Faculty Bibliography

Paraplegia secondary to spinal cord ischemia is a too frequent devastating complication of thoracic aneurysm surgery. We examined the ability of veno-arterial bypass (VAB) to ensure adequate spinal cord blood flow during aortic cross-clamping by monitoring spinal cord function via somatosensory evoked potentials (SEP's) and postoperative motor function. Dogs were placed on VAB using a heparin-bonded roller pump circuit without systemic heparinization. SEP latency and amplitude were monitored continuously. The respirator FIO2 was set at 100% while the aorta was cross-clamped for one hour with the bypass adjusted to keep distal arterial pressure at greater than 60 mmHg. After one hour the aorta was unclamped, bypass discontinued, and the animals recovered. SEP's were always present during VAB as long as the distal pressure was kept at greater than 60 mmHg. There were several transient hypotensive episodes (less than 5 min) which were accompanied by reversible loss of SEP's. None of the animals displayed any gait abnormalities post-op. These findings using this simple bypass technique suggest the following conclusions: (1) SEP's degenerate (increased latency and decreased amplitude) in response to hypoxia; (2) spinal cord function can be maintained for up to one hour during hypoxic conditions; (3) SEP's can be used to monitor sensory spinal cord function under these conditions; and (4) heparinless VAB can provide spinal cord protection while also allowing monitoring of SEP's to ensure adequate spinal cord perfusion

The purpose of this experimental study was to examine the differences between peripheral nerve stimulation and direct spinal stimulation in generating cortical somatosensory-evoked potential (SEP) responses for monitoring spinal cord ischemia during thoracic aorta cross-clamping. Adult mongrel dogs (n = 6) were placed under general anesthesia and a left thoracotomy was performed. A conventional stimulating electrode was placed over the posterior tibial nerve (PN-SEP), and a special bipolar electrode was placed epidurally over the spinal cord at L1-2 (SC-SEP). The aorta was cross-clamped proximal to the left subclavian artery. Stimulations were alternately performed through both electrodes, and SEP responses were continuously monitored. The cross-clamp was released after one hour and the animal was observed for another hour prior to sacrifice. Excellent SEPs were obtained with six stimuli over 3 sec via the SC-SEP stimulus in contrast to the 200 stimulations over 90 sec required for the PN-SEP stimulus. Aortic cross-clamping resulted in a significantly longer mean time to loss of SEPs for SC-SEP (mean +/- SEM, 13.7 +/- 1.0 min for SC-SEP vs 11.3 +/- 0.7 min for PN-SEP, P less than 0.05). Likewise, unclamping of the aorta consistently resulted in a shorter mean time to return of SEPs for SC-SEP compared with PN-SEP. These data indicate that direct epidural stimulation for evoked cortical responses is a more sensitive means of determining the adequacy of posterior spinal cord blood flow as reflected by posterior spinal cord function.(ABSTRACT TRUNCATED AT 250 WORDS)

Current use of angioplasty, thrombolysis, and surgical techniques for prompt reperfusion of an acute myocardial infarction raises questions concerning the optimum reperfusion technique for maximum myocardial salvage. Alterations in the conditions of reperfusion and/or the composition of the initial reperfusate can exert a significant effect on the extent of myocardial salvage. In an effort to define an optimum reperfusion technique, we used 40 dogs in a series of experiments in which the left anterior descending coronary artery (LAD) was snared for 2 hr followed by reperfusion by one of five methods for 4 hr. In addition, in a control group(group I, n = 6) the LAD was occluded for 6 hr without any reperfusion. In group 2 (n = 12), simulating medical reperfusion, reperfusion was achieved by simply releasing the snare for 4 hr. Group 3 dogs (n = 6) were placed on pulsatile left atrial-femoral bypass throughout 4 hr of reperfusion. Group 4 dogs (n = 9) were placed on percutaneous, synchronized pulsatile cardiopulmonary bypass during reperfusion. The procedure in group 5 (n = 7) dogs simulated coronary artery bypass grafting with cardiopulmonary bypass and cold blood, low-Ca++ cardioplegia during reperfusion. Group 6 (n = 6) was treated similarly except that during reperfusion amino acid-enriched cardioplegia was administered by warm induction techniques. At the end of 4 hr of reperfusion, the left ventricular area of infarction was determined by triphenyltetrazolium chloride staining and expressed as a percentage of the left ventricular area at risk for infarction (area of infarction [AI]/area at risk [AR]).(ABSTRACT TRUNCATED AT 250 WORDS)

To assess the intraoperative and postoperative hemodynamic effects of beta-blockade and its benefits in limiting myocardial ischemia and infarction, a group of 32 patients scheduled for abdominal aortic aneurysm (AAA) surgery (group 1) was treated with oral metoprolol immediately before surgery and with intravenous metoprolol during the postoperative period. Mean age was 71 years, and mean ejection fraction was 56% (range 36% to 83%). Eight patients had a preoperative history of angina, 13 had a history of myocardial infarction, and five had electrocardiographic evidence of prior myocardial infarction. A group of 51 closely matched patients with AAA who did not receive metoprolol served as controls (group 2). In group 1, overall hemodynamic tolerance of metoprolol intraoperatively and postoperatively was good, and there was no incidence of congestive heart failure, hypotension, or asthma. Furthermore, in group 1 significant reduction of systolic blood pressure and heart rate was consistently noted at frequent intraoperative intervals and for 48 hr after surgery, with only a transient reduction of cardiac index. In group 1, only one patient (3%) suffered an acute myocardial infarction. In contrast, nine group 2 patients (18%; p less than .05) suffered perioperative myocardial infarction. Furthermore, only four (12.5%) group 1 patients developed significant cardiac arrhythmias as opposed to 29 group 2 patients (56.9%; p less than .001). These data demonstrate that beta-blockade with metoprolol is effective in controlling systolic blood pressure and heart rate both intraoperatively and postoperatively in patients undergoing repair of AAA and can significantly reduce the incidence of perioperative myocardial infarction and arrhythmias

Percutaneous total cardiopulmonary bypass offers the advantage of rapid, simple implementation without the need for thoracic incision and provides the ability to support both left and right ventricular failure as well as pulmonary insufficiency. Previous studies using roller pump percutaneous bypass were only partially successful because of the inability to effectively unload the left ventricle. In the present experiment we attempted to determine in a normal canine model whether use of synchronous pulsatile pumping for percutaneous bypass could overcome this problem. Fourteen dogs were placed on percutaneous bypass for 1 hour. A roller pump was used in seven and a synchronous pulsatile pump with an electrocardiogram triggering mechanism in the other seven. All animals were maintained on percutaneous bypass for 1 hour. In the pulsatile pump group there was a significantly greater percent decrease from baseline in tension-time index (-56.3% versus -19.1%, p less than 0.01) and in myocardial oxygen consumption (-45.8% versus +2.1%, p less than 0.05) and a significantly greater percent increase in the endocardial/epicardial blood flow ratio (27.6% versus -6.5%, p less than 0.01) than in the roller pump group. These results show that superior unloading can be achieved by percutaneous pulsatile bypass compared with percutaneous roller pump bypass. The findings suggest that percutaneous total cardiopulmonary bypass with a synchronous pulsatile pump offers a relatively simple but effective method for providing appropriate patients with temporary hemodynamic stability before cardiac catheterization or medical or surgical revascularization

The purpose of this study was to determine the factors influencing successful experimental cardiopulmonary bypass studies using pulsatile flow perfusion and the medications and methodology necessary to produce successful bypass in calves. In six calves showing no cardiopulmonary pathology prior to bypass procedures, successful anesthesia and surgical intervention was accomplished. Animals were maintained on 5 hours of pulsatile flow bypass perfusion. Successful recovery from the procedures was accomplished. In two calves with pre-existing pulmonary pathology, anesthetic and surgical intervention was accomplished with the utilization of extensive anesthetic management and cardiac supportive medications until the animals could be initiated into 5 hours of pulsatile flow bypass perfusion, in spite of major pulmonary dysfunction. In these two animals, attempts to resuscitate upon termination of pulsatile flow perfusion were unsuccessful due to pre-existing excessive lesions in the lungs. This study shows a contrast between complete success of a pulsatile flow system in normal subjects versus the ultimate failure in experimental animals with pre-existing pulmonary pathology. The inability of experimental calves with a diseased lung to resume spontaneous cardiopulmonary function after the challenges of thoracic intervention indicates the unsuitability of animals with marked pre-existing pulmonary disease status for use in cardiopulmonary bypass studies

This investigation examined the efficacy of right atrial-pulmonary artery bypass (RA-PA) during acute ischemia of the right ventricle. The right coronary artery (RCA) was ligated in 25 open chest, open pericardium sheep. Control animals (n = 15) were resuscitated with only intravenous fluids. In the experimental animals (n = 10) RA-PA bypass was initiated 5 minutes after right coronary occlusion. Sixty percent (9/15) of the control animals died within 90 minutes of RCA occlusion from refractory ventricular arrhythmia or right ventricular failure. Four of 10 RA-PA animals died within 2 hours of RCA occlusion from severe pulmonary hemorrhage and arterial oxygen desaturation when high flow rates (2.5 to 3.5 L/min) were initially instituted. In these animals, lung histologic findings demonstrated extensive hemorrhage into the alveolar spaces. After 6 hours of RCA occlusion in the six surviving control animals, there were significant increases in central venous pressure and right ventricular end-diastolic cord length (relative ventricular volume change measured by ultrasonic crystal analysis), and a significant decrease in the cardiac output. In contrast, during RCA occlusion in the six surviving animals on RA-PA bypass, cardiac output was well maintained, and there was a significant decrease in central venous pressure and end-diastolic length. The percent of change from baseline in end-diastolic length correlated inversely with the percent of change from baseline in cardiac output (r = -0.81, p less than 0.01). By crystal violet and triphenyltetrazolium chloride dye techniques, the mean percentage area of necrosis to area of risk was significantly less for the RA-PA group compared with the control group (5.6% versus 67.1%, p less than 0.0001). In this experimental model, RA-PA bypass effectively unloaded the acutely ischemic right ventricle, maintained systemic cardiac output, and significantly reduced right ventricular infarction size. Further investigations with this ventricular support modality are needed to determine its effects on pulmonary pathophysiology