Abdominal Compartment Syndrome (ACS) occurs when pressure builds up dangerously inside the abdominal cavity. This pressure increase involves the body’s largest internal space and many vital organs. The sustained high pressure quickly restricts blood flow and organ function, leading to a high risk of multi-organ failure and death. ACS is an urgent medical emergency most often encountered in critically ill patients in the intensive care unit, such as those with severe trauma, burns, or sepsis. Rapid diagnosis and intervention are necessary.
Intra-Abdominal Pressure and Defining the Syndrome
The foundation of understanding this condition lies in the concept of Intra-abdominal Pressure (IAP), the steady-state pressure naturally contained within the abdominal cavity. In a healthy adult, this pressure is typically low, ranging from zero to five millimeters of mercury (mmHg). A sustained pathological elevation of IAP to 12 mmHg or greater is defined as Intra-abdominal Hypertension (IAH). IAH is categorized into four grades of increasing severity, beginning at Grade I (12–15 mmHg). Abdominal Compartment Syndrome (ACS) is specifically defined as a sustained IAP greater than 20 mmHg that is associated with new or worsening organ dysfunction or failure. Measuring IAP is performed indirectly, involving measuring pressure within the urinary bladder via a Foley catheter.
Identifying the Causes
The development of high IAP stems from two main clinical pathways: primary and secondary causes. Primary ACS arises from a condition or injury directly within the abdomen that immediately increases volume. Examples include severe pancreatitis, major abdominal trauma resulting in massive internal bleeding (hemoperitoneum), or ruptured abdominal aortic aneurysms. Secondary ACS occurs when the pressure buildup is caused by conditions outside the abdomen that lead to a massive accumulation of fluid. This fluid accumulation is often a result of systemic capillary leak due to a widespread inflammatory response. Key scenarios include severe sepsis, extensive burns, and aggressive, large-volume fluid resuscitation for shock.
How High Pressure Affects Body Systems
The sustained pressure of ACS has devastating consequences on multiple major organ systems.
Respiratory System
The upward force exerted by the pressure pushes the diaphragm higher into the chest cavity. This significantly limits the lungs’ ability to expand, reducing tidal volume and leading to impaired pulmonary compliance. The resulting difficulty in ventilation can quickly progress to respiratory distress and failure, often requiring mechanical support.
Cardiovascular System
The cardiovascular system is severely compromised by the pressure. The high IAP compresses the inferior vena cava, drastically reducing the amount of venous blood that can return to the heart. This decreased venous return directly lowers the heart’s stroke volume, causing a drop in cardiac output and systemic blood pressure. The pressure also restricts the heart’s ventricles, further impairing its pumping action.
Renal System
The renal system is highly sensitive to the pressure changes. Elevated IAP compresses the renal veins and arteries, dramatically reducing blood flow to the kidneys. This decreased perfusion pressure across the glomerulus leads to a rapid decline in the glomerular filtration rate. Acute kidney injury, often first manifesting as severely reduced urine output (oliguria), is one of the earliest and most common signs of ACS.
Relieving the Pressure
The management of ACS requires immediate intervention aimed at lowering the IAP to prevent irreversible organ damage. The first line of approach involves non-operative management to reduce the abdominal volume and improve abdominal wall compliance. This includes heavy sedation and neuromuscular paralysis to relax the abdominal muscles. Draining accessible fluid collections, such as large-volume ascites, using a percutaneous catheter (paracentesis) can also provide immediate decompression. If these measures fail, the definitive treatment is an emergency surgical procedure called decompressive laparotomy. This involves surgically opening the abdomen to immediately relieve the constricting pressure. The abdomen is left open, often with a temporary closure method, because closing the incision under tension would recreate the syndrome.