What two steps should the nurse anticipate when preparing to measure intra‑abdominal pressure in a patient with ileus?

Preparing to Measure Intra-Abdominal Pressure in a Patient with Ileus

The nurse should ensure the patient is in full supine position and measure IAP at end-expiration. These are the two critical standardized steps required for accurate and reproducible IAP measurement according to consensus guidelines from the World Society of the Abdominal Compartment Syndrome. 1

Correct Positioning: Full Supine Position

The patient must be positioned completely flat in the supine position—not semi-Fowler's or any degree of head elevation. 2, 3

• Head-of-bed elevation significantly increases measured IAP values and introduces clinically meaningful measurement error. 4
• Elevating the head of bed to 15 degrees increases IAP by approximately 1.5 mmHg, while 30-degree elevation increases IAP by 3.7 mmHg compared to supine measurements. 4
• Lateral decubitus positioning should never be used for IAP measurement, as it produces IAP readings approximately 4-5 mmHg higher than supine position. 5
• The 2024 Intensive Care Medicine positioning guidelines specifically recommend avoiding upper body elevation with flexion of knees and hips in patients with elevated IAP or at risk for it. 1

Correct Timing: End-Expiration Measurement

IAP must be measured at end-expiration to eliminate the confounding effect of respiratory muscle activity on abdominal pressure. 2, 3

• Measuring during active inspiration or expiration introduces artifact from diaphragmatic movement and changes in intrathoracic pressure. 2
• The end-expiratory phase represents the most stable and reproducible point in the respiratory cycle for pressure measurement. 2
• This timing standard applies whether the patient is spontaneously breathing or mechanically ventilated. 3

Critical Pitfall to Avoid: Abdominal Muscle Contraction

Never measure IAP while the patient contracts or holds abdominal muscles—this is the opposite of correct technique. 2, 3

• Abdominal muscle activity artificially elevates IAP readings and produces inaccurate measurements. 2
• Patients must be adequately relaxed, which may require ensuring appropriate sedation and analgesia in critically ill patients. 1
• If the patient cannot relax abdominal muscles voluntarily, consider brief neuromuscular blockade as a temporizing measure when accurate IAP measurement is critical for clinical decision-making. 1

Additional Technical Considerations

While not among the two items asked about, these standardization steps are essential for accurate measurement:

• Use the mid-axillary line at the iliac crest as the zero reference point for transducer leveling. 2, 3
• Instill a maximum of 25 mL of sterile saline into the bladder when using the transvesicular (bladder) technique, which remains the gold standard. 1, 3
• Ensure the patient has been in the supine position for at least a few minutes before measurement to allow pressure equilibration. 4

Clinical Context for Ileus Patients

Patients with ileus are at particular risk for intra-abdominal hypertension due to bowel distension and increased intra-abdominal contents. 1, 6

• The World Society of the Abdominal Compartment Syndrome recommends measuring IAP when any known risk factor for IAH/ACS is present, and ileus with bowel distension qualifies as such a risk factor. 1
• Serial measurements every 4-6 hours are indicated once IAH is detected or when organ dysfunction develops. 1
• Consistent positioning and timing across all measurements is essential for accurate trending and clinical decision-making. 4