Preoperative preparation for surgery in thyrotoxicosis
THE CONTEXT
Preparation may aim for biochemical euthyroidism with carbimazole or rapid control of clinical manifestations with β-adrenergic blockade.
Traditional preparation
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The aim is biochemical euthyroidism at operation. Preparation is usually outpatient, coordinated with endocrinology input.
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Hospital admission is rarely required, but may be necessary for severe presenting symptoms, failure to control hyperthyroidism or non-compliance with medication.
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Carbimazole 30–40 mg/day is the drug of choice. Euthyroidism is reached after 8–12 weeks, after which the dose may be reduced to 5 mg every 8 hours.
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Alternatively, a block and replace regimen continues high-dose carbimazole to inhibit T3 and T4 production and adds thyroxine 0.1–0.15 mg daily.
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The last carbimazole dose may be given on the evening before surgery.
β-Adrenergic blockade
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β-Adrenergic blockers abolish clinical manifestations by acting on target organs rather than the thyroid gland. Propranolol also inhibits peripheral conversion of T4 to T3.
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Propranolol 40 mg three times daily is described. The dose is increased according to clinical response; propranolol 80 mg three times daily or nadolol 320 mg once daily may be required.
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The clinical response is rapid, allowing clinical euthyroidism and operation within days rather than weeks.
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These drugs do not inhibit thyroid hormone synthesis. Hormone levels remain high during treatment and for some days after thyroidectomy, so blockade should continue for 7 days postoperatively.
Adjunctive iodine
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Iodine may accompany carbimazole or a β-adrenergic blocker for 10 days before operation.
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Iodide alone produces transient remission and may reduce vascularity, marginally improving operative safety. It is not used alone for preparation because more effective treatment is available.
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Iodine preparations are not used universally. They provide additional safety if the morning β-blocker dose is mistakenly omitted on the day of operation.