MANEJO DO HIPOTIREOIDISMO PÓS TIREOIDECTOMIA

FOLLOW-UP AND MONITORING — Beta blockers, if administered, should be tapered and discontinued after thyroidectomy. Antithyroid drugs can be discontinued at the time of thyroidectomy.
Hypoparathyroidism — Hypoparathyroidism is the most frequent complication of near-total thyroidectomy. Transient hypoparathyroidism occurs in up to 20 percent of patients after surgery for thyroid cancer and permanent hypoparathyroidism occurs in 0.8 to 3 percent of patients after total thyroidectomy and is more common when the goiter is extensive and anatomic landmarks are displaced and obscured. Chvostek's and Trousseau's signs are indicative of neuromuscular irritability due to hypocalcemia. Current requirements for short hospital stays argue for early treatment of hypocalcemia. We generally use the following regimen:
• Patients with symptomatic hypocalcemia (circumoral and distal extremity paresthesias) or a serum calcium concentration below 7.8 mg/dL (2.0 mmol/L, with correction for any abnormality in the serum albumin concentration) should be treated with calcitriol 0.5 mcg twice daily and calcium carbonate 500 mg four times daily. For patients who absorb calcium carbonate poorly, calcium citrate may be used. Calcium glubionate is available as a liquid, although calcium carbonate can be crushed and mixed with water to form a drinkable slurry.
• Patients with more severe symptoms (muscle cramps) or a serum calcium concentration below 7.5 mg/dL (1.9 mmol/L) should also receive calcium gluconate by continuous intravenous drip for 24 to 36 hours or until the serum calcium concentration rises and is maintained above 8.0 mg/dL (2.0 mmol/L). Details on preparing the intravenous calcium solution are found elsewhere.
• Emergency therapy is indicated in patients with tetany, seizures, laryngospasm or markedly prolonged QT intervals on the electrocardiogram. Treatment is initiated with the intravenous administration of one 10 mL ampule of 10 percent calcium gluconate over 5 to 10 minutes, followed by the intravenous infusion suggested in the prior paragraph.
• If the vitamin D and calcium carbonate cannot be tapered and then discontinued over the next two to eight weeks, the hypoparathyroidism may be permanent. Measurement of serum parathyroid hormone concentrations when serum calcium is low can confirm the permanent need for treatment.
An alternative approach is to treat all patients undergoing thyroidectomy with calcitriol and calcium carbonate starting the day before surgery in an effort to avoid the post-operative hypocalcemia with a plan to taper and eventually discontinue these medications over the next few weeks. The role of recombinant human PTH (teriparatide) is under investigation.
Hypothyroidism — The frequency of postoperative hypothyroidism is dependent upon the size of the surgical remnant. For patients with Graves’ disease or toxic MNG who had near-total or total thyroidectomy, thyroid hormone replacement (thyroxine, T4) should be initiated prior to discharge in a euthyroid patient at a dose of approximately 1.6 mcg/kg body weight daily. If the patient was still hyperthyroid at the time of surgery, thyroid hormone replacement should be delayed until levels fall into the normal range; the interval can be estimated based on the week-long half-life of T4. Elderly patients and those with coronary disease or multiple coronary risk factors should be treated with less than full replacement dose (ie, 50 to 75 mcg daily). Serum TSH should be measured in six to eight weeks and the dose increased by 12 to 25 mcg/day if the TSH remains above the normal reference range. Serum TSH should be measured six to eight weeks after each dose adjustment.
Patients with Graves’ disease who have subtotal thyroidectomy and are not hypothyroid soon after surgery need to be monitored for possible hypothyroidism (or recurrent hyperthyroidism) for the rest of their lives.
Dose and monitoring — The average replacement dose of T4 in adults is approximately 1.6 mcg/kg body weight per day (112 mcg/day in a 70-kg adult), but the range of required doses is wide, varying from 50 to 200 mcg/day. T4 requirements correlate better with lean body mass than total body weight. The necessary dose per kg body weight is higher in infants and children.
The dose may vary according to the cause of hypothyroidism. In a study of patients receiving chronic T4 therapy who were clinically euthyroid and had serum free T4 index values within the upper half of the normal range and normal serum TSH concentration, 73 patients with hypothyroidism caused by chronic autoimmune thyroiditis or radioiodine therapy were receiving less T4 (118 mcg/day, 1.6 mcg/kg/day) than 36 patients with thyroid cancer after near-total thyroidectomy (152 mcg/day, 2.1 mcg/kg/day). In 36 patients with central hypothyroidism and similar serum free T4 index values, the T4 dose was higher (155 mcg/day, 1.9 mcg/kg/day). These results suggest that both normal amounts of TSH and the presence of residual thyroid tissue are determinants of T4 dose in patients with hypothyroidism.

REFERÊCIAS:
http://www.uptodate.com/contents/surgical-treatment-of-differentiated-thyroid-cancer?source=see_link&anchor=H16#H16
http://www.uptodate.com/contents/surgery-in-the-treatment-of-hyperthyroidism-indications-preoperative-preparation-and-postoperative-follow-up?source=search_result&search=thyroidectomy&selectedTitle=2~108