Impact of continuous intraoperative neuromonitoring on autonomic nervous system during thyroid surgery

Background. Continuous intraoperative neuromonitoring (CIONM) via vagal nerve stimulation (VNS) is a new option for recurrent laryngeal nerve (RLN) protection during thyroid surgery. The aim of this study was to evaluate the safety of VNS for CIONM and to assess its effects on the autonomic nervous system (ANS) through analyzing heart rate variability (HRV). Methods. In a prospective, nonrandomized controlled study 5 patients received VNS for CIONM and 5 were operated on with conventional intermittent intraoperative neuromonitoring (IONM). HRV was analyzed in accord with patient-specific reference values. Results. VNS resulted in significantly altered ANS balance. Relative parasympathetic activity increased during VNS. Yet, no relevant cardiac arrhythmias or hemodynamic alterations were observed during VNS. Conclusion. HRV analysis revealed a distinct impact of VNS for CIONM on ANS balance. VNS caused parasympathetic predominance that was not countered by increased sympathetic activity. © 2010 Wiley Periodicals, Inc. Head Neck, 2011