Comparison Of Tibial Nerve Somatosensory Evoked Potential Signal-To-Noise Ratios During Anaesthesia

Monitoring the function of the central nervous system of a patient during a surgery where an injury to the nerves can occur is important in securing the safety of the patient. The somatosensory tract of patients undergoing corrective surgery for scoliosis were monitored using tibial nerve somatosensory evoked potentials (tSEP) by stimulating the tibial nerve from the ankle and recording the responses from electroencephalography (EEG) electrodes placed on the scalp of the patient.The recorded EEG was segmented off-line into different epochs on the basis of spontaneous neuronal activity overlaying the tSEPs. The epochs were: bursts, suppressions, spindles and technical artefacts. Ensemble averaging was carried out over the epochs to discover how quickly the overall tSEP signal-to-noise ratio (SNR) increases as a function of N.The tSEP SNR increased most rapidly during the suppression epochs which contain only little spontaneous EEG activity in comparison with the tSEPs recorded during the burst and spindle epochs. Fast and reliable results can be achieved in the operating room by using deep propofol anaesthesia where the spontaneous EEG activity is mostly low, selecting only high SNR epochs and using ensemble averaging on those to form the overall tSEP response.