intra -abdominal hypertension (IAH) and abdominal compartment syndrome (ACS)

Last edited 03/2020

Compartment syndrome occurs when pressures increase within a fixed cavity of the body, leading to ischemia, muscle damage, and organ dysfunction

  • these "fixed" spaces are constrained by muscular and fascial boundaries, which may have limited compliance when they become swollen (1)
  • intra-abdominal hypertension is defined as the sustained intra-abdominal pressure (IAP) above 12 mmHg. 

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) - are frequently encountered in critically ill patients in the intensive care unit (ICU) and result in significant morbidity and mortality (2)

  • ACS results from the progression of steady-state pressure within the abdominal cavity to a repeated pathological elevation of pressure above (> 20mmHg) with associated organ dysfunction
  • failure to recognize and immediately manage ACS can lend to poor prognosis as ACS is recognized as an independent predictor of mortality
  • high clinical suspicions with protocolized monitoring and management should be adapted when treating the critically ill, especially those with significant fluid shifts. This clinical diagnosis should be considered in patients with tense or distended abdomen with associated instability; however, it may also be seen without abdominal distention 

NICE state with respect to abdominal compartment syndrome (3):

  • be aware that people can develop abdominal compartment syndrome after endovascular aneurysm repair (EVAR) or open surgical repair of a ruptured abdominal aortic aneurysm (AAA)
  • assess people for abdominal compartment syndrome if their condition does not improve after EVAR or open surgical repair of a ruptured AAA

The World Society of the Abdominal Compartment Syndrome has published evidence-based medicine consensus guidelines for diagnosing and managing elevated intra-abdominal pressure (IAP) (1).

Definitions and diagnostic criteria for intra-abdominal hypertension/abdominal compartment syndrome:

  IAP (intra-abdominal pressure) is the steady-state pressure concealed within the abdominal cavity
  APP (abdominal perfusion pressure) = MAP (mean arterial pressure) - IAP
  FG (filtration gradient) = GFP (glomerular filtration pressure) -PTP (proximal tubular pressure) = MAP - 2 × IAP
 
  • IAP should be expressed in mmHg and measured at end-expiration in the complete supine position after ensuring that abdominal muscle contractions are absent and with the transducer zeroed at the level of the mid - axillary line
 
  • the reference standard for intermittent IAP measurement is via the bladder with a maximal instillation volume of 25 mL of sterile saline
  Normal IAP is approximately 5-7 mm Hg in critically ill adults
  IAH is defined by a sustained or repeated pathologic elevation of IAP ≥ 12 mmHg
  IAH is graded as follows:
  • Grade I: IAP 12-15 mmHg
  • Grade II: IAP 16-20 mmHg
  • Grade III: IAP 21-25 mmHg
  • Grade IV: IAP > 25 mmHg
  ACS is defined as a sustained IAP > 20 mmHg (with or without an APP < 60 mmHg) that is associated with new organ dysfunction/failure
 
  • Primary ACS is a condition associated with injury or disease in the abdomino-pelvic region that frequently requires early surgical or interventional radiological intervention
 
  • Secondary ACS refers to conditions that do not originate from the abdomino-pelvic region
 
  • Recurrent ACS refers to the condition in which ACS redevelops following previous surgical or medical treatment of primary or secondary ACS

ACS: Abdominal compartment syndrome; APP: Abdominal perfusion pressure; FG: Filtration gradient; GFP: Glomerular filtration pressure; IAH: Intra-abdominal hypertension; IAP: Intra-abdominal pressure; MAP: Mean arterial pressure; PTP: Proximal tubular pressure.

The abdomen is a closed anatomic space and increase in intraabdominal volume results in proportional increase in IAP. The abdominal compliance is largely determined by the elastic recoil of the abdominal wall and the diaphragm

  • decreased abdominal wall compliance, increased intraluminal contents, collection of contents in the abdominal cavity, capillary leak and fluid resuscitation are the broad categories that lead to the development of IAH and ACS.

Risk factors include:

Reduced abdominal wall compliance

  • obesity
  • abdominal surgery
  • prone positioning
  • rectus sheath haematoma
  • burns with abdominal eschars
  • mechanical ventilation with high positive end-expiratory pressure
  • ventilator dyssynchrony


Increased intra-luminal contents

  • abdominal tumor
  • intra-abdominal or retroperitoneal tumor
  • damage control laparotomy
  • enteral feeding
  • gastric distention
  • gastroparesis
  • colonic pseudo-obstruction
  • volvulus

Abdominal cavity collections

  • laparoscopy with excessive inflation pressures
  • peritoneal dialysis
  • abdominal inflammation-peritonitis, pancreatitis
  • abdominal abscess
  • ascites
  • haemoperitoneum
  • pneumoperitoneum
  • major trauma


Capillary leak and fluid resuscitation

  • trauma
  • sepsis
  • large volume fluid resuscitation
  • major burns
  • acidosis
  • hypothermia
  • coagulopathy
  • massive transfusion

Reference: