Non-neural Vocal Changes After Thyroidectomy

The optimum size of endotracheal tube (ETT) for general anaesthesia remains a matter of debate. Choice of ETT size may be of particular pertinence during thyroid surgery, for a number or reasons. Because of the strong attachments of the thyroid gland to the trachea, intraoperative mobilization of the thyroid will lead to inevitable movement of the trachea and larynx against the fixed ETT, with consequent risk of traumatic injury to tracheal mucosa, vocal cords, and arytenoids. Thus thyroidectomy is likely to be associated with a greater risk of laryngeal trauma related to the ETT than operations outside the Head and Neck region where there is no movement of the larynx. On top of this, postoperative vocal impairment comprises one of the most important concerns after thyroidectomy, usually attributed to impaired vocal fold function secondary to recurrent laryngeal nerve injury. However, post-thyroidectomy vocal impairment can also occur in cases where the recurrent laryngeal nerve is preserved. Thus, concerns regarding vocal outcomes after thyroidectomy tend to be foremost in the mind of both the surgeon and the patient, and any measures which can be taken to minimize post-thyroidectomy hoarseness, which might include choosing the optimal ETT size, would appear to constitute a worthwhile endeavor.

Laryngeal trauma due to endotracheal intubation is probably more common than appreciated, however, given that symptoms of sore throat and hoarseness after most operations are generally self-limiting, this is not usually a major cause of concern. On the other hand, postoperative vocal symptoms may be a major cause of anxiety after thyroidectomy, due to fear of damage to the recurrent laryngeal nerve or the external branch of the superior laryngeal nerve (SLN). Laryngeal trauma without impairment of vocal fold function has been reported to be a significant cause of vocal symptoms after thyroid surgery. However, no previously published study has attempted to correlate post-thyroidectomy vocal symptoms or signs of laryngeal trauma with ETT size.

The hypothesis of the present study was that intubation with a smaller size ETT would lead to less trauma to the larynx during thyroidectomy than intubation with a standard size tube, and this would be reflected through less postoperative throat symptoms and objective laryngeal alterations. The rationale for this hypothesis was that a smaller caliber tube would be less unyielding when the larynx is moved against it, and thus would lead to less laryngeal injury. In order to address this question, the investigators designed a randomized controlled trial, comparing the impact of intubation with a smaller size tube (size 6.5 for females, and size 7 for males) with that of intubation with ETTs of the standard size used in the investigators department (size 7.5 for females, and size 8 for males).