Predicting a low response to ACTH in the critically ill

Objective

To determine the risk factors for a low adrenocortical response to adrenocorticotropic hormone (ACTH) in critically ill patients.

Design

A retrospective cohort study in the general ICU of a university hospital.

Patients

Five hundred and twenty consecutive critically ill patients in a 3-year period, who underwent a 250 μg ACTH stimulation test for RAI, because of hypotension or prolonged need for vaso-pressor/inotropic therapy.

Methods

The test was performed by i.v. injection of 250 μg synthetic ACTH and measuring cortisol immediately before and 30 and 60 min after injection.

Measurements and results

A low adrenal response was defined as an increase in circulating cortisol <250 nmol/l and occurred in 60% of patients. Variables were collected at the onset of admission and at the day of testing. Risk factors, in multivariate analysis, included sepsis, positive local cultures if not from urine or sputum, mechanical ventilation and high inspiratory O₂ fraction, metabolic acidosis, low platelets, absence of prior cardiovascular disease or cardiac surgery, independently of baseline cortisol and albumin levels. The baseline cortisol/albumin levels, as an index of free cortisol, related directly and the increases inversely to the sequential organ failure assessment score.

Conclusion

In the critically ill, sepsis and its sequelae are major risk factors of a low adrenocortical response to ACTH, independent of baseline cortisol values and cortisol binding capacity in blood. The data may help to delineate relative adrenal insufficiency.