What levothyroxine dose should be given to a patient undergoing cardiac surgery to achieve a euthyroid state, with adjustments for weight, age ≥65 years, and coronary artery disease?

Levothyroxine Dosing for Cardiovascular Surgery

Continue the patient's usual levothyroxine dose on the morning of surgery without interruption, and resume it immediately postoperatively when oral intake is tolerated—no stress-dose adjustment is needed. 1

Perioperative Levothyroxine Management

Continue Usual Dose Through Surgery

• Levothyroxine must be continued on the morning of surgery without interruption to prevent perioperative complications and maintain stable thyroid hormone levels. 1
• No stress-dose adjustment is required for levothyroxine, unlike glucocorticoids, as it does not increase bleeding risk or interfere with anesthesia. 1
• For patients already on chronic levothyroxine replacement therapy undergoing coronary bypass surgery, routine thyroxine administration (their usual dose) is all that is required for satisfactory outcomes—no supplemental dosing is needed. 2

Timing of Surgery in Hypothyroid Patients

• Delay elective cardiac surgery until euthyroidism is achieved whenever feasible to reduce perioperative risks including heart failure, gastrointestinal complications, and neuropsychiatric complications. 1, 3
• Even subclinical hypothyroidism (TSH 4.5-10 mIU/L) increases perioperative cardiovascular risks, particularly in cardiac surgery patients. 1, 3

Standard Levothyroxine Dosing for Hypothyroidism

Initial Dosing in Adults with Coronary Artery Disease

• For adults with underlying cardiac disease or coronary artery disease, start with a lower dose (less than 1.6 mcg/kg/day) to avoid exacerbation of cardiac symptoms. 4
• Specifically, elderly patients and those with coronary artery disease should start at 12.5 to 50 mcg per day. 5
• The full replacement dose for most adults is 1.6 mcg/kg/day, but this should not be used as the starting dose in cardiac patients. 4

Dose Titration in Cardiac Patients

• Titrate dosage every 6 to 8 weeks (not the standard 4-6 weeks) in patients at risk for atrial fibrillation or with underlying cardiac disease. 4
• Increase by 12.5 to 25 mcg increments until the patient is euthyroid based on serum TSH or free-T4. 4
• The peak therapeutic effect of a given dose may not be attained for 4 to 6 weeks. 4

Monitoring Parameters

• In adult patients with primary hypothyroidism, monitor serum TSH levels 6 to 8 weeks after any change in dosage. 4
• In patients on stable replacement dosage, evaluate clinical and biochemical response every 6 to 12 months. 4

Postoperative Management

Resuming Levothyroxine After Surgery

• Resume oral levothyroxine as soon as the patient can tolerate oral intake after surgery. 1
• Administer as a single dose, preferably on an empty stomach, one-half to one hour before breakfast with a full glass of water. 1

Critical Monitoring

• Monitor for signs of severe hypothyroidism including lethargy, prolonged ventilation requirements, and hypotension, particularly in patients with coronary artery disease. 1
• Watch for gastrointestinal and neuropsychiatric complications postoperatively. 1

Critical Pitfalls to Avoid

Do Not Hold Levothyroxine

• Never hold levothyroxine perioperatively, as interruption destabilizes thyroid status and worsens surgical outcomes. 1, 3
• This is a common error that significantly increases perioperative morbidity. 1

Rule Out Adrenal Insufficiency First

• Rule out adrenal insufficiency before initiating or continuing levothyroxine therapy, as hypothyroidism treatment is contraindicated until adrenal insufficiency is corrected. 1
• Maintain high clinical suspicion for relative adrenal insufficiency throughout the perioperative period. 1

Avoid Etomidate in Hypothyroid Patients

• Avoid etomidate for induction when possible, as it suppresses cortisol production. 1

Do Not Overlook Subclinical Hypothyroidism

• Even patients with TSH between 4.5-10 mIU/L face increased perioperative cardiovascular risks. 1, 3
• These patients warrant careful perioperative monitoring despite "subclinical" designation. 1