Marked attenuation of the amplitude of transcranial motor-evoked potentials after intravenous bolus administration of ketamine: a case report

Abstract

BackgroundIt is believed that ketamine does not affect motor-evoked potential amplitude, whereas various anesthetic drugs attenuate the amplitude of transcranial motor-evoked potential. However, we encountered a patient with marked attenuation of motor-evoked potential amplitude after intravenous bolus administration of ketamine.Case presentationA 15-year-old Japanese girl with a diagnosis of adolescent idiopathic scoliosis was admitted to our hospital to undergo posterior spinal fusion at T4–L3. After induction of general anesthesia using a continuous infusion of propofol and remifentanil, we confirmed that transcranial electrical motor-evoked potentials were being recorded correctly. Ketamine 1.25 mg/kg was administered intravenously for intraoperative and postoperative analgesia. About 3 minutes later, the motor-evoked potential amplitude was markedly attenuated. No other drugs were administered except for ketamine. The patient’s vital signs were stable, and the surgery had not yet started. The motor-evoked potential amplitude was recovered at about 6 minutes after administration of ketamine. The surgery was performed uneventfully, and the patient had no neurologic deficit when she emerged from general anesthesia.ConclusionsAlthough there is a widely held belief in the field of anesthesiology that ketamine does not affect motor-evoked potential amplitude, it has been suggested that ketamine could affect its monitoring.

A Bolus Dose of Ketamine Reduces the Amplitude of the Transcranial Electrical Motor-evoked Potential: A Randomized, Double-blinded, Placebo-controlled Study

“…Previous studies suggested that a low-dose bolus (0.5 mg/kg) with or without infusion (0.24 mg/kg/h) of ketamine does not suppress the amplitude of MEP 9,11. However, the present study and a recent case report12 confirm that bolus administration of ketamine (1 to 1.25 mg/kg) can reduce MEP amplitudes. Bolus administration of ketamine (4 mg/kg) has also been found to decrease the amplitude of MEP in a rabbit model 7.…”

“…However, a recent case report suggested that a bolus dose of ketamine (1.25 mg/kg) administered in an adolescent patient with idiopathic scoliosis significantly reduced MEP amplitude 12. Although a previous study concluded that ketamine (1 mg/kg) did not affect mean MEP amplitude, MEP was evoked by transcranial magnetic stimulation 13.…”