Ira M. Nathan

Prevention of Ischemic Spinal Cord Injury Following Aortic Cross-Clamping: Use of Corticosteroids

Prior to proximal aortic cross-clamping, baseline measurements of spinal cord blood flow and function were done. Blood flow was evaluated with radioactive microspheres and function determined by assessment of somatosensory evoked potential (SEP). Group 1 (N = 6) animals had aortic cross-clamping for 5 minutes after ischemic spinal cord dysfunction (SEP loss) was documented. Group 2 (N = 9) underwent aortic cross-clamping for 10 minutes after loss of SEP. Group 3 (N = 6) also underwent 10 minutes of cross-clamping after initial SEP loss, but were treated intravenously with methylprednisolone (30 mg per kilogram of body weight) 10 minutes prior to cross-clamping and again 4 hours postoperatively. After release of the cross-clamp, the animals were allowed to recover and serial evaluations of spinal cord blood flow and neurological status were carried out for seven days. Group 1 animals recovered uneventfully without evidence of neurological injury. Group 2 animals sustained a 67% incidence of permanent spastic paraplegia (p = 0.02 versus Group 1). In contrast, methylprednisolone-treated animals sustained no clinically detectable neurological injury (p = 0.02 versus Group 2). Measurements of spinal cord blood flow at the time of SEP loss revealed similar degrees of spinal cord ischemia in all groups. No significant differences were observed in the duration of aortic cross-clamping prior to SEP loss among the three groups. The data indicate that short periods of cross-clamping (5 minutes) following SEP loss are well tolerated, whereas longer periods (10 minutes) are associated with a high incidence of paraplegia.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental and clinical assessment of the adequacy of partial bypass in maintenance of spinal cord blood flow during operations on the thoracic aorta.

We studied both experimentally and clinically the efficacy of partial bypass techniques in maintaining spinal cord blood flow and physiological function during surgical procedures on the thoracoabdominal aorta. We attempted to define the level of distal aortic pressure required to safely ensure normal neurological function in the absence of critical intercostal occlusion. Six dogs underwent left thoracotomy with baseline measurements of spinal cord blood flow and spinal cord impulse conduction (somatosensory evoked potentials). Following exclusion of the entire descending thoracic aorta from the left subclavian artery to the T-13 level, partial left atrium-femoral artery bypass was instituted, and baseline levels of proximal and distal aortic pressure were maintained during a 30-minute stabilization period. Mean distal aortic pressure then was progressively altered at 30-minute intervals to 100, 70, and 40 mm Hg. Measurements of spinal cord blood flow and somatosensory evoked potential were repeated at the end of each interval for comparison with baseline. No significant changes in spinal cord blood flow or somatosensory evoked potential were observed in any animal with a distal aortic pressure greater than or equal to 70 mm Hg. With a pressure of 40 mm Hg, normal flow and somatosensory evoked potentials were maintained in 5 of the 6 dogs. Loss of somatosensory evoked potential, with simultaneous loss of spinal cord blood flow at the T-6 level, occurred in 1 dog. Restoration of distal aortic pressure to 70 mm Hg in all animals resulted in immediate return of somatosensory evoked potential. Loss of somatosensory evoked potential routinely occurred in animals with a distal aortic pressure less than 40 mm Hg. Clinically, 9 patients have undergone operation for lesions of the thoracoabdominal aorta using shunt or bypass techniques. Normal somatosensory evoked potentials were preserved in 7 patients with maintenance of adequate distal aortic pressure (greater than or equal to 60 mm Hg) without evidence of postoperative neurological deficit. Two patients showed hypotensive somatosensory evoked potential loss (distal aortic pressure less than 40 mm Hg). Prolonged distal hypotension (85 minutes of aortic cross-clamping) in the latter resulted in paraplegia. We conclude that maintenance of a distal aortic pressure greater than 60 to 70 mm Hg will uniformly preserve spinal cord blood flow in the absence of critical intercostal exclusion. Should distal aortic pressure be inadequate, early reversible changes in the somatosensory evoked potential will alert the surgeon. Failure to institute measures to reverse these changes may result in paraplegia.

Long-Term Results of Open Radical Mitral Commissurotomy: Ten Year Follow-Up Study of 202 Patients

Two hundred two patients undergoing open radical mitral commissurotomy for mitral stenosis between 1967 and 1978 were evaluated. Follow-up data were obtained in 98 percent of patients (follow-up range 1 to 122 months, mean 42). One hundred forty-four patients (71 percent) underwent only commissurotomy; 58 patients required associated cardiac procedures. One hundred twenty-eight patients (63 percent) had a history of rheumatic fever and 15 (7 percent) had undergone prior closed mitral commissurotomy. Preoperative emboli were recorded in 25 percent. Cardiopulmonary bypass and left atriotomy were utilized to perform a radical valvulotomy, not only eliminating the mitral valve gradient, but also opening the valve as much as possible without producing insufficiency. The left atrial appendage was routinely checked for thrombus and usually closed with sutures. Induced aortic regurgitation by retrograde insertion of a perforated catheter was utilized to detect mitral insufficiency after commissurotomy. Mitral anulopiasty was performed when necessary. The operative mortality rate was 1.7 percent and the long-term mortality rate 2.5 percent. Preoperatively, 155 patients (77 percent) were in New York Heart Association functional class III or IV. At follow-up examination, 90 percent (178) were in functional class I or II. Postoperative emboli were rare (3 percent), but occurred more often after preoperative embolism or failure to obliterate the left atrial appendage. Multifactorial analysis showed that the presence of a residual mitral gradient or regurgitation indicated a poor prognosis. The 5 year complication-free survival rate in this group was significantly less than that in patients without residual valve dysfunction (75 versus 87 percent, p < 0.05). Open radical mitral commissurotomy appears to be a safe method for relieving valve obstruction. It allows removal of thrombus and oversewing of the left atrial appendage, which may reduce the possibility of significant postoperative embolic events. Reduction in turbulent blood flow by creating a widely patent and competent mitral valve diminishes progressive valve fibrosis and generally obviates the need for future valve replacement.

The role of endoscopic retrograde cholangiopancreatography and cholangiography in the laparoscopic era.

OBJECTIVE The authors reviewed the results of endoscopic retrograde cholangiopancreatography (ERCP) and intraoperative cholangiography in a series of patients who underwent laparoscopic cholecystectomy. SUMMARY BACKGROUND DATA The indications for preoperative and postoperative ERCP and intraoperative cholangiography as adjuncts to laparoscopic cholecystectomy are evolving. The debate regarding the use of selective or routine intraoperative cholangiography has intensified with the advent of laparoscopic cholecystectomy. METHODS The authors reviewed the records of 343 consecutive patients who underwent laparoscopic cholecystectomy during a 1-year period. Historical, biochemical, and radiologic findings for the patients who underwent ERCP and intraoperative cholangiography were analyzed. RESULTS Three hundred forty- three patients underwent laparoscopic cholecystectomy during the period reviewed. Preoperative ERCP was performed in 42 patients. Twenty-seven of these patients (64%) had common bile duct (CBD) stones, which were cleared with a sphincterotomy. Intraoperative cholangiography was performed for 101 patients (29%). Three cholangiograms had false- positive results (3%), leading to two CBD explorations, in which no CBD stones were found, and one normal ERCP. Six patients underwent postoperative ERCP, three for the removal of retained CBD stones (0.9%), all of which were cleared with a sphincterotomy. Fifteen patients had gallstone pancreatitis, six of whom had CBD stones (40%) that were cleared by ERCP. There were 33 complications (10%) and no CBD injuries. CONCLUSION The use of routine intraoperative cholangiography is discouraged in view of its low yield and the significant rate of false positive cholangiogram results.

Definition of the safe lower limits of aortic resection during surgical procedures on the thoracoabdominal aorta: Use of somatosensory evoked potentials

The technique of intraoperative monitoring of somatosensory evoked potentials was applied to a canine model of spinal cord ischemia in an attempt to determine the safe lower limits of aortic resection during thoracic aortic surgery. Fifteen animals underwent left thoracotomy with institution of partial left atrial/femoral artery bypass for maintenance of distal aortic perfusion after proximal descending thoracic aortic exclusion. In Group I animals (n = 6, control), no further interventions were performed so that the effect of exclusion of vessels noncritical to spinal cord blood supply could be assessed by measurements of spinal cord blood flow and somatosensory evoked potentials. In Group II animals (n = 8), the level of distal aortic exclusion was progressively lowered until loss of somatosensory evoked potential (critical vessel exclusion) occurred. The effect of critical vessel exclusion on spinal cord blood flow was then assessed. Exclusion of multiple vessels noncritical to spinal cord blood supply (Group I) had no effect on spinal cord blood flow or function (somatosensory evoked potentials). Exclusion of vessels critical to spinal cord blood supply resulted in significant spinal cord ischemia (83.4% flow reduction, probability [p] less than 0.05 versus baseline) and ischemic spinal cord dysfunction (loss of somatosensory evoked potential).(ABSTRACT TRUNCATED AT 250 WORDS)

Lordosimetry: a new technique for the measurement of postural response to materials handling.

A. device was designed and constructed which maps the configuration of the vertebral column. It was used to record changes in spinal configuration and general posture of a group of female subjects engaged in the holding of loads of different weights and bulk/weight ratios. This new apparatus provides a potentially useful procedure of the simple measurement of postural reaction to physical work stress during manual materials handling in industrial practice. In the course of the pilot study, measurement procedures were validated and standardized; the effects of body type, load bulk, and load weight on postural reaction are discussed.

Epidural-evoked potentials: A more specific indicator of spinal cord ischemia

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)

Increased release of cyclic adenosine monophosphate into jugular vein in response to isoproterenol administration

Catecholamine administration elevates plasma cyclic AMP (cAMP) levels but the source of the cAMP is unknown. To determine possible sources, plasma cAMP levels were determined in blood vessels across the head, liver, kidney and lung in anesthetized dogs infused with the beta-adrenergic agonist, isoproterenol. Only the head showed an increased release of cAMP into the blood. The kidneys removed cAMP from the blood while liver and lung showed no change. This in vivo demonstration of release of cAMP from the head represents contributions from brain and facial muscles and may be a useful approach to study brain involvement in the action of various hormones and drugs.