Why is monitoring hormones pre-operatively important?

Preoperative Hormone Monitoring: Critical for Preventing Life-Threatening Complications

Preoperative hormone monitoring is essential to identify and correct endocrine deficiencies that can cause intraoperative cardiovascular collapse, adrenal crisis, and postoperative mortality if left untreated.

Primary Rationale: Prevention of Adrenal Crisis

The most critical reason for preoperative hormone monitoring is identifying adrenal insufficiency before surgery to prevent fatal adrenal crisis 1. Key considerations include:

• Adrenal insufficiency causes volume-resistant hypotension during surgery that can progress to shock and death if glucocorticoid replacement is not initiated preoperatively 1
• Thyroid hormone therapy increases metabolic clearance of glucocorticoids, meaning initiating levothyroxine before glucocorticoid replacement can precipitate acute adrenal crisis in patients with undiagnosed adrenal insufficiency 2
• Stress-dose steroids must be administered perioperatively in patients with known or suspected adrenal insufficiency to prevent cardiovascular collapse 3
• The surgical stress response significantly elevates cortisol requirements, and patients without adequate adrenal reserve cannot mount this response 4

High Prevalence of Hypopituitarism in Surgical Populations

For patients with pituitary lesions specifically, comprehensive preoperative endocrine evaluation is mandatory because hypopituitarism is present in 37-85% of patients with nonfunctioning pituitary adenomas 1, 3. The prevalence of specific deficiencies includes:

• Adrenal insufficiency: 17-62% of patients 1, 3
• Hypothyroidism: 8-81% of patients 1
• Hypogonadism: 36-95% of patients 1
• Growth hormone deficiency: 61-100% of patients 1

Failure to identify and treat these deficiencies preoperatively can lead to adrenal crisis during surgery 3.

Cardiovascular Risk Mitigation

Preoperative hormone assessment is critical for preventing cardiac complications in vulnerable populations 2:

• Untreated hypothyroidism or over-replacement with levothyroxine can precipitate arrhythmias, angina, or myocardial infarction during surgery, particularly in elderly patients or those with underlying cardiovascular disease 2
• Thyroid hormone status directly affects perioperative outcomes in cardiac surgery, with levothyroxine replacement associated with better 30-day, 1-year, and 2-year survival after heart transplantation 5
• Monitoring allows for appropriate dose adjustments to avoid cardiac complications while ensuring adequate replacement 2

Detection of Occult Hormone Hypersecretion

Beyond deficiency states, preoperative monitoring identifies clinically silent hypersecretion syndromes that alter surgical risk 1:

• Hyperprolactinemia occurs in 25-65% of patients with nonfunctioning pituitary adenomas, which may indicate a different tumor type requiring modified surgical approach 1
• Biochemical screening for pheochromocytoma must be performed before any planned surgery in at-risk patients, as undiagnosed catecholamine-secreting tumors cause intraoperative hypertensive crisis 1
• Pre-operative alpha-adrenergic blockade is essential when pheochromocytoma is identified to prevent life-threatening blood pressure fluctuations 1

Optimization of Metabolic Status

Hormone monitoring enables correction of metabolic derangements that impair surgical outcomes 1:

• Hyponatremia is common with adrenal insufficiency and must be corrected preoperatively to prevent neurological complications 1
• Glycemic control may worsen when thyroid hormone replacement is initiated, requiring adjustment of diabetes medications before surgery 2
• The surgical stress response causes predictable hormonal changes (elevated cortisol, catecholamines) that patients with endocrine deficiencies cannot mount 4

Specific Testing Algorithm

All anterior pituitary hormone axes must be assessed preoperatively 1, 3:

• Morning cortisol and ACTH to evaluate adrenal axis 3
• TSH, free T4, and free T3 to assess thyroid function 3
• Testosterone (men) or estradiol/LH/FSH (women) for gonadal axis 3
• IGF-1 to screen for growth hormone deficiency or excess 1, 3
• Prolactin to exclude hyperprolactinemia 1, 3
• Plasma or urinary metanephrines in patients with genetic risk for pheochromocytoma 1

Timing of Hormone Replacement

Replacement therapy must be initiated before surgery when deficiencies are identified 3:

• Glucocorticoid replacement should be started immediately when adrenal insufficiency is diagnosed 3
• Significant hypothyroidism requires correction preoperatively, though levothyroxine must never be started before glucocorticoid replacement in patients with potential adrenal insufficiency 3, 2
• The goal is physiologic replacement preoperatively with stress-dose coverage perioperatively 3

Common Pitfalls to Avoid

Critical errors in preoperative hormone management include:

• Starting levothyroxine before excluding or treating adrenal insufficiency, which can precipitate adrenal crisis 2
• Failing to provide stress-dose steroids perioperatively in patients with known adrenal insufficiency 3
• Not screening for pheochromocytoma in at-risk patients before surgery, risking hypertensive crisis 1
• Assuming normal hormone function without testing in patients with pituitary lesions, given the 37-85% prevalence of hypopituitarism 1, 3
• Discontinuing chronic glucocorticoid therapy without appropriate stress-dose coverage 1