Intraoperative monitoring of the blink reflex response can be a useful addition to free-running and stimulated EMG in neurosurgical procedures when the seventh cranial nerve is at risk of injury. Extensive troubleshooting of stimulation and recording parameters is often required to record reliable blink reflex responses in the setting of general anesthesia. Despite troubleshooting measures, only the R1 response of the blink reflex can be reliably recorded under general anesthesia. Parameters that can be adjusted to optimize the R1 response include proper placement of needle electrodes for stimulation and recording, adjustment of high and low frequency filters, using a train of multiple stimuli, adjusting inter-pulse interval, and altering pulse width. Ensuring optimal anesthetic regimen (use of total intravenous anesthetic and ensuring neuromuscular blockade is fully reversed) is also critical to successful blink reflex monitoring. In addition, we have found that the use of biphasic stimulation may help produce more consistent blink reflex responses. In order to ensure the CMAP response recorded from orbicularis oculi is not a result of direct activation, a test stimulation of using a lower number of pulses can be used to ensure latency of response does not change, indicative of a reflex response.
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