MONITORING EVOKED-POTENTIALS DURING SURGERY TO ASSESS THE LEVEL OF ANESTHESIA

The hypnotic and analgesic components of anaesthesia can be assessed u sing middle latency auditory evoked potentials (MLAEPs) and somatosens ory evoked potentials (SEPs). To monitor these potentials reliably dur ing clinical anaesthesia, we have developed an evoked potential (EP) s ystem based around a portable personal computer, a DSP board and an is olated pre-amplifier unit. Unlike many currently available systems, th is amplifier is largely immune to diathermy interference due to excell ent isolation via a digital fibre optical link, small size and RF scre ening and filtering. The pre-amplifier unit has integral auditory and somatosensory stimulators, and automatic calibration and impedance che cking. Stimulus intensity and profile are under software control and S EP stimulus level is constantly monitored. The unit is powered by two AA cells and battery status continuously monitored by the PC software. Up to eight channels of EEG may be recorded and displayed in a smooth ly scrolling window and as moving average MLAEPs and SEPs.