Critically ill patients develop a capillary permeability syndrome resulting in intravascular fluid extravasation into the extravascular tissue. During the initial 12 to 36 hours of critical illness, when fluid resuscitation is commonly occurring, much of the intravenous fluid infused into the patient is lost into this extravascular space resulting in edema. One of the primary areas of the body where the fluid accumulates is in the intraabdominal tissues such as the bowel wall and mesentery. As extravascular fluid accumulates in the abdominal tissues, the abdomen accommodates by expanding. However, after several liters have accumulated, the abdominal wall compliance threshold is crossed and any further fluid sequestration leads to rapid increases in the pressure within the abdominal cavity. Pressures in excess of 12 mm Hg result in substantial pathophysiologic changes to the cardiovascular, pulmonary, gastrointestinal, renal and nervous systems – this is defined as “Intra-Abdominal hypertension (IAH).” If the syndrome progresses unabated and the pressures rise beyond 20 mm Hg, organ failure often develops – this is defined as “Abdominal Compartment Syndrome (ACS).”¹
¹ Cheatham ML, Malbrain ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. II. Recommendations. Intensive care medicine 2007;33:951-62.