American Journal of Respiratory and Critical Care Medicine vol:Ahead of print
Typical for critical illnesses are substantial alterations within the hypothalamic-anterior-pituitary-peripheral-hormonal axes that are proportionate to the risk of poor outcome. These neuroendocrine responses to critical illness follow a biphasic pattern. The acute phase (first hours to days) is characterized by an increased release of anterior pituitary hormones while altered target-organ sensitivity and hormone metabolism result in low levels of the anabolic peripheral effector hormones and contribute to the substantailly elevated levels of the catabolic hormone cortisol. The prolonged phase of critical illness is hallmarked by a uniform suppression of the neuroendocrine axes, predominantly of central/hypothalamic origin, which contributes to the low (or insufficiently high in the case of cortisol) circulating levels of the target-organ hormones. Several of the acute phase adaptations to critical illness are due to or accentuated by the concomitant fasting. Accepting the lack of macronutrients as well as the neuroendorine responses to such fasting in the acute phase of critical illness has shown to beneficially affect outcome. In contrast, the neuroendocrine alterations that occur in the chronic phase of illness while patients are fully fed contribute to bone and skeletal muscle wasting and impose risk of adrenocortical atrophy. The combined administration of those hypothalamic releasing factors, that have been identified as suppressed or deficient during prolonged critical illness, may be a promising strategy to enhance recovery. The potential impact of treatment with such hypothalamic releasing factors on recovery from critical illness as well as on long-term rehabilitation should be investigated in future randomized controlled clinical trials.