How should hypothyroidism be managed perioperatively?

Perioperative Management of Hypothyroidism

Patients with well-controlled hypothyroidism on stable levothyroxine therapy can safely proceed to surgery without dose adjustment, while those with untreated or poorly controlled hypothyroidism should have thyroid replacement optimized before elective surgery whenever possible.

Preoperative Assessment and Optimization

Patients with Known Hypothyroidism

• Continue levothyroxine at the usual maintenance dose throughout the perioperative period 1, 2
• Document euthyroid status preoperatively by measuring serum TSH, targeting 0.5-2.0 mIU/L for most patients 3
• Levothyroxine can be taken on the morning of surgery with a sip of water, as it has a long half-life (6-7 days) and missing 1-2 doses has minimal clinical impact 1

Patients with Untreated or Poorly Controlled Hypothyroidism

• Delay elective surgery until euthyroidism is achieved whenever feasible, as untreated hypothyroidism increases risk of heart failure, gastrointestinal complications, and prolonged ventilation requirements 4, 5
• Start levothyroxine 1.6 mcg/kg/day for most adults, but use lower starting doses (12.5-25 mcg/day) in elderly patients or those with coronary artery disease to avoid precipitating myocardial ischemia 1, 3
• Recheck TSH after 6-8 weeks of therapy before proceeding with elective surgery 1, 2

Critical Exception - Coronary Artery Disease

In patients requiring urgent coronary artery bypass grafting or cardiac intervention, address coronary blood flow FIRST before initiating thyroid hormone replacement, as levothyroxine can increase myocardial oxygen demand and worsen ischemia 5

Intraoperative Management

Medication Administration

• Levothyroxine can be held for 1-2 days perioperatively without clinical consequence due to its long half-life 1
• If NPO status extends beyond 5-7 days, consider IV levothyroxine at 75% of the oral dose (though this is rarely necessary) 1
• Avoid etomidate for induction if possible, as it suppresses cortisol production; if used, maintain high clinical suspicion for relative adrenal insufficiency 4

Monitoring Considerations

• Patients with hypothyroidism undergoing CABG have higher incidence of postoperative heart failure and gastrointestinal complications 4
• Subclinical hypothyroidism (TSH 4.5-19.9 mIU/L) may increase risk of postoperative atrial fibrillation, particularly with TSH ≥10 mIU/L 4
• Rarely, severe hypothyroidism can manifest postoperatively as lethargy, prolonged ventilation requirement, and hypotension requiring thyroid replacement 4

Postoperative Management

Resuming Levothyroxine

• Resume oral levothyroxine at the preoperative maintenance dose as soon as oral intake is tolerated 1, 2
• No stress-dose adjustment is needed for levothyroxine, unlike glucocorticoids 4
• If prolonged NPO status (>7 days), use IV levothyroxine at 75% of oral dose until enteral route available 1

Monitoring and Dose Adjustment

• Recheck TSH 6-8 weeks after surgery if there were perioperative complications or prolonged NPO status 1, 2
• For patients who underwent thyroidectomy, calculate initial LT4 dose based on weight (1.6 mcg/kg/day), height, age, sex, and calcium supplementation status, as weight-based dosing alone achieves target TSH in only 30% of patients 6
• Obese patients often require lower weight-based doses than predicted by simple weight calculations 6, 7

Critical Pitfalls to Avoid

Do NOT Confuse with Euthyroid Sick Syndrome

• Low T3 and T4 with normal or low TSH in critically ill surgical patients represents euthyroid sick syndrome, NOT hypothyroidism 5
• Do not initiate thyroid hormone replacement for euthyroid sick syndrome, as there is no evidence of benefit and potential for harm 5
• True hypothyroidism shows elevated TSH with low free T4 2, 3

Do NOT Delay Urgent Surgery

• For urgent/emergent surgery in untreated hypothyroid patients, proceed with surgery and initiate levothyroxine postoperatively 5
• The risks of delaying necessary surgery outweigh the risks of operating on a hypothyroid patient 5

Do NOT Confuse with Adrenal Insufficiency

• Hypothyroidism is contraindicated for treatment until adrenal insufficiency is corrected, as thyroid hormone accelerates cortisol clearance and can precipitate adrenal crisis 8, 1
• In patients with suspected pituitary/hypothalamic disease causing secondary hypothyroidism, always assess and treat adrenal insufficiency FIRST before starting levothyroxine 3

Do NOT Over-Supplement

• Avoid empiric stress-dose thyroid hormone supplementation, as overtreatment increases risk of atrial fibrillation and bone loss 3
• Unlike glucocorticoids, thyroid hormone does not require stress dosing during surgery 4