The incidence of hypothyroidism is approximately 1% in the adult population, and 5% in adults older than 50 years (154). In women older than 60 years, the incidence of hypothyroidism may approach 6% (168). Hypothyroidism is 10 times more common in women than in men (154). Many such cases are secondary to previous antithyroid therapy (radioactive iodine or thyroidectomy) for hyperthyroidism. The most common primary cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune condition (154). A history of lethargy, cold intolerance, lassitude, weight gain, ﬂuid retention, constipation, dry skin, hoarseness, periorbital edema, and brittle hair can be indicative of inadequate thyroid function. In this setting, physical findings of increased relaxation phase of deep tendon reﬂexes, cardiomegaly, pleural or pericardial effusions, or peripheral edema should stimulate further investigation of thyroid function by assessment of TSH and free T4 levels. Hypothyroidism decreases cardiac output by 30% to 50% as a result of decreased stroke volume and heart rate (171). Hyponatremia may be associated with hypothyroidism because of the inability of the kidneys to excrete water (171). When elective surgery is planned for severely hypothyroid patients, surgery should be postponed until thyroid replacement therapy is initiated (154). In patients with mild or moderate hypothyroidism, the delay of surgery is controversial (154).
For young patients with mild to moderate hypothyroidism, a starting dose of 1.6 μg/kg of thyroid hormone replacement can be given. In elderly patients, thyroxin dosage (0.025 mg once a day) should be given with interval dose increases every 4 to 6 weeks until the patient is euthyroid (168). Dosage levels can ultimately be titrated against TSH levels. In severely hypothyroid patients requiring urgent or emergent surgery, intravenous T3 or T4 may be given, along with intravenous corticosteroids to avoid consequences of unrecognized adrenal insufficiency (151,154).
In the immediate postoperative setting, T4 therapy can be held for 5 to 7 days while waiting for return of bowel function because the half-life of circulating T4 is approximately 5 to 9 days (170). If more than 5 to 7 days of decreased bowel function are expected, T4 can be given by the intramuscular or intravenous route at approximately 80% of the oral dose (171,172).
Adrenal Insufficiency Adrenal insufficiency may result in catastrophic postoperative complications, including death. The most common cause of adrenal insufficiency in the surgical patient is secondary to the exogenous use of corticosteroids. The physician should ascertain whether a patient used exogenous steroids for asthma (including inhaled steroids), malignant conditions, arthritis, or irritable bowel syndrome. The type of steroid use, the route, the dose, the duration, and the temporal relationship to the timing of the surgical procedure must be determined. The type of surgical procedure and its associated stress should be taken into consideration. The use of high doses of exogenous steroids for prolonged periods can cause circulatory collapse, and they have adverse effects on wound healing and immunocompetence.