Intraoperative facial nerve monitoring: a comparison between electromyography and mechanical-pressure monitoring techniques.

OBJECTIVES

To examine the hypothesis that for intraoperative facial nerve monitoring, an EMG monitor is more sensitive than a mechanical-pressure monitor. To compare the threshold sensitivity of the two facial nerve monitoring methods-mechanical-pressure versus EMG--by using them simultaneously during surgery. To assess and compare their true- and false-positive responses in otologic and neurotologic procedures.

SETTING

A tertiary referral private otology/neurotology practice.

STUDY DESIGN

Prospective case-controlled study.

PATIENTS AND METHODS

The facial nerve of 46 consecutive patients undergoing various otologic and neurotologic procedures was stimulated intraoperatively using a pulsed constant-current. Facial responses were monitored using the Silverstein WR-S8 Monitor/Stimulator and the Brackmann EMG System simultaneously. The threshold (i.e., minimal) current level required to elicit a response from each monitor was recorded. Monitor responses to facial nerve manipulation (including false-positive responses) were assessed by continuous recording of all responses, using the Wiegand Monitoring System, and noting the causative event for each response.

RESULTS

The EMG monitor responded to lower current threshold (p < 0.001) in every surgical procedure and for every nerve segment studied. However, the average threshold difference was <0.05 mAmps and in clinical practice, when using above threshold stimulation, becomes negligible. In posterior fossa surgery, the EMG monitor showed higher sensitivity by responding earlier to various manipulations of the bare facial nerve. The EMG had more false-positive responses than the mechanical-pressure monitor.

CONCLUSIONS

In otologic surgery, if monitoring is required, the mechanical-pressure monitor is used. In neurotologic surgery, both monitors are used simultaneously.