This patient most likely has primary adrenal failure due to bilateral adrenal hemorrhage. He has acute onset nausea, lightheadedness, back and abdominal pain, and hypotension. While nonspecific, these findings are consistent with adrenal failure. Additionally, laboratory studies show hyponatremia, hyperkalemia, and hypocortisolemia, which are also consistent with the diagnosis. A sudden drop in the hemoglobin and hematocrit, as seen in this patient, may be present without evidence of bleeding elsewhere. Risk factors for adrenal hemorrhage include anticoagulant therapy (and may occur with treatment levels within the therapeutic range), the postoperative state, abnormalities of hemostasis (such as heparin-induced thrombocytopenia or antiphospholipid antibody syndrome), and sepsis. Because adrenal hemorrhage is uncommon and the associated findings may be relatively nonspecific, an increased level of suspicion is required for the diagnosis in at-risk patients; failure to identify acute adrenal failure in a timely manner may lead to cardiovascular collapse. Adrenal hemorrhage can often be visualized on abdominal CT imaging. Treatment of acute adrenal failure is with stress-dose glucocorticoids (hydrocortisone, 50-100 mg intravenously every 6-8 hours) and supportive care with intravenous fluids and vasopressors as needed for hemodynamic compromise.

Although autoimmune adrenalitis may cause primary adrenal failure and is associated with the presence of other autoimmune diseases (such as hypothyroidism in this patient), the onset of symptoms related to hypocortisolism are usually more gradual, and skin hyperpigmentation is often seen on examination.

Chronic administration of long-acting opiate medications is a known cause of hypogonadotropic hypogonadism and a potential etiology of secondary adrenal insufficiency. The administration of relatively short-acting opiates (oxycodone) on an as-needed basis for postoperative pain is unlikely to cause clinically significant hypothalamic-pituitary-adrenal axis disturbance. Hypogonadotropic hypogonadism would also not present with hyperkalemia because mineralocorticoid secretion is preserved.

Pituitary apoplexy results from acute hemorrhage into the pituitary and may result in adrenal insufficiency. Although this patient might be at increased risk due to anticoagulation, he does not have headache or visual disturbances, which are common in pituitary apoplexy. Because pituitary apoplexy causes secondary adrenal insufficiency, it would not result in hyperkalemia.