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EVOLUTION OF BURN WOUND CARE

(THE CONCEPT OF EARLY WOUND CLOSURE WITH SKIN, SKIN SUBSTITUTES)

The predominant approach to the management of burns throughout history has been to alter the burn surface in an attempt to improve healing. Initial approach were based on the "theories of the time" and appears quite unusual to us now. However, it is important to recognize that our current understanding of wound healing has evolved only recently and is still evolving.

Current concepts of wound healing principles are only just beginning to be recognized and implemented.

 

A description of wound care (1500 BC) using a frog dipped in oil to rub across the wound

Application of agents to the burn surface (now antibacterial) is now being considered to be a temporary approach on the way to definitive wound closure. Changes in treatment over the centuries, especially over the past 30 years are based on our understanding of the:

• local factors impeding healing
• systemic effects of a open burn wound

 

Local Factors Impeding Healing

tissue hypoxia -low blood flow -eschar on exudate tissue desiccation -occurs with open wound -impedes epithelial migration -risk of wound conversion wound exudate -released proteases -injures new tissue -uses wound oxygen wound infection -due to impaired local defense -exposure to microbes in the environment -increases inflammation induced injury wound trauma -environmental insult -use of toxic chemicals -traumatic dressing changes

 

Systemic Effects of the "Open" Burn Wound inflammatory response - Hypermetabolism - Catabolism pain induced "stress response" heat loss induced stress response increased local infection leading to systemic sepsis

 

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Partial thickness burn with surface desiccation

Note: dry surface with thin surface eschar

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Superficial burn with surface exudate

Note: thin layer of a gelatinous exudate. The exudate contains protein, neutrophils, proteases

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A) WHAT IS THE OPEN OR EXPOSURE METHOD?

One approach to burn management is the open or exposure method whereby the wound is exposed to air usually with some form of topical antibiotic. Copeland in 1887 and several other burn clinicians (1900-1910) popularized this method to avoid infection under a dressing.

Remember: There were no effective topical antibiotics in the early 20th century

Desiccation, scabbing, wound conversion and infection were common. Current use of this method is for burns on areas difficult to apply a dressing such as face and perineum.

 

Open (Exposure) Method Advantages easier than use of dressings less risk of closed space infection applicable today to areas difficult to apply dressings Disadvantages increased wound desiccation increased water and heat loss, and pain increased risk of infection

 

B) THE "CLOSED DRESSING" METHOD.

In the 1990’s evidence mounted that the use of occlusive dressings decreased infections and exudate buildup as they were absorbent Decreased pain and heat loss were also noted. Several decades later Caldwell demonstrated that the decrease in heat loss markedly attenuated the post burn hypermetabolism with the availability of effective topical antibiotics combined with the closed dressing method, infection rate and resulting morbidity, mortality decreased markedly.

The approach was most effective once effective topical antibiotics were developed.

 

Closed (Dressing) Method Advantages  Decreases risk of wound desiccation Decreased heat loss Decreased risk of cross-contamination Debriding effect on wound More comfortable Disadvantages  More time consuming and expensive Increased risk of infection (if not changed frequently)

 

A dressing covers but does not "close" the wound

Adherence to the wound surface along with environmental protection and restoration of optimal healing occurs with wound closure.

Skin or a skin substitute is required to close the wound.

It is important to distinguish wound dressing from skin substitutes. The role of dressings is to cover the wound but not "close" the wound. In fact, frequent changes are required on partial thickness wounds to avoid exudate buildup if standard dressing material is used.

C) TYPES OF STANDARD WOUND DRESSINGS

Most dressings for wounds are composites of several dressings, each with a specific role, i.e. adherence, occlusion, absorption. The variety of available dressings can readily be categorized. The basic categories are described below.

Primary and Secondary Dressings

All dressings can be classed as either primary or secondary types. A primary dressing is placed in direct contact with the wound and may provide absorptive capacity and prevent desiccation and infection. A secondary dressing is placed over a primary dressing to provide further protection, absorptive capacity, compression, and occlusion. The selection of materials for primary or secondary dressings is based by the particular application. Cotton, rayon and polyurethane are most commonly used. They are inexpensive and can be designed in many configurations.

Absorbent Dressings

The accumulation of wound fluid or exudate will retard healing. An absorbent dressing should therefore absorb exudate but without becoming moist on the external surface. If wetness on the outer surface occurs a microorganism can enter the wound from the outside.

An absorbent dressing should be designed to meet the exudation characteristics of the wound it is meant to cover. Acute wounds have a large exudate, especially when using topical antibiotics. Chronic wounds exude more slowly.

Non-Adherent Dressings

Non-adherent dressings are designed to not stick to the wound. Gauze is often impregnated with petroleum jelly or ointment based antibiotics for use as a non-adherent dressing. A secondary dressing is used with a non-adherent dressing to absorb exudate, and cover the surface to prevent desiccation.

In addition to the impregnated gauze type, often non-adherent dressings consist of an absorbent pad faced by a perforated, non-adherent film layer. Adherence may be reduced by keeping the dressing moist.

Occlusive/Semi occlusive Dressings

Occlusive dressings provide an excellent environment for a clean, minimally exudative wound and can be used to protect uninvolved tissue from wound exudate.

Experimentally polyvinyl and polyethylene films increase epidermal healing compared to untreated control. Adhesive polyurethane film dressings are probably the most common type. Faster re-epithelialization of lower sites has been reported with polyurethane dressings compared with traditional dressings. However, these are not adherent dressings. The dressings are impermeable to microbes but minimally permeable to water vapor (and oxygen). Hydrocolloid dressings are also occlusive. However, the above dressings do not adhere allowing development of an inflammatory exudate (or infection if the surface is colonized). Nor do they provide a temporary dermis or dermoid healing properties.

Adherent Dressings (Temporary Skin Substitutes)

There are a few high tech types of adherent dressings available for use which are actually skin substitutes, mostly for partial thickness burns. The properties are usually an inner layer of a collagen and fabrin to chemically bond to the wound followed by an outer synthetic layer which decrease evaporative water loss and is impermeable to bacteria. The tight adherence decreases exudate, maintains a moisture layer and increases the optimum healing environment. A clean wound bed is essential for use of an adherent dressing. Firm adhesive to the wound is necessary to avoid exudate or fluid buildup.

D)   SOLVING THE PROBLEM OF WOUND CONVERSION IN THE PARTIAL THICKNESS BURN

The burn wound is defined in terms of a evolving injury. The histologic description is defined in terms of specific areas of ongoing pathologic change called zones. Three zones have been classically described. The actual pathophysiology is now recognized to be much more complex than the terms used for defining the zones.

• zone of coagulation (necrosis)
• zone of stasis (injury
• zone of hyperemia

Zone of coagulation

This zone comprised the surface tissue necrosis in a superficial burn or the initial burn eschar in a deeper burn. The surface injury is caused mainly by the heat or chemical insult. Obviously this zone has an irreversible injury.

Zone of stasis

Deep and peripheral to the zone of coagulation, there is a sizable area of tissue injury where cells are viable but can easily be further damaged. The term "stasis" or ischemia was used because the progressive injury, in this area was felt to be due to capillary thrombosis from injured endothelium, leading to ischemia induced cell death. Fibrin deposition, vasoconstriction and thrombosis indeed to occur, most likely as a result of continued release of mediators. However, early epithelial cell death in this area, unrelated to blood flow, is reported to be quite high, leading to slowing of healing. Epithelial cells are particularly prone to environmental insults such as desiccation and inflammation induced injury and must be protected. This zone is most prominent in mid dermal burns where there is less reserve in the remaining viable cells and less blood flow. Temporary skin substitutes should have the properties which will protect the impaired cells and optimize healing.

Zone of hyperemia

Peripheral and deep to the zone of stasis is the zone of hyperemia. The area is characterized by minimal cell injury but with vasodilatation due to neighboring inflammation induced mediators. Complete recovery of the tissue is usually expected unless there is an additional severe insult such as an invasive infection or profound tissue inflammation.

Wound Conversion

This term refers to the dynamic process whereby the Zone of Injury connects to a Zone of Tissue Necrosis thereby deepening the wound.

Zones of Injury in Two Burn Depths. The Zones of Stasis or Injury and Hyperemia

(reaction) are much larger in a mid dermal burn compared to a superficial burn. This larger zone of injury exceeds the increase in size of the zone of coagulation (necrosis) between the two depths. The reason is that:

1. the best blood flow is present in the superficial dermis and ischemia is a greater risk beyond that point,
2. once through the epidermis, the heat transfer increases into the dermis such that a deeper area of heat and inflammatory injury results.
3. A mid (or deep) dermal is much more prone to further injury during the treatment period.

 

Superficial dermal burn from hot water. Epidermal layer sloughing.

Mid dermal burn appearance is less wet and red rather than pink. Anatomical differences are quite subtle.

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RISK FACTORS FOR WOUND CONVERSION
Local	Systematic
Impaired blood flow	Septicemia
Increased inflammation (Infection, Open Wound, Irritants)	Hypovolemia
Surface desiccation	Malnutrition
Surface exudate buildup	Excess catabolism
Mechanical trauma (Dressing changes, shearing)	Chronic illness
Chemical trauma - topical agents

 

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EXAMPLE OF WOUND CONVERSION

 

E)   SUMMARY

The combination of evidence that early wound closure is optimum care and the verification of this concept by our current knowledge of wound healing has led to the increasing role of skin substitutes (temporary and permanent) in burn care.

The quality and cost effectiveness of current skin substitutes and those in the developmental stages reflects an even greater use in the near future.

 

The use of skin substitutes both temporary and permanent is becoming increasingly important for optimizing outcomes in burns.