General Medical Information

Thyroid and Parathyroid Disorders

David M. Barrs

Patients with hypothyroidism may undergo emergency surgery with little increase in morbidity. For elective surgery, gradual replacement of hormone is preferred because rapid repletion can lead to relative adrenal insufficiency and angina in patients with coronary insufficiency. Synthetic levothyroxine with a usual daily dose of 0.1 to 0.2 mg is the preferred replacement medication and may be given orally or intravenously in the same dose. In severe myxedema, hydrocortisone also should be given because adrenocorticotropin pituitary responsiveness to stress may be decreased. Free water clearance is also diminished, and care must be taken with hypotonic intravenous solutions.

In thyrotoxicosis, the primary concern is development of thyrotoxic crisis (i.e., thyroid storm). Elective surgery in hyperthyroid patients should be delayed, if possible, until the patient is in a euthyroid state. If urgent surgery must be performed in the thyrotoxic patient, iodines, propranolol, and antithyroid drugs, such as propylthiouracil or methimazole, should be used to reduce the risk of thyrotoxic crisis. Propylthiouracil blocks thyroid hormone production, inhibits the conversion of thyroxine to triiodothronine, and usually is given in an oral dose of 100 to 150 mg three times daily. Iodides induce a transitory inhibition of thyroid hormone production and release from the gland and decrease vascularity of the gland, which lasts 10 to 14 days. Iodides can be given as a saturated solution of potassium iodide at a dose of five drops orally every 6 hours. Palpitations, tachycardia, and tremor can be controlled with propranolol in an initial dose of 20 to 40 mg taken orally four times daily or 1 to 2 mg given intravenously every 4 to 6 hours. Hydrocortisone should be given to counter relative adrenal insufficiency.

Thyrotoxic crisis manifests by severe exaggeration of the classic symptoms of thyrotoxicosis and may develop intraoperatively or in the immediate postoperative period. The patient may suffer a marked fever, sweating, tachycardia, vomiting, abdominal pain, and delirium. Large doses of the same medications are given. Supportive therapy includes temperature control with acetaminophen or a cooling blanket. Sedation and oxygen therapy may be needed, and the patient should receive adequate glucose-containing intravenous solutions due to the high metabolic rate.

Hypocalcemia may develop in any person undergoing thyroid or parathyroid surgery. After either surgery, serum calcium levels should be determined every 12 hours for the first several days, followed by daily levels thereafter. If the calcium level falls below 8.0 mg/dL, signs or symptoms of latent tetany should be sought. A positive Chvostek or Trousseau sign, hyperreflexia, numbness or tingling in the extremities, or circumoral paresthesias are indications to begin calcium replacement. Laryngeal stridor or overt tetany are medical emergencies and require i.v. calcium replacement. Calcium gluconate (10%) is less irritating than calcium chloride and is given as two ampules (20 mL) diluted in 50 to 100 mL of dextrose solution infused over 10 minutes. Each ampule contains 1 g of calcium gluconate and 93 mg of elemental calcium. This emergency infusion of calcium gluconate is followed by a slow infusion of calcium gluconate, 0.5 to 2.0 mg/kg hourly. Deficiencies in magnesium, sodium, and albumin must be excluded. The patient should be reassured, because hyperventilation will cause a respiratory alkalosis with resultant worsening of the hypocalcemia. Patients with prolonged hypocalcemia may require oral calcium replacement with 1.5 to 3 g each day of elemental calcium and vitamin D. Perioperatively, the serum calcium levels should be maintained near 8 mg/dL.