From the FDA Drug Label
Hypothyroidism decreases and hyperthyroidism increases the sensitivity to oral anticoagulants. Treatment of patients with thyroid hormones requires the periodic assessment of thyroid status by means of appropriate laboratory tests besides the full clinical evaluation. The FDA drug label does not answer the question.
From the Research
For patients with uncontrolled hypothyroidism (elevated TSH) scheduled for major surgery, postponing elective surgery is recommended until thyroid function is normalized, as supported by the most recent evidence 1.
Key Considerations
- Start levothyroxine replacement therapy immediately, typically beginning with 1.6 mcg/kg/day for most adults, though lower doses (25-50 mcg/day) may be appropriate for elderly patients or those with cardiovascular disease.
- Thyroid function should be reassessed every 4-6 weeks, with dose adjustments of 12.5-25 mcg until TSH normalizes.
- If surgery cannot be delayed, proceed with caution while understanding the increased risks of cardiovascular instability, impaired drug metabolism, and poor wound healing.
- In urgent cases, consider IV levothyroxine (typically 70-80% of oral dose) if oral administration isn't possible.
- Patients should be closely monitored perioperatively for signs of myxedema coma, hemodynamic instability, and hypothermia.
- The anesthesiologist should be informed about the patient's thyroid status, as hypothyroid patients may have increased sensitivity to anesthetics and opioids.
Rationale
The approach is based on the understanding that uncontrolled hypothyroidism increases surgical risks through impaired cardiac function, altered drug metabolism, and compromised wound healing capabilities, as highlighted in earlier studies 2, 3.
Additional Guidance
For patients who remain symptomatic on levothyroxine therapy, a trial of combination therapy with liothyronine (T3) may be considered, as suggested by recent guidelines 1, 4. However, the primary focus for preoperative management should be on normalizing thyroid function with levothyroxine to minimize surgical risks.