Abstract
IntroductionThe assessment of adrenal function in critically ill patients is problematic, and there is evidence to suggest that measurement of tissue glucocorticoid activity may be more useful than estimation of plasma cortisol concentrations. Interstitial cortisol concentrations of cortisol represent the available pool of glucocorticoids able to enter the cell and bind to the glucocorticoid receptor. However the concentrations of plasma cortisol may not accurately reflect interstitial concentrations. We elected to perform a preliminary study into the feasibility of measuring interstitial cortisol by microdialysis, and to investigate the relationship between total plasma cortisol, free plasma cortisol and interstitial cortisol in patients with severe burns.MethodsA prospective observational study carried out in a tertiary intensive care unit. Ten adult patients with a mean total burn surface area of 48% were studied. Interstitial cortisol was measured by microdialysis from patient-matched burnt and non-burnt tissue and compared with that of 3 healthy volunteers. Plasma sampling for estimations of total and free cortisol concentrations was performed concurrently.ResultsIn the burn patients, mean total plasma and free plasma cortisol concentrations were 8.8 +/- 3.9, and 1.7 +/- 1.1 mcg/dL, (p < 0.001), respectively. Mean subcutaneous microdialysis cortisol concentrations in the burn and non-burn tissue were 0.80 +/- 0.31 vs 0.74 +/- 0.41 mcg/dL (p = 0.8), respectively, and were significantly elevated over the mean subcutaneous microdialysis cortisol concentrations in the healthy volunteers. There was no significant correlation between total plasma or free plasma and microdialysis cortisol concentrations. Plasma free cortisol was better correlated with total burn surface area than total cortisol.ConclusionsIn this preliminary study, interstitial cortisol concentrations measured by microdialysis in burnt and non-burnt skin from patients with severe thermal injury are significantly elevated over those from healthy volunteers. Plasma estimations of cortisol do not correlate with the microdialysis levels, raising the possibility that plasma cortisol may be an unreliable guide to tissue cortisol activity.
Highlights
The assessment of adrenal function in critically ill patients is problematic, and there is evidence to suggest that measurement of tissue glucocorticoid activity may be more useful than estimation of plasma cortisol concentrations
There was no significant correlation between total plasma or free plasma and microdialysis cortisol concentrations
In this preliminary study, interstitial cortisol concentrations measured by microdialysis in burnt and nonburnt skin from patients with severe thermal injury are significantly elevated over those from healthy volunteers
Summary
The assessment of adrenal function in critically ill patients is problematic, and there is evidence to suggest that measurement of tissue glucocorticoid activity may be more useful than estimation of plasma cortisol concentrations. A number of studies have demonstrated increases in total plasma cortisol and adrenocorticotrophic hormone (ACTH) concentrations in the days following thermal injury [1,2,3]. Urinary free cortisol levels have been shown to be increased after burns for up to 100 days [4]. All of these changes would support the concept of an exaggerated adrenal response. ACTH: adrenocorticotrophic hormone; CBG: cortisol binding globulin; ELISA: enzyme linked immunosorbent assay; GC: glucocorticoids; MDB: microdialysis concentrations from burn tissue; MDNB: microdialysis concentrations from non-burned tissue; PFC: plasma free cortisol; SD: standard deviation; TBSA: total burn surface area; TC: total cortisol
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