Thyroid dysfunction is ubiquitous in the general population, with approximately 4–21% of females and 3–16% of males having abnormal thyrotropin (thyroid-stimulating hormone or TSH) values.1 Thyroid hormones affect several systemic functions that impact the perioperative period. While routine testing of thyroid parameters in patients with known stable disease is not necessary, clinical assessment of patients with known or suspected thyroid dysfunction and optimization of these conditions are essential to mitigating adverse perioperative outcomes. In addition, both subclinical and overt hyperthyroidism and hypothyroidism are present in millions of patients, so a higher index of suspicion is warranted to recognize these subclinical variants and determine if management changes in the perioperative period are warranted.
Preoperative Evaluation and Risk Assessment
Hypothyroidism affects many body systems including cardiac, pulmonary, hematologic, gastrointestinal, and free water and electrolyte balance.2 Retrospective studies report intraoperative hypotension, sensitivity to opioids and sedatives, ileus, and altered mentation and delirium as significant side effects. In the absence of randomized trial data, experts historically have recommended that patients achieve clinical and laboratory parameters of a euthyroid state prior to surgery. However, retrospective data does not support this blanket recommendation.3–6 It should be noted that the definitions of severity of hypothyroidism vary between studies and are often inconsistent.
A retrospective case control study of 59 hypothyroid patients and 59 euthyroid matched controls undergoing surgery at Mayo Clinic found no significant differences in perioperative outcomes, complications, or length of hospital stay. No differences were noted based on serum thyroxine level, however only seven patients were severely hypothyroid as defined with a thyroxine level of < 1 mcg/dl. The authors concluded that it is safe to proceed with elective surgery in patients with mild to moderately severe hypothyroidism; no definitive conclusion could be made regarding severely hypothyroid patients.3
Another study of 40 hypothyroid surgical patients compared with 80 matched controls noted a higher rate of intraoperative hypotension, gastrointestinal, and neuropsychiatric complications in hypothyroid patients as well as an increased rate of heart failure in cardiac surgery patients. No differences were noted in perioperative blood loss, length of stay, arrhythmia, anesthesia recovery, pulmonary complications, or death. No clear association was noted between clinical and biochemical features of hypothyroidism to define patients at risk.4
A large study of 800 patients undergoing noncardiac surgery at Cleveland Clinic who were biochemically hypothyroid (TSH > 5.5) and 5612 biochemically euthyroid patients (TSH < 5.5) found no differences in postoperative mortality, wound, or cardiovascular outcomes, leading the authors to suggest that postponing surgery to initiate therapy in an asymptomatic patient is likely not necessary. The same group did an analysis of cardiac surgical patients evaluating cardiac complications (MI, cardiac arrest, and atrial fibrillation), vasopressor use, and wound infections, and found hypothyroid patients actually had a lower rate of atrial fibrillation than euthyroid patients, and corrected ...