[Influence of different sevoflurane concentration on somatosensory evoked potentials monitoring in spinal cord surgery].

OBJECTIVE

To evaluate the effects of different end-tidal concentrations of sevoflurane on somatosensory evoked potentials, to explore the feasibility of sevoflurane applied in such kind of surgery, so as to provide useful information in making anesthesia plan for spinal cord surgery.

METHODS

Thirty-two patients scheduled for spinal cord surgery (ASA I-II, 18-65 years old) were enrolled. After induction of anesthesia, they were assigned to receive sevoflurane anesthesia of increment end-tidal concentration in the sequence of 0.0%, 0.5%, 1.0% and 1.5% respectively, under a background intravenous infusion of propofol and remifentanil. Remifentanil infusion rate was 0.2 µg·kg⁻¹ ·min⁻¹, while the propofol infusion rate was adjusted to maintain BIS values within the range of 30-50. The amplitude and latency of each SSEPs were recorded and compared.

RESULTS

Sevoflurane inhibited SSEPs in a dose-dependent manner, SSEPs amplitude significantly decreased following increased end-tidal sevoflurane concentration. The amplitudes of the left side were 2.36 (0.42-9.87), 2.14 (0.52-9.44), 1.94 (0.47-9.44), 1.64 (0.36-7.46) µV respectively (F = 21.66, P < 0.01). The amplitudes of the right side were 2.71 (0.43-7.1), 2.73 (0.43-7.1), 2.34 (0.44-6.6), 1.64 (0.39-6.15) µV respectively (F = 33.94, P < 0.01). SSEPs latencies were significantly prolonged, on the left side, the latencies were (41.48 ± 3.45), (42.45 ± 3.60), (43.20 ± 3.42), (44.38 ± 3.78) ms, respectively (F = 68.07, P < 0.01). On the right side, the latencies were (40.65 ± 4.91), (41.53 ± 4.76), (42.31 ± 4.93), (43.39 ± 4.79)ms, respectively (F = 56.52, P < 0.01). Yet, as a monitoring modality for dynamic observation, SSEPs still could be monitored successfully under sevoflurane anesthesia in all these 32 patients.

CONCLUSIONS

Sevoflurane has depression effects on SSEPs in a dose-dependent manner. It can decrease the amplitudes and prolong the latencies. Considering significant individual difference, the feasibility of sevoflurane in such kind of surgery can be determined by measuring base amplitude of SSEPs under total intravenous anesthesia.