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KEY POINTS
■ Abdominal compartment syndrome (ACS) is less common than compartment syndrome of the limbs but is more dangerous because of the vital functions of the organs contained within the abdominal compartment. Clinicians may easily overlook ACS or mistake it for something else.
■ ACS is subdivided into three types: primary, secondary, and recurrent. Primary ACS occurs when the causal pathology is intra-abdominal. Secondary ACS usually occurs in the medical or burn patient in the absence of abdominal injury or surgery and commonly follows conditions requiring aggressive fluid resuscitation. Recurrent ACS is a return of ACS symptoms.
■ The physical examination is not reliable for diagnosing IAH or ACS. The most important tool in diagnosing ACS is measurement of IAP. The gold standard is the transvesical technique.
■ No single treatment strategy exists for ACS because it has many different causes and can occur in a widely diverse patient population. Treatment may be medical, surgical, or both.
Compartment syndrome is almost always thought of in association with the limbs, but any area of the body bounded by fascia and bone is capable of experiencing a rise in pressure as a result of trauma or some other pathology. This pressure, when applied to intracompartmental organs and tissues, can cause ischemia and dysfunction—the definition of
compartment syndrome. And although abdominal compartment syndrome (ACS) is less common than compartment syndrome of the limbs, ACS is more dangerous simply because of the vital functions of the organs contained within the abdominal compartment; indeed, it is fatal if left untreated.
1
ABDOMINAL COMPARTMENT SYNDROME
This dangerous problem is compounded by the fact that clinicians may easily overlook it or mistake it for something else; the differential diagnosis is extensive (Table 1). ACS generally occurs in patients who are already extremely sick, and an intubated patient may not be able to help identify the pain that indicates the condition's onset. Furthermore, many of the signs and symptoms of compartment syndrome may be misinterpreted as being related to the primary condition that brought the patient to the ICU in the first place. The hypotension and organ failure of ACS can easily be mistaken for those of shock, but since the treatments are quite different, the misdiagnosed patient is unlikely to survive to correct the doctors. To help bring focus and attention to and improve survival in patients with ACS, the World Society of the Abdominal Compartment Syndrome (WSACS) was organized in 2004.1
Pathophysiology In a healthy person, intra-abdominal pressure (IAP) should average 0 mm Hg or less, but this figure can fluctuate from moment to moment in response to normal activities such as physical activity, respiration, sneezing, and defecation. Obese and pregnant persons can also have higher than normal IAPs, but because these pressures rise gradually, no adverse effects are experienced. The clinical picture is complicated by the fact that IAP is frequently higher in critically ill patients, running 5 to 7 mm Hg.1
The abdominal perfusion pressure (APP) is more important than a simple measurement of IAP. APP is a measurement of how well the abdominal viscera are supplied by oxygenated blood. If IAP is high in, say, a pregnant woman, her increased mean arterial pressure (MAP) counterbalances the IAP, so her still-normal APP prevents ischemia or dysfunction of her abdominal organs. In other words, APP = MAP − IAP.1 So the pathology of ACS results from much more than a simple rise in IAP.
ACS is first preceded by intra-abdominal hypertension (IAH), which causes organ system dysfunction. IAH, as defined by the WSACS, is an intra-abdominal pressure of greater than 12 mm Hg. IAH is graded according to severity (Table 2). When IAP is measured, the patient should be supine and as relaxed as possible (particularly in the abdominal muscles), and the measurement should be made at the end of expiration. The WSACS has defined ACS as both an IAP of greater than 20 mm Hg and new-onset failure of one or more organ systems.1
Types ACS may be primary, secondary, or recurrent. Primary ACS occurs when the causal pathology is intra-abdominal. Examples of this type include abdominal trauma, acute pancreatitis, retroperitoneal hemorrhage, and liver transplantation; primary ACS can also occur in a patient who has just undergone routine abdominal surgery. Secondary ACS usually occurs in the medical or burn patient in the absence of abdominal injury or surgery; it commonly follows conditions requiring aggressive fluid resuscitation (eg, sepsis, significant burns) and is related to the edema and ascites that ensue. Because the cause of secondary ACS is extra-abdominal, it can be difficult to diagnose; but given the frequency of the shock patient and fluid resuscitation, secondary ACS should not be far from mind with these patients. Recurrent ACS is a return of ACS symptoms, thought to be due to the "second hit" phenomenon or reperfusion injury, when blood flow increases to formerly hypoxic tissues, causing a vicious cycle of further edema and increased pressure on the dysfunctional organs.1