Intravenous anesthetic alterations on the spinal-sciatic evoked response in swine

Sciatic evoked responses (ScER) are used to monitor the integrity of the anterior spinal cord during spinal surgery. To evaluate the effects of intravenous anesthetics on the lumbar spinal evoked potential (SpEP) and ScER, 28 swine were anesthetized with halothane and an intravenous infusion of ketamine. After experimental preparation, anesthesia was maintained with ketamine, and the swine were divided into four equal groups (n = 7). The evoked responses were generated by delivering an electrical stimuli to the interspinous ligaments caudal to T1 and T2. The lumbar SpEP was recorded from the interspinous ligaments caudal to L2 and L3. The ScERs were recorded bilaterally from electrodes placed adjacent to the sciatic nerves. In Group 1 the effects of bolus dose administration of ketamine were evaluated. In Groups 2-4 anesthesia was maintained with ketamine by continuous infusion and the effects of fentanyl, sufentanil, and propofol on the L2 SpEP and ScER were evaluated. There was no significant change in either the amplitude or latency of the L2 SpEP with any anesthetic studied. Ketamine administered in bolus doses (2.5, 5, and 10 mg/kg) did not alter the ScER. After bolus doses of fentanyl 10 micrograms/kg or sufentanil 1 micrograms/kg, there was a similar decrement in the amplitude of the ScER (P < 0.05) that recovered at 10 min without changes in latency. There were no changes in the ScER associated with infusion of fentanyl 1-5 micrograms.kg-1 x h-1 or sufentanil 0.1-0.5 microgram.kg-1 x h-1.(ABSTRACT TRUNCATED AT 250 WORDS)