The impact of air leakage on negative pressure delivery to a simulated wound site: comparison of two negative pressure wound therapy systems

Introduction: Microstrain and blood flow are reported mechanisms of action of negative pressure wound therapy (NPWT) that are modulated by negative pressure (NP) magnitude.^1,2 Clinical situations in which air leakage is present was hypothesized to inhibit the delivery of target/prescribed NP delivery to the wounds if the NPWT systems do not have wound pressure-regulating technology (PRT).

Objective: To evaluate the latest versions of two NPWT brands to deliver prescribed NP to simulated wounds during air-leakage.

Materials and Methods: Three units each of NPWT-A (with PRT; set at-125 mmHg) and NPWT-B (without PRT; set at -120 mmHg) were each tested with 2 respective dressings (n=6 runs/group). Pressures at the simulated wound were measured over 6 minutes or until the therapy unit switched off automatically, whichever occurred earlier. Extrinsically controlled air leak rates of 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 L/min were created using needle valves and measured with flow meters.  Statistical analyses were performed using the Wilcoxon Signed Rank test.

Results/Discussion: NP delivered by NPWT-A to simulated wounds was within acceptable range (within ± 10 mmHg of target) at each of the 6 air leak rates.  These results are consistent with those reported in a previous study³. In contrast, while NPWT-B delivered acceptable level of NP at 0.5, 1.0 and 1.5 L/min, NP delivered  was lower than target NP by 13.1 ±  0.3 (standard error) mmHg at 2.0 L/min, 21.0 ± 0.4 at 3.0 L/min, and 30.8 ± 0.5 mmHg at 4.0 L/min (each at p=0.0313).  

Conclusion: NPWT-A delivered target wound NP under simulated clinically challenging conditions of air leakage at the dressing; NPWT-B did not. Thus, different NPWT systems are not necessarily equivalent.