Relative adrenal insufficiency in critical illness

Objective: To review the effects of critical illness on hypothalamic-pituitary-ad renal (HPA) function in human and veterinary medicine. Data sources: Data from human and veterinary literature was reviewed. Human data synthesis: Relative adrenal insufficiency (RAI) appears to be common in critically ill human patients with sepsis or septic shock. Hypotension that is refractory to fluid therapy and requires vasopressors is the most common presentation of RAI in the human intensive care unit (ICU). Many investigators now advocate the use of a low-dose adrenocorticotropin hormone stimulation test to diagnose RAI. It is important to evaluate for the presence of adrenal dysfunction, because current data suggest that treatment with 'stress' or low doses of glucocorticoids (200-300 mg hydrocortisone daily) may improve patient outcome in humans. Veterinary data synthesis: There is a paucity of controlled studies in the veterinary literature regarding the effects of critical illness on HPA function. The results of these studies are varied. However, research models of sepsis and hemorrhagic shock suggest the existence of RAI in animals. Prospective clinical studies are needed to further examine pituitary-adrenal response to severe illness in veterinary patients, and to determine if there are therapeutic options, including glucocorticoid administration, which will improve patient outcome in animals. Conclusions: RAI is well documented in critically ill human patients, yet little is known about adrenal dysfunction in veterinary critically ill patients. A small number of studies suggest that RAI may exist in certain subpopulations of veterinary patients. The syndrome of RAI could be considered as a differential diagnosis in seriously ill veterinary patients that fail to respond to appropriate therapy, especially when hypotension refractory to fluid and vasopressor therapy is encountered. This disorder may represent a previously unidentified syndrome in critically ill veterinary patients with important therapeutic implications.