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Device Technologies and Biomedical Robotics

Undergraduate Advances in Device Technologies

Tummy Tuck: Abdominal Wall Tension as an Indirect Measure of Intra-Abdominal Pressure

Saturday, October 26, 2024
9:15 AM – 9:30 AM EST
Location: Room 327

Introduction:  Abdominal compartment syndrome (ACS) is a condition caused by high intra-abdominal pressure (IAP, >20 mmHg) that negatively impacts oxygen delivery to organs, ultimately causing organ failure. In neonates, even a slightly elevated IAP of 5 mmHg, well before the threat of ACS, can result in extreme discomfort and difficulty feeding as introducing more fluid into the abdominal area further elevates IAP, progressing the infant to ACS. The gold standard method of quantifying IAP is a peritoneal catheter; however, catheterization of neonates is invasive and risky, potentially requiring sedation or paralysis for accurate measurements. Practitioners have utilized palpation as an alternative to catheterization; however, palpation was found to misdiagnose intra-abdominal hypertension (IAP > 12 mmHg) approximately 40% of the time in other studies. Given the inaccuracy of palpation and invasiveness of catheterization, a non-invasive method of measuring IAP would increase the standard of patient care and improve clinical outcomes.

Previous literature has demonstrated a significant correlation between abdominal wall tension (AWT) and IAP in adults, but not in neonates. As a result, the goal of our project is to establish AWT as an indirect measure of IAP in neonates. Potential complications include inter-individual differences in the measurement, suggesting that any developed techniques should standardize the measurement across individuals. Providing a standardized, quantitative, non-invasive method of measuring IAP would allow physicians to make more accurate assessments of a patient’s condition, mitigating potential complications from IAP such as ACS.

Materials and

Methods:  A VPOER 0.1 N resolution digital force gauge (Model: VDGF-50) (Fig. 1A) was outfitted with a custom, 50 mm x 50 mm, 3D printed (polylactic acid (PLA), 50% cubic infill) attachment (“shield”) (Fig. 1B), with a similarly 3D printed 8 mm tip. The shield was designed with a threaded shaft, allowing it to screw onto the threaded terminal of the digital force gauge. Wall tension was measured by attaching the shield to the force sensor, pressing the 8 mm tip into a tissue phantom, recording the force measured by the force gauge, and correlating the force measurements to the internal pressure of the tissue phantom.

Recreating the properties of a human abdomen in the lab for validating the device was difficult due to the elasticity of available materials. Validation was attempted using three different phantoms; a size 6 basketball; PreemieNatalie, an infant mannikin; and a DIXIE EMS blood pressure cuff. The basketball and PreemieNatalie were quickly abandoned due to difficulty in quantifying the internal pressure of the phantoms in the biologically relevant ranges of IAP (0-40 mmHg). Measurements (n=3) using the blood pressure cuff were taken from 20 mmHg to 100 mmHg in increments of 10 mmHg to simulate different levels of IAP. In addition to these validation tests, testing inter-individual variation was a significant area of concern for the study. Six individuals performed the test allowing us to assess variation in the measurements across different individuals.

Results, Conclusions, and Discussions: The internal cuff pressure was found to have a positive linear correlation with the cuff’s wall tension, suggesting that wall tension does correlate with internal pressure (and possibly IAP) (Fig. 2A). The least squares regression line (LSRL) given by measurements performed by a single individual (n=3, error bars represent standard deviation) was Y = 0.1578x + 12.505 with an R-squared value of 0.9801. Coefficients of variation (CV) ranged from a low of 1.02%, to a high of 8.41%, indicating high repeatability in the measurements by a single individual.

There were large variations in measurements between colleagues in the lab, but an overall positive correlation between wall tension and inner pressure was observed (Fig. 2B). The LSRL was Y = 0.2088x + 7.6192, with CV ranging from 7.47 to 26.5%, indicating high inter-individual variability. However, both measurements from a single individual, and measurements from six different individuals demonstrate positive linear correlations between AWT and internal pressure of the tissue phantom, suggesting that AWT could be an indirect measure of IAP.

Validating wall tension as an indirect measure of internal pressure is only the project's first step. Even though the blood pressure cuff allowed us to better simulate AWT and IAP than the other models we tried (basketball and PreemieNatalie), the cuff did not allow us to test ranges below 20 mmHg, as the cuff does not maintain its shape below 20 mmHg, simply collapsing and reporting a AWT of 0 mmHg. Therefore, more work is needed to find an appropriate benchtop model to validate AWT across the entire biologically relevant IAP range (0-40 mmHg). Furthermore, given the variability in measurements across individuals, developing a method to reduce the variability is necessary to ensure accurate and repeatable measurements between individuals. We are currently outfitting the device with sensors to measure tilt and penetration depth, to standardize how the measurements are taken, and reduce variability between individuals. Following additional benchtop validation, an observational study in a clinical setting will be used to test the device in vivo.

Acknowledgements (Optional):