Intra-operative neuromonitoring of the vagus nerve during thyroidectomy. A prospective study

ObjectivesTo determine whether intra-operative neuromonitoring (IONM) of the vagus nerve during thyroidectomy can predict postoperative vocal fold palsy. DesignA single-centre, prospective study. SettingUniversity Hospital. ParticipantsA total of 95 patients underwent thyroid surgery. A total of 160 vagus nerves were studied. The amplitude of the action potential of vocal muscles was recorded intra-operatively by indirect supramaximal stimulation of the vagus nerve. All patients underwent flexible fibre-optic laryngoscopy on postoperative day 1 to detect the presence of vocal fold palsy. Main outcome measuresThe primary outcome measure was the difference of the action potential amplitude of the vagus nerve before and after resection of the thyroid lobe. Statistical analysis determined the amplitude variation cut-off able to accurately predict postoperative vocal fold palsy. ResultsTransient vocal fold palsy was observed in 4.375% of cases, and permanent fold palsy was observed in 1.25% of cases. A decrease of the action potential amplitude by more than 61% was statistically significantly associated with postoperative vocal fold palsy. A greater than 87% decrease of the amplitude of the action potential was correlated with permanent postoperative vocal fold palsy. ConclusionIONM of the vagus nerve during thyroidectomy may accurately predict postoperative vocal fold palsy.