Anesthesia and hypothyroidism: a review of thyroxine physiology, pharmacology, and anesthetic implications

Hypothyroidism produces major derangements of normal physiology. Depression of myocardial function, decreased hypoxic and hypercapnic ventilatory responses, abnormal baroreceptor function, and reductions in plasma volume may all be present. In addition, the presence of anemia, hypoglycemia, hyponatremia, decreased free water excretion, and impaired hepatic drug metabolism may all adversely influence responses to anesthesia. Most reported complications have occurred in patients with unrecognized hypothyroidism. Preoperative recognition of hypothyroidism is essential for the safe anesthetic management of these patients. Elective surgical procedures should not be undertaken in the presence of untreated hypothyroidism. Thyroid supplements should be untreated hypothyroidism. Thyroid supplements should be given preoperatively to hypothyroid patients before emergency surgery. Intraoperative and postoperative hypothermia and electrolyte disturbances are relatively common and must be guarded against.