Somatosensory evoked potentials during isoflurane anaesthesia

Area of Science:

• Neuroscience
• Anesthesiology
• Clinical Neurophysiology

Background:

• Short latency somatosensory evoked potentials (SEPs) are valuable for monitoring neurological function during anesthesia.
• Isoflurane is a common inhalation anesthetic agent whose effects on SEPs require detailed investigation.

Purpose of the Study:

• To evaluate the impact of increasing isoflurane concentrations on the characteristics of SEPs.
• To determine if SEPs can be reliably recorded during different levels of electroencephalogram (EEG) suppression induced by isoflurane.

Main Methods:

• SEPs were recorded in 12 patients undergoing elective surgery at various isoflurane concentrations (awake, 1 MAC, 1.5 MAC, and EEG burst/continuous suppression).
• The peak latency and amplitude of the N20 wave were measured.
• Anesthesia was subsequently lightened to 1 MAC to observe recovery.

Main Results:

• SEP latencies significantly increased with rising isoflurane concentrations.
• At high isoflurane levels, the N20 wave showed reduced amplitude and altered morphology (nearly monophasic).
• No direct correlation was found between specific EEG suppression patterns and SEP changes, suggesting differential effects on neural generators.

Conclusions:

• Isoflurane concentration directly influences SEP latency and amplitude, with higher doses causing significant alterations.
• SEPs remain recordable even during isoflurane-induced EEG suppression, indicating their potential utility in monitoring.
• EEG and SEP generators appear to be differentially affected by increasing isoflurane concentrations.