SECTION VII: Surgical Excision & Grafting Management

Deep partial thickness burns fit into this category as healing takes longer than 3 weeks and hypertrophic scars or scar breakdown often is the result of primary healing.  Early excision and grafting should be considered as a treatment option for all burns that will not heal by primary intention within 3 weeks.  Full-thickness burns will by definition require grafting unless smaller than 3 to 4 cm in diameter.  The more rapidly the wound is closed with skin grafts, the better.  Burns, less than 30% of total body surface can be, at least theoretically, rapidly closed because adequate donor sites are available.  Larger burns will be more difficult, if not impossible, to completely graft early.  Initial coverage is often accomplished using available skin along with temporary skin substitute to cover ungrafted areas until skin is available. The other option is the use of a permanent skin substitute.  Deep partial thickness burns are also difficult to assess clearly as to time of healing.  Considerable judgment and assessment skills are therefore essential for this approach to yield optimal results.

The topics to be discussed in this chapter include both the indications and the general and specific techniques used:

A.     General Principles of Early Excision

B.     Types of Surgical Excision

Tangential (Sequential) Excision

Excision to Fascia

C.     Obtaining Skin Grafts (Donor Sites)

D.     Grafting and Dressing the Wound

E.     Wound Conversion

There are two key judgments that are required:

The first judgment is determination of cardiopulmonary stability and operative risk.  The patient should be reasonably stable.

The second judgment is a determination as to potential morbidity of the wound itself if not rapidly removed.  This judgment takes into consideration wound depth, functional loss, and the risk of the inflammatory wound on the host.  A key component of this assessment is defining wound depth, i.e., what will heal and what will not heal. 

 

The following facts which can aid in decision making: 

•           Infants and the elderly tolerate burn inflammation and infection poorly so early burn removal is preferred.

•      Burns in infants and the elderly are usually deeper than initially perceived.

•      Burns can get deeper over the first several days as a result of necrosis of ischemic areas. (conversion)

•      Burns caused by direct contact with flames, hot grease, chemicals, or electricity are invariably deeper than first appearances would suggest.

•      Burns on the low back, scalp, palms, and soles usually have sufficient remaining dermis to allow primary healing in 3 to 5 weeks.

•      Large full-thickness burns are life-threatening until closed. 

General Principles

There are a number of general principles that apply to all methods of excision and grafting: 

The first principle is that the patient must be thermodynamically stable before considering excision.  Pulmonary function can be impaired, but the patient must be able to be safely moved to the operating room and back. 

The second principle is the potential for significant blood loss must be recognized and adequate amounts of red cells, plasma, and platelets, if indicated, are available before starting an excision procedure.

The third principle is that major pulmonary abnormalities in the burn patient can become very problematic with general anesthesia if preplanned safeguards are not initiated.  Stiff lungs and increased dead space often require special mechanical ventilatory needs, which must be prepared for and met in the operating room.

The fourth principle is that hypothermia must be avoided during surgery.  The operating room and fluids used must be warmed to avoid severe hypothermia, a major hazard.  The operating room temperature should be maintained between 80° and 85° F to minimize hypothermia and postoperative problems. 

The fifth principle is that the stress induced by anesthesia and surgery must be limited to that which the patient can safely tolerate.  The time in the operating room should be carefully controlled, again to avoid postoperative complications.  A 2-3 hr operative period is best for a large burn.  It is better to do several moderate operative procedures 1 or 2 days apart than one massive procedure.  The exception is children, i.e., older than 5 years old, who tolerate large excision procedures much better than adults.  A reasonable operating time limit, including anesthesia, is 2-3 hours.  A shorter period is indicated for elderly or compromised patients.  Total blood loss per procedure should be restricted to avoid development of a coagulopathy.

The sixth principle is that blood loss should be replaced with blood products rather than crystalloid in the major burn patient.  Typically the patient already has massive edema in the first week and red cell production will be markedly depressed until the wound is healed, especially in a massive burn.  It is therefore unrealistic to assume that red blood cell mass will quickly return to baseline by increased production.

Timing of Excision

Timing of excision relative to changes in the wound itself is crucial to minimize risks.  Blood flow to the burn wound is markedly increased beginning about 4 days after injury and peaking between 5 and 14 days.  The increasing blood flow, which parallels the development of wound inflammation, is present in the viable tissue beneath the eschar.  A significant increase in blood loss should be expected with wound excisions after 5 to 6 days.  Clotting abnormalities at this stage can also be a major problem.

In addition, colonization of the wound develops during the first week and manipulation of the colonized or infected wound runs an increasing risk of bacteremia.  Because of these facts, the size of the planned excision must be determined based on a clear understanding of increasing risks of blood loss and bacteremias.

General Principles for Burn Excision and Grafting

n The patient must be thermodynamically stable before considering excision

n The potential for significant blood loss must be recognized

n Pulmonary problems clearly present & require a plan of management in the OR

n Hypothermia must be avoided during surgery

n The stress induced by anesthesia and surgery must be limited to that which the patient can safely tolerate

n Significant blood loss in a major burn should be replaced with blood products

B.   Types of Surgical Excision

There are two types of surgical procedures to remove the eschar: tangential excision and excision to fascia.  There are also several types of grafts and dressing techniques, which will be described.

 1. Tangential (Sequential) Excision

The principle is to excise the wound in thin layers using a blade held at a very acute angle with the skin surface.  The objective is to remove only the nonviable tissue, sparing, in particular, as much viable dermis as possible in the case of the deep dermal burn.  The dermis contains the elasticity in skin.  In addition, the viable dermal surface is an excellent base for grafting.  Fat is a less attractive bed for skin grafting because of decreased vascularity as well as the difficulty of determining viable fat on inspection.

The excision is performed with a hand-held dermatone using guards of variable thickness (0.008 to 0.020 inch) to help control depth of excision.  A back and forth motion is utilized for cutting with very little forward force. Control of depth is based not only on  the gauge of the guard, but also on the angle of the blade in relation to the surface.  A sharp blade is needed for this approach, and frequent blade changes are required.  A Goulian or a Watson knife is used, depending on the area being excised.  The Watson, being larger, is used for larger flatter surfaces, whereas the Goulian is used over curvilinear areas, e.g., over bony prominences or on fingers, toes, neck, and occasionally, face.  Excision over bony surfaces can be aided by injecting sale beneath the eschar to flatten and push the wound surface away from the bone.  The endpoint of excision is brisk punctuate bleeding and a completely viable wound base.  Viable dermis is white and shiny in color.   One or two large bleeders can make the wound look red, so careful inspection and considerable experience is needed to assess the adequacy of the wound bed.  Injured fat is particularly difficult to diagnose.  Any fat that is dark yellowish-brown in color should be removed.

Healthy fat is light yellowish in color and shiny.  It is easy to under-excise, leaving a poor bed for graft take.  In addition, it is easy to excise too much tissue, thereby removing potentially viable dermis.

Over-excision would be particularly detrimental if done on hands, neck or face, or over joint surfaces.  It is very difficult to detect accurately the proper endpoint of this technique using tourniquets to control bleeding and therefore tourniquets are usually not used.   

The procedure itself should be performed by excising small burn areas at a time controlling hemostasis in each excised area before continuing on to other areas.  Usually,  a maximum of 18 to 25% of total body surface can be excised at one time.  Normally, this much is only feasibly excised on the first operation if done 1 to 3 days postburn.  Later excisions are usually limited to 9% total body surface or less because of blood loss.  Cautery is typically the first approach to bleeding.  The smaller punctuate bleeding from dermal vessels can often be stopped by application of the skin graft.   The exposed collagen on the dermal surface of the graft stimulates hemostasis.

Other approaches to hemostasis include application of topical thrombin or a solution of 1/10,000 epinephrine.  If epinephrine or thrombin is used, one must be assured of the adequacy of the wound bed before their application, since bleeding ceases, making a subsequent assessment very difficult.  Microcrystalline collagen can also be applied, but a coagulum is left on the wound surface, which should be removed before graft placement. 

Once the wound is excised, the wound bed must be closed.  Usually, immediate application of skin grafts is performed. Sheet or mesh grafts can be used.  Sheet grafts result in a better cosmetic effect but there is an increased risk of bleeding beneath the graft, impeding take while meshing with minimal opening of the mesh allows for drainage of blood or plasma.  Wider meshing is used to cover larger surface areas when there is a shortage of donor skin.  A functional skin will result with a wider mesh but a cosmetic problem is inevitable.   The mesh, used with tangential excision, is usually no greater than 1.5 to 1 to avoid any excessive exposure of viable tissue, especially fat, which can then desiccate and form new eschar.  A temporary skin (allograft or synthetic) substitute can be applied over the graft if a wider mesh, e.g. 3:1 is used to protect the interstices.  A skin substitute can also be used on an area excised and not grafted.  Any neighboring burn must continue to be treated with an antibacterial agent. 

	Mesh graft appearance will diminish with time but will not disappear

The advantages and disadvantages of tangential approach are listed:

Tangential Excision

Advantages:    Optimal functional and cosmetic result    Can be performed rapidly

Disadvantages:    Large blood loss    Difficult endpoint to define    Excise to excise too much or too little

2. Excision to Fascia

Excision of the burn wound to fascia is used in cases of very large full-thickness burns or with very deep burns that extend well into the fat or underlying tissues. This approach is used in the large burn with limited donors for the following reasons.   

First, this endpoint of excision is well defined and graft take is always excellent.  Therefore less experience is required to define an adequately excised wound surface.

Second, wider meshed skin grafts can be used as the fascia appears to be less vulnerable to desiccation than fat or dermis especially when covered with a skin substitute.

Third, a large excision, when performed early, can be done in most body areas (exception being the face and perineum) with only modest blood loss.  In the case of the very deep small wound, excision to this depth or deeper is required because of the extent of the injury itself. 

Excision is performed using a combination of sharp dissection, constant tension, and electric cautery.  The vessels encountered at the fascial plane are fewer in number and larger in size than encountered in a tangential excision and easier to control with cautery and ligatures.  If performed in the first several days, the edema fluid separates fascia from overlying subcutaneous tissue, making excision very easy.  The major bleeding occurs from the wound edge. 

This bleeding can often be better controlled and the exposure of fat on the wound edge minimized if the skin edge is sutured to the fascia.  This form of marsupialization can also decrease the total size of the wound as the edges are pulled toward the middle.  Total excision per operation should be limited to 18 to 20% of total body surface.  Tourniquets are also applicable in cases of extremity excision, especially if delayed for several days, because the endpoint is an anatomic one rather than punctuate bleeding.

Fascial excision becomes less feasible with time after burn injury.  Initially the burn edema layer helps separate the fascial plane from the fat. The reabsorption of edema over 5 to 7 days and the increase in wound blood flow increases the difficulty and risks.  The separation of the fascial plane becomes more difficult.  Beyond 7 days when the eschar is heavily colonized and the subeschar space is infected, fascial excision can be very dangerous.  Complications of bleeding and septicemia will be much higher with time postburn.  It is important to remember that this procedure is usually performed on large burns, and therefore patients tend to be at greater risk for perioperative problems. 

Timing of fascial incision is very important: the earlier the better.

There are a number of disadvantages to this approach that must be outweighed by the advantages.  The major disadvantage is a potential impairment in long-term function to the excised and grafted areas, especially extremities.  Distal edema becomes a problem because of removal of superficial veins and lymphatics.  However, in many cases they have already been heat destroyed.  In addition, removal of cutaneous nerves will lead to impaired sensation.  Sensation on any skin graft is decreased compared with normal skin.  There is, also, a significant risk of injury to other superficial nerves that have motor function.  In addition, exposure of the relatively avascular fascia near joints along with potential exposure of tendons will result in a non-graftable surface that is now prone to desiccation.  Coverage of this area becomes a major problem.  The second problem of fascial excision is cosmetic, since a rim of tissue remains at the edge of the excised and non-excised tissue producing a step up defect, especially on the extremities.  Tapering of the excision at its endpoints can help decrease this problem.  The cosmetic defect is persistent, particularly in the obese patient.  Frequently, a combination of fascial and tangential excision is used in the patient to maximize benefits of early wound closure and minimize complications. 

Once excised, the fascial surface must be covered.  Since donor sites are usually limited, a wider meshed graft is often used.  Skin substitutes are very effective in occluding the fascial wound until the mesh fills in (10 to 14 days) or until new donor sites become available with re-healing (10 to 14 days).

Advantages Can be done rapidly with much less blood loss Well-defined endpoint of excision Can be done using tourniquets Can use wide mesh grafts

Disadvantages           Risk of injury to nerves           Risk of increasing distal edema           Risk of exposing joints, tendons           Cosmetic defect

C.   Obtaining Skin Grafts (Donor Sites)

Donor sites are obtained wherever unburned skin is available (exception: face, hands).  Preferred areas are thighs, buttocks, and abdomen.  However, large burns have limited donors and other areas need to be used, e.g. arms, lower legs, back and soles of feet.  The scalp is an excellent donor site when needed.  As opposed to most other areas that require 14 days or more to heal sufficiently before reuse, scalp heals in 7 days and can be re-harvested 3 to 4 times.  The only area in which color match between donor and recipient site is of significant concern is the face and neck.  Upper chest and upper back are a good color match for face and neck.  Split-thickness skin can be removed using a variety of dermatomes.  Air pressure driven or electric powered dermatomes are the most common.  Small free hand skin grafts can also be obtained using the Goulian knife used for tangential excision.  Injection of saline beneath the dermis will greatly assist the removal of split-thickness skin from areas around changes in contour or from the scalp.

Depth is usually the upper third of the dermis which includes mainly papillary dermis, leaving sufficient number of epidermal cells, in skin appendages, to heal. 

Bleeding from a donor site is similar in amount to that of tangential excision of a fresh, deep dermal burn, i.e., diffuse, punctuate, and profuse.  Bleeding from a re-use donor is even more profuse and again an analogy can be made with tangential excision of a hyperemic wound.  Because blood loss will be substantial, hemostasis at the donor site should be controlled before pursuing wound excision.  The ideal situation is the use of two teams, one whose role is to obtain skin grafts and maintain hemostasis.  Pressure followed by application of fine mesh gauze or Xeroform gauze, again followed by pressure (1 to 2 minutes), is usually adequate to control bleeding.  As with the excised wound, topical thrombin or dilute epinephrine solution can also be used. 

A number of dressings can be used on donor sites.  Fine mesh or grease gauze is porous and allows the initial bleeding to exit from the wound surface as well as the exit of blood and plasma that leak during the postoperative period.  Gauze, however, is not flexible and is not sufficiently occlusive to control pain.  In fact, ambulation or motion is very difficult with donor sites covered with these dressings.  In addition, there are minimal to no antibacterial properties, increasing the potential for infection if nearly open burn wounds are present.  Application of moist antibiotic-moistened gauze over the xeroform for 24 to 48 hours assists in removal of blood beneath the dressing as well as provides antibacterial protection.  Dilute bacitracin, neomycin, or mafenide solutions have been used with success.  After 2 to 3 days, the donor site should be left exposed and the dressing allowed to dry.  The exception would be if an open wound is adjacent, in which case the antibacterial solution should continue or the wound should be occluded from nearby burn.  Gauze dressings are applied over the donor site covered by an outer moderate compression dressing to maintain hemostasis.  The outer dressings are changed until the wound can be exposed to air.  Grease gauze impregnated with antibacterial ointment, e.g., scarlet red, provides some protection against infection, but it also  impairs removal of clot or exudates because of the multiple layers of gauze used.  An effective alternative dressing is a skin substitute, such as biobrane or polyurethane dressing such as Opsito.  The skin substitute will provide a seal, thereby eliminating the risk of external infection as well as diminishing pain.  Disadvantages, however, are that excellent hemostasis must be obtained before application.  In addition, these dressings have no antibacterial properties.  This is less of a problem with biobrane if adherence to the wound is good.  Dry dressings and moderate compression maintain hemostasis while allowing optimum wound adherence over the first 24 to 48 hours.  The inner donor site dressing is gradually removed at 10 to 14 days with re-epithelialization.

It is best to place grafts on the wound at the time of excision.  Since the graft itself controls hemostasis and protects the wound, it makes little sense to wait 24 to 48 hours until bleeding has stopped. This approach requires an additional procedure and there is a significant risk of the wound bed becoming desiccated or reinfected.

Even if skin meshing is not going to be performed, a number of small slits can be placed along the skin lines to allow efflux of any blood or plasma that collects.  Grafts are best placed longitudinally in most areas and transversely across the joints to match the normal skin lines and forces during movement.  It is better to have a slight overlap of skin on the wound rather than to leave excised wound uncovered.  Hypertrophic scarring will result and most evident at the edges of the graft, especially if a ridge of open wound is left to heal primarily.  It is important to avoid the edges of the graft from rolling up, thereby preventing skin adherence in this area.  Adjacent grafts should be carefully approximated.  Sutures can be used but are very time consuming.  Staples or Steri-strips usually work very well to secure the graft in place.

E.   Wound Conversion

This term refers to the dynamic process whereby the Zone of Injury progresses to the Zone of Tissue Necrosis thereby deepening the wound. Conversion is more likely with a mid to deep dermal injury because of less blood flow, longer time to healing and increased risk of excess inflammation and infection. Also environmental hazards can readily lead to conversion of an open wound.

Sect. VISect. VIiI