Changes in Tracheal Tube Cuff Pressure and Recurrent Laryngeal Nerve Conductivity During Thyroid Surgery

The aetiology of recurrent laryngeal nerve (RLN) neurapraxia is unclear in most RLN palsies post-thyroidectomy. We hypothesised that high intralaryngeal pressures impede RLN conductivity, in turn contributing to RLN palsy. Therefore, we measured tracheal tube (TT) cuff pressure (as a surrogate for intralaryngeal pressure) and RLN conduction during ten standard manoeuvres in thyroidectomy, to assess for correlation between cuff pressure and RLN conductivity.

A prospective cohort study of thyroidectomy during 2018. For each thyroid lobe, TT cuff pressure was continuously measured via an air pressure transducer. RLN conduction (amplitude and latency) was measured using continuous neuromonitoring. Changes in mean TT cuff pressure and median nerve conduction from baseline measurements were analysed using Student's t test and Wilcoxon signed-rank test.

In a total of 50 RLNs, the mean baseline TT cuff pressure of 19.5 ± 8.9 mmHg increased significantly to 22.0 mmHg during anteromedial rotation of the thyroid (p < 0.05). RLN conduction changed during manipulation of the superior thyroid pole with shortening of latency (-0.49% from baseline, p = 0.05) and reduction in amplitude (-12.0% from baseline, p = 0.02). The timing of these deviations did not correlate with the increased TT cuff pressure. In three cases of temporary RLN palsy, the mean cumulative case TT cuff pressure was significantly higher (24.8 mmHg, p = 0.02).

This study demonstrates that TT cuff pressure and RLN conductivity can change significantly with manipulation of the thyroid and that high TT cuff pressures may be associated with RLN injuries.