Changes in serum cortisol with age in critically ill patients

Abstract

Background: Mortality in the intensive care unit (ICU) rises with age, a high basal serum cortisol and a small response to adrenocorticotropin (ACTH) stimulation. Even slight impairment of the adrenal response during severe illness can be lethal.

Objectives: To determine if age is associated with changes in basal or stimulated serum cortisol in critically ill patients.

Methods: We studied 2 groups of surgical ICU patients with hypotension despite > or = 6 h of catecholamine therapy. Group 1 comprised 7 patients aged <30 (mean 22.9 +/- 3.7) years, and group 2 comprised 8 patients aged >60 (mean 75.8 +/- 10.3) years (p < 0.001). We compared baseline serum cortisol levels and the serum cortisol response 30 and 60 min after stimulation with low-dose (1 microg) and 2 h later standard-dose (250 microg) ACTH. We also determined the incidence of adrenal insufficiency in each group using standard criteria and compared selected clinical variables.

Results: There was no significant difference in the mean serum cortisol at baseline although it tended to be higher in older patients. Group 2 patients had a significantly smaller response to the low-dose test at 30 min (p = 0.002), and to the standard-dose test at both 30 (p = 0.02) and 60 min (p = 0.04). There was no significant difference in the incidence of adrenal insufficiency between the 2 groups: 1/7 or 14.3% in group 1 vs. 1/8 or 12.5% in group 2 (p = 1.0). There was no significant difference between the 2 groups in the mean acute physiology score, blood pressure, serum albumin, dopamine, or dobutamine dose (p > 0.05). Creatinine clearance was significantly lower in group 2 (p > 0.001) and endogenous ACTH significantly higher (p = 0.04). Significantly more patients in group 1 (5/7, 72%) than group 2 (1/8, 12.5%) had a diagnosis of trauma on admission (p = 0.04). Seven of the eight patients (88%) in group 2 vs. 1/7 (14%) of patients in group 1 died in the ICU, but this difference was not statistically significant (p = 0.18).

Conclusion: In this small exploratory study, baseline serum cortisol tended to be higher in older patients and older patients had a significantly smaller response to ACTH stimulation on both low-dose and standard-dose tests. In view of the high death rate in the older ICU patients, the findings in this study need to be confirmed in a larger study. The mechanism and clinical significance of these findings remain to be determined but may be related to deterioration in renal function with age.