Once considered as normal adrenal function, adrenal insufficiency may developed later with chronic critical illness as adrenal exhaustion syndrome. It is easily overlooked and is possible due to the chronic secretion of systemic cytokines or other HPA axis-suppressive substances. There is still no consensus how often adrenal function testing should be repeated, although a re-evaluation should be considered if clinical symptoms and signs suggest adrenal insufficiency or deteriorating clinical condition.