Evaluating the Impact of Exudate Viscosity and Airflow on the Pressure Delivered to a Model Wound During Negative Pressure Wound Therapy

Introduction: A negative pressure dressing represents a dynamic system constantly changing during negative pressure wound therapy (NPWT). A dressing air leak rate will change over time, increasing or decreasing in leak rate. The patient’s wound will change, hopefully im- proving and reducing in size, but can also experience complications that lead to negative changes such as increased exudate viscosity, for example, changing from serous to thick purulent exudate (or vice versa). Negative pressure wound therapy devices must adapt to these changes to deliver effective pressure to the wound bed.1 Previously, our group demonstrat- ed the importance of airflow in an NPWT dressing, demonstrating that wound pressure decays in a closed system, leading to inadequate therapy, and that a small controlled air leak allows a single-lumen system to deliv- er accurate pressure at the wound bed with normal serous exudate.2 This study expands on the initial research to evaluate how exudate viscosity and airflow impact pressure and exudate management in wound models. Methods: The study evaluates a single-lumen system with air filter technology (SLA), a dual-lumen system with air filter technology (DLA), and a dual-lumen system without air filter technology (DL) using simu- lated exudate at two viscosities: normal viscosity ( 1.158 cP)3 and thick viscosity (35.5 cP).4 We primed the systems with 170 mL of simulated exudate followed by a rate of 4 mL/hr, the maximum exudate rate for home use for a minimum of 12 hours, with systems delivering -125 mmHg therapy. Each condition was tested in triplicate. Air pressure sensors con- nected below the dome monitored pressure at 10Hz. Descriptive statistics and 99.7% (3σ) confidence intervals (CI) were used to compare pressure management between systems. Results: Under normal exudate viscosity conditions, the air leak tech- nology allowed the two systems to stay within 10 mmHg of the targeted therapy (DLA: 122.89±3.63 mmHg (99.7%); DL: 122.78±14.69 mmHg; SLA: 121.65±6.94 mmHg). The combination of dual lumen and air filter technology allowed DLA to maintain the highest accuracy of pressure at the wound bed with thick viscosity exudate (DLA: 124.36±10.50 mmHg, DL: 123.95±14.16 mmHg; SLA: 115.29±8.65 mmHg). Each system effectively recovered exudate in the canister under all conditions tested. Discussion: This study demonstrates how exudate viscosity can impact the accuracy of wound pressure at the wound bed. This study also shows how controlled airflow through a dome-incorporated air filter combined with a dual-lumen system can improve pressure management at the wound bed.