Effects of volatile anesthetics on short-latency somatosensory evoked potentials / 中华麻醉学杂志

ABSTRACT

ve In order to improve the reliability of somatosensory evoked potentials (SSEP) monitoring during anesthesia, we compared the effects of three commonly used volatile anesthetics on SSEP to choose suitable volatile anesthetic and determine the appropriate end-expiratory concentrations which have least effects on SSEP monitoring. Methods Sixty ASA I - II patients undergoing elective intracranial surgery were randomly divided into three groups group A received enflurane; group B isoflurane and group C desflurane. The demographic data including age, body weight, height and sex were not significantly different between the three groups. In addition to SSEP, ECG, BP, SpO2, PET CO2 and end-tidal concentration of inhalation anesthetic were monitored. The SSEP electrodes were placed on N13 on the neck and N20 on the scalp. Before experiment the patient was asked to lie quietly for 10 min, then the patient started breathing 100% O2 and fresh-gas-flow (FGF) was set at 5 L/min. Median nerve on one side was stimulated and SSEP waves from cortex and cervical spinal cord were recorded as baseline tracing before anesthesia. The concentration of inhalation anesthetic was gradually increased from 0 to 0.3, 0.5, 0.75, 1.0 and 1.5 MAC. Each concentration was maintained for 15 min and SSEP waves were recorded. During experiment if the patient developed respiratory depression, oral airway was inserted and assisted ventilation was performed to maintain PETCO2 at 35-45minHg. If the patient developed hypotension, fluid was infused at an increased rate and vasopressor was given if necessary to maintain normal BP (baseline ? 20 % ) . Results The three volatile anesthetics did not change N13 latency and amplitude. Increasing concentrations of enflurane, isoflurane and desflurane were associated with graded reduction in N20 amplitude and increase in N20 latency and N13-N20 interpeak latency. Conclusions The results suggest (1) cortical SSEPs are moresensitive to the volatile anesthetics than subcortical SSEPs, (2) end-tidal concentration of enflurane less than 0.75 MAC is compatible with effective SSEP monitoring, whereas the end-tidal concentration of isoflurane or desflurane compatible with effective SSEP monitoring was less than 1.0 MAC. Enflurane has greater effect on SSEP than isoflurane and desflurane.