MATERIAL and METHODS: Twenty-four patients underwent elective surgery under general anaesthesia that was administered through Target Controlled Infusion (TCI) for effect-site concentration (Ce) of Propofol and Remifentanil, targeting the Bispectral Index (BIS) in the 40-60 intervals. The stimulating intensity of transcranial motor evoked potentials (tMEP), BIS, Propofol and Remifentanil Ce were collected at MEPs threshold (T) definition (respectively BIS@T, CeProp@T and CeRemi@T). Intraoperative seizure, explicit recall for intraoperative awareness and clinical motor status were assessed.

RESULTS: CeProp@T and CeRemi@T ranged respectively between 1.5-2.2 ?g/ml (Median 1.6 ?g/ml) and 3.5-18 ng/ml (Median 8 ng/ml) that were effective in keeping the BIS@T between 40 and 60 in all surgeries. tMEP thresholds ranged between 45 and 120 mA. There was no correlation between CeProp@T, CeRemi@T and tMEP, as well as between BIS@T and respectively tMEP, CeProp@T, CeRemi@T. None of patients had induced electrical seizure or explicit recalls. Motor scores were equal to preoperative values in 22/24 patients.

CONCLUSION: BIS-guided general anaesthesia within a 40-60 interval, with low Ce of Propofol (?2 ?/ml) and high analgesic regime allow reliable tMEP measurements, avoiding postoperative neurological impairment and major adverse outcomes, such as seizure and awareness. Keywords : Bispectral index, Brain motor area, Motor evoked potentials, Propofol, Remifentanil