The Dept of Anaesthesia & Intensive Care, CUHK
- life threatening clinical extreme of hyperthyroidism
- usually occurs in patients with poorly controlled or unrecognized hyperthyroidism
- other precipitants include excessive palpation of thyroid, incomplete pre-op preparation, inadequate peri-operative dose of beta blockers, use of radio-iodine in unprepared patients, drugs such as iodides in patients with impaired autoregulation, haloperidol, massive overdose of thyroid hormone
Exacerbation of features of hyperthyroidism
- malignant hyperpyrexia
Treatment to reduce thyroid hormone concentrations
- iodine: in large doses inhibits release of thyroid hormones. Generally given > 1 h after PTU/carbimazole/methimazole, as otherwise, it may lead to an increase in thyroid hormone synthesis. Use Lugol's iodine (16 mg bd PO), potassium iodide (50 mg bd PO) or sodium iodide (0.5 mg bd IVI). Iodine containing contrast media may specifically ameliorate cardiac effects of thyroxine, are potent blockers of peripheral conversion of T4 and may block peripheral thyroid hormone receptors (iopanoic acid 1-3 g daily or sodium ipodate 0.5 mg/day). ? drugs of choice. Lithium carbonate (300 mg qds titrated to a serum lithium level of 0.7-1.4 mmol/l) is an alternative in patients who are allergic to iodine. Has similar action in blocking thyroid hormone release
- propylthiouracil (inhibits conversion of T4 to T3 as well as blocking iodination of tyrosine and hence secretion of T4). PO/NG 1 g loading followed by 200-300 mg 4-6 hrly. GI absorption impaired or unreliable in thyroid crisis but there is no parenteral formulation. Rapid onset of action. Alternatives are methimazole and carbimazole (metabolized to methimazole). Methimazole may be absorbed more slowly than PTU but is longer acting. Does not affect peripheral conversion of T4. Transient leucopenia common with antithyroid drugs (20%) but agranulocytosis is rare
Treatment to reduce peripheral action of thyroid hormones
- beta blockade: IV propranolol - titrate against heart rate using increments of 0.5 mg to a total of 10 mg. Give further doses 4-6 hrly. Drug of choice: inhibits peripheral conversion of T4 to T3. Tachycardia, fever, hyperkinesis, tremor, proximal myopathy, periodic paralysis, bulbar palsy and hypercalcaemia respond. Beta1 selective agents do not inhibit T4 to T3 conversion as effectively but may be preferred in patients with reactive airways or heart failure. Esmolol useful because of short half-life
- although b blockers are of benefit in thyroid storm precipitated by high catecholamine concentrations associated with surgery it is not clear if thyroid storm due to other causes is as responsive to b blockade
- diltiazem, reserpine and guanethidine should be considered in patients in whom beta blockade is contraindicated
-contrast media may block peripheral thyroid hormone receptor
- glucocorticoids, PTU, oral contrast media, amiodarone block peripheral conversion of T4 to T3
- glucose for nutrition.
- postpone operation if possible. If not, take measures outlined above before operation rather than after development of symptoms.
Weiss RE, Refetoff S. Thyroid disesase. In Hall JB, Schmidt GA, Wood LH (eds). Principles of Critical Care, 2nd ed., 1998. McGraw-Hill, New York. pp 1205-19.
© Charles Gomersall November 1999
February, 2014 unless
otherwise stated. The author, editor and The Chinese University of Hong Kong
take no responsibility for any adverse event resulting from the use of this