CHAPTER 114

#### KEY POINTS

• Abdominal compartment syndrome (ACS) is caused by an acute increase in intra-abdominal pressure resulting from a number of medical and surgical conditions.

• Abdominal compartment syndrome and intra-abdominal hypertension are often unrecognized causes of organ dysfunction in critically ill patients.

• The reference standard for measurement of intra-abdominal pressure is via bladder catheter using a standardized protocol.

• Primary ACS results from direct, abdominopelvic pathology, whereas secondary ACS does not.

• By elevating the diaphragm and decreasing respiratory system compliance, ACS causes a restrictive respiratory defect. However, ACS affects a number of other organs, especially the kidneys, and may cause multiorgan system failure.

• Diagnosis relies on maintaining a high degree of clinical suspicion, measurement of intra-abdominal bladder pressure, and identification of organ dysfunction.

• The abdomen should be decompressed before critical organ dysfunction develops.

• Failure to recognize and treat ACS portends a poor prognosis.

#### DEFINITION AND DIAGNOSIS

Compartment syndrome occurs when tissue pressure within a confined compartment threatens perfusion within and through the compartment. Compartment syndrome can be seen in upper and lower extremities, where there are multiple fascial compartments, as well as the abdomen. Abdominal compartment syndrome (ACS) was first described in 1863 by the French surgeon Etienne-Jules Marey, who described the relationship between respiratory function and intra-abdominal pressure.1 The abdominal compartment is delineated by the pelvis, lumbar spine, abdominal musculature and soft tissues, diaphragm, and ribs. As described further below, ACS is defined by the World Congress on Abdominal Compartment Syndrome as sustained intra-abdominal hypertension (above 20 mm Hg; IAH) with attendant organ dysfunction.2,3

The diagnosis of ACS should be considered in any patient with a tense or distended abdomen who also has hemodynamic instability, a falling urine output, mental status changes, progressive organ failure, or lactic acidosis. Development of ACS during ICU stay is an independent predictor of mortality, with high mortality in established ACS.4 Failure to recognize that IAH can occur without abdominal distension, or that multiorgan failure is a manifestation of ACS, is a potentially lethal error.

Paramount to defining IAH or ACS is how intra-abdominal pressure (IAP) is measured. Clinical examination has been shown to be inaccurate at indicating increased IAP.5,6 Although there are clues to IAH on abdominal CT, definitive diagnosis requires estimation of IAP.7 Several techniques have been described,8,9 but the most widely adopted method is to transduce the bladder pressure, a simple, safe, and inexpensive procedure.3,9 The patient should be supine and the bladder catheter connected to a pressure transducer zeroed at the level of the superior iliac crest in the midaxillary line.2 The catheter is instilled with 25 mL of sterile saline and the detrusor muscle is allowed to relax for 30 to 60 seconds. IAP is estimated as the bladder pressure at end expiration, although a case has been made to instead approximate the mean IAP ...

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