Are endogenous glucocorticoid levels adequate in septic shock?

The immunoneuroendocrine axis in critical illness: beneficial adaptation or neuroendocrine exhaustion?

PURPOSE OF REVIEW

Over the last years, endocrinology has been incorporated in critical care medicine, and acknowledgment of the complex neuro-endocrine adaption of critical illness has led to new insights and major breakthroughs in clarifying pathophysiological mechanisms and the targeting of therapeutic strategies. This review focuses on the important role of the hypothalamic-pituitary-adrenal (HPA) axis during critical illness and the occurrence of neuroendocrine failure.

RECENT FINDINGS

The distinction between acute (activated anterior pituitary function and inactivated peripheral anabolic pathways) and prolonged (reduced neuroendocrine stimulation) critical illness as different neuroendocrine paradigms has brought a new approach to the critically ill patient. The HPA adaptation in the prolonged phase is characterized by hypercortisolism induced by non-ACTH driven pathways as ACTH levels are low. In spite of the high-normal (total) cortisol levels, HPA insufficiency appears to be quite common. On the other hand, there is a marked depletion of corticosteroid-binding globulin (CBG) in the acute phase of critical illness, resulting in increased free and biologically active cortisol. There is a persistent marked depletion of dehydroeplandrosterone sulfate, possibly indicating adrenal exhaustion, while macrophage inhibitory factor is upregulated in sepsis, affecting and contraregulating the biological effects of glucocorticoids.

SUMMARY

The endocrine system is highly interrelated with the immune and neural systems, the neuroimmunoendocrine axis is subject to clear biphasic changes in the acute and chronic phases of critical illness, most likely reflecting a beneficial adaptation. These neuroendocrine dynamics should be considered when assessing the neuroendocrine system, in particular the HPA axis.

Clinical review: corticotherapy in sepsis

The use of glucocorticoids (corticotherapy) in severe sepsis is one of the main controversial issues in critical care medicine. These agents were commonly used to treat sepsis until the end of the 1980s, when several randomized trials casted serious doubt on any benefit from high-dose glucocorticoids. Later, important progress in our understanding of the role played by the hypothalamic–pituitary–adrenal axis in the response to sepsis, and of the mechanisms of action of glucocorticoids led us to reconsider their use in septic shock. The present review summarizes the basics of the physiological response of the hypothalamic–pituitary–adrenal axis to stress, including regulation of glucocorticoid synthesis, the cellular mechanisms of action of glucocorticoids, and how they influence metabolism, cardiovascular homeostasis and the immune system. The concepts of adrenal insufficiency and peripheral glucocorticoid resistance are developed, and the main experimental and clinical data that support the use of low-dose glucocorticoids in septic shock are discussed. Finally, we propose a decision tree for diagnosis of adrenal insufficiency and institution of cortisol replacement therapy.

The hypothalamic-pituitary-adrenal axis and low-dose glucocorticoids in the treatment of septic shock

Severe sepsis is the leading cause of death among patients in intensive care units. Recombinant activated protein C is the only substance known to directly improve morbidity and mortality. Adrenal insufficiency occurs frequently in patients with sepsis and is associated with poor outcome. Although high-dose glucocorticoids have not positively affected clinical outcome, small trials in which low-dose glucocorticoids were administered to patients with septic shock and relative adrenal insufficiency have shown decreased mortality. The main effect of glucocorticoids in low-doses apparently is exerted through correction of suppression of the hypothalamic-pituitary-adrenal axis. However, the therapeutic benefits of glucocorticoids may be related to their antiinflammatory properties and endogenous catecholamine-enhancing effects.

Adrenocortical response and cortisone replacement in systemic inflammatory response syndrome

The use of steroids as an adjunct to antimicrobial therapy has been controversial for many decades. Recent reports of the use of steroids in supraphysiological rather than in "industrial" doses in patients with sustained circulatory instability has re-ignited the debate. Anecdotal reports of adrenal insufficiency in septic patients have suggested a relative cortisol deficiency in these patients with poor survival if not given supplementary steroids. The possibility that the hypothalamic pituitary adrenal axis is intimately involved in the pathogenesis of this entity has not previously been highlighted. This review looks at the relationship of sustained cytokine release and the possibility of altering the stress response with progressive loss of adrenocorticotrophic hormone release and subsequent diminution in adequate cortisol levels. The reliance on, and misinterpretation of, the short synacthen test in diagnosing the possibility of this condition is emphasized.