For surgeries requiring the monitoring of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) in patients without significant neurological impairment, a balanced anesthetic regimen is often utilized. This method combines a low-dose inhalation anesthetic, such as up to 0.5 MAC of sevoflurane, with a low- to medium-dose of propofol, ranging from 0 to 75 mcg/kg/min IV, and a relatively high dose of an opioid, like remifentanil at 0.1 to 0.3 mcg/kg/min. This approach offers several advantages: it minimizes movement during motor stimulation, which is especially important in intracranial aneurysm surgeries; it reduces the risk of the patient becoming aware under anesthesia by including a 0.3 to 0.5 MAC inhalation agent; it allows for a lower dose of propofol, facilitating faster wakeup times and earlier neurological assessments compared to total intravenous anesthesia (TIVA); and it decreases the likelihood of mechanical failures, such as kinked or infiltrated IV catheters or tubing, ensuring continuous infusion of anesthetic agents.
In rare instances where the evoked potentials are insufficient, it may be necessary to switch to a total intravenous anesthesia (TIVA) approach by discontinuing the inhalation agent. This transition will require an increased dosage of propofol. To avoid excessively high doses of propofol, which can hinder the recording of motor evoked potentials (MEPs), adding ketamine and lidocaine to the regimen might be beneficial when appropriate.
