AP

Open Wound Management (OWM)

Moist Wound Healing (MWH) and Moisture Retentive Dressings (MRD)

  • MWH: process of creating a wound environment that optimizes the body’s healing using specialized primary layers called moisture retentive dressings (MRD).

  • MRD characteristics:

    • Usually non-adherent and occlusive, protecting and retaining wound fluid.

    • Currently considered standard of care for wound management.

  • What makes a MRD?

    • Based on moisture vapor transmission rate (MVTR) and transepidermal water loss (TEWL).

    • TEWL for intact skin: TEWL = 4 to 9 g/m^2/hr

    • TEWL increases to 80 to 90 g/m^2/hr in partial/full-thickness wounds.

    • MVTR measures occlusiveness; low MVTR correlates with better healing when other variables are constant.

    • Example MVTR values:

    • Hydrocolloid: MVTR approx. 11.2 g/m^2/hr

    • Polyurethane film: MVTR approx. 13.7 g/m^2/hr

    • Polyurethane foam: MVTR approx. 33.4 g/m^2/hr

    • Gauze: MVTR approx. 67.0 g/m^2/hr

    • Dressings with an MVTR < 35 g/m^2/hr are considered moisture retentive.

    • MVTR of hydrocolloid and polyurethane film are close to the TEWL of skin.

    • MVTR can be reduced by adding petrolatum or antibiotic ointment.

MRD – Advantages

  • WBCs remain in the wound rather than migrating into the open gauze (selective autolytic debridement).

  • Lower infection rates in moist wounds by occlusive barriers, desiccation prevention, necrosis prevention, improved antibiotic concentration in the wound, and enhanced WBC activity.

  • Wound remains at physiological temperature, supporting proteases and growth factor function.

  • Maintains proper moisture, limiting expansion of necrosis from desiccation, reducing scarring, and reducing aerosolization of bacteria during changes.

  • Occlusive/ nonadherent MRDs are less painful to remove; patients often report comfort.

  • Water-proof properties prevent contamination from urine or environmental fluids.

  • Fewer bandage changes due to moisture retention can speed healing and reduce costs.

MRD – Disadvantages

  • Higher initial cost for dressings.

  • Excess exudate can macerate peri-wound skin and wound bed.

  • Requires more intellectual planning to select the most appropriate dressing.

Wet-to-Dry vs MRD – General Comparison

  • Wet-to-dry is non-moisture-retentive and more debridement-focused, while MRDs maintain moisture and support autolytic processes.

  • In many cases, MRD-based approaches are preferred; Wet-to-Dry remains a fallback in certain scenarios.

MRD – The Big 4 (Materials Often Used as MRDs)

  • Calcium alginate

  • Polyurethane foam

  • Hydrogel

  • Hydrocolloid

  • Decision guided by exudate quantity and wound needs (debridement or granulation).

Choosing the Correct MRD

  • MRDs can be used across all phases of wound healing with appropriate modifications.

  • Selection is driven by wound exudate, phase of healing, and desired wound response.

Characteristics and Placement of MRDs

  • MRDs are typically placed after surgical debridement and lavage (or sooner in severely compromised patients).

  • Dressing fit: sterile gloves to handle; cut to fit to contact wound surface (not surrounding skin).

  • Place MRD, then cover with a traditional 3-layer Robert Jones bandage.

  • Change frequency:

    • Inflammatory phase (highest exudate): every Q2-3 days.

    • After granulation tissue forms: change to a less absorptive dressing (e.g., hydrocolloid) every Q5-7 days.

  • Change whenever the dressing becomes oversaturated or dries out, or if strike-through/soiling occurs, regardless of time since placement.

Wound Management Case Example (Overview)

  • Case examples illustrate MV/MD use: initial wet-to-dry approach for short-term management, then transition to MRD (e.g., hydrocolloid) as healing progresses.

  • Specific cases include transitions from wet-to-dry for 3 days, then MRD changes over several days.

Alternative Strategies (Manuka Honey)

  • Manuka honey as an OWM adjunct:

    • Antimicrobial/antifungal activity due to high osmolarity, drawing lymph into wound and creating an acidic environment; deleterious to bacteria; promotes oxygen release and fibroblast activity.

    • Glucose oxidase produces hydrogen peroxide (H₂O₂).

    • Accelerates sloughing of necrotic tissue; provides local nutrition; reduces inflammatory response; improves epithelialization.

    • Honey source: Manuka honey from nectar of Leptospermum scoparium (New Zealand).

    • UMF rating (Unique Manuka Factor) assesses non-peroxide antimicrobial rating; prefer UMF > 10+.

  • Clinical notes: Good for foot wounds with persistent bacterial contamination; effective against Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus spp., E. coli, Proteus mirabilis, Serratia, Salmonella, and Candida.

Alternative Strategies (Sugar)

  • Antimicrobial effects via high osmolality:

    • A 1–2 cm layer of sugar on the wound draws water and nutrient-rich lymph to the wound to promote rapid healing.

    • High osmotic stress interferes with bacterial signaling and causes bacterial death; provides superficial debridement.

    • Inexpensive and readily available.

  • Application: pour sugar layer, cover with absorbent primary layer (gauze), then a typical modified Robert Jones bandage.

  • Frequency: require frequent changes (every 24 hours or more often if sugar saturates).

  • Stop once granulation tissue develops.

Alternative Strategies (Low-Level Laser Therapy - LLLT)

  • LLLT has been shown to significantly decrease time to wound healing.

Alternative Strategies (Cold Plasma)

  • Very effective at killing all organisms; useful for wounds with resistant infections and chronic/poorly healing wounds.

  • Painless application; no sedation required; multiple treatments required.

  • High initial cost.

Negative Pressure Wound Therapy (NPWT)

  • Also known as:

    • Topical negative pressure therapy

    • Vacuum-assisted closure (VAC)

    • Sub-atmospheric wound therapy

    • Closed-suction wound drainage

    • Micro-deformational wound therapy

  • Mechanism:

    • Application of a vacuum evenly across the wound surface, usually via a foam dressing (open-cell polyurethane or polyvinyl alcohol foam).

    • Wound is sealed from the environment with an occlusive drape.

    • Specialized tubing connects the dressing to a programmable vacuum pump, delivering negative pressure to the whole wound.

    • Exudate is collected in a canister attached to the pump.

  • Typical operating pressure: programmable from 75 to 150 mm Hg, with 125 mm Hg commonly used for open wounds.

  • Suction can be continuous or cyclic.

NPWT – Equipment

  • Self-contained VAC unit.

  • Collection canister.

  • Open-cell foam.

  • Tubing to connect foam to unit.

  • Adhesive drape and adhesive spray/paste.

NPWT – Goals of Treatment

  • Remove wound exudate.

  • Decrease interstitial edema.

  • Draw wound edges together.

  • Promote blood supply to the wound.

  • Stimulate cells involved in modulating inflammatory and proliferative responses to injury.

NPWT – Mechanism (MOA)

  • Precise cellular and molecular mechanisms are still being elucidated.

  • Postulated benefits include cycling of increased blood flow (oxygenation/nutrient delivery) and periods of decreased blood flow (hypoxic stimulation of angiogenesis and fibroplasia).

  • Studies indicate that at 125 mm Hg NPWT increases blood flow, accelerates granulation tissue formation, decreases bacterial counts, and improves flap survival.

NPWT – Indications and Contraindications

  • Indications:

    • Large open wounds or wounds devoid of granulation tissue; allows longer intervals between bandage changes.

    • Chronic non-healing wounds.

    • Extremity wounds treated by second intention.

    • Postoperative management of tissue flaps/grafts.

    • Open abdominal management for septic abdomen.

    • Broad range of expanding applications.

  • Contraindications:

    • Poor peri-wound skin condition.

    • Necrotic or devitalized tissue.

    • Coagulopathy.

    • Exposed major vessels or open joints.

    • Uncontrolled neoplasm.

    • Untreated osteomyelitis.

    • Very small wounds or lack of overnight care.

    • Note: SNAP portable NPWT systems are now available for animals.

NPWT – Clinical Case (Overview)

  • Illustrates NPWT application in a case scenario (RUSVM Confidential references in slides).

“Homemade” NPWT System (Overview)

  • Demonstrates a DIY approach to NPWT for chronic wounds.

  • Key components include:

    • Open-cell foam packed into the wound.

    • Fenestrated red rubber catheter to connect to suction.

    • Adhesive materials to seal around the wound and prevent leaks.

    • Connection to wall suction; a simple attachment to create negative pressure.

  • This approach highlights practical adaptability in resource-limited settings.

Practical Considerations and Ethical/Clinical Implications

  • Open wound management requires balancing infection control, wound environment, patient comfort, and owner expectations.

  • Choosing debridement method and dressings should consider tissue viability, pain, and potential damage to healthy tissue.

  • MRD-based approaches align with modern wound care principles emphasizing moisture, temperature, and protease/cytokine balance to optimize healing.

  • Cost-benefit considerations: MRD materials may be pricier upfront but can reduce bandage changes and improve healing times; Wet-to-Dry methods may be cheaper initially but can prolong healing and require more frequent changes.

  • Practical constraints (e.g., owner compliance, clinic resources) influence the choice of therapy (e.g., Wet-to-Dry vs MRD, or NPWT feasibility).

Quick Reference Values and Formulas

  • TEWL of intact skin: TEWL -> 4 to 9 g/m^2/hr

  • TEWL in partial/full-thickness wounds: TEWL -> 80 to 90 g/m^2/hr

  • MVTR thresholds for MRD:

    • MRD: MVTR < 35 g/m^2/hr

  • Example dressing MVTRs:

    • Hydrocolloid: MVTR around 11.2 g/m^2/hr

    • Polyurethane film: MVTR around 13.7 g/m^2/hr

    • Polyurethane foam: MVTR around 33.4 g/m^2/hr

    • Gauze: MVTR around 67.0 g/m^2/hr

Note: When using dressings with occlusive properties or petrolatum/antibiotic ointments, MVTR can be further modulated to tailor moisture retention and wound physiology.

Summary Takeaways

  • Open Wound Management emphasizes creating an optimal wound environment through debridement, appropriate bandage architecture, and moisture management.

  • Debridement choices (Surgical, Autolytic, Mechanical) should balance speed, selectivity, tissue preservation, and patient pain.

  • Bandage design (primary, secondary, tertiary layers) and contact layer selection are critical for wound environment, pain management, and healing trajectory.

  • Moisture Retentive Dressings (MRD) represent a modern standard of care, leveraging MVTR/TEWL concepts to maintain moisture, support autolytic processes, and reduce infection risk.

  • Alternative strategies (Manuka honey, sugar, LLLT, cold plasma) offer adjunct options with specific antimicrobial, debridement, or healing-promoting effects.

  • Negative Pressure Wound Therapy (NPWT) provides powerful wound management by removing exudate, reducing edema, and promoting wound edge apposition, with defined indications, contraindications, and practical equipment considerations.

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Key Terms and Definitions

  • Moist Wound Healing (MWH): Process of creating a wound environment that optimizes the body’s healing using specialized primary layers called moisture retentive dressings (MRD).

  • Moisture Retentive Dressings (MRD): Specialized primary layers that are usually non-adherent and occlusive, protecting and retaining wound fluid, considered standard of care for wound management.

  • Moisture Vapor Transmission Rate (MVTR): A measure of a dressing's occlusiveness; low MVTR correlates with better healing when other variables are constant. Dressings with an MVTR < 35 g/m^2/hr are considered moisture retentive.

  • Transepidermal Water Loss (TEWL): The rate at which water passes through the epidermis and evaporates from the skin surface. For intact skin, it is 4 to 9 g/m^2/hr, increasing significantly in partial/full-thickness wounds.

  • Autolytic Debridement: A selective debridement process where WBCs remain in the wound rather than migrating into open gauze, facilitated by moist wound environments.

  • Manuka Honey: An alternative wound management adjunct with antimicrobial/antifungal activity due to high osmolarity, an acidic environment, and hydrogen peroxide production via glucose oxidase.

  • UMF Rating (Unique Manuka Factor): Assesses the non-peroxide antimicrobial rating of Manuka honey; UMF > 10+ is preferred.

  • Sugar (in wound care): Used for its antimicrobial effects via high osmolality, drawing lymph and nutrients to the wound, causing bacterial death, and providing superficial debridement.

  • Low-Level Laser Therapy (LLLT): A therapy shown to significantly decrease time to wound healing.

  • Cold Plasma: An alternative strategy very effective at killing all organisms, useful for resistant infections and chronic/poorly healing wounds.

  • Negative Pressure Wound Therapy (NPWT): Also known as VAC, this therapy applies a vacuum evenly across the wound surface to remove exudate, decrease edema, draw wound edges together, promote blood supply, and stimulate cellular responses.