MAGNETIC-EVOKED COMPOUND MUSCLE ACTION-POTENTIAL NEUROMONITORING IN SPINE SURGERY

Study Design. Muscle action potentials elicited by paired transcranial magnetic stimulation were recorded during spine surgery in 34 patient s. Anesthesia was based on ketamine and fentanyl. Objectives. To evalu ate the optimal anesthetic regimen to be used for transcranial magneti c stimulation, and to determine the clinical import of magnetic-evoked compound muscle action potentials. Summary of Background Data. Muscle ;action potential by transcranial magnetic stimulation has been diffic ult to record under general anesthesia. Ketamine is known to not suppr ess the muscle responses, although no conclusive clinical study has be en reported. Methods. Paired transcranial magnetic stimulation was del ivered as muscle action potentials were recorded from the limb muscula ture. Results. Neuromonitoring was reliable in 56% of total cases and in 82% of the recent cases after reducing fentanyl dosage. Paired magn etic stimulation was an excellent facilitation technique for reliable monitoring. At higher dosages, fentanyl and ketamine decreased the rep roducibility of the responses. Conclusions. Magnetic-evoked compound m uscle action potential neuromonitoring is a a sensitive and selective motor pathway monitoring method that covers the-entire motor pathway, including the white and gray matter of the spinal cord. Ketamine-based anesthesia is a good choice for this purpose.