7 - Negative Pressure Wound Therapy

Question 1

Introduction

Answer 1

• Vacuum Assisted wound Closure = “VAC therapy”
• Continuous or intermittent sub atmospheric pressure delivered to wound through closed system
• Promotes optimal moist wound healing environment

Question 2

History

Answer 2

• 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

Question 3

Mechanism of action or purpose of wound VAC

Answer 3

Accelerates normal wound healing

Question 4

Phases of wound healing

Answer 4

o	Inflammation (Substrate or Lag)
o	Proliferation (Fibroblastic)
o	Maturation (Remodeling)

Question 5

Inflammatory phase

Answer 5

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

Question 6

Proliferative phase

Answer 6

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

Question 7

Maturation phase

Answer 7

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

Question 8

Systemic factors that can delay wound healing

Answer 8

o Metabolic (i.e. Hyperglycemic state) – diabetics
o Ischemia
o Malnutrition

Question 9

Local factors that can dealy wound healing

Answer 9

o	Desiccated tissue
o	Tissue edema 
o	Excessive exudate (drainage) 
o	Poor tissue apposition (size of wound)
o	Infection

Question 10

Sub atmospheric pressure

Answer 10

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

Question 11

Direct effets of wound vac

Answer 11

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

Question 12

Indirect effects

Answer 12

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

Question 13

Summary of clinical benefits

Answer 13

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

Question 14

Indications for NPWT

Answer 14

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

Question 15

Contraindications for NPWT

Answer 15

• Malignancy within the wound
• Untreated osteomyelitis
• Fistulas to organs or body cavities
• Necrotic tissue within wounds
• Wounds with exposed vessels

Question 16

Treatment principles

Answer 16

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

Question 17

KCI VAC system

Answer 17

• 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

Question 18

Components of KCI VAC system

Answer 18

-	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.

Question 19

Typical VAC settings

Answer 19

• 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)

Question 20

Lower extremity settings

Answer 20

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)

Question 21

Necrotic heel ulcer case study

Answer 21

• 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

Question 22

Open amputation case study

Answer 22

• 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

Question 23

SUMMARY OF IMPORTANT CONCEPTS

Answer 23

• Indications and contraindications
• Treatment principles
  o Wound bed preparation
  o Grafts
• Wound healing mechanism of action
  o Direct and indirect effects on wound healing