How should NPWT parameters be selected for chronic wounds?

A practical guide based on evidence-based evidence

Focuses on five major types: diabetic foot, venous ulcers, pressure ulcers, arterial ulcers, and non-healing wounds | Evidence base: 2017 Expert Consensus; Gibson, 2022; IWGDF/NPUAP Guidelines

Following the publication of our previous article "Selection of NPWT Parameters for Acute Wounds," numerous clinical practitioners have reported that chronic wounds represent the "most challenging aspect" of NPWT application—characterized by complex wound types, prolonged disease duration, varying levels of exudation, and diverse infection statuses; even minor deviations in parameter selection may compromise overall therapeutic efficacy. Today, we will systematically review the core parameters for NPWT applied to chronic wounds, aiming to assist clinicians in making rapid and precise decisions.

This article covers five types of chronic wounds (C1–C5), addressing topics ranging from recommended negative pressure ranges and dressing selection to dressing change frequency and comparisons between PU/PVA foam dressings; all data are annotated with evidence-based sources and can be directly utilized as clinical references.

C1 | Diabetic Foot Ulcer (DFU)

Clinical Scenarios

Wagner grade 2–4 diabetic foot ulcers, accompanied by infection or deep tissue involvement, require adequate drainage and promotion of granulation tissue formation. DFU represents one of the most widely applied domains for NPWT in chronic wounds and is also among the most challenging types of wounds to manage clinically—cases involving coexisting plantar sinus tracts, tunnel spaces, and mixed infections are particularly common.

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Suture material selection: PU vs. PVA – how should this be chosen for DFU cases?

The most significant clinical challenge in DFU management lies in the high heterogeneity of wound morphology—wherein a single patient may present with both extensive ulcerated areas and deep sinus tracts. The selection of dressing materials must be precisely tailored according to the specific anatomical characteristics of the wound:

PU black foam: exhibits excellent granulation-promoting properties and is suitable for wound preparation of large-area ulcerated wounds; however, the risk of tissue ingrowth is more pronounced in DFU cases involving frequent dressing changes.

PVA foam: High tensile strength is its core advantage—ensuring it does not fracture during the removal of plantar sinus tracts; its low adhesion properties protect fragile wounds, making it suitable for tunnel-or transcutaneous-type DFUs.

Composite strategy: PVA-filled sinus tracts + PU coverage of the wound bed; this approach can simultaneously ensure both wound debridement safety and adequate drainage.

Gibson 2022 Evidence: Caution is warranted regarding PVA high-negative-pressure techniques

Evidence-based rationale: Risk of high-negative-pressure failure of PVA foam

Research published by Gibson DJ at JWOCN 2022 demonstrates that PVA foam begins exhibiting deviations in central pressure transmission at 140 mmHg; at 200 mmHg, 50% of the samples fail, and 93% of the samples exhibit uneven edge pressure distribution. During the DFU infection period, -175 mmHg is recommended as it approaches the critical failure threshold for PVA; recommendations are as follows:

• When high negative pressure (>175 mmHg) drainage is required during the infection phase, switch to PU black foam.

• During PVA dressing application, closely monitor the drainage efficacy at the wound edges; if local exudate accumulation is observed, consider changing the dressing.

Clinical Pain Points

Avoiding Common Pitfalls Reminder

Improper DFU sinus tract packing is one of the most common causes of NPWT failure; cases where tissue ingrowth following PU foam packing leads to rupture during removal or exacerbated pain are not uncommon. PVA white foam must be used for sinus tract packing.

C2 | Venous Ulcer (VLU)

Clinical Scenarios

Lower extremity venous ulcers are superficial with moderate exudation, often recur frequently, and require long-term management. Patients with venous ulcers typically have a prolonged disease course, require repeated medical visits, and bear a significant psychological burden; the NPWT low-pressure continuous mode can thereby reduce both the pain associated with frequent dressing changes and the associated economic burden.

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Why is PVA the preferred choice for VLU?

VLU is one of the optimal indications for PVA foam  in NPWT therapy, based on three reasons:

1.For superficial wounds, low pressure is sufficient for adequate drainage: within the range of-50 to-80 mmHg, PVA exhibits uniform pressure distribution, eliminating any risk of high negative pressure failure.

2.Low adhesion reduces pain associated with repeated dressing changes: long-term repeated dressing changes represent the primary source of pain, where the low-adhesive properties of PVA significantly outperform those of PU. The 2022 Gibson study explicitly noted that PVA foam exhibits "gentler" characteristics.

3.The 3M WhiteFoam product manual explicitly recommends superficial wounds as its indicated indications, with VLU representing a typical superficial wound.

Expert consensus support

Evidence-based guideline: 2017 Expert Consensus

The 2017 expert consensus states: for chronic wounds, NPWT parameters of –16.6 to –6.6 kPa (–125 to –50 mmHg) are recommended; the evidence level is B. VLU recommends low-pressure continuous mode (–50 to –80 mmHg), which fully falls within the scope of this consensus.

clinical Tips

In patients with VLU undergoing NPWT, pressure therapy (elastocuffs/elastomeric bandages) should be administered concomitantly; NPWT promotes wound healing, while pressure therapy corrects venous hypertension – together forming the standard treatment regimen. NPWT cannot substitute for pressure therapy.

C3 | Pressure Ulcer (Decubitus Ulcer)

Clinical Scenarios

Stage III–IV pressure ulcers, characterized by tissue loss and undermining or sinus tract formation, are most commonly observed in the sacrococcygeal region or heel area. Patients with pressure ulcers typically include those who have been bedridden for an extended period, suffer from poor nutritional status, or exhibit reduced sensation; therefore, NPWT serves as a critical intervention for wound preparation in Stage III–IV pressure ulcer patients.

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The "layered strategy" for NPWT in pressure ulcer management

The NPWT management of pressure ulcers requires the implementation of a "layered strategy" based on the wound stage; this is the core principle that distinguishes NPWT management from that used for other chronic wounds:

For Stage III superficial pressure ulcers: PVA white foam is the preferred choice. It provides adequate drainage for superficial wounds under low pressure, and its low adhesion makes it suitable for wounds that require frequent assessment.

Stage IV deep, extensive pressure ulcers: PU Black Foam is suitable for wound preparation, provides excellent granulation-promoting effects, and prepares the site for subsequent surgical closure.

Stage IV with tunneling/sinus tract: A combined strategy of PVA filling of the sinus tract followed by PU coverage of the wound bed is recommended. The use of PU within the sinus tract is not permissible—removal may result in rupture due to tissue ingrowth.

Analysis of differences from the 2017 expert consensus

Evidence-Based Validation

The 2017 expert consensus recommends NPWT parameters of-10.6 kPa (approximately-80 mmHg) for pressure ulcers, with an evidence level of B; in contrast, the Excel parameter matrix recommends values between-125 and-175 mmHg, with the upper limit significantly exceeding the range recommended by the consensus.

Note: The consensus-recommended overall negative pressure value is-80 mmHg; however, for Stage IV deep pressure ulcers accompanied by infection or significant exudation, higher negative pressures are often clinically required. It is recommended to set the negative pressure according to the specific condition of the wound: for superficial or stable stages, use-80 mmHg; for deep or infected stages, use-125 to-175 mmHg, but the suitability of PVA must be evaluated in such cases.

C4 | Arterial Ulcer

Clinical Scenarios

Peripheral arterial disease-induced lower extremity ischemic ulcers present with deep wound surfaces, minimal exudate, and extremely slow healing. Arterial ulcers represent the most challenging type of chronic wound to manage with NPWT—where insufficient blood supply constitutes the primary obstacle to healing, and the "additional negative pressure" employed in NPWT may further exacerbate ischemia.

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Key prerequisite: Blood supply assessment

Absolute contraindication: severe ischemia

For patients with severe ischemia (ABI<0.5) who have not yet undergone revascularization, NPWT is contraindicated. The Guiding Principles for the Registration Review of Negative Pressure Wound Therapy Devices (2024 Revision) explicitly list "severe ischemia without prior revascularization" as an absolute contraindication.

The core principle of NPWT for arterial ulcers is "low pressure, continuous application, and close monitoring":

Eligibility criteria: ABI> 0.5; undergone or eligible for revascularization; and sufficient blood supply has been assessed.

Low-pressure settings: The low-pressure continuous mode of-40 to-80 mmHg is sufficient to meet drainage requirements and prevents high pressure from exacerbating ischemia.

Both PVA and PU are suitable: within the low-pressure range, neither PVA nor PU carries a failure risk; the choice depends on the wound morphology (sinus tract → PVA; large-area wound → PU).

Close monitoring: During each dressing change, assess the wound color, changes in exudate, and pain intensity; if any deterioration occurs, immediately suspend NPWT and re-evaluate the blood supply.

Evidence-Based Evidence

Both the IWGDF 2019 guidelines and the TASC II guidelines emphasize that blood supply must be assessed prior to applying NPWT for ischemic wounds, and in cases of severe ischemia, revascularization should be performed first. The 2017 expert consensus also lists severe ischemia as a contraindication for NPWT application.

C5 | Non-healing wounds (prolonged duration>4 weeks)

Clinical Scenarios

When wounds fail to heal due to various etiologies for more than 4 weeks, NPWT should be employed as a wound preparation modality. Such wounds represent the "last line of defense" indication for NPWT—namely, salvage therapy following failure of conventional wound care.

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The evidence-based rationale for choosing between the "Continuous" versus "Intermittent" modes

Non-healing wounds are explicitly identified as scenarios where the intermittent mode can be utilized in the 2017 expert consensus. The 2017 consensus states: intermittent mode (5 min on/2 min off), Evidence Level B.

Continuous mode: Suitable for the early stage of infection characterized by significant exudation and uncontrolled infection.

Intermittent mode: Suitable for the stable phase following reduced exudation; this mode employs intermittent negative pressure to simulate "micro-deformation," thereby promoting granulation tissue growth.

PU vs. PVA: Granulation tissue assessment determines the optimal choice

The key to selecting PU/PVA for non-healing wounds does not lie in the type of wound, but rather in the assessment of granulation tissue growth status:

4.Excessive granulation tissue hyperplasia → PVA white foam. Gibson (2022) confirmed that PVA foam exhibits high density and small pore size, thereby limiting tissue ingrowth. The 3M product manual also recommends the use of PVA in scenarios where excessive granulation tissue hyperplasia needs to be controlled.

5.Insufficient granulation tissue growth → PU black foam. The large-pore open structure promotes granulation tissue ingrowth and tissue hyperplasia.

6.Uncertainty in assessment: It is recommended to first use PU to promote granulation tissue growth; once the wound has reduced in size, switch to PVA for maintenance.

Evidence-Based Validation

The 2017 expert consensus explicitly lists chronic non-healing wounds as an indication for NPWT, recommending parameters ranging from –16.6 to –6.6 kPa (–125 to –50 mmHg), with a Grade B evidence level; in contrast, the Excel parameter matrix recommends values between –125 and –175 mmHg—the lower limit aligns with the consensus recommendation—while the upper limit of –175 mmHg significantly exceeds the consensus-recommended upper limit of –50 mmHg.

Recommendations: A starting pressure of-125 mmHg can cover most non-healing wounds; the upper limit is recommended to be moderately reduced from-175 mmHg to-125–-150 mmHg; if high-pressure drainage is indeed required, a short-term application of-175 mmHg may be considered, provided that the suitability of PVA is thoroughly evaluated.

PU vs. PVA: Quick Reference Guide for Chronic Wound Selection

A systematic comparison based on Gibson's 2022 study and 3M product manuals, designed to assist clinicians in making rapid decisions:

Contraindications Quick Reference

NPWT is absolutely contraindicated (neither PVA nor PU is applicable).

1. Malign tumor wounds (may promote tumor growth)

2. Untreated osteomyelitis

3. Uncontrollable active hemorrhage

4. Exposed organs in cases of non-enteric fistula

5. Severe ischemia (ABI<0.5) without undergoing revascularization

6. Necrotic tissue has not been debrided

References: Guiding Principles for Product Registration Review of Negative Pressure Drainage Devices (2024 Revision); 3M V.A.C. User Manual

The three major clinical challenges of NPWT for chronic wounds

Pain Point 1: A "one-size-fits-all" approach to dressing selection

In clinical practice, the uniform use of PU black foam for all chronic wounds is common. However, different types of wounds exhibit vastly varying requirements for PVA/PU materials—PU used for sinus tracts may fracture, while PU applied to superficial wounds may lead to excessive granulation tissue formation; therefore, a precise selection must be made based on the anatomical structure of the wound and its current granulation status.

Pain point 2: Pressure settings do not account for PVA tolerance.

In clinical practice, negative pressure for chronic wounds is typically set uniformly between-150 and-175 mmHg; however, Gibson et al. (2022) demonstrated that PVA foam begins to fail when the negative pressure exceeds 140 mmHg. When PVA is used in high-negative-pressure settings, the drainage efficacy must be evaluated, and PU or a combination strategy should be considered if necessary.

Pain Point 3: Neglecting the value of intermittent mode

Long-term use of continuous negative pressure therapy for chronic wounds may lead to "negative pressure fatigue" —characterized by a decline in wound adaptation. The 2017 expert consensus recommends transitioning from a stable phase to an intermittent mode (5 min on/2 min off) to stimulate micro-deformation and promote granulation tissue growth; however, clinical implementation of this approach remains insufficient.

Sources of Evidence and Citations

1. Chinese Journal of Burns. National expert consensus on the application of negative pressure wound therapy (NPWT) in burn surgery (2017 edition) [J]. Chinese Journal of Burns, 2017,33(3):129–135.

2. IWGDF Guidelines 2019. International Working Group on Diabetic Foot Guidelines. https://iwgdfguidelines.org/

3. 3M/Solventum V.A.C. – WhiteFoam and GranuFoam product manuals. https://www.solventum.com/

4. Gibson DJ. A Comparison of the Biomechanical Performance of 3 NPWT Foams. JWOCN 2022;49(1):51-58.

5. Guiding Principles for Product Registration Review of Negative Pressure Drainage Devices (2024 Revision). NMPA. https://www.nmpa.gov.cn/

6. NPUAP/EPUAP Pressure Ulcer Prevention and Treatment Guidelines 2019.

7. TASC II Guidelines (Peripheral Artery Disease Guidelines of the Pan-Athletic Society). https://www.tasc-2-pad.org/

This article is compiled based on evidence-based medical evidence and is intended solely as a reference for clinical professionals. The specific treatment plan should be determined by a licensed physician based on the individual circumstances of each patient.