The causes of IAH are myriad, and as a result a simple classification system is helpful. They can be divided into:
- Those that increase intra-abdominal volume
- a)Intra-luminal causes include ileus, severe constipation or added colonic volume (such as may occur as result of clostridium difficile infection).
- b)Extra-luminal increases include free fluid, blood or air. Imaging is often necessary to investigate these causes.
- Those that decrease abdominal wall compliance
- a)Abnormalities in body habitus (namely obesity).
- b)Effects of abnormalities within the abdominal wall itself.
- c)Effects of other pathology/ treatment on abdominal wall compliance such tight abdominal wall closure post-surgery, pronation or burn eschars. Pathology that increases capillary wall leakage, such as sepsis and pancreatitis, may also contribute. It is worth noting that large volume resuscitation can result in capillary leak, and as such it is one of the biggest risk factors for the development of IAH.
