Hypothyroidism Revealed During General Anesthesia in a Patient With Treatment-Resistant Depression: A Case Report

General anesthesia in patients with undiagnosed hypothyroidism can lead to neurological, pulmonary, and cardiovascular complications. We report a case of hypothyroidism in a patient with treatment-resistant depression detected intraoperatively based on multiple clinical findings. A 49-year-old woman was scheduled for orthognathic surgery for mandibular prognathism. She had depression since the age of 36 and was taking multiple psychotropic medications. After induction, she had persistent hypotension, bradycardia, low bispectral index, and hypothermia that were resistant to treatment. After ruling out common causes and reducing the anesthetic agents, blood tests were performed intraoperatively to examine thyroid function which revealed hypothyroidism. No delayed recovery or postoperative abnormalities were observed. Lithium carbonate was identified as the most likely cause of hypothyroidism by an endocrinologist. Given the overlap in signs and symptoms, hypothyroidism may be overlooked in a patient with depression. The possibility of hypothyroidism should be considered especially noted in patients taking lithium carbonate. Furthermore, suspicion of hypothyroidism based on clinical findings during anesthesia may prompt the need for further evaluation.