Incidence of blockage alarms when dressing connector orifices are blocked: Comparison of two negative pressure wound therapy systems

Introduction: The ability for a negative pressure wound therapy (NPWT) system to correctly indicate blockage is important in delivering prescribed therapy and mitigating risks associated with pooled fluids such as maceration,¹ and hence infection.²   Design elements of some NPWT systems may not allow for blockage alarms to be triggered in clinically relevant conditions, particularly if the NPWT systems do not have wound pressure-regulating technology (PRT).

Objective: Evaluate the ability of the latest versions of 2 NPWT brands to trigger blockage alarms when dressing connector orifices are blocked.

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 3 respective dressings (n=9 runs/group). The orifice of the connector to the dressing placed on a simulated wound was completely blocked.  Pressures at the dressing and near the canister were measured for 10 min or until the unit had a blockage alarm, whichever occurred earlier.  Blockage alarm incidence was statistically analyzed using the Fisher Exact test and differences from target NP using the Wilcoxon Signed Rank test.

Results/Discussion: NPWT-A had a blockage alarm in each of the 9 runs, while NPWT-B did not have a single blockage alarm (p<0.0001).  The NP at the simulated wounds for both groups was ~0 mmHg consistent with a complete blockage situation.  In contrast, NP near the canister was at target NP (~-120 mmHg) for NPWT-B and at -195.5 ± 0.1 mmHg for NPWT-A, which was significantly different from target (p=0.0039) as a result of the PRT attempting to resolve the low wound NP by increasing the pump duty cycle.

Conclusion: NPWT-A consistently had a blockage alarm when there was a blockage at the dressing connector orifice, while NPWT-B did not. Thus, different NPWT systems are not necessarily equivalent.