Objective: To study the diurnal variation of melatonin and cortisol in critically ill patients and to assess whether the severity of organ dysfunction, sedation and sympathetic activity correlate with the production of these hormones.
Design: Prospective clinical study.
Setting: Surgical intensive care unit in a university hospital.
Patients: Forty non-septic patients without brain injury and treatment with adrenergic agonists or corticosteroids. Twenty-five of the patients were sedated with benzodiazepines.
Interventions: None.
Measurements and results: The pattern of melatonin production was monitored by the determination of 6-sulphatoxymelatonin (aMT6s) in urine. The 12-h aMT6s excretions at nights (11.8 +/- 8.9 microg, mean +/- SD) were higher than in the daytime (6.8 +/- 7.5 microg; P < 0.0001), and benzodiazepine treatment did not abolish the diurnal periodicity of aMT6s excretion during the entire 3-day study period. Serum cortisol concentrations at noon (524 +/- 276 nmol/l, mean +/- SD) were higher than at midnight (415 +/- 172 nmol/l; P < 0.0001), and the decrease at midnight was significant also in the patients treated with benzodiazepines. Sympathetic activity was monitored with urine vanillylmandelic acid (VMA). The 12-h VMA excretions did not show a diurnal variation, but a significant positive relationship between the 12-h VMA and aMT6s excretions was observed. The severity of organ dysfunction did not correlate either with the aMT6s and VMA excretion or with serum cortisol concentration.
Conclusions: The diurnal variation of melatonin and cortisol is maintained in non-septic intensive care unit patients. Benzodiazepines do not impair the diurnal variation of melatonin and cortisol.