Patients with chronic adrenal insufficiency usually present with a history of weakness, weight loss, anorexia, lethargy, slowed mentation, and general failure to thrive. Some patients complain of nausea, vomiting, abdominal pain, and diarrhea. Clinical signs include orthostatic hypotension and, rarely, hyperpigmentation (primary adrenal insufficiency). Laboratory testing may demonstrate hyponatremia, hyperkalemia, hypoglycemia, and a normocytic anemia.74,104 This presentation contrasts with the features of acute adrenal insufficiency (Table 79-2). Hypotension refractory to fluids and requiring vasopressors is the most common feature of acute adrenal insufficiency in critically ill patients.71,74,104 Patients usually have a hyperdynamic circulation, which may compound the hyperdynamic profile of septic patients.71 However, the systemic vascular resistance, cardiac output, and pulmonary capillary wedge pressure can be low, normal, or high.72 The variability in hemodynamics reflects the combination of adrenal insufficiency and the underlying disease. Importantly, acute adrenal insufficiency always should be excluded in critically ill patients requiring vasopressor support. CNS dysfunction is common, frequently compounded by the underlying disease. However, adrenal failure may present with altered mental status, particularly unexplained confusion, as the major clinical finding. Lethargy, weakness, anorexia, and abdominal complaints are common. Furthermore, in critically ill patients with unexplained fever, adrenal failure should be excluded. Laboratory assessment may demonstrate eosinophilia and hypoglycemia. Hyponatremia and hyperkalemia are uncommon. Many patients have a mild metabolic acidosis.