URING THE PRACTICE of clinical anesthesia, D it is not uncommon to encounter patients with varying degrees of hypothyroidism, ranging from those who have been rendered essentially euthyroid by treatment with exogenous supplements, to those with overt myxedema. Despite the relative frequency of this condition, there is, however, little current information in the anesthesia literature regarding either the abnormal physiology found in hypothyroidism or the duration of treatment required for its

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... ersal (1). Although the incidence of perioperative morbidity associated with undiagnosed or untreated hypothyroidism is unknown, major complications have been reported (2). These included severe hypotension (3-7) or cardiac arrest (3) following induction of anesthesia, extreme sensitivity to narcotics and anesthetics with prolonged unconsciousness (4,8), and hypothyroid coma following anesthesia and surgery (6, 7) . This review briefly discusses thyroid physiology and regulation and examines some of the biochemical, metabolic, and pharmacologic derangements that can occur. Assessment of the adequacy of thyroid replacement therapy, as well as the time course for reversal of hypothyroidism, are also considered. Finally, the anesthetic management of the hypothyroid patient is