The Incidence of Bite Injuries Associated with Transcranial Motor-Evoked Potential Monitoring

Abstract

Bite injuries are a disturbing complication of transcranial motor-evoked potential (TcMEP) monitoring. We sought to determine the incidence, type, and severity of bite injuries, and to analyze possible related factors to determine methods of minimizing injury during TcMEP monitoring. We reviewed the incident reports of TcMEP-associated bite injuries from 17,273 consecutive surgical procedures. Cases were reviewed for type and number of bite blocks, positioning, anesthesia, and stimulus variables. There were 111 bite injuries in 109 patients for a total incidence of 0.63% including 88 (79.3%) tongue injuries, 22 (19.8%) lip injuries, and 1 (0.9%) broken incisor. One patient had both tongue and lip injured; another had a lip injury and a broken tooth. Severity of bite injuries ranged from minor bruising to deep lacerations requiring suture repair. The total incidence of injury severe enough to require sutures was 25 patients (0.14%). All but 2 patients had some form of bite block used. Anterior approaches were more prevalent than posterior in the injured group although not significantly. The incidence of bite injuries was higher when the Axon NIM-Eclipse system was used (1.37%) compared with the Xltek Protektor (0.6%). Stimulus intensity was maximized in 77 cases (70.6%). In 22 cases, displacement of bite block or of the tongue was documented. Bite injuries associated with transcranial electric stimulation are an uncommon but disturbing complication of TcMEP monitoring occurring with an incidence of 0.63% (95% confidence interval: 0.52%-0.76%), the most severe of which requiring sutures at an incidence of 0.14% (95% confidence interval: 0.09%-0.21%). Injuries of the tongue occur approximately 4 times as frequently as injuries of the lip. Despite placement of bite blocks, shifting of the bite block during stimulation or positioning is a possible cause of failure. High-intensity transcranial stimulation may increase the risk of bite injuries. We suggest consistent use of properly sized and secured bite blocks with periodic inspection to minimize risk of bite injuries. Future study is needed to determine optimal bite block configuration.