Evolution and progress of continuous intraoperative neural monitoring

Electrophysiological nerve mapping and monitoring devices have been forthcoming since the 1970s, facilitating intraoperative identification and functional checks of recurrent laryngeal nerve (RLN) function during neck surgery. Although the clinical importance of intraoperative nerve monitoring (IONM) has become obvious in the past two decades, the inability of intermittent IONM to seamlessly monitor RLN function as the dissection progresses in the neck has prevented more widespread application of this technology. With the advent of continuous IONM in the new millennium, unsupervised intervals during nerve monitoring have virtually ceased to exist, pushing the envelope further. Continuous IONM has taken our understanding of functional RLN injury to unprecedented levels. Remarkably, traction on the nerve causes distinct electromyographically changes appearing as loss of signal (LOS), which typically is reversible upon prompt release of the nerve. Continuous IONM (I) reflects nerve electrophysiology more accurately than intermittent IONM; (II) flags impending RLN injury earlier, yielding more lead time for corrective action; and (III) predicts early postoperative vocal cord palsy more reliably. The present review provides a comprehensive summary of the evolution and future perspectives of continuous IONM.