Overview
Definition:
Negative pressure therapy (NPT), also known as vacuum-assisted closure (VAC) therapy, is a technique that applies controlled sub-atmospheric pressure to a wound bed or graft site to promote healing
When applied over a skin graft, it aims to improve graft adherence, reduce fluid accumulation, and enhance vascularization, thereby increasing graft survival rates.
Epidemiology:
The application of NPT over skin grafts is a common adjunct in reconstructive surgery, particularly for challenging wounds or grafts in areas with poor vascularity
Its use is widespread in burns, trauma, and reconstructive procedures, with incidence varying based on surgical complexity and patient factors
Studies report improved graft take rates with NPT application, ranging from 70% to over 90% in select patient populations.
Clinical Significance:
Effective skin graft take is paramount for successful wound closure and functional restoration
NPT over skin grafts offers a significant advantage in optimizing graft adherence, reducing seroma and hematoma formation, promoting granulation tissue formation, and enhancing microcirculation, all of which are critical for graft survival
This translates to reduced revision surgeries, shorter hospital stays, and improved patient outcomes.
Indications And Contraindications
Indications:
Meshed or non-meshed skin grafts placed on well-prepared wound beds
Grafts in avascular or compromised beds
Large or complex reconstruction sites
Presence of significant exudate
To prevent seroma or hematoma formation
To promote early graft adherence and vascularization.
Contraindications:
Untreated osteomyelitis
Necrotic tissue with eschar present on the wound bed
Untreated coagulopathy
Active, uncontrolled bleeding
Presence of exposed vessels, nerves, or organs without adequate protection
Allergy to NPT components
Unstable patient.
Mechanism Of Action
Macro Deformation:
NPT causes macro-deformation of the graft and wound edges, bringing them into closer contact and enhancing adherence.
Micro Deformation:
It induces micro-deformation, which may stimulate cellular proliferation and migration, including keratinocytes and fibroblasts.
Fluid Removal:
NPT effectively removes exudate, seroma, and hematoma from the graft-wound interface, preventing their accumulation and potential separation of the graft.
Increased Blood Flow:
The negative pressure is thought to increase local blood flow and promote angiogenesis, leading to better vascularization of the graft.
Edema Reduction:
It reduces interstitial edema, improving the microcirculation and nutrient supply to the graft.
Bacterial Load Reduction:
NPT may help reduce the bacterial load within the wound by removing fluid containing microorganisms.
Npt Application Technique
Wound Preparation:
Thorough debridement of the wound bed
Hemostasis must be achieved
Ensure the wound bed is free of non-viable tissue
Mechanical or enzymatic preparation may be required.
Graft Placement:
Careful placement of the skin graft (meshed or non-meshed) onto the prepared wound bed
Ensure intimate contact between the graft and the recipient site.
Foam Placement:
A sterile, porous foam dressing (e.g., polyurethane or polyvinyl alcohol) is cut to fit the entire graft and surrounding skin, extending beyond the graft edges by at least 2-3 cm
The foam should not overlap the graft itself significantly.
Sealant Drape Application:
An adhesive transparent drape is applied over the foam, creating an airtight seal
Ensure the drape extends onto intact skin surrounding the wound.
Port Insertion:
A port or connector is inserted through the drape and into the foam dressing, ensuring it does not directly contact the graft
The port is then connected to the NPT device.
Therapy Initiation:
The NPT device is turned on, typically set to a continuous or intermittent pressure setting
Common initial pressures range from -75 mmHg to -125 mmHg (or -10 to -16.6 kPa).
Monitoring And Dressing Changes:
Dressings are typically changed every 48-72 hours, or more frequently if indicated by excessive drainage
During changes, the graft adherence and wound bed are assessed.
Advantages And Disadvantages
Advantages:
Improved graft adherence and survival rates
Reduced seroma and hematoma formation
Accelerated wound healing
Decreased bacterial colonization
Reduced frequency of dressing changes in some cases
Can be used on various graft types and wound locations
Facilitates granulation tissue formation.
Disadvantages:
Requires specialized equipment and trained personnel
Can be costly
Potential for pain or discomfort if not applied correctly
Risk of graft desiccation if the seal is compromised
Potential for foam adherence to the graft if not managed properly
Not suitable for all wound types or patient conditions.
Complications
Graft Failure:
Partial or complete graft loss due to inadequate adherence, infection, or compromised vascular supply
Prevention involves meticulous wound bed preparation and proper NPT application.
Pain:
Discomfort or pain at the application site or with dressing changes
Management includes adequate analgesia, proper foam placement to avoid direct pressure on sensitive areas, and gentle dressing removal.
Bleeding:
Can occur if NPT dislodges a clot or if applied over an inadequately hemostatic wound
Careful hemostasis prior to application is crucial
Intermittent pressure may be preferred initially.
Infection:
Despite potential bacterial reduction, infection can occur if sterile techniques are not maintained or if the wound was already heavily colonized
Close monitoring for signs of infection is essential.
Skin Maceration:
Maceration of the surrounding intact skin can occur if the sealant drape is not applied correctly or if there is excessive leakage
Regular inspection of the skin around the drape is important.
Key Points
Exam Focus:
Understand the physiological benefits of NPT for skin grafts: adherence, fluid removal, vascularity enhancement
Know the typical pressure settings and change intervals
Differentiate between meshed and non-meshed graft application considerations.
Clinical Pearls:
Ensure meticulous hemostasis before applying NPT over a graft
The foam should cover the entire graft and extend onto healthy skin for a good seal
Avoid excessive overlap of the foam directly onto the graft itself to prevent adherence issues
Monitor graft take closely during dressing changes.
Common Mistakes:
Applying NPT over a non-hemostatic wound bed
Inadequate sealing of the drape leading to air leaks
Foam not extending sufficiently beyond the graft edges
Applying pressure that is too high or too low without clinical justification
Failing to monitor for early signs of graft failure or infection.