Degree of thyroid dysfunction
Laboratory findings
Elective
Urgent/emergent
Treatment
Subclinical
■ Increased TSH
■ Normal free T4
■ Proceed
■ Proceed
■ None
Mild–moderate
■ Increased TSH
■ Low free T4
■ Delay
■ Proceed
■ Standard replacement (1.7mcg/kg PO Qday. Adjust dose q4–6weeks based on TFTs)
■ Severe
■ Myxedema comaa
■ Free T4 < 1ug/dL
■ Delay
■ Proceed
■ Endocrinology consultation
■ Emergent hormone replacementb
■ Hydrocortisone 100 mg IV Q8 h
Patients with subclinical hypothyroidism (elevated TSH, normal free T4 and T3) can typically proceed with elective surgeries.
If surgical intervention is necessary or emergent, surgeons, anesthetists, and internists should be aware that perioperative complications may occur in those with mild to moderate hypothyroidism [3, 11, 12, 14]. Close cardiovascular, respiratory, and renal monitoring is suggested (Table 15.2).
Table 15.2
Perioperative complications in patients with hypothyroidism
■Decreased cardiac output from decreased heart rate and stroke volume contractility |
■Decreased total blood volume from increased peripheral vascular resistance (increased mean arterial pressure suppresses the renin-angiotensin-aldosterone system which in turn decreases sodium absorption and blood volume) |
■Respiratory failure from decreased hypoxic and hypercapnic ventilatory drive |
■Respiratory muscle weakness |
■Decreased renal perfusion |
■Inappropriate secretion of antidiuretic hormone leading to alterations in fluid and electrolyte balance |
■Decreased renal clearance of medications/anesthesia |
■Delayed gastric emptying and gut motility |
■Delayed metabolism leading to prolonged half-life of certain medications |
■Impaired ability to mount a febrile response |
Thyroid Function in the Critically Ill [18–21]
Critical illness is associated with alterations in concentrations of thyroid hormones. Previously known as “euthyroid sick syndrome,” this syndrome is now termed “non-thyroidal illness.” Laboratory data suggests transient central hypothyroidism:
T3 usually low
T4 and free T4 low or normal
TSH low or normal
The degree of illness generally correlates with the degree of thyroid hormone abnormalities. There is no evidence that thyroid hormone replacement is beneficial and may be harmful. Thyroid function should not be checked in critically ill patients unless there is strong suspicion and/or clinical evidence of thyroid dysfunction (e.g., bradycardia, hypothermia, altered mental status, etc.).
The Hypothyroid Patient Undergoing Cardiovascular Surgery
Thyroid hormone has profound effects on the cardiovascular system [22], but replacement is controversial in cardiac surgeries.
Replacement may precipitate acute coronary syndromes.
Untreated hypothyroidism may precipitate or exacerbate heart failure and/or hypotension in the perioperative period.
Minimal data available, but prior studies suggest no adverse events in mild to moderate hypothyroidism when hormone replacement deferred [23, 24].
Decision to initiate thyroid hormone replacement should be made based on the degree of hormone imbalance, severity of heart failure, and hemodynamic instability.
Myxedema Coma
In rare cases, the stress of surgery can trigger myxedema coma in patients with hypothyroidism: severe hypothyroidism representing a medical emergency with a high mortality rate [3, 15, 25]. The clinical presentation of myxedema coma includes:
Decreased level of consciousness
Hypothermia
Cardiovascular effects: hypotension, bradycardia, and cardiac arrhythmias
Hypoventilation
Hyponatremia
Hypoglycemia [14]
The diagnosis is based on a high TSH, very low free T4, and the clinical presentation. If myxedema coma is suspected, cortisol and cosyntropin stimulation test should be sent if possible to assess for associated adrenal insufficiency or hypopituitarism. Treatment usually requires intensive supportive measures, depending on the severity of hypothyroidism [16]:
Admission to intensive care unit
Mechanical ventilation
Rewarming
Volume resuscitation and/or vasopressor support
Cardiac monitoring
Stress dose steroids until adrenal insufficiency excluded [15]
Hyperthyroidism
Non-thyroid Surgery
There are scant data evaluating the risk of hyperthyroidism in non-thyroid surgery. One small retrospective study in elderly patients undergoing surgical fixation for hip fractures found that overt hyperthyroidism on admission was associated with an increased risk for 30-day postoperative complications. [29] In addition, hyperthyroidism has significant cardiopulmonary effects that may increase the risk of surgery [30, 31] (see Table 15.3). Care should usually be coordinated with a thyroid specialist, but general principles include:
Table 15.3
Perioperative complications in patients with hyperthyroidism
Cardiovascular [35] |
■Arrhythmias, e.g., atrial fibrillation [36] |
■Tachycardia, systolic hypertension, widened pulse pressure from decreased peripheral vascular resistance |
■Congestive heart failure |
■Angina from increased myocardial oxygen demand |
Pulmonary |
■Dyspnea due to increased oxygen consumption and CO2 production |
■Respiratory and skeletal muscle weakness |
■Decreased lung volume |
Gastrointestinal |
■Increased gut motility with malabsorption, malnutrition |
Metabolic |
■Increased basal metabolic rate |
Psychiatric |
■Delirium, psychosis, decreased mental status |
Patients with known hyperthyroidism should continue hyperthyroid medications throughout the perioperative period including the morning of surgery.
Elective surgery should be postponed in patients with poorly controlled or untreated hyperthyroidism until they are euthyroid, due to the risk of thyroid storm (see Table 15.4).
Table 15.4
Perioperative management of patients with hyperthyroidism
Degree of thyroid dysfunction
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