British journal of anaesthesia
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The hypothalamic-pituitary-adrenal (HPA) axis is a neuro-endocrine system that regulates circulating levels of glucocorticoid hormones. These hormones are vital for normal homeostasis and play a pivotal role in the response to stress. Levels of cortisol fluctuate throughout the day in a diurnal rhythm, underlying which is an ultradian rhythm of approximately hourly pulses, and this pulsatility directly affects transcriptional outcomes. ⋯ Levels of cortisol in both normal and illness states are highly dynamic and so previously used static assessment tools for diagnosing corticosteroid related critical illness insufficiency (CRCI) are not likely to be useful. Therapeutic regimens have also failed so far, to take secretory patterns into account. In this review we look at the dynamic control and effects of glucocorticoids and frame in this context the current evidence surrounding steroid use in critical care and major surgery.