What are the intraoperative concerns with coexisting thyroid disease?
The first concern is airway management. The first deci-sion to be made is whether to secure the airway before or after induction of anesthesia. This decision will be deter-mined primarily by the results of the physical examination and radiological studies. There are many different modali-ties available for safely securing the abnormal airway. They include: awake or asleep fiberoptic intubation, awake intubation through a laryngeal mask airway (LMA), or inhalation induction followed by direct laryngoscopy. The uncompromised airway can be maintained with an endo-tracheal tube or an LMA. Endotracheal tubes should be reinforced or secured so that they cannot kink when warmed to body temperature. With an LMA, there is the risk of laryngospasm from surgical manipulation or nerve damage.
Thyroidectomy can be performed under bilateral super-ficial cervical plexus block and unilateral deep cervical plexus block. Bilateral deep cervical blocks should be avoided because of the risk of causing bilateral recurrent laryngeal nerve blockade. This technique requires a motivated patient, and a surgeon and anesthesiologist comfortable with the technique.
Patients who are clinically hyperthyroid presenting for emergency surgery will be oversensitive to β-adrenergic stimulation. They will have an exaggerated response to endogenous catecholamines released during the stress response, as well as to exogenous catecholamines adminis-tered for hypotension. Phenylephrine may be preferable, since it does not cause β-adrenergic stimulation. Hypothyroid patients, on the other hand, will be insensi-tive to catecholamines and will require larger doses than normal.
The minimal alveolar concentration (MAC) of inhalation agents does not change. However, these patients may require support or control of hemodynamic parameters when normal doses of anesthetics are administered. The volume of distribution and clearance of drugs may be affected by thyroid status.