The Effect of Anesthetics on Somatosensorily Evoked Potentials during Surgery / 대한마취과학회지

BACKGROUND: Many methods are available for the monitoring of spinal cord injury during an operation. During anesthesia, somatosensily evoked potentials (SSEP) may undergo substantial changes in the latencies and amplitudes which may be interpreted as pathological. It is essential for the anesthesiologist to know the potential interactions between anesthetic drugs and neurophysiologic responses during operation. The depressant effect of inhalation agents on the central nervous system exceeds commonly used intravenous anesthetics. Therefore, intravenous anesthesia is preferred to inhalation agents. This study was designed to compare the effects of intravenous anesthetics (propofol and fentanyl) and inhalational anesthetics (enflurane and nitrous oxide) used in the operation room. METHODS: According to the inclusion criteria of ASA I-II, 40 patients who were free of neurologic disease with electric abdominal operations were randomly selected. The baseline of the SSEPs were recorded with stimulation of the posterior tibial nerve at the ankle. After obtaining the baseline (preinduction) of the SSEPs, intravenous anesthetics (propofol 10 mg/kg/h, fentanyl 1 2 microgram/kg) and inhalational anesthetics (end tidal enflurane concentration 1.0 vol %, 50% nitrous oxide in oxygen) were administered. 30 minutes after induction (steady state), additional SSEPs were recorded. Mean arterial pressure, heart rate, temperature and arterial blood carbon dioxide tension were monitored. RESULTS: There were no significant differences in the baseline of SSEPs between the intravenous anesthetics group and the inhalational anesthetics group. There were no significant differences in latencies and amplitudes between the preanesthesia state and the postanesthetia state in the intravenous anesthetics group. But the inhalational anesthetics group revealed prolonged latencies in the postanestesia state as compared with their preanesthesia state. CONCLUSIONS: The above findings suggest that the use of intravenous anesthetics can be beneficial to intraoperative SSEP monitoring for possible damage to the central nervous system during operations.

The Availability of Total Intravenous Anesthesia on Somato-Sensory Evoked Potential during Spinal Surgery / 대한마취과학회지

BACKGROUND: Somatosensory evoked potential (SSEP) has been used to help minimize neurologic morbidity during spinal surgery. But, SSEP is affected by various factors, namely technical errors, anesthetics and physiologic aspects (systemic blood pressure, temperature, blood gas tensions). We experienced 40 cases of spinal surgery done with total intravenous anesthesia under SSEP monitoring. We reviewed these cases with the availability of total intravenous anesthesia during SSEP monitoring. METHODS: Forty patients, ASA class I-II, free of neurologic disease and scheduled for elective spinal surgery were randomly selected for the study. All of the operations were performed under general anesthesia employing the method of total intravenous anesthesia with propofol and fentanyl, and monitored by SSEP. We recorded latency and amplitude of SSEP in the pre-induction, post-induction, during-instrument insertion and post-distraction periods. RESULTS: There were no statistical differences in latencies among pre-induction, post-induction, screw insertion and post-distraction period. The amplitude of the post-induction period was statistically higher than pre-induction period (p<0.05), but there were no differences in other periods. None of cases showed abnormal findings (i.e., delay of latency over 10% or decrease of amplitude over 50%). CONCLUSIONS: SSEP monitoring may be helpful in identifying potentially neurologically threatening surgical maneuvers during spinal surgery. To achieve better outcomes, we should consider the effects of various factors on SSEP. Total intravenous anesthesia may be useful method, which has lifter influence on SSEP monitoring.