Optimal placement of recording electrodes for quantifying facial nerve compound muscle action potential.

OBJECTIVE

To analyze optimal placement of recording-needle electrodes surrounding the eye and lip for facial nerve monitoring by identifying the maximum compound muscle action potential (CMAP) recorded by electrode pairs of different spatial configurations.

STUDY

DESIGN

Prospective clinical trial.

SETTING

Ambulatory surgery at a tertiary care center.

PATIENTS: Thirty adults undergoing chronic ear surgery such as tympanoplasty, mastoidectomy, ossicular chain reconstruction, stapedectomy, and cochlear implantation.

INTERVENTION: Facial nerve monitoring.

MAIN OUTCOME MEASURE: Suprathreshold (threshold + 0.2 V) CMAP responses are recorded from referential paired needle electrodes placed into orbicularis oculi (1.5-cm spacing; n = 15) and orbicularis oris (1.0-cm spacing; n = 15) muscles. Optimal recording electrode placement is inferred by identifying the maximum evoked CMAP amplitude.

RESULTS

For the eye, placement of electrodes by the orbital rim and into the upper eyelid is significantly better (Friedman test; p < 0.01) than the other 2 configurations. For the lip, placement of electrodes into the oral commissure and either the upper or lower lip is satisfactory because there is no statistically significant difference among the configurations (Friedman test; p > 0.2).

CONCLUSION

Recording electrode placement configurations that capture the largest CMAP responses are recommended as standard operating procedure for intraoperative facial nerve monitoring.