[Effects of intravenous and inhalational anesthetics on short-latency somatosensory evoked potentials].
OBJECTIVE
To choose suitable general anesthetics dosages when short-latency somatosensory evoked potentials (SLSEP) is monitored during operation.


METHODS
150 ASA I-II neurosurgical patients undergoing elective operations were randomly divided into intravenous anesthesia group of 90 patients and inhalation anesthesia group of 60 patients. The intravenous anesthesia group was further divided into 9 subgroups of 10 patients treated with different anesthetics of different dosages: propofol (1.5 mg/kg, 2 mg/kg, and 3 mg/kg), midazolam (0.2 mg/kg, 0.3 mg/kg, and 0.4 mg/kg), and etomidate (0.15 mg/kg, 0.3 mg/kg, and 0.4 mg/kg). The intravenous anesthetics were given and upper limb SLSEP was monitored continuously. The inhalation anesthesia group was further divided into enflurane, isoflurane and desflurane subgroups of 20 patients each. The inhalational anesthetics were given at the concentrations corresponding to the end-expiratory concentrations of 0 to 0.3, 0.5, 0.75, 1.0 and 1.5 MAC. The changes of N(14), N(20) and central conduction time (CCT) were recorded. In addition to SLSEP, EKG, NIBP, SpO(2), P(ET) CO(2) were monitored as well as end-tidal anesthetic concentration. During the experiment SpO(2) was maintained > 95% and P(ET) CO(2) was maintained at the range of 35 - 45 mmHg by mask oxygen or assisted ventilation.


RESULTS
The intravenous anesthetic propofol significantly decreased N(20) amplitude and produced less effect on the latency of N(14), N(20) and CCT. Midazolam significantly decreased the N(20) amplitude and prolonged the latency of N(20) and CCT. Etomidate significantly increased the N(20) amplitude, and the change did not recover when the patients had opened their eyes 10 minutes after medication. All three inhalational anesthetics significantly decreased the N(20) amplitude and prolonged the N(20) latency and CCT. N(20) amplitude disappeared in some patients treated with enflurane when the end-expiratory concentration was 1.0 MAC, while disappeared in some patients treated with isoflurane and desflurane when the end-expiratory concentration was 1.5 MAC for these 2 drugs.


CONCLUSIONS
When using SLSEP monitoring, the most suitable general anesthetic is etomidate during the induction stage and isoflurane and desflurane during the maintenance stage with the end-expiratory concentration below 1.0 MAC.
Liang
Wei-min
WM
Deportment of Anesthesia, Huashan Hospital, Fudan University, Shanghai 200040, China.
Zhang
Jun
J
Gu
Hua-hua
HH
Tang
Jun
J
Huang
Qi-zhi
QZ
D000293:Adolescent; D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000927:Anticonvulsants / Q000494:pharmacology; D000077335:Desflurane; D004333:Drug Administration Routes; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D005260:Female; D006801:Humans; D007430:Intraoperative Care; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D008874:Midazolam / Q000494:pharmacology; D008875:Middle Aged; D015742:Propofol / Q000494:pharmacology
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D000927:Anticonvulsants; D000077335:Desflurane; D007530:Isoflurane; D008874:Midazolam; D015742:Propofol