Evaluation of the Effect of the Facial Nerve Monitoring in Mastoid Surgery

Objectives: 1.To evaluate role of facial nerve monitoring in mastoid surgeries. 2. To define the cutoff limit for electrical dehiscence of facial nerve. Methodology: 60 patients of chronic otitis media undergoing mastoid surgery were divided into 30 each for intra-operative facial nerve monitoring (group A) and those without monitoring (group B). Minimum level of current strength for stimulation of facial nerve was noted. Post operative facial nerve status and disease clearance was compared between two groups. Results: In group A, 10 exhibited surgical dehiscence of facial nerve and responded to electrical stimulation of 0.5mA or less. Hence, we defined the facial nerves that responded to electrical stimulation of 0.5 mA or less with a constant, unipolar current with a frequency of 3 pulses/ second for 200 μs as “electrically dehiscent”. Total “electrically dehiscent” cases were 16 (53.3%) Disease could not be cleared completely in 1 patient in group A and 3 in group B. Facial nerve integrity was maintained in all patients in group A but injured in 1 in group B. Conclusions: Facial nerve monitor is a useful tool to be used in mastoid surgery as it reassures the surgeon when in doubt. All facial nerves which get stimulated with a current of 0.5mA or less can be taken as electrically dehiscent.