7 - Negative Pressure Wound Therapy Flashcards
Introduction
- Vacuum Assisted wound Closure = “VAC therapy”
- Continuous or intermittent sub atmospheric pressure delivered to wound through closed system
- Promotes optimal moist wound healing environment
History
- 1841 – Junod applied vacuum bells to various body parts to create negative pressure to draw blood away from diseased organs
- 1950’s – Studies on peripheral vessel responses to changes in pressure
- 1956 – Erler and Itting designed vacuum-compression chamber allowing pressures up to 150mmHg
Mechanism of action or purpose of wound VAC
Accelerates normal wound healing
Phases of wound healing
o Inflammation (Substrate or Lag) o Proliferation (Fibroblastic) o Maturation (Remodeling)
Inflammatory phase
o Begins immediately, comprises 10% of healing process
o Cellular proteins recruited (i.e. substrate phase)
o Vasodilation and edema, angiogenesis and capillary budding
o Fibroblasts start to lay down collagen tensile strength
o Epidermal epithelialization begins
o Lasts 3-4 days
Proliferative phase
o Fibroblastic phase
o Accounts for ~ 20% of healing process
o Starts 3rd-4th day and lasts up to 21 days.
o Wound continues to granulate until wound contracts and epithelialization is complete
o Fibroblasts are primary cell type present
o Tensile strength of the wound is ~35% of skins original strength
Maturation phase
o ~70% of the healing process, lasts from 3 weeks – 1 year
o Collagen fibers laid down during proliferation enzymatically debrided by macrophages
o New fibers produced and aligned in response to mechanical forces
o Wound contraction occurs toward center of the wound (can completely heal wound)
o Linear scar contraction
Systemic factors that can delay wound healing
o Metabolic (i.e. Hyperglycemic state) – diabetics
o Ischemia
o Malnutrition
Local factors that can dealy wound healing
o Desiccated tissue o Tissue edema o Excessive exudate (drainage) o Poor tissue apposition (size of wound) o Infection
Sub atmospheric pressure
Improves wound environment
o Sucks the bad out and in doing so, pulls in the products you need for healing and granulation tissue
Direct and Indirect effects
o Accelerated healing
o Reduced time to wound closure
Direct effets of wound vac
Semi-permeable dressing maintains moist, warm environment
Foam (sponges)
o Open porous design which transmits negative pressure to wound surface
o Wound deforms and contracts, which is important for stimulating tissue remodeling at cellular level
Closed system
o There is a pressure gradient between the wound surface and canister
o This promotes fluid transport from wound bed and interstitial space and therefore reduces edema
Indirect effects
o Increases blood flow
o Decreases inflammatory response, which reduces systematic and local mediators of inflammation
o Decreases in bacterial burden and alters wound biochemistry
o Mechanical forces alter wound environment
- Mechanotransduction – conversion of mechanical forces into chemical activity
–> Increased fibroblast growth and migration
Summary of clinical benefits
o Removal of excess fluid and inhibitory agents
o Reduces bacterial load
o “Splints” the wound and promotes perfusion
o Helps to approximate wound edges and promotes optimal wound environment
o Promotes formation of granulation tissue
Indications for NPWT
Chronic wounds
o Diabetic ulcers, Pressure ulcers, Venous stasis ulcers
Acute wounds
o Orthopedic trauma, Partial thickness burns, Open abdominal wounds, Surgical dehisced wounds, Exposed hardware and tendons, Skin flaps, Skin grafts, Degloving injuries
Contraindications for NPWT
- Malignancy within the wound
- Untreated osteomyelitis
- Fistulas to organs or body cavities
- Necrotic tissue within wounds
- Wounds with exposed vessels
Treatment principles
Dressing changes:
o Frequency
Wound bed preparation:
o Vascular supply, bleeding, fibrosis, undermining
Non-Adherent barrier:
o Tendons and grafts
o Do not have direct contact between tendon and VAC, use a barrier
Bridging
o More than one wound
o Plantar wounds (so they aren’t walking on the tubing)
Grafts:
o Protective barrier
o Caution when removing dressing
o What if VAC leaks/malfunctions –> it can be very frustrating when the wound VAC is removed and the skin graft gets peeled off with it, so it needs to be removed carefully
KCI VAC system
- Invented by Louis Argenta, MD and Michael Morykwas, PhD from Wake Forest University School of Medicine
- FDA cleared for marketing in 1995
- Received Medicare approval in 2000
- Extensively researched for clinical efficacy in various medical specialties
Components of KCI VAC system
- Foam Dressings – sterile open cell
o GranuFoam - black
o Vers-foam – white
o Specialty – heel, abdominal, thin, round, hand
- T.R.A.C. Pad
o Transmits vacuum suction to wound dressing via tubing and connectors
- Drapes – provide wound occlusion
- Canisters – collect wound fluid
- Tubing, connectors , etc.Typical VAC settings
- Dependent on wound type and location
- Keep therapy in progress while dressing is in place to help minimize infection (therapy should be active 22 of 24 hours/day)
Lower extremity settings
Chronic ulcers (diabetic, pressure)
o Continuous @ 125mmHg for first 48 hours
o Intermittent (5 min ON/ 2 min OFF) @ 125 mmHg
o Change every other day (Mon – Wed – Fri)
Skin Grafts
o Continuous @ 75 to 125 mmHg for 4-5 days
Surgical Dehiscence
o Continuous @ 125 mmHg for duration of therapy
o Change every other day (Mon – Wed – Fri)
Necrotic heel ulcer case study
- Pseudomonas-looking wound
- Debride to the granular base – it will be bigger than before debridement
- Cut sponge to size
- Bridging example – so that tract pad goes up to the top of the foot and he can walk, just need to have it all connected under dressing
- Base layer of the tape dressing on normal skin surrounding the VAC because it will macerate normal skin
- After 1st dressing change, it has started to heal, epithelialized islands have started to form
- Centrally there is a fibrotic area that needs to be cleaned out again
- Wound healed over 8 weeks
Open amputation case study
- 64 year old type 2 diabetic admitted by PCP with diabetic foot ulcer
- X-rays showed gas in soft tissue of foot which rapidly spread proximally
- Taken to surgery emergently for open amputation and re-admitted to floor for IV antibiotics
- Radical open amputation that needed to be healed – no healthy skin flaps present to work with
- Plantar aspect of foot is flat so he would be able to ambulate
- Eventually a flap was able to be sutured together with an absorbable suture
- Initiated wound VAC which progressed the healing, did a skin graft once
- Healing occurred at 10 weeks, complete healing
SUMMARY OF IMPORTANT CONCEPTS
- Indications and contraindications
- Treatment principles
o Wound bed preparation
o Grafts - Wound healing mechanism of action
o Direct and indirect effects on wound healing
