Abdominal compartment syndrome

Abdominal compartment syndrome (ACS) is a disease defined by the presence of new end-organ dysfunction secondary to elevated intra-abdominal pressure (IAP). Radiological diagnosis is difficult and usually suggested when a collection of imaging findings are present in the appropriate clinical setting or if the signs on sequential imaging studies are seen to progress. Diagnosis is usually clinically supported by elevated intravesicular pressure which closely parallels intra-abdominal compartment pressure.

Terminology

Abdominal compartment syndrome is formally defined as a persistently elevated intra-abdominal pressure >20 mmHg with concomitant organ dysfunction or failure ¹⁰. Abdominal perfusion pressure (APP) is a supplementary measurement, with values less than 60 mmHg concerning for compromised organ perfusion. 

Pathologically elevated intra-abdominal compartment pressures exceeding 12 mmHg define intra-abdominal hypertension (IAH), which is further subdivided into four grades based on the degree of elevation. 

Clinical presentation

Patients present with one or many organs failing due to the elevated pressure in the abdomen having direct or indirect effects on the major body systems. Most patients will have abdominal distension.Patients often have multifactorial diseases and injuries, and abdominal compartment syndrome is particularly associated with:

• sepsis

• acute respiratory distress syndrome (ARDS)

• hypovolaemic shock

• systemic inflammatory response syndrome (SIRS)

• multiorgan dysfunction syndrome (MODS)

Typically, the severely ill patient is in the intensive care unit (ICU) and clinically presents with massive abdominal distension, anuria, or progressive oliguria despite adequate cardiac output and/or increasingly difficult mechanical ventilation. 

Pathology

Aetiology

The elevated intra-abdominal pressure in abdominal compartment syndrome has numerous causes which can be subdivided accordingly:

• primary (abdominopelvic disease or injury)

  • trauma

    • high-grade liver trauma

    • pelvic fractures

    • haemoperitoneum

    • penetrating abdominopelvic trauma

  • surgery

    • liver transplantation

    • abdominal surgery in obese patients

    • post-operative haemoperitoneum

    • abdominal packing for bleeding

  • pancreatitis

  • ruptured abdominal aortic aneurysm

  • ascites

  • pneumoperitoneum

• secondary (disease or injury outside the abdomen and pelvis)

  • burns

  • sepsis

  • rapid fluid resuscitation

Radiographic features

The ratio of maximal anteroposterior to transverse abdominal diameter (>0.8) and the peritoneal to abdominal height ratio (PAR ≥0.52) in CT seem to be statistically associated with elevated intra-abdominal pressure in critically ill patients ⁶.  Several other overlapping CT and sonographic signs may support the diagnosis, but none are considered sensitive or specific for abdominal compartment syndrome ²:​

• rounded appearance of the abdominal wall (round belly sign ⁴): a product of the ratios noted above

• elevated diaphragm

• flattened inferior vena cava and renal veins

• displacement of solid abdominal viscera

• mosaic liver perfusion

• increased bowel and gastric wall thickening and enhancement

• shock bowel ⁶

• gastric distension

• pathological intra-abdominal fluids (e.g. ascites, haematoma, haemoperitoneum, pancreatic fluid collection) ⁶

• increase in ascites over subsequent scans

• bilateral inguinal herniation

• pneumoperitoneum

• pulmonary basal consolidation, collapse and/or pleural effusion

• dense infiltration of the retroperitoneum out of proportion to peritoneal disease ⁵

Ultrasound

• reduced diastolic flow in portal, hepatic, and/or renal veins

Treatment and prognosis

Mortality is high in abdominal compartment syndrome, in the range of 60-70% ². Treatment of abdominal compartment syndrome requires restoration of the perfusion gradient across the abdomen, and broadly involves four approaches:

• removal of intraperitoneal collections and intraluminal bowel contents ⁸

  • paracentesis of ascites or haemoperitoneum, if present

  • gastric decompression with an orogastric tube

• addressing factors decreasing abdominal wall compliance

  • optimisation of analgesia and sedation

• optimise fluid status

  • fluids, diuresis or dialysis to acheive euvolemia ⁹

• surgical management with decompressive laparotomy

Complications

• renal failure

• ischaemic bowel

• respiratory failure causing hypercapnia and respiratory acidosis from reduced diaphragmatic efficiency and resulting compressive atelectasis

• heart failure from reduced cardiac output and decreased venous return