Emerging Trends for Vagus/Recurrent Laryngeal Nerve Monitoring

Over the past five decades, intraoperative nerve monitoring (IONM) has been utilized increasingly within a multitude of surgical specialties including head and neck surgery, endocrine surgery, and neurosurgery. There have been many advances in the field of IONM over this time, with refinements and standardization of techniques and methodology. These advances are ongoing and are the source of frequent clinical studies and publications in scientific literature. In this chapter, emerging trends for monitoring the recurrent laryngeal and vagus nerves during thyroid and parathyroid surgery will be discussed. The chapter will be divided into two main sections – emerging trends for intermittent IONM (IIONM) and emerging trends for continuous IONM (CIONM). Recent advances in each form of monitoring will be highlighted as well as the advantages and disadvantages for each of these advances. For IIONM, the section is subdivided into novel methodologies for laryngeal nerve stimulation versus novel methodologies for recording vocal fold electromyographic potentials in response to direct vagal or recurrent laryngeal nerve stimulation. All existing IIONM techniques elicit compound muscle action potential (CMAP) responses in laryngeal adductor muscles. For CIONM, the section is subdivided into methodologies that elicit compound muscle action potentials in the vocal folds compared to the methodology of utilizing a laryngeal adductor reflex response in vocal fold adductor muscles. At the conclusion of this chapter, the reader should have a broad knowledge of the recent developments in the different forms of nerve monitoring, recognizing the benefits and limitations of the different methodologies and ongoing controversies in IONM for neck endocrine procedures.