(see also Compartment Syndrome; Intra-abdominal Hypertension)
Abdominal compartment syndrome (ACS) is defined as sustained intra-abdominal pressure of >20 mm Hg with the onset of organ dysfunction or failure, despite supportive management. This is a medical emergency. Key point: Intra-abdominal hypertension (IAH) is defined as an intra-abdominal pressure of >12 mm Hg. ACS is caused by high IAH, and the two terms are not interchangeable. Risk factors for abdominal compartment syndrome can be divided into three groups:
- Primary (cause is within the abdominal cavity itself). Frequently due to:
- Penetrating or blunt abdominal trauma
- Intra-abdominal or peritoneal hemorrhage (ruptured abdominal aortic aneurysm)
- Liver transplant
- Pancreatitis
- Peritonitis
- Abdominal surgery (perforated peptic ulcer, etc.)
- Pelvic fracture (measuring bladder pressure may not be accurate)
- Bowel distention
- Secondary, due to:
- Shock (sepsis, other)
- Aggressive or large-volume rapid fluid resuscitation (>3 L)
- Burns that cover >30% of the body
- Blunt or possible penetrating trauma without any noted injury
- Packing (closure of fascial layer after abdominal surgery increases incidence)
- Chronic, due to:
- Peritoneal dialysis
- Liver failure with cirrhosis
- Morbid obesity
- Mass within the abdomen
The diagnosis of this syndrome is difficult because it appears in critically ill patients that are suffering from other causes of failure as well. ACS should always be considered, however, if the patient has acute circulatory failure with wide systolic-diastolic pressure variation and elevated filling pressures. Patients may present with a bloated abdomen, abdominal pain, difficulty breathing, and oliguria.
The effect of abdominal compartment syndrome is widespread and can result in a cascade of problems to other systems:
- Cardiac (decreased venous return, cardiac output, hypotension, increased CVP, tachycardia)
- Pulmonary (hypoxia, hypercarbia, respiratory failure, increased mean airway pressures, decreased lung volumes, difficulty ventilating)
- Renal (renal vein compression, renal artery constriction) Key point: Oliguria may begin with the IAP at 15 mm Hg, and anuria will occur with an IAP at 30 mm Hg
- GI (bowel ischemia, translocation of bacteria into the bloodstream, sepsis leading to multisystem organ failure, GI bleeding)
- Liver (decreased liver metabolism leading to lactic acidosis)
- Neuro (increased ICP)
- Circulatory (often nonresponsive to resuscitation, IV fluids, blood products, and /or pressors)
Intra-abdominal Pressure Measurement (Bladder Pressure)
Direct measurement of the intra-abdominal pressure is an important procedure to determine pressures within the abdomen and , ultimately, perfusion to vital organs. To measure intra-abdominal pressure:
- Place the patient in a supine position. Maintain consistent body positioning with each measurement.
- Clamp the urinary drainage tube, connected to the urethral catheter, close to and below the level of the specimen aspiration/injection port (see diagram).
- Cleanse the specimen aspiration/injection part thoroughly. Once dry, attach a three-way stopcock to the end of a flushed sterile pressure transducer and then attach all to the specimen aspiration/injection part on the urinary drainage tube via the Luer-Lock mechanism (needless connection).Note: A needless connection between the pressure tubing and the urinary catheter is preferred over a needle for safety reasons, and inserting a three-way stopcock allows connection of a Luer-Lock syringe, filled with 20 to 25 mL of sterile saline, for injection into the bladder.
- Zero the transducer at the midaxillary line (transducer does not have to be taped to the abdomen).
- Label the transducer pressure tracing on the bedside monitor.
- Aseptically add 20 to 25 mL of sterile normal saline into the bladder via the stopcock attached to the specimen aspiration/injection port of the urethral catheter. Ensure that the catheter is filled with fluid, because air will alter the results. Measure the intra-abdominal pressure at end expiration, optimally during absence of abdominal muscle contractions and /or spasms. Unclamp the catheter and drain the sterile saline after the measurement is taken.
- Normal intra-abdominal pressure in a critically ill adult is 5 to 7 mm Hg. A value of >12 mm Hg constitutes intra-abdominal hypertension, and severity is ranked according to grades:
- Grade I (12 to 15 mm Hg): May be normal if morbidly obese or pregnant
- Grade II (16 to 20 mm Hg): Potential for abdominal compartment syndrome
- Grade III (21 to 25 mm Hg): Potential for abdominal compartment syndrome
- Grade IV (Above 25 mm Hg): Abdominal compartment syndrome likely
- After obtaining the intra-abdominal pressure reading, the abdominal perfusion pressure (APP) should be determined. This value indicates the overall perfusion to the vital organs of the abdomen. An APP of >60 mm Hg or greater is reflective of a better survival rate. The calculation is done by noting the systemic mean blood pressure (MAP) and subtracting the intra-abdominal pressure: MAP − IAP = APP.
Figure 4.1
Treatment
Surgical decompression of the abdomen (decompressive laparotomy) has long been considered the definitive therapy for ACS, particularly when it is primary. In the case of secondary ACS, however, surgical intervention may no longer be the treatment of choice. The World Society of the Abdominal Compartment Syndrome has more recently recommended medical treatment options such as perfusion support and optimized fluid management, nasogastric decompression, or percutaneous drainage of fluid collections. Only when these options fail to lower IAP and organ failure persists is surgical laparotomy recommended.