DIURNAL RHYTHM OF CORTISOL SECRETION

Detection of the Diurnal Rhythm of Cortisol Secretion

Detection of the Diurnal Rhythm of Cortisol Secretion

Introduction

Cortisol is a hormone plays a role in the metabolism of proteins, lipids, and carbohydrates. It affects blood glucose levels, helps maintain blood pressure, and helps regulate the immune system. Most cortisol in the blood is bound to a protein; only a small percentage is "free" and biologically active. Free cortisol is excreted into the urine and is present in the saliva. This test measures the amount of cortisol in the blood, urine, or saliva (Bert & Bowen, 1991: 285).

The level of cortisol in the blood normally rises and falls in a "diurnal variation" pattern. It peaks early in the morning, then declines throughout the day, reaching its lowest level about midnight. This pattern can change when a person works irregular shifts (such as the night shift) and sleeps at different times of the day, and it can become disrupted when a disease or condition either limits or stimulates cortisol production.

Methods

Study design

The plasma and microdialysis data for this study were obtained in conjunction with a separate study investigating antibiotic pharmacokinetics. A burn site- and patient-matched paired comparison of burnt and non-burnt tissue cortisol microdialysate levels was conducted together with a non-paired comparison of microdialysate levels from non-burnt tissue sites in burn patients and healthy volunteers. Corresponding unbound plasma cortisol concentrations were obtained simultaneously (Pemberton & Stein, 1988: 257).

Ethical review

The protocol received approval from the Royal Brisbane Hospital and University of Queensland Human Research Ethics Committees. Written informed consent was obtained from the legal guardians of enrolled patients and from the healthy volunteers.

Patient and volunteer enrolment

Ten adult patients with a mean ± standard deviation (SD) age of 32 ± 11 years and total burn surface area (TBSA) of 48 ± 15% were enrolled in the study. The patients were admitted to the Royal Brisbane & Women's Hospital intensive care unit between February 2005 and February 2006 and received eschar debridement and grafting surgery within the first few days post-injury, during which time the studies were conducted. Exclusion criteria included age younger than 18 years, existing bacterial infection and known infection with hepatitis A, B or C or HIV (Fuchs & Groger , 2007: 662).

Patients were resuscitated during the burn shock phase using the Parkland formula adjusted to patients' requirements. No patients had been on chronic steroid therapy prior to enrollment or received etomidate or hydrocortisone during the period of the study. Inotropic or vasopressor support was instituted at the treating clinicians' discretion. Three volunteers with a mean ± SD age of 35 ± 5 years were recruited exclusively from within the research group associated with the study. Exclusion criteria included age younger than 18 years or poor health as assessed by a medical practitioner.

Burn patient and healthy volunteer study protocols

Patient studies were conducted during debridement and grafting procedures within five days of trauma (mean post-trauma delay before grafting: 2.2 ± 1.2 days; mean surgery duration: 5.7 ± ...