The effects of propofol and isoflurane on intraoperative motor evoked potentials during spinal cord tumour removal surgery - A prospective randomised trial.

Background and Aims: Transcranial electrical stimulation (TES) elicited intraoperative motor evoked potentials (iMEPs), are suppressed by most anaesthetic agents. This prospective randomised study was carried out to compare the effects of Isoflurane and Propofol on iMEPs during surgery for spinal cord tumours.

Methods: A total of 110 patients were randomly divided into two groups. In group P, anaesthesia was maintained with intravenous propofol (6.6 ± 1.5 mg/kg/hr) and in group I anaesthesia was maintained with isoflurane (0.8 ± 0.1% minimal alveolar concentration (MAC). An Oxygen- air mixture (FiO2-0.3) was used in both groups. TES-iMEPs were recorded from tibialis anterior, quadriceps, soleus and external anal sphincter muscles in 60 of 90 patients. Statistical analysis was performed with Pearson correlation and Paired 't' tests.

Results: Successful baseline iMEPs were recorded in 74% of patients in Group P and in 50% of patients in Group I. Age and duration of symptoms influenced the elicitation of baseline iMEPs under isoflurane (r = -0.71, -0.66 respectively, P < 0.01) as compared to propofol (r = -0.60, -0.50 respectively, P < 0.01). The mean stimulus strength required to elicit the baseline iMEPs were lesser in propofol (205 ± 55Volts) as compared to isoflurane (274 ± 60 Volts). Suppression of the iMEP responses was less under propofol (7.3%) as compared to isoflurane anaesthesia (11.3%) in patients with no preoperative neurological deficits.

Conclusion: iMEPs are better maintained under propofol anaesthesia (6-8 mg/kg/hr) when compared with isoflurane (0.7-0.9 MAC). in patients undergoing surgery for excision of spinal cord tumours.