The neuroendocrine system contributes significantly to the regulation of important body functions and responds to stressful events to maintain homeostasis. This mechanism assures the availability of metabolic substrates to both critical organs and the immune system during this essential phase. In prolonged critical illness, the expression of certain neuroendocrine transmitters is reduced. This results in difficulty in maintaining homeostasis and appropriate immune function. Clinical manifestations of the resultant neuroendocrine disorder were first described by Selye as a triad of:

•Adrenal enlargement

•Gastrointestinal ulceration

•Thymicolymphatic involution

These symptoms are reflective of the impact of the stress induced response and can be commonly found in critically ill patients. In the critically ill, the hypothalamus responds to stressors such as surgical intervention, trauma