Epidemiology & Risk Factors

Sustained intra-abdominal pressure (IAP) > 20 mmHg associated with new end-organ dysfunction.
Risk Factors:
- Massive volume resuscitation (> 5 L crystalloid or blood products in 24 h; e.g., severe burns, septic shock, major trauma).
- Severe acute pancreatitis (retroperitoneal edema, third-spacing).
- Abdominal trauma / Damage-control surgery (hemoperitoneum, abdominal packing).
- Ruptured AAA repair (large retroperitoneal hematoma, visceral edema).
- Acute bowel obstruction, ileus, or mesenteric ischemia with massive distension.
- Large volume ascites or intra-abdominal tumors (less acute, but predisposing).

Clinical Features

Abdominal: Tense, distended, “rock-hard” / rigid abdomen.
Pulmonary:
- ↑ Peak inspiratory pressures (PIP) on mechanical ventilation (diaphragmatic elevation).
- Hypoxemia, hypercapnia, atelectasis, difficult ventilation.
Cardiovascular:
- Hypotension, tachycardia.
- ↓ Cardiac output (CO) and ↓ venous return (inferior vena cava [IVC] compression).
- Falsely elevated CVP / PCWP (due to transmitted intrathoracic pressure).
Renal:
- Oliguria or anuria (renal vein and parenchymal compression → ↓ renal blood flow and ↓ GFR).
- Poor response to fluid boluses (further fluid worsens intra-abdominal pressure).
Neurological:
- ↑ Intracranial pressure (ICP), altered mental status (impaired cerebral venous return via jugular veins due to high intrathoracic pressure).

Initial & Confirmatory / Gold Standard:
- Intravesical pressure measurement via Foley catheter transducer (bladder pressure reflects IAP).
- Diagnostic criteria: Sustained IAP > 20 mmHg + new-onset organ failure (pulmonary, renal, or cardiovascular).
- Normal IAP: 0–5 mmHg; critically ill baseline: 5–7 mmHg; Intra-abdominal hypertension (IAH): ≥ 12 mmHg.
- Abdominal Perfusion Pressure (APP = MAP - IAP): Target > 60 mmHg.
Key Labs:
- Elevated BUN and Cr (prerenal/compression acute kidney injury).
- Lactic acidosis / metabolic acidosis (tissue and splanchnic hypoperfusion).
Imaging:
- POCUS / Bedside US: Flattened IVC, evaluation for free fluid/ascites.
- CT Abdomen/Pelvis: Often avoided due to hemodynamic instability; findings include “round belly sign” (increased AP diameter), compressed IVC/renal veins, and bowel wall thickening.

Tension Pneumothorax:
- Diff: Also causes ↑ PIP and hypotension, but presents with unilateral absent breath sounds, hyperresonance, and tracheal deviation. IAP is normal.
Hypovolemic / Hemorrhagic Shock:
- Diff: Presents with hypotension, flat neck veins, and oliguria, but the abdomen is not rigidly tense; responds initially to IVF (IVF precipitously worsens ACS).
Cardiac Tamponade:
- Diff: Elevated CVP, hypotension, distant heart sounds (Beck triad), pulsus paradoxus. Bladder pressure is normal; bedside echo shows pericardial effusion and RV diastolic collapse.
Acute Tubular Necrosis (ATN):
- Diff: Causes oliguria and azotemia, but lacks the respiratory failure (↑ PIP) and distended, rigid abdomen seen in ACS. IAP is normal.

1. Supportive / Medical Decompression (IAP 12–20 mmHg or temporizing for > 20 mmHg):
- Improve abdominal wall compliance:
  - Adequate sedation and analgesia.
  - Neuromuscular blockade (paralytics) to relax abdominal musculature.
- Evacuate intraluminal contents:
  - Nasogastric (NG) / orogastric tube decompression.
  - Rectal tube / enemas, prokinetic agents.
- Evacuate extraluminal collections:
  - Percutaneous paracentesis/drainage of large-volume ascites or hematoma.
- Optimize fluid administration:
  - Avoid over-resuscitation; judicious fluid restriction.
  - Diuresis or ultrafiltration / CRRT if hemodynamically stable.
- Optimize perfusion:
  - Vasopressors to maintain MAP and keep APP (MAP - IAP) > 60 mmHg.
2. Definitive Management (Refractory IAP > 20 mmHg with organ dysfunction):
- Emergency surgical decompression: Decompressive laparotomy.
- Abdomen is left open with temporary abdominal closure (e.g., negative-pressure wound therapy, Bogota bag, Barker vacuum pack).
- Delayed primary closure performed days later after swelling subsides.

Ischemia-Reperfusion Syndrome (immediate post-decompression):
- Sudden release of tamponade causes profound hypotension (sudden vasodilation), hyperkalemia, and lactic acid washout, potentially leading to asystole/cardiac arrest.
Bowel ischemia, necrosis, and perforation.
Permanent renal failure / ESRD requiring dialysis.
Enterocutaneous fistula or large ventral hernia (secondary to open abdomen management).
Multisystem organ dysfunction syndrome (MODS) and death.

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