Abdominal compartment syndrome

Intra-abdominal pressure - the steady-state pressure concealed within the abdominal cavity

• It is approximately 5-7mmHg in the critically ill adult
• Primary - injury or disease in the abdo/pelvis
• Secondary - does not originate in the abdominopelvic region, but as a consequence of capillary leak leading to the accumulation of fluid in bowel wall and retroperitoneum, e.g. sepsis/burns

Intra-abdominal HTN (IAH) is defined as >= 12mmHg

ACS is defined as IAP >20mmHg associated with new organ dysfunction

• End-stage of IAH

Abdominal perfusion pressure = MAP - IAP

• APP < 50 or 60 leads to reduced perfusion

Risk factors

• History of transfusion >10 units
• Infusion >7.5L crystalloid
• Presence of coagulopathy
• pH < 7.2

Aetiology

• Increased intra-abdominal volume
  • Intra-luminal
    • Colitis (e.g. C. dif)
    • Distension post-scope
    • Severe constipation
  • Extra-luminal
    • Pancreatitis
    • Abdo sepsis
    • Abdo haematoma
• Decreased abdominal wall compliance
  • Body anthropomorphism/habitus
  • Abdo wall (e.g. burn eschars, tight bandages, rectus sheath haematoma)
  • Comorbidities

Situations where it commonly occurs

• Intra-abdominal/retroperitoneal haemorrhage, with trauma laparotomy closed primarily
• GI bleeding
• Liver transplant
• SMV thrombosis
• Pelvic fractures
• Ruptured AAA

Presentation/pathophysiology

• Cardiovascular
  • Cardiac compression by cranial movement of diaphragm impairs cardiac function
  • Reduced venous return due to obstructed IVC
  • Pooling in legs, increasing risk of DVT
  • Elevated central venous pressure due to diminished venous return
• Pulmonary
  • Increased peak airway pressures - harder to ventilate
  • Reduced spontaneous tidal volumes
• Renal
  • Renal vein compression causing venous ischaemia - major cause
  • Also renal artery vasoconstriction from activation of SNS and RAAS
  • Oliguria generally develops at 15mmHg and anuria and 30mmHg
• GIT
  • Reduced mesenteric blood flow
  • Intestinal mucosal perfusion starting at 20mmHg
  • Reduced hepatic function
• CNS
  • ICP increases in persistent ACS

Measurement

• It should be measured via the bladder at end-expiration in the supine position after ensuring that abdominal muscle contractions are absent (I think this means the patient must be paralysed) and with the transducer zeroed at the level of the midaxillary line
• Disconnect the IDC from the urine bag, instil 25mL of water, and elevate the disconnected IDC perpendicular to the supine patient and bed. The height of the column of water is the IAP in cmH2O (*0.735 for mmHg)
• Physically examination is not helpful to detect it
• Grading
  • I: 12-15
  • II: 16-20
  • III: 21-25
  • IV: >25

Management

IAH initial management:

• Treat aggressively to prevent progression to ACS - usually works
• Continue checking pressure q4-6h
• Evacuate intraluminal contents
  • NGT +/- rectal tube, IDC
  • Prokinetics
  • Consider an enema to evacuate large stool burden
  • Diurese
• Evacuate intra-abdominal spaces
  • Drain ascites
• Improve abdo wall compliance
  • Ensure good analgaesia
  • Remove anything constrictive - abdo dressings/eschars
  • Reverse Trendelenburg can be helpful
  • Consider neuromuscular blockade - does decrease intra-abdominal pressure, but data is quite patchy, and blockade is contra-indicated in most patients anyway (increased VAP, peripheral nerve injury, skin breakdown and VTE)
• Optimise fluid administration
• Support at-risk organs
  • Lungs - use of lower mean airway pressures, lower than normal tidal volumes

Indications for surgical decompression:

• IAP > 20 and new organ dysfunction
  • Inability to ventilate
  • AKI
  • Haemodynamic instability
  • Metabolic failure
  • GIT failure
  • ICH

Sudden increase in pressure is worse than gradual

Decompressive laparotomy

• Generous midline from xiphisternum to pubis
• Avoid subcostal/paramedian incisions because much harder to manage in open abdomen stage
• Remember to warn intensivists/anaesthetist that laparotomy can be sudden reperfusion event - they will sometimes give bicarb immediately prior

Open abdomen management

• See separate topic