A longitudinal evaluation of thyroid function in critically ill surgical patients.

Area of Science:

• Endocrinology
• Surgical Physiology
• Metabolic Response to Stress

Background:

• Thyroid hormone alterations, termed sick-euthyroid syndrome, are frequently observed post-major surgery.
• The temporal dynamics of these thyroid function changes and their recovery have not been extensively studied in large surgical cohorts.

Purpose of the Study:

• To longitudinally investigate the time course of thyroid hormone and thyroid-stimulating hormone (TSH) alterations following major surgery.
• To examine the relationship between TSH suppression and perioperative dopamine levels.
• To document thyroid function changes in hypothyroid patients undergoing major surgery.

Main Methods:

• Prospective study of 59 patients undergoing major surgeries (coronary artery bypass grafting, pneumonectomy, subtotal colectomy).
• Serial measurements of serum T4, T3, free T3, free T4, T3 resin uptake, reverse T3, and TSH.
• Thyrotropin-releasing hormone (TRH) stimulation tests were performed.
• Correlation analysis between TSH suppression and plasma dopamine concentrations.

Main Results:

• Significant decreases in serum T4, T3, free T3, and TSH were observed within 6 hours post-surgery, normalizing by 1 week.
• Serum reverse T3 and T3 resin uptake increased; free T4 remained unchanged.
• Postoperative TSH response to TRH was suppressed, correlating with elevated dopamine levels.
• Three hypothyroid patients showed similar thyroid hormone changes, with suppressed TSH responses to TRH.

Conclusions:

• The sick-euthyroid syndrome manifests rapidly within hours of major surgery and resolves with convalescence.
• Postoperative TSH suppression can obscure the diagnosis of hypothyroidism, necessitating careful interpretation of thyroid function tests.
• Awareness of these perioperative thyroid function dynamics is crucial for surgical consultants.