A case in which motor evoked potential could be elicited despite an increase in remifentanil dose during craniotomy.

We performed anesthetic management for craniotomy, during which motor evoked potential (MEP) was elicited by direct motor cortex stimulation (DMS), in a female patient with brain aneurysm. Propofol and remifentanil were used for anesthetic induction and maintenance. The propofol concentration was adjusted in accordance with bispectral index value, and the remifentanil concentration was adjusted in accordance with the hemodynamic values. Although we planned to use a remifentanil dose of 0.2 �og/kg/min on the basis of a previous report, the dose had to be increased to 0.5�og/kg/min, the effect-site concentration was calculated to be 17.2 ng/mL by using a pharmacokinetic simulation, which was in accordance with the hemodynamic values. However, MEP could be well elicited throughout MEP monitoring. This finding was consistent with that of previous studies in which MEP was elicited by transcranial electrical stimulation (TCS) or transcranial magnetic stimulation (TMS). Emergence from anesthesia is well, and no side effects or new neurological deficits occurred. It is thought remifentanil might have also a wide dosage window with respect to monitoring MEP elicited by DMS.