Intra-Abdominal Pressure (IAP) Monitoring in ICU

1. Introduction

According to the World Society of the Abdominal Compartment Syndrome (WSACS) guidelines, routine measurement of IAP is recommended in high-risk ICU patients.

2. Normal Physiology of IAP

3. Indications for IAP Monitoring 

Measure IAP in:

• Major trauma
• Massive fluid resuscitation (>5L/24h)
• Severe pancreatitis
• Sepsis with capillary leak
• Major burns
• Post-abdominal surgery
• Distended abdomen
• Unexplained organ dysfunction
• Oliguria not responding to fluids

WSACS strongly recommends monitoring in high-risk ICU patients.

4. Methods of IAP Measurement

Gold Standard: Intravesical (Bladder) Pressure Measurement

Because the bladder behaves as a passive diaphragm, transmitting abdominal pressure.

Technique: Step-by-Step

🔹 Equipment

• Foley catheter
• 3-way stopcock
• Sterile saline (25 mL)
• Pressure transducer or manometer

🔹 Procedure

1. Patient supine
2. Zero transducer at mid-axillary line (iliac crest level)
3. Instill ≤25 mL sterile saline into bladder
4. Wait 30–60 seconds
5. Measure at end-expiration but Why End-Expiration?

During inspiration:

• Diaphragm descends
• IAP transiently increases

Therefore:Always measure at end-expiration to avoid overestimation.

6. Ensure no abdominal muscle contraction

 Do NOT use large instillation volumes (overestimates IAP).

👉 Bladder method = Standard of care

5. Abdominal Perfusion Pressure (APP)

APP=MAP−IAP

Normal APP: > 60 mmHg

Low APP → impaired organ perfusion.

WSACS recommends targeting:APP ≥ 60 mmHg

8️⃣ Measurement Frequency

• High-risk but stable → Every 4–6 hours
• IAH → Every 2–4 hours
• ACS suspected → Continuous or frequent

9️⃣ Factors Affecting Accuracy

❌ Incorrect zeroing
❌ Not measuring at end-expiration
❌ Patient coughing
❌ Large bladder instillation
❌ Head of bed elevation (>30° increases IAP)

🔟 Clinical Interpretation

 IAP and Mechanical Ventilation

Effects:

• ↑ Plateau pressure
• False high PEEP requirement
• Auto-PEEP

Important concept:

Plateau pressure = Chest wall + Lung pressure

High IAP → stiff chest wall → falsely elevated plateau.