and angioplastic techniques is available for similar high cardiac risk patients with aortoiliac occlusive disease. The haemodynamic consequences of aortic cross-clamping, especially in aneurysm patients, include a significant reduction in stroke volume, cardiac index, and myocardial oxygen consumption with an increased systemic vascular resistance. Patients with coronary artery disease may respond to aortic cross-clamping by increasing pulmonary capillary wedge pressure and by demonstrating ECG evidence of myocardial ischaemia. Pulmonary artery catheterization is especially indicated in patients with a history of previous myocardial infarction, angina or signs of cardiac failure and in patients with evidence of diminished ejection fraction, abnormal ventricular wall motion or myocardial redistribution on preoperative scanning. The more widespread application of intraoperative transoesophageal two-dimensional echocardiography and radionuclide cardiography monitoring techniques into anaesthetic practice will enable measurement of left ventricular dimensions, myocardial performance and wall motion. Suggested guidelines for anaesthetic management are presented in Table VI. A combined opiate-oxygen-volatile anaesthetic agent technique will best ensure a hypodynamic circulation with preservation of myocardial oxygenation.(ABSTRACT TRUNCATED AT 400 WORDS)

Intraoperative management of abdominal aortic aneurysms. The anesthesiologist's viewpoint

Factors that influence the choice of anesthetic, monitoring methods, and fluid management for aneurysm repair are reviewed, with particular attention to epidural anesthesia and analgesia and the pulmonary artery catheter. Management of bleeding, renal preservation, temperature control, and myocardial ischemia are discussed, and special anesthetic issues associated with ruptured aneurysms and juxtarenal and suprarenal surgery are summarized.

Fractional change in blood volume following normal saline infusion in high-risk patients before noncardiac surgery

Patients with multiple-system disease were considered to be at high-risk to develop cardiac complications when undergoing an elective noncardiac surgical procedure. Their operative risk was prospectively assessed by a protocol that included recording the presence of established clinical risk factors and measuring the hemodynamic response to an intravenous infusion of up to 2 L of normal saline given over a two-hour period. The day prior to their operations, 126 patients were admitted to the Surgical Intensive Care Unit, where pulmonary artery catheters were inserted without serious complications. One hundred and eleven patients tolerated the entire 2-L infusion. The hemoglobin concentration of blood was measured before and after the infusion. The fractional change in blood volume (BV after/BV before) calculated with hemoglobin data was 1.06 +/- 0.06 (mean +/- SD). A multivarient discriminant analysis showed that the fractional change in blood volume was a covariant with a higher correlation rank than the hemodynamic data in identifying patients at risk for an adverse outcome.

Effect of calcium entry and beta blockade during infrarenal aortic clamping

Clamping and declamping during aortic surgery produce a hemodynamically significant myocardial stress. The cardiovascular (CV) response to this stress may be adversely altered by calcium antagonists and beta-adrenoreceptor blockade employed to control symptomatic coronary artery disease. This study evaluated the effect of verapamil (V), propranolol (P), and their combination (P + V) on the CV response to infrarenal abdominal aortic cross-clamping and declamping in anesthetized dogs. Six dogs received P as a bolus of 0.5 mg/kg 20 min before clamping. Six additional dogs received V as a 300 micrograms/kg bolus followed by a V infusion of 6 micrograms/kg/min for 20 min before clamping. A third group of six dogs received the P bolus followed 20 min later by the V regimen (P + V). In both the V and P + V groups, 6 micrograms/kg/min V was infused throughout the clamping and declamping sequence. A fourth group of six control dogs received no cardioactive drugs during the experiment. Heart rate, mean aortic blood pressure, left ventricular end-diastolic pressures, peak rate of rise of left ventricular pressure, cardiac output, and systemic vascular resistance were measured in all animals before aortic cross-clamping, at 5 and 40 min after clamping, and 5 min after declamping. The results demonstrated additive negative chronotropic and inotropic properties of P + V therapy with a more significantly adverse effect than that of either drug alone. The implications of this study warrant added caution when patients treated with these drugs undergo abdominal aortic surgery.

Effects of nifedipine on the hemodynamic response to clamping and declamping of the abdominal aorta in dogs

Clamping and declamping of the infrarenal abdominal aorta may adversely affect cardiovascular function, particularly in the presence of heart disease. This effect may be further altered by drugs used in the treatment of symptomatic coronary artery disease. The effect of nifedipine on the hemodynamic response to aortic clamping and declamping was determined in 12 dogs anesthetized with 50% nitrous oxide and 0.6% end-tidal isoflurane and monitored with aortic, left ventricular (LV), and thermodilution pulmonary artery catheters. Six dogs received a nifedipine bolus of 100 micrograms/kg followed by an infusion of 4 micrograms/kg/min. Six dogs did not receive any nifedipine and served as controls. Before clamping, nifedipine produced immediate decreases in arterial pressure, systemic vascular resistance (SVR), and LV dP/dt, and a modest increase in cardiac output (CO). During aortic clamping, nifedipine-treated dogs demonstrated marked increases in heart rate (HR), dP/dt, and CO while maintaining a low SVR. There were no significant changes upon declamping. The nifedipine-treated animals maintained a high CO and low SVR. Thus, nifedipine greatly altered the hemodynamic responses to aortic clamping and declamping. Awareness of these alterations is important when caring for patients being treated with nifedipine who are undergoing aortic surgery.

The reason for cardiac output reduction after aortic cross-clamping

The hypothesis that a decrease in cardiac output during infrarenal aortic cross-clamping is related to a decrease in oxygen consumption in the perfused tissues (cross-clamp-adapted oxygen consumption) rather than to deterioration of myocardial performance has been tested. Twenty-two patients undergoing excision of an aortic abdominal aneurysm were randomly divided into two groups of equal number. During aortic cross-clamping, Group 1 patients received nitroglycerin infusion, 1 to 2 micrograms.kg-1.min-1, whereas Group 2 patients did not receive a nitroglycerin infusion. During aortic cross-clamping, cross-clamp-adapted body oxygen consumption decreased equally in both groups by 40 to 42 percent of baseline values, whereas cardiac output decreased by 17 percent in Group 2 but did not change significantly in Group 1. Mixed venous oxygen content increased significantly after induction of anesthesia and prior to aortic cross-clamping in both groups. During cross-clamping, the values of mixed venous oxygen content remained increased in Group 2 and increased further in Group 1. The data support our hypothesis since a decrease in cardiac output was not associated with an increase in filling pressures during aortic cross-clamping, but was instead associated with an increase in mixed venous oxygen content and a decrease in the arteriovenous oxygen content difference. Nitroglycerin infusion was associated with a further increase in mixed venous oxygen content during aortic cross-clamping and a decrease in the arteriovenous oxygen content difference, without a concomitant increase in oxygen utilization.