Intraoperative neurophysiological monitoring of the afferent pain pathway in cardiac surgery patients

ObjectiveNo specific and sensitive method is available in routine clinical practice to detect pain in anaesthetised patients during surgery. The main aim of the present study was to investigate whether intraoperative somatosensory evoked potentials, the bispectral index, electroencephalogram, blood pressure and heart rate change during painful stimulation in cardiac surgery patients.MethodsAfter induction of anaesthesia, 37 cardiac surgery patients were subjected to increasing electrical stimulation of both the median nerves and subsequent intravenous infusion of remifentanil to suppress this painful stimulation.ResultsThe higher intensities of electrical stimulation significantly modified the cortical evoked potentials, the electroencephalogram spectral edge frequency and blood pressure. We also observed the appearance of a middle-latency component in the somatosensory evoked cortical potentials between 60 and 70 ms. These neurophysiological and clinical responses were significantly reduced by remifentanil administration.ConclusionsThe data suggest that somatosensory evoked potentials might be used to detect and monitor painful stimulation during surgery, unlike the bispectral index, which does not seem to be highly sensitive to intraoperative pain.SignificanceMeasurement of intraoperative somatosensory evoked potentials provides a specific and sensitive method to monitor the afferent pain pathway in anaesthetised patients.

► The present study investigated whether SEP, EEG and BIS might allow better assessment of intraoperative analgesia. ► Both short and medium-latency SEP findings can detect the integrity of pain pathways during surgery. ► The neuropathic pain model induced by painful electrical stimulation of the median nerves could also be used to evaluate the analgesic efficacy of different anaesthetic medications during surgery.