Issues in the Optimal Selection of a Cranial Nerve Monitoring System

Optimal Stimulus Duration for Intraoperative Facial Nerve Monitoring

“…Stimulation parameters are selected that are intended to produce the greatest degree of neuromuscular response with the least amount of delivered current. Selesnick and Goldsmith 11 in 1993 suggested 3 to 5 square pulses per second, with a minimum reliable pulse duration of 50 microseconds; similarly, they noted that 0.1 or 0.2 mA is generally sufficient to stimulate a bare intracranial facial nerve. In theory, it is possible that direct stimulation of a nerve can lead to nerve damage, but this has not been found in animal models, or clinically in the operating room 12‐14 …”

Predictive Value of Facial Nerve Electrophysiologic Stimulation Thresholds in Cerebellopontine‐Angle Surgery

“…Although microdissection of tumor off of an attenuated facial nerve is the primary traumatic event resulting in facial paresis, direct electrical trauma by nerve stimulation must be considered another potential source of facial paralysis. The safety of IOFNM, however, has been well established in animal models and clinical practice 16‐19 …”

“…When shunting occurs by low‐impedance fluids and current levels are set, there is a compensatory increase in stimulation voltage in order to maintain the selected current level. If these fluids are suctioned away quickly, there is a possibility that the targeted nerve may receive a suprathreshold burst of voltage before the stimulation source adjusts the voltage to an appropriate level 11,16,17,20,21 . The problem of shunting may be minimized by using“flush‐tipped” probes that are insulated, up to their tips, from low‐impedance fluids.…”

“…Kartush, et al 16 studied the guinea pig facial nerve and found both constant‐current and constant‐voltage systems to be of equal benefit and safety when employed properly. From a practical standpoint, however, most commercially available systems for IOFNM in the United States today use a default constant current system, so that developing a standard with the constant‐current system may have greater applicability 17 . Furthermore, since diagnostic neurophysiologists traditionally use constant‐current systems, there is a natural acceptance for these systems.…”