Protecting the ischemic spinal cord during aortic clamping. The influence of anesthetics and hypothermia.

Infrarenal circumaortic occlusion devices were operatively placed in 74 New Zealand white rabbits. Two days after operation the animals were randomly assigned to one of seven treatment groups: I, control, n = 23; II, halothane, n = 8; III, thiopental, n = 12; IV, ketamine (30 mg/kg intravenously), n = 6; V, halothane+hypothermia, n = 8; VI, thiopental+hypothermia, n = 12; VII, ketamine+hypothermia, n = 5. In each group, the infrarenal aorta was occluded for 21 minutes. Final neurologic recovery after restitution of blood flow was graded as acute paraplegia, delayed paraplegia (neurologic deficit developing after initial recovery), or normal. Halothane alone was of no benefit. Hypothermia with any anesthetic was completely protective and reduced neurologic deficits to 0% compared with 91% in controls (p less than 0.05). Thiopental and ketamine treatment each reduced acute paraplegia to 17% (as compared with 61% in controls) and increased delayed paraplegia from 30% in controls to 75% and 50%, respectively (p less than 0.05 for thiopental, p = 0.10 for ketamine). The authors interpret the increase in delayed deficits and decrease in acute deficits as being the result of partial spinal cord protection. These findings document that this model of spinal cord ischemia is sufficiently sensitive to identify interventional treatments that protect the ischemic spinal cord.