Abdominal compartment syndrome

Abdominal compartment syndrome (ACS) is a disease defined by the presence of new end-organ dysfunction secondary to elevated intraabdominal 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

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

Pathologically elevated intraabdominal compartment pressures exceeding 12 mmHg define intraabdominal 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 disease and injuries, and abdominal compartment syndrome is particularly associated with:

• sepsis
• acute respiratory distress syndrome (ARDS)
• hypovolemic shock
• systemic inflammatory response syndrome (SIRS)
• multiorgan dysfunction syndrome (MODS)

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

Pathology

Etiology

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

• primary (abdominopelvic disease or injury)
  • trauma
    • high-grade liver trauma
    • pelvic fractures
    • hemoperitoneum
    • penetrating abdominopelvic trauma
  • surgery
    • liver transplantation
    • abdominal surgery in obese patients
    • post-operative hemoperitoneum
    • 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 .  There are several other overlapping CT and sonographic signs that may support the diagnosis but none of these are considered specific or sensitive for abdominal compartment syndrome (ACS) :

• peritoneal-to-abdominal height ratio (PAR ≥ 0,52) 
• ratio of maximal anteroposterior to transverse abdominal diameter (> 0,8) 
• rounded appearance of the abdominal wall (round belly sign ) (the/a product of the ratios noted above)
• elevated diaphragm
• hemoperitoneum
• 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
• gastric distention
• increase in ascites over subsequent scans
• pathological intra-abdominal fluids (e.g. ascites, hematoma, hemoperitoneum, pancreatic fluid collection) 
• bilateral inguinal herniation
• pneumoperitoneum
• pulmonary basal consolidation, collapse and/or pleural effusion
• dense infiltration of the retroperitoneum out of proportion of peritoneal disease

Ultrasound

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

Treatment and prognosis

Mortality is high in abdominal compartment syndrome ranging between 60-70% . 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
  • paracentesis of ascites or hemoperitoneum, if present
  • gastric decompression with an orogastric tube
• addressing factors decreasing abdominal wall compliance
  • optimization of analgesia and sedation
• optimize fluid status
  • fluids, diuresis or dialysis to acheive euvolemia
• surgical management with decompressive laparotomy

Complications

• renal failure
• ischemic 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