Anesthetic management of four cases of craniotomy with alternate monitoring of motor and somatosensory evoked potentials

We experienced four cases of craniotomy in which motor evoked potential (MEP) and somatosensory evoked potential (SEP) were monitored alternately. Anesthesia was induced with propofol and fentanyl, and it was maintained with continuous infusion of propofol. Intermittently, propofol and fentanyl were administered as needed. Inhalation of 66% nitrous oxide did not prolong latency, but significantly reduced the amplitude of MEP. We could obtain the largest amplitude of MEP using five consecutive stimuli of which duration and frequency were 0.5 milliseconds and 500 Hz, respectively. Anesthetic management using propofol and fentanyl is useful for craniotomy with monitoring of MEP and SEP.