Thyroid Disease and Anesthetic Considerations

1. Jose Soliz, M.D. LBJ Grand Rounds February 2004 Thyroid Disease and Anesthetic Considerations

2. Basic Thyroid Gland Physiology Hormones triiodothyronine (T3) and thyroxine (T4) are bound to proteins and stored in the thyroid gland. T3 is more potent and less protein bound, most T3 is made in peripheral tissues from the de-iodination of T4 Both hormones increase carbohydrate and fat metabolism, increasing metabolic rate, minute ventilation, heart rate and contractility, water / electrolyte balance, normal function of CNS.

3. HyperthyroidismCauses • Graves Disease-most common • toxic multinodular goiter • TSH hormone secreting pituitary tumors • functioning thyroid adenomas • overdose of thyroid replacement medication

4. Hyperthyroidism • Diagnosis: made by abnormal TFT’s, elevated total and free T4, T3 low TSH, elevated free thyroxine index • Medical Treatment consists of drugs that inhibit hormone synthesis (PTU-propylthiouracil, MMI-methimazole), inhibit hormone release (potassium, or sodium iodide) or mask the signs of adrenergic activity (Beta-blocker) • While Beta blockade does not affect thyroid gland function, it does decrease the peripheral conversion of T4 to T3. • Radioactive iodine and subtotal thyroidectomy are other alternatives to medical therapy

5. HyperthyroidismClinical Manifestations • Weight loss • heat intolerance • muscle weakness • diarrhea • hyperactive reflexes • nervousness / anxiety • Physical: fine tremor, exophthalmos, goiter, warm clammy skin, fine brittle hair • Cardiac: sinus tach, A Fib, increase in contractility, CO

6. HyperthyroidismAnesthetic considerations-Preoperative • Antithyroid medications and beta-blockers should be continued through the morning of surgery. • Miller: Ideally patient should be rendered euthyroid prior to any elective procedure. Beginning pre-op antithyroid meds take 2-6weeks for effect, can use KI with Beta-blocker in addition, or alternative • Benzodiazepines are good choice for pre-operative sedation • Careful evaluation of patients airway

10. HyperthyroidismAnesthetic considerations-Intraoperative • No controlled study suggest advantages of particular anesthetic drug or technique for hyperthyroid patients, however: • Drugs that stimulate sympathetic nervous system should be avoided because of the possibility of large increases in blood pressure and heart rate. Ex. Ketamine. Pancuronium, atropine, ephedrine, epi • Thiopental may be induction agent of choice as it possess antithyroid activity at high doses.

11. HyperthyroidismAnesthetic considerations-Intraoperative • Close monitoring of cardiac function and body temperature is required. Need for invasive monitoring? • Adequate anesthetic depth should be obtained prior to laryngoscopy or surgical stimulation to avoid tachycardia, hypertension, ventricular dysrhythmias • Eye protection

13. HyperthyroidismAnesthetic considerations-Intraoperative • Anticipate exaggerated hypotensive response during induction as patient may be hypovolemic • Muscle relaxants can be given safely. Note patients with autoimmune thyrotoxicosis are associated with an increase risk of myopathies and myasthenia gravis. Reversal with glycopyrrolate instead of atropine • Hyperthyroidism does NOT increase MAC requirements, volatile agents can be used safely

14. HyperthyroidismAnesthetic considerations-Postoperative • Thyroid storm is most serious post-op problem • Characterized by: hyperpyrexia, tachycardia, altered consciousness, and hypertension • Precipitating factors: infection, trauma, surgery • Incidence is 10% in patients hospitalized for thyrotoxicosis • Onset is usually 6-24 hours after surgery, but can happen intraoperatively mimicking malignant hyperthermia • Unlike MH, not associated with muscle rigidity, elevated CPK, or marked degree or lactic or respiratory acidosis

15. HyperthyroidismAnesthetic considerations-Thyroid Storm • Treatment: ABC’s • IV Hydration, cool patient • IV propanolol (.5mg increments)/esmolol to control heart rate until less than 100. • Propylthiouracil 250mg Q6 hours orally or by NG tube • Sodium Iodide 1 gram over 12 hours • correction of any precipitating events (infection) • Cortisol is recommended if there is any coexisting adrenal gland suppression • Mortality rate is approximately 20%

16. Anesthetic ConsiderationsSubtotal Thyroidectomy • Associated with several complications: • Recurrent laryngeal nerve palsy may cause hoarseness if unilateral, or stridor if bilateral • Vocal cord function may be evaluated by DL after deep extubation if there is concern • Hematoma formation may cause airway compromise. May require immediate opening of neck wound • Hypoparathyroidism may result from unintentional removal of parathyroid glands. Hypocalcemia will result within 24-72 hours • Pneumothorax

17. Hypothyroidism Causes • Primary hypothyroidism • Autoimmune (Hashimoto’s thyroiditis) • post thyroidectomy • post radioactive iodine • overdosage of antithyroid medication • iodine deficiency • secondary hypothyroidism (failure of the hypothalamic-pituitary axis)

18. Hypothyroidism • Incidence: 1% of adult population, ten times more prevalent in women • Diagnosis: can be confirmed by low free thyroxine levels and elevated TSH (if primary) • Medical Treatment: consist of oral replacement

19. Hypothyroidism Clinical Manifestations • Hypothyroidism in early neonatal development may result in cretinism. • In adults, manifestations can be subtle: weight gain, cold intolerance, muscle fatigue, lethargy, constipation, hypoactive muscle reflexes, depression, periorbital or pretibial swelling • Heart rate, contractility, stroke volume, and cardiac output decrease, extremities may be cold, hair may be coarse and brittle.

20. HypothyroidismAnesthetic considerations-Preoperative • Patients with uncorrected severe hypothyroidism (T4<1 ug/dL) or myxedema coma should not undergo elective surgery. Potential for severe cardiovascular instability intraoperatively and myxedema coma. • If emergency surgery is necessary, in patients with overt disease or myxedema coma, IV thyroxine and steroid coverage. • Euthyroid state is ideal, however, subclinical cases of hypothyroidism has not been shown to significantly increase risk of surgery • Continue thyroid replacement meds on morning of surgery

21. HypothyroidismAnesthetic considerations-Preoperative • Airway eval: patients tend to be obese, large tongue, short neck, goiter, swelling of upper airway • Pre-op sedation should be administered cautiously if at all, as patients are more prone to drug included respiratory depression from sedatives and narcotics • Consider aspiration prophylaxis with Bicitra, Reglan as many hypothyroid patients have delayed gastric emptying times

22. HypothyroidismAnesthetic considerations-Intraoperative • Patients are more sensitive to hypotensive effects of anesthetic agents because decreased cardiac output, blunted baroreceptor reflexes, and decreased intravascular volume. Invasive monitoring on a per patient basis • Ketamine or Etomidate may be induction agents of choice • Succinylcholine and non-depolarizing muscle relaxants are generally safe for use. Monitor with peripheral nerve stim. • Controlled ventilation is recommended as patients tend to hypoventilate

23. HypothyroidismAnesthetic considerations-Intraoperative • Hypothermia occurs quickly and difficult to prevent and treat • MAC is essentially unchanged • Hematological (anemia, platelet, coag dysfx), electrolyte imbalances, and hypoglycemia is common and require close monitoring intraoperatively • Consider co-existed adrenal insufficiency in causes of refractory hypotension

24. HypothyroidismAnesthetic considerations-Myxedema Coma • Rare form of decompensated Hypothyroidism • characterized by stupor or coma, hypoventilation, hypothermia, bradycardia, hypotension, and severe dilutional hyponatremia(SIADH), CHF • Medical emergency with mortality rate of 15-20% • Infection, trauma, cold, CNS depressants predispose hypothyroid patients, especially in elderly

27. HypothyroidismAnesthetic considerations-Myxedema Coma • Treatment • IV thyroxine is indicated (L-thyroxine loading dose 300-500ug, followed by 50ug/day for 24-48hrs) • IV hydration with dextrose containing crystalloid, correction of electrolyte abnormalities • Support cardiovascular and pulmonary systems as necessary

28. HypothyroidismAnesthetic considerations-Postoperative • Extubation/Emergence may be delayed secondary to hypothermia, respiratory depression, or slowed drug metabolism • Awake extubation, try to maintain normothermia • Cautiously administer opioids post-op, consider regional techniques or Ketorolac for post-op pain control

29. References: 1. Graham, GW, Unger, BP, Coursin DB. Perioperative Management of Selected Endocrine Disorders. International Anesthesiology Clinics. 38(4) pp..31-67, 2000 2. Langley RW, Burch HB. Perioperative Management of the Thyrotoxic Patient. Endocrinology and Metabolism Clinics of North America. 32, 519-534, 2003 3. Miller, RD, Cucchiare RF, Miller ED, et al. Anesthesia, 5th ed. Churchiill-Livingston. New York, pp.927-933, 2000. 4. Morgan GE, Mikhail MS. Clinical Anesthesiology, New York, McGraw-Hill, 1996, 639-641 5. Murkin, JM. Anesthesia and Hypothyroidism: A Review of thyroxine physiology, pharmacology, and anesthetic complications. Anesthesia and Analgesia. Vol61(4) April 1982

30. References:(cont.) 6. Nicoloff JT, LoPresti JS: Myxedema Coma: A Form of Decompensated Hypothyroidism. Endocrinology Clinics of North America, Philadelphia, WB Saunders, June 1993 279-290 7.Stathalos N, Wartofsky L. Perioperative Management of Patients with Hypothyroidism. Endocrinology Clinics of North America. 32, pp..503-518, 2003 8. Wall R. Unusual Endocrine Problems. Anesthesiology Clinics of North America 14, 471-493, 1996 9. Weinberg AD, Brennan MD, Gorman CA et al. Outcome of Anesthesia and Surgery in Hypothyroid patients. Arch Intern Med 143:893-897, 1983