PARAPLEGIA FOLLOWING THORACIC AORTIC CROSS-CLAMPING IN DOGS - NO DIFFERENCE IN NEUROLOGICAL OUTCOME WITH A BARBITURATE VERSUS ISOFLURANE

Background and Purpose: We compared the incidence and severity of para plegia following thoracic aortic cross-clamping in dogs for two anesth etic regimens. Animals were randomly assigned to receive methohexital (group M; n=9) or isoflurane (group 1; n=9). We expected a better neur ological outcome in animals administered methohexital because of super ior neuronal protection and greater spinal cord perfusion pressure (me an arterial pressure below the cross-clamp site minus mean cerebrospin al fluid pressure). Methods: After surgical preparation and a 30-minut e stabilization period, dogs in group M received 14+/-6 mg . kg-1 IV m ethohexital to induce an isoelectric electroencephalogram followed by a continuous infusion of methohexital at 20 mg . kg-1 . h-1. Dogs in g roup I received 1.4+/-0.2% end-tidal isoflurane (1 minimum alveolar co ncentration). The thoracic aorta was then occluded 2.5 cm distal to th e left subclavian artery for 30 minutes and then released. Hemodynamic s and cerebrospinal fluid pressure were measured at (1) baseline, (2) 2 minutes after aortic cross-clamping, (3) 20 minutes after aortic cro ss-clamping, (4) 5 minutes after aortic unclamping, and (5) 30 minutes after resuscitation. At 24 hours a neurological assessment was perfor med. After the clinical assessment the dogs were killed and the spinal cord removed immediately for histopathologic study. Results: There we re no differences in nasopharyngeal temperature, PaCO2, pH, or hemoglo bin at any time between groups. With cross-clamping, the spinal cord p erfusion pressure decreased precipitously. However, there was no diffe rence in spinal cord perfusion pressure between groups at any time (P= .5555). The neurological outcome, assessed at 24 hours after thoracic aortic cross-clamping by a veterinarian unaware of the anesthetic prot ocol, was not different between groups (P>.5, two-tailed Mann-Whitney rank-sums test). When anesthetized with methohexital 5 of 9 dogs were paraplegic; with isoflurane 7 of 9 dogs were paraplegic. By Spearman's rank test, a strong inverse correlation between the Tarlov score and the ratio of dead to total lumbar anterior spinal cord neurons was see n (Spearman's correlation coefficient=-.8358; P=.0001). Conclusions: W e conclude that no advantage was offered by the choice of anesthesia t o neurological outcome after 30 minutes of thoracic aortic cross-clamp ing in this canine model.