P1.224: A Novel Approach to Measuring Intra-abdominal Pressure (IAP) in Neonates: Abdominal Wall Tension (AWT)

Background: Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in infants, occurring in about 1 in 1000 live births. NEC is caused by a bacterial infection of the intestinal wall, and results in cellular destruction, inflammation, and perforation. With a mortality rate of 50% and specific cause of the infection unknown, early treatment is critical to mitigating high severity cases. Intra-abdominal pressure (IAP) is a key indicator of malfunction in the abdomen, suggesting viability as a diagnostic tool for NEC. The gold standard for measuring IAP is an intravesical catheter; however, catheterizing neonates is invasive and risky, potentially requiring sedation and paralysis. Screening methods rely on palpation to estimate IAP. However, studies have shown that palpation misdiagnoses up to 60% of patients. Given the importance of accurate IAP measurements for early detection of NEC, a device that non-invasively and reliably measures IAP will improve standard of care for NEC and other abdominal complications.

Methods: We developed a handheld device for measuring abdominal wall tension (AWT) and correlating these measurements to IAP in a tissue phantom. A 0.1 N resolution digital force gauge was outfitted with a custom, 50 mm x 50 mm, 3D printed attachment (the “shield”), with a similarly 3D printed 5 mm “tip.” An endotracheal tube (ETT) was used as a tissue phantom due to its ability to inflate to physiological relevant pressures (5-20 mmHg). ETT pressure was measured with a digital manometer and regulated with a medical syringe. We measured AWT by attaching the shield to the digital force gauge and by pressing the 5 mm tip into the phantom until the shield lightly touches the phantom (Fig. 1D). To evaluate the effect of skin and fat tissue on the AWT and IAP measurements, the phantom was modified by placing medical-grade gel (Humimic gel #5) of four different thickness (5-8 mm) on top of the ETT (Fig. 1F). The device was outfitted with an accelerometer and a proximity sensor to guide users during the measurement. Using the accelerometer, the device displays a digital bubble-level on an integrated display (Fig. 1C) that helps keep the user leveled as they lightly press the tip into the phantom (and ultimately a neonate’s abdomen). Proximity sensors positioned underneath the shield provide feedback to the user to ensure the tip isn’t pressed too far into abdomen.

Results: Benchtop tests demonstrated a quadratic relationship between IAP and AWT with (Fig. 1G) and without simulated subcutaneous tissue. (Fig. 1H). However, the sensitivity of the relationship with simulated tissue were inversely proportional to the thickness of the gel.

Conclusion: Our findings illustrate a relationship between AWT and IAP measurements using an ETT as a tissue phantom with promising results motivating future work in vivo.