Abdominal compartment syndrome

Definition

• Intra-abdominal compartment syndrome refers to organ dysfunction caused by intra-abdominal hypertension
• Intra-abdominal hypertension
  • Causes intra-abdominal compartment syndrome
  • Defined as sustained intra-abdominal hypertension >12mmHg.
• Intra-abdominal perfusion pressure
  • MAP + IAP = IPP

Grading

• Normal < 12mmHg
• Grade 1 - IAP 12-15mmHg
• Grade 2 - IAP 16-20mmHg
• Grade 3 - IAP 21-25mmHg
• Grade 4 - IAP 25+mmHg

Risk factors

• Trauma
• Burns
• Liver transplant
• Ruptured AAA, pelvis fracture, pancreatitis.
• Patient who has been shocked and resuscitated with large volumes of fluid
• Poor abdominal wall compliance

Classification

• Primary (intra-abdominal)
  • Mass (cancer or benign)
  • Pancreatitis
  • Trauma
  • Severe infections
  • AAA
  • Ischaemic gut
  • Bowel obstruction/ileus
• Secondary (extra-abdominal)
  • Burns
  • Trauma
  • Sepsis and SIRS
  • Cardiac - post arrest, IHD, CABG

Pathophysiology

• Caused by
  • Increasing accumulation of fluid
  • Increasing abdominal content from oedema, inflammatory process or tumour
• As the pressure increases capillary perfusion pressure is compromised leading to ischaemia
• IAH can impair the function of nearly every organ system causing ACS
  • Cardiovascular - decreased venous return by obstructing IVC and thus decreased cardiac output.
  • Respiratory - reduced tidal volumes from elevation of the diaphragm - causing hypercarbia, hypoxia, atelectasis.
  • Renal - compression of renal vein from pressure. Arteriolar vasoconstriction causing sympathetic nervous system
  • GI - venous congestion and arterial occlusion lead to gut ischaemia.
  • Liver - reduced ability to remove lactic acid

Clinical

• Symptoms
  • Usually patients are unable to communicate - symptoms would be pain, bloating, SOB.
• Signs
  • Tense distended abdomen
  • Oliguria.
  • Increasing ventilatory requirements
  • Hypotension, tachycardia,
  • Elevated JVP
  • Evidence of hypoperfusion - cool skin, lactic acidosis.

Diagnosis

• Imaging
  • Usually not helpful but may reveal compression of IVC or renal vin, bowel wall thickening, bilateral inguinal herniation.
• Measurement of intra-abdominal pressure
  • Intra-vesical measurement is gold standard.
  • Is a good reflection of intra-abdominal pressure - use with caution for patients with pelvic packing, pelvic fracturs or haematomas, or a neurogenic bladder.
• How to do
  • Empty the bladder
  • Instill 25mls N saline into the bladder.
  • Place a pressure transducer onto the foley catheter which will measure the pressure in the bladder (the transducer should be zeroed at the level of the patient - iliac crest.
  • Measure the pressure and end expiration.
• Measure when
  • End of expiration
  • Supine
  • zeroed at iliac crest in the mid-axillary line (WSACS recommendation; other sources suggest using the pubic symphysis)
  • instillation of 25mL of saline into the bladder (1ml/kg for children up to 25 kg, minimum of 3 mL)
  • measured 60 seconds after instillation to allow detrusor muscle relaxation o In absence of active abdominal muscle contraction

Management

• Supportive care
  • Place patient supine (not head up)
  • Increase abdominal wall compliance – Analgesia, NM blockade, sedation
  • Evacuate intra-luminal contents - NGT, rectal tube, IDC, prokinetics
  • Evacuate abdominal fluids - Paracentesis, percutaneous drainage
  • Correct positive fluid balance - Avoid excess resus, diuretics, dialysis
  • Organ support
• Indications for abdominal decompression
  • Sustained IAP > 20mmHg that is associated with organ dysfunction of failure.
  • See: Laparostomy

Outcomes

• Mortality if high in patients undergoing laparostomy - 50% at 1 year.