Stephen D. Parker

Perioperative Morbidity in Patients Randomized to Epidural or General Anesthesia for Lower Extremity Vascular Surgery

Background:Perioperative morbidity may be modifiable in high risk patients by the anesthesiologists choice of either regional or general anesthesia. This clinical trial compared outcomes between epidural (EA) and general (GA) anesthesia/analgesia regimens In a group of patients at high risk for cardiac and other morbidity who were undergoing similarly stressful surgical procedures. Methods:One hundred patients scheduled for elective vascular reconstruction of the lower extremities were randomized to receive either EA for surgery followed by epidural analgesia, or GA for surgery followed by intravenous patient-controlled analgesia. Hemodynamic monitoring, blood pressure, and heart rate limits were determined prior to randomization. Management of anesthesia in the immediate postoperative period was standardized. The data collected included continuous electrocardiographic monitoring from the day before surgery through the third postoperative day, serial electrocardiograms, and cardiac enzymes. Cardiac ischemia, myocardial infarction, unstable angina, and cardiac death were identified by a cardiologist blinded to the type of anesthesia received. Other major morbidity was determined at the time of hospital discharge and at 1 and 6 months after surgery. Results:Eleven patients who received GA required regrafting or an embolectomy during their hospital stay, compared with two patients who received EA. This association of GA with reoperation remained significant after adjustment for baseline differences. Cardiac outcomes were similar in the two groups with respect to perioperative death (1 EA and 1 GA), death within 6 months (4 EA and 3 GA), nonfatal myocardial infarction within 7 days (2 EA and 2 GA), unstable angina (0 EA and 2 GA), and myocardial ischemia following randomization (17 EA and 23 GA). Rates of major infections in the two groups (1 EA and 2 GA), renal failure (3 EA and 3 GA), and pulmonary complications (3 EA and 7 GA) also were similar. Conclusions:Carefully conducted epidural and general anesthesia appear to be associated with comparable rates of cardiac and most other morbidity in patients undergoing lower extremity vascular surgery. However, compared with general anesthesia, epidural anesthesia is associated with a lower incidence of reoperatlon for inadequate tissue perfusion and, therefore, may be advantageous for this surgical population.

The effects of different anesthetic regimens on fibrinolysis and the development of postoperative arterial thrombosis

Background:The purpose of this clinical trial was to compare the effects of different anesthetic and analgesic regimens on hemostatic function and postoperative arterial thrombotic complications. Methods:Ninety-five patients scheduled for elective lower extremity vascular reconstruction were randomized to receive either epidural anesthesia followed by epidural fentanyl (RA) or general anesthesia followed by intravenous morphine (GA). Intraoperative and postoperative care were controlled by protocol using predetermined limits for heart rate, blood pressure, and other monitoring criteria. Data collection included serial physical examinations, electrocardiograms, and cardiac isoenzymes to detect arterial thrombosis (defined as unstable angina, myocardial infarction, or vascular graft occlusion requiring reoperation). Fibrinogen, plasminogen activator inhibitor-1 (PAI-1), and D-dimer levels were measured preoperatively and at 24 and 72 h postoperatively. Results:Preoperative fibrinogen levels were similar in both groups, remained unchanged after 24 h, and increased equally (45%) in the first 72 h postoperatively. PAI-1 levels in the GA group increased from 13.6 ± 2.1 activity units (AU)/ml to 20.2 ± 2.6 AU/ml at 24 h and returned to baseline at 72 h. In contrast, PAI-1 levels in the RA group remained unchanged over time. Twenty-two of 95 patients (23%) had postoperative arterial thrombosis, 17 of whom had received GA and 5 of whom, RA. Preoperative PAI-1 levels were higher in patients who developed postoperative arterial thrombosis (20.5 ± 3.6 AU/ml vs. 11.2 ± 1.4 AU/ml). Multiple logistic regression analysis indicated that GA and preoperative PAI-1 levels were predictive of postoperative arterial thrombotic complications. Conclusions:Impaired fibrinolysis may be related causally to postoperative arterial thrombosis. Because RA combined with epidural fentanyl analgesia appears to prevent postoperative inhibition of fibrinolysis, this form of perioperative management may decrease the risk of arterial thrombotic complications in patients undergoing lower extremity revascularization.

Epidural versus general anesthesia, ambient operating room temperature, and patient age as predictors of inadvertent hypothermia.

To elucidate the multifactorial nature of perioperative changes in body temperature, the influence of several clinical variables, including anesthetic technique, ambient operating room temperature, and age, were evaluated. Perioperative oral sublingual temperatures were measured in 97 patients undergoing lower extremity vascular surgery randomized to receive either general (GA) or epidural (EA) anesthesia. Surgery and anesthesia were performed in operating rooms (OR) with a relatively warm mean ambient temperature (24.5 +/- 0.4 degrees C) (GA, n = 30; EA, n = 33) or relatively cold mean ambient temperature (21.3 +/- 0.3 degrees C) (GA, n = 21; EA, n = 13). Patients were 35-94 yr old, with a mean age of 64.5 +/- 1.1 yr. A regression analysis was performed to determine the variables that correlated with intraoperative decrease in temperature and postoperative rewarming rate. The major correlates of greater intraoperative decrease in temperature were 1) GA (P = 0.003); 2) cold ambient OR temperature (P = 0.07); and 3) advancing patient age (P = 0.03). There was significant interaction between ambient OR temperature and type of anesthesia (P = 0.03): there was a greater intraoperative decrease in temperature with GA compared to EA in a cold OR but a similar decrease with GA and EA in a warm OR. The data also suggest an interaction between type of anesthesia and patient age (P = 0.06), showing a greater decrease in temperature with GA compared to EA in the younger patients, but a similar decrease between GA and EA in older patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of Catecholamine and Cortisol Responses to Lower Extremity Revascularization

BackgroundSurgical trauma elicits diffuse changes in hormonal secretion and autonomic nervous system activity. Despite studies demonstrating modulation of the stress response by different anesthetic/analgesic regimens, little is known regarding the determinants of catecholamine and cortisol responses to surgery. MethodsPlasma catecholamines and cortisol secretion data were obtained from 60 patients undergoing lower extremity revascularization. Patients were randomized to receive either general anesthesia combined with patient-controlled intravenous morphine (GA) or epidural anesthesia combined with epidural fentanyl analgesia (RA). All aspects of intra-and postoperative clinical care were defined by written protocol. Plasma catecholamines were measured before Induction, intraoperatively, and for the first 18 h postoperatively (by HPLC). Urine cortisol was measured intra-and postoperatively using RIA. Data were evaluated using univariate and multivariate analyses to evaluate demographic and perioperative variables as determinants of stress hormone secretion. ResultsPlasma catecholamines Increased during skin closure in the GA group, and remained higher relative to the RA group in the postoperative period. Multivariate analysis indicated that age and anesthetic regimen predicted increases in catecholamines during skin closure (P < 0.005), although duration of surgery, blood loss, and body temperature were not correlated. Early postoperative norepinephrine concentrations were correlated with pain score and duration of surgery (P < 0.004), but not with anesthetic management, blood loss, or body temperature. All postoperative norepinephrine levels were highly correlated (r = 0.7) with norepinephrine levels during skin closure. Cortisol excretion was higher postoperatively than intraoperatively. No patient or perioperative variable predicted cortisol excretion, and cortisol excretion was not correlated with catecholamine levels at any time. ConclusionsThese data Indicate that patient factors, such as age and Inherent sympathetic responsivity, are important determinants of the catecholamine response to surgery. Modulation of the norepinephrine response by regional anesthesia/analgesia appears to be related, in part, to superior analgesia. The lack of correlation between catecholamine and cortisol secretion indicates that the stress response may consist of discrete systems responding to different stimuli.

Catecholamine and cortisol responses to lower extremity revascularization: Correlation with outcome variables

OBJECTIVE To determine whether catecholamine and cortisol secretory responses to surgery contribute to postoperative complications. DESIGN Prospective, randomized, case series. SETTING A university hospital operating suite and surgical intensive care unit. PATIENTS Sixty patients undergoing lower extremity vascular surgery. INTERVENTIONS Patients were randomized to receive either epidural anesthesia/epidural opiate analgesia (regional anesthesia) or general anesthesia/intravenous patient-controlled analgesia (general anesthesia). MEASUREMENTS AND MAIN RESULTS Anesthesia was managed according to a prospectively designed protocol. Hemodynamic parameters and plasma catecholamine concentrations were determined at specific intraoperative and postoperative time points. Intraoperative and postoperative urine samples were collected and analyzed for free cortisol concentrations. Outcomes evaluated were cardiac (nonfatal myocardial infarction and cardiac death) and surgical (graft occlusion). Mean arterial pressure during emergence from anesthesia and in the early postoperative period correlated positively with plasma norepinephrine concentration (p < .01). In addition, plasma catecholamine concentrations were higher in patients with postoperative hypertension. Plasma norepinephrine concentrations at the time of emergence from anesthesia and postoperatively were also higher in patients requiring repeat surgery for graft revision, thrombectomy, or amputation (p < .05). Multivariate analysis indicated that the norepinephrine concentration at the time of emergence, but not type of anesthesia, correlated with reoperation for graft occlusion, suggesting that the previously reported beneficial effect of regional anesthesia may be due to modulation of the stress response. Myocardial infarction or cardiac death occurred in three patients. These patients had markedly increased catecholamine concentrations. CONCLUSIONS The catecholamine response to lower extremity vascular surgery contributes to the development of postoperative hypertension and may also be important in the development of thrombotic complications.

Does the routine prophylactic use of antiemetics affect the incidence of postdischarge nausea and vomiting following ambulatory surgery?: A systematic review of randomized controlled trials.

THE rapid increase in ambulatory surgery procedures performed over the past 10 yr has resulted in greater focus directed toward the control of postoperative nausea and vomiting (PONV), sometimes appropriately termed the “big, little problem.” The incidence of this complication is variable, but PONV has emerged as one of the commonest complications following ambulatory surgery, and the one that patients would most like to avoid. Specifically, the postdischarge period has been poorly studied but is important from the patient’s perspective. Despite the increasing availability of newer and more expensive drugs for the prevention of PONV, some authors question the routine use of single-drug prophylaxis in low-risk patients. The long-term ( 6 h) effect of antiemetics is even more uncertain in the ambulatory setting, because the focus of attention has previously been on the management of early PONV (in the day surgical unit). As many as 35–50% patients continue to have postdischarge nausea and vomiting (PDNV). It is important to control this symptom after discharge, because resumption of normal activities may be delayed if PONV is prolonged and ambulatory surgical patients are not under direct medical supervision after discharge. In our experience, few centers routinely provide antiemetics for the control of PDNV at home. Numerous systematic reviews have now been published in the literature on PONV, but only one has focused on PONV after hospital discharge in ambulatory surgical patients. This systematic review was completed to address the question of whether the routine prophylactic use of antiemetics affects the incidence of PDNV following ambulatory surgery. We restricted our analysis to randomized, controlled studies published in the English literature.

Moderate hypothermia, with partial bypass and segmental sequential repair for thoracoabdominal aortic aneurysm

PURPOSE Ischemic injury to the spinal cord, kidneys, and viscera occurs in a significant number of patients undergoing surgical repair of thoracoabdominal aortic aneurysms. Partial bypass has been used to perfuse the arterial system distal to the cross-clamp, but the primary determinant of ischemic morbidity remains the duration of aortic cross-clamping. Hypothermia may favorably affect outcome during these procedures, but moderate or deep hypothermia has traditionally required full cardiopulmonary bypass with cardiac arrest. METHODS In a series of patients undergoing thoracoabdominal (n = 14) or thoracic (n = 4) aneurysm repair, we used moderate hypothermia (30 degrees C) and partial bypass (aortofemoral or atriofemoral) while maintaining an intrinsic cardiac rhythm. Body temperature was controlled with a heat exchanger in the bypass circuit, which allowed for rapid cooling and rewarming. In addition to hypothermia and bypass, a segmental sequential surgical repair was used to minimize the duration of ischemia to any given vascular bed. RESULTS All patients survived the surgical procedure, and 16 patients survived until discharge from the hospital. None of the 18 patients had paraplegia or significant renal dysfunction. The only complication related to hypothermia was atrial fibrillation, which occurred in three patients and was amenable to therapeutic measures. CONCLUSIONS We conclude that moderate hypothermia, partial bypass, and segmental sequential repair may reduce ischemic injury. This combination of adjuncts was not associated with significant complications in this series of patients.

Changes in Cerebrospinal Fluid Pressure and Lactate Concentrations during Thoracoabdominal Aortic Aneurysm Surgery

Background Although ischemic injury to the spinal cord is a well‐known complication of aortic surgery, no metabolic markers have been identified as predictors of an adverse outcome. This study evaluated the effect of cerebrospinal fluid (CSF) drainage, with and without distal femoral perfusion or moderate hypothermia on blood and CSF lactate concentrations and CSF pressure during thoracoabdominal aortic aneurysm surgery. Methods Three nonconcurrent groups of patients were studied prospectively: patients with normal body temperature (35 degrees Celsius) but without distal femoral bypass (n = 6), patients with normal body temperature with bypass (n = 7), and patients with hypothermia (30 degrees Celsius) and bypass (n = 8). In all patients, CSF pressure was recorded before, during, and after aortic cross‐clamping. During the surgical repair, CSF drainage was performed using a 4‐Fr intrathecal silicone catheter. Blood and CSF lactate concentrations were measured throughout the operation. Results Significant increases in blood (490%) and CSF (173%) lactate concentrations were observed during and after thoracic aortic occlusion in patients with normothermia and no bypass (P < 0.02 and 0.05, respectively). Distal perfusion attenuated the increase in both blood and CSF lactate (P < 0.01), and a further reduction was achieved with hypothermia of 30 degrees Celsius (P < 0.001). Patients who became paraplegic showed a greater increase in CSF lactate concentrations after aortic clamp release compared with those who suffered no neurological damage (275% vs. 123% of baseline; P < 0.05). Increased CSF pressure of 42–60% (P < 0.005) was noted soon after thoracic aortic occlusion, both with and without distal femoral bypass. Conclusions Incremental reductions in CSF lactate concentrations were achieved using distal femoral bypass and hypothermia. The reduction in CSF lactate correlated with the methods used to protect the spinal cord during thoracoabdominal aortic aneurysm surgery and was associated with better outcome. Decompression by distal bypass of the hemodynamic overload caused by aortic occlusion was insufficient to eliminate the acute increase in CSF pressure. Cerebrospinal fluid lactate measurements during high aortic surgery may accurately represent the spinal cord metabolic balance.

Spinal cord stimulation evoked potentials during thoracoabdominal aortic aneurysm surgery

Although monitoring of somatosensory evoked potentials elicited from stimulation of lower extremity peripheral nerves has been suggested as a method for assessing neural function during thoracoabdominal aortic aneurysm surgery, this technique has been reported to yield a large number of false positives. It was believed that direct stimulation of the spinal cord would eliminate some of the problems associated with peripheral evoked potentials. The present study compared in 18 patients the use of scalp recorded evoked potential following stimulation of either the posterior tibial nerve via percutaneous needles or the spinal cord via an epidural electrode previously placed fluoroscopically. In 10 patients in whom distal bypass or shunt was not used, peripheral evoked potentials totally disappeared within 5-30 min of aortic clamping. Spinal cord stimulation evoked potentials disappeared permanently in 2 patients shortly after aortic cross-clamping; 1 died shortly after the procedure, and the other awoke densely paraplegic and died the next day. When distal perfusion was maintained by shunt or bypass, the disappearance of both peripheral and spinal evoked potentials accurately predicted the neurologic outcome of 1 paralyzed patient. Loss of spinal cord stimulation evoked potentials was found to be correlated with adverse neurologic outcome. Over the period of aortic clamping a gradual decrease in mean amplitude (50% at 45 min [P less than 0.05]) and a 20% increase in mean latency time were observed. Maintenance of adequate distal perfusion may permit the use of peripheral evoked potentials in the assessment of spinal cord ischemia during aortic cross-clamping.(ABSTRACT TRUNCATED AT 250 WORDS)

Perioperative rate-related silent myocardial ischemia and postoperative death

A case is presented that demonstrates heart rate (HR)--related silent myocardial ischemia occurring preoperatively, subsiding intraoperatively, then recurring and leading to a post-operative cardiac death in a patient undergoing peripheral vascular surgery. This case illustrates that patients may have an ischemic threshold for HR whereby recurrent depression of the ST segment may occur during increase of HR to rates as low as 80 to 85 beats per minute (bpm), even in the absence of acute blood pressure (BP) changes. Myocardial ischemia may be HR related; however, the authors are not aware of a case that demonstrates repeated episodes of rate-related ischemia occurring at HRs well below the 100 bpm traditional definition of tachycardia. The authors conclude that patients at risk for perioperative myocardial ischemia should be identified and the hemodynamic management of these patients should include control of HR. This implies control of the physiologic variables that influence HR, along with the use of beta-adrenergic blockers. This case also demonstrates the value of Holter monitoring for ischemia, which, when done preoperatively, can detect patients at risk for unfavorable cardiac outcomes. Ischemia monitoring also may be useful during the intraoperative and postoperative periods, a time when ischemia is often silent and undetected. The early recognition of ischemia would allow for anti-ischemic interventions, which could decrease the morbidity and mortality of patients at risk for perioperative cardiac complications.