Defining normal adrenal function testing in the intensive care unit setting: a canine study.

OBJECTIVE: To determine whether intensive care medicine therapies and testing influence hypothalamic-pituitary-adrenal test results. It is routine in intensive care medicine to measure hypothalamic-pituitary-adrenal function, commonly utilizing the adrenocorticotropic hormone stimulation test to diagnose absolute or relative adrenal insufficiency.
DESIGN: Prospective, 96-hr animal study.
SETTING: Research laboratory.
SUBJECTS: Twenty-four healthy canines.
INTERVENTIONS: Animals were randomized into two groups--awake and unrestrained or treated with intensive care medicine therapies, including sedation, intubation, and mechanical ventilation. Animals were further randomized to receive dexamethasone (or placebo) or undergo either a total of four or seven adrenocorticotropic hormone stimulation tests over 96 hrs.
MEASUREMENTS AND MAIN RESULTS: Sedation, intubation, and mechanical ventilation transiently increased both basal and postadrenocorticotropic hormone total and free cortisol concentrations >2-fold as compared with baseline for the first 24 hrs (p < or = .05 for both). Performance of seven stimulation tests increased both basal and postadrenocorticotropic hormone total and free cortisol concentrations from baseline by >1.5-fold for the duration of the 96-hr study (p < or = .05). Neither sedation, intubation, and mechanical ventilation nor the performance of more stimulation tests affected delta cortisol measurements (total or free cortisol, p = NS). In contrast, dexamethasone suppressed basal total cortisol concentrations by >2-fold (p < or = .005) at all time points and transiently increased delta total cortisol by approximately 35% during the first 24 hrs of the study (p < or = .05).
CONCLUSIONS: Total and free cortisol measurements--whether pre- or post- adrenocorticotropic hormone or as a calculated delta--were altered by intensive care therapies or frequent adrenocorticotropic hormone stimulation testing with one exception. Delta free cortisol was the only hypothalamic-pituitary-adrenal measurement unaffected by sedation, intubation, and mechanical ventilation, completion of more adrenocorticotropic hormone stimulation tests, or dexamethasone therapy. These findings support the need to determine normal ranges for hypothalamic-pituitary-adrenal testing in subjects receiving intensive care medicine before establishing laboratory criteria for the diagnosis of relative adrenal insufficiency.