13. Abdominal Compartment Syndrome

Quick Recap

GI & Hepatology System, Protocol 13/13 — completing the GI & Hepatology System.

1. Definitions (World Society of the Abdominal Compartment Syndrome Consensus)

Intra-abdominal pressure (IAP): steady-state pressure within the abdominal cavity, normally 5-7 mmHg in critically ill adults.

Intra-abdominal hypertension (IAH): sustained or repeated pathologic elevation of IAP >=12 mmHg.

Abdominal compartment syndrome (ACS): sustained IAP >20 mmHg (with or without an abdominal perfusion pressure <60 mmHg) associated with NEW organ dysfunction/failure — the organ dysfunction component is what distinguishes ACS from IAH alone; elevated pressure without organ dysfunction is IAH, not yet ACS.

IAH Grading: Grade I (12-15 mmHg), Grade II (16-20 mmHg), Grade III (21-25 mmHg), Grade IV (>25 mmHg).

Primary ACS: associated with injury/disease in the abdominopelvic region itself, often requiring early surgical/interventional management (trauma, hemoperitoneum, pancreatitis, post-abdominal-surgery).

Secondary ACS: arises from conditions NOT originating in the abdomen (massive fluid resuscitation, sepsis, burns, capillary leak states) — important because the abdomen may look/feel unremarkable on exam despite dangerously elevated pressure, since the driver is systemic fluid shift rather than a local abdominal catastrophe.

2. Pathophysiology

Rising IAP compresses abdominal and thoracic structures via a cascade of organ effects:

• Cardiovascular: direct IVC/venous compression -> diminished venous return -> reduced preload -> reduced cardiac output; also increases afterload via direct aortic/vascular compression
• Renal: direct renal vein/parenchymal compression plus reduced cardiac output -> reduced renal perfusion -> oliguria/AKI, often DISPROPORTIONATE to the degree of systemic hypotension, since local compression adds to (rather than merely reflecting) systemic hemodynamics
• Respiratory: diaphragmatic elevation/splinting -> reduced total lung capacity and functional residual capacity -> on the ventilator, this manifests as diminished tidal volumes with ELEVATED PEAK PRESSURES for a given ventilator setting — a key bedside clue often mistaken for a primary pulmonary process
• Splanchnic: reduced mesenteric perfusion -> bowel ischemia risk, further capillary leak and edema -> a self-perpetuating vicious cycle where elevated IAP itself worsens bowel wall edema, further raising IAP

3. Recognition — Clinical Signs

Abdominal distension (though a tense, distended abdomen is neither perfectly sensitive nor specific — some ACS occurs with a deceptively unremarkable-feeling abdomen, especially obese patients or those with a compliant abdominal wall), diminished tidal volumes with elevated peak airway pressures on the ventilator, decreased urine output, and decreased blood pressure. Clinical exam ALONE is unreliable for diagnosis — objective IAP measurement is required whenever ACS is suspected based on risk factors or these clinical clues.

4. Risk Factors

Diminished abdominal wall compliance (mechanical ventilation, particularly with high PEEP or patient-ventilator dyssynchrony; obesity; abdominal surgery with tight fascial closure), increased intraluminal contents (ileus, gastroparesis, colonic pseudo-obstruction — see Intestinal Obstruction protocol), increased abdominal contents (hemoperitoneum, ascites, pneumoperitoneum, intra-abdominal/retroperitoneal tumor or collection), capillary leak/fluid resuscitation (massive crystalloid resuscitation, especially in burns, trauma, sepsis/septic shock, damage control resuscitation for hemorrhagic shock), and others (pancreatitis, laparoscopy with pneumoperitoneum, morbid obesity, mechanical ventilation itself).

5. Measurement Technique — Intra-Bladder (Intravesical) Pressure

The standard, validated method: transduce bladder pressure via a Foley catheter connected to a pressure transducer (or a simple water column technique where dedicated equipment is unavailable), with the patient supine and ideally paralyzed (or at minimum without active abdominal wall muscle contraction/straining, which will falsely elevate the reading) at end-expiration, using the pubic symphysis as the zero reference point (not the mid-axillary line used for vascular pressures).

Instill a small, standardized volume of saline into the bladder (typically 25 mL, per WSACS consensus) before measurement — too little volume gives an unreliable reading, too much volume itself falsely elevates the measured pressure.

Important confounders that can produce a falsely elevated bladder pressure reading: lack of paralysis/active abdominal wall contraction, and baseline obesity (chronically elevated baseline IAP in obese patients means the same absolute pressure threshold may represent a different degree of acute pathology than in a non-obese patient) — interpret the absolute number in the context of these confounders rather than applying the threshold rigidly and in isolation.

6. Immediate Stabilization (ABCDE)

Airway/Breathing: anticipate elevated peak pressures/reduced compliance on the ventilator; avoid unnecessarily high PEEP where it is not otherwise indicated, since it can compound the IAP-driven reduction in venous return and further impair ventilation mechanics.

Circulation: recognize that hypotension in this setting may be DIRECTLY due to IAP-mediated venous return impairment, not (or not only) volume depletion — reflexive additional fluid resuscitation for "hypotension" in a patient with rising IAP can worsen the underlying problem by further increasing abdominal/bowel wall edema, perpetuating the vicious cycle described in Section 2. This is a genuine diagnostic trap: the instinct to give more fluid for hypotension is often exactly wrong once ACS is established.

Checklist:

7. Medical Management (Before/Alongside Considering Surgical Decompression)

Per the general IAH/ACS management hierarchy, address contributing factors first where feasible:

• Improve abdominal wall compliance: adequate sedation/analgesia, neuromuscular blockade in refractory cases, avoid tight abdominal binding/dressings, patient positioning (avoid excessive HOB elevation which can increase IAP — balance against aspiration risk/ventilator needs)
• Evacuate intraluminal contents: NG decompression, rectal tube decompression, prokinetic agents for ileus, colonoscopic decompression for colonic pseudo-obstruction (see Intestinal Obstruction protocol)
• Evacuate abdominal fluid collections: percutaneous drainage of ascites, hematoma, or abscess where a drainable collection is identified as a significant contributor
• Optimize fluid balance: AVOID further aggressive crystalloid resuscitation where possible once ACS is suspected (per the Section 6 trap); consider diuresis or CRRT-based ultrafiltration for fluid removal once the patient is otherwise stabilizing, to actively reduce the fluid burden contributing to visceral/bowel wall edema
• Optimize systemic/regional perfusion: targeted hemodynamic support to maintain adequate abdominal perfusion pressure (MAP minus IAP) without resorting to indiscriminate fluid loading

8. Surgical Decompression — The Definitive Intervention for Established ACS

A bladder pressure exceeding 20 mmHg WITH resultant organ dysfunction requires EMERGENT surgical decompression (decompressive laparotomy) — medical measures alone are insufficient once true ACS (not just IAH) is established with objective organ dysfunction evidence.

Decompressive laparotomy relieves the compartment pressure immediately, typically leaving the abdomen open (temporary abdominal closure device/vacuum dressing) given the bowel edema present — primary fascial closure at the index procedure should generally be AVOIDED if closure appears difficult or would require excessive tension, since forceful closure simply recreates the compartment syndrome physiology that was just relieved. "Damage control" open abdomen management with staged, delayed closure as bowel edema resolves over subsequent days is standard practice in this scenario.

9. Organ Support

Mechanical ventilation with awareness of IAP-driven compliance changes; hemodynamic support targeting abdominal perfusion pressure without reflexive over-resuscitation; CRRT/diuresis for fluid removal once appropriate; NG/rectal decompression; standard ICU supportive care for the underlying primary or secondary ACS etiology.

10. Consultation Matrix

11. Monitoring Framework

Serial bladder pressure measurement (frequency proportional to risk/trend — can be as often as every few hours in high-risk patients), ventilator mechanics trend (peak pressure, compliance), urine output trend, hemodynamic monitoring, fluid balance tracking (a key modifiable driver of secondary ACS).

12. Complications

Progressive multi-organ failure if unrecognized/untreated (cardiovascular, renal, respiratory as described in Section 2), bowel ischemia from sustained splanchnic hypoperfusion, open-abdomen management complications (fluid losses, enteroatmospheric fistula, delayed closure morbidity, ventral hernia). Prevention: proactive IAP monitoring in at-risk patients, avoiding reflexive over-resuscitation once ACS is suspected, addressing reversible contributors early (Section 7). Rescue: decompressive laparotomy for confirmed ACS with organ dysfunction.

13. Escalation & De-escalation

Escalate: IAP >20mmHg with new/worsening organ dysfunction despite medical measures -> emergent decompressive laparotomy.

De-escalate: IAP trending down with medical management, no organ dysfunction, or successfully decompressed with resolving bowel edema -> wean monitoring frequency, plan staged fascial closure once feasible for open-abdomen patients.

14. ICU Discharge Criteria

IAP normalized or IAH well-controlled without organ dysfunction, fascial closure achieved (or a defined staged closure plan for open-abdomen patients), organ function (renal, respiratory, cardiovascular) recovered or stable, underlying primary or secondary ACS etiology addressed.

15. Documentation & Medicolegal Checklist

16. Key Guidelines

Kirkpatrick AW, Roberts DJ, De Waele J, et al. Intra-abdominal hypertension and the abdominal compartment syndrome: updated consensus definitions and clinical practice guidelines from the World Society of the Abdominal Compartment Syndrome. Intensive Care Med. 2013;39:1190-1206 — primary reference underlying all definitions and thresholds in this protocol.

17. Controversies

The precise IAP threshold at which to intervene surgically (vs continued medical management) involves genuine clinical judgment beyond the numeric 20mmHg + organ dysfunction definition, since the RATE of rise and the specific organ dysfunction pattern may matter as much as the absolute number. Optimal fluid management strategy once ACS is suspected (how aggressively to pursue negative fluid balance/ultrafiltration vs accepting some ongoing volume needs for the underlying critical illness) requires individualized balancing rather than a fixed protocol. Timing of fascial closure in open-abdomen management (early aggressive closure attempts vs prolonged staged approach) varies by institutional practice and patient-specific bowel edema trajectory.

18. References

1. Kirkpatrick AW, Roberts DJ, De Waele J, et al. Intra-abdominal hypertension and the abdominal compartment syndrome: updated consensus definitions and clinical practice guidelines from the WSACS. Intensive Care Med. 2013;39:1190-1206.
2. Acute Abdomen in the Intensive Care Unit chapter (ACS section). Washington Manual of Critical Care, 4th ed, 2025 (Ch. 74).
3. Malbrain ML, Cheatham ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. Intensive Care Med. 2006;32(11):1722-1732.

See also: Intestinal Obstruction, Perforation, Peritonitis, Acute Pancreatitis (GI & Hepatology System) for the primary/secondary ACS risk contexts that commonly precede this syndrome.