Cross-Clamping in Dogs

Background and Purpose: We compared the incidence and severity of paraplegia following thoracic aortic cross-clamping in dogs for two anesthetic regimens. Animals were randomly assigned to receive methohexital (group M; n=9) or isoflurane (group I; n=9). We expected a better neurological outcome in animals administered methohexital because of superior neuronal protection and greater spinal cord perfusion pressure (mean arterial pressure below the cross-clamp site minus mean cerebrospinal fluid pressure). Methods: After surgical preparation and a 30-minute stabilization period, dogs in group M received 14±6 mg. kg` IV methohexital to induce an isoelectric electroencephalogram followed by a continuous infusion of methohexital at 20 mg* kg-'. h`. Dogs in group I received 1.4±0.2% end-tidal isoflurane (1 minimum alveolar concentration). The thoracic aorta was then occluded 2.5 cm distal to the left subclavian artery for 30 minutes and then released. Hemodynamics and cerebrospinal fluid pressure were measured at (1) baseline, (2) 2 minutes after aortic cross-clamping, (3) 20 minutes after aortic cross-clamping, (4) 5 minutes after aortic unclamping, and (5) 30 minutes after resuscitation. At 24 hours