Pathophysiology of the burn wound

The pathophysiology of the burn wound is characterized by an inflammatory reaction leading to rapid oedema formation, due to increased microvascular permeability, vasodilation and increased extravascular osmotic activity. These reactions are due to the direct heat effect on the microvasculature and to chemical mediators of inflammation. The earliest stage of vasodilatation and increased venous permeability is commonly due to histamine release. Damage to the cell membranes partly caused by oxygen-free radicals released from polymorphonuclear leucocytes would activate the enzymes catalyzing the hydrolysis of prostaglandin precursor (arachidonic acid) with rapid formation of prostaglandin as the result. Prostaglandins inhibit the release of norepinephrine and may thus be of importance in modulating the adrenergic nervous system which is activated in response to thermal injury. The morphological interpretations of the changes in the functional ultrastructure of the bloodlymph barrier following thermal injury seem to be an increase in the numbers of vacuoles and many open endothelial intercellular junctions. Furthermore changes of the interstitial tissue after burn trauma are of great importance. The continuous loss of fluid from the blood circulation within the thermally damaged tissue causes increased haematocrit levels and a rapid fall in plasma volume, with decreased cardiac output and hypoperfusion on the cellular level. If the fluids are not adequately restored burn shock develops. Furthermore, the burn wound provides a vast area of entry of surface infection with a high risk of septic shock. Four main principles are of utmost importance in the current management of patients with severe thermal injury, namely early wound closure, prevention of septic complications, adequate nutrition and control of the external environment.     

Management of the burn wound

Thermal injury sets off a chain of pathophysiologic events that evolve into the problems encountered in management of the burn wound. This article reviews those events and presents a method of caring for wounds sustained from thermal injury.     

Monitoring free flap perfusion by serial fluorometry

An efficient method to evaluate the patency of microvascular anastomoses and to predict flap viability is crucial when free flaps are used in reconstructive surgery. We report a study of 60 neurovascular island flaps in rats where the nutrient artery and/or vein were transected and anastomosed. Fluorescein dye was injected immediately after anastomosis, and the uptake and elimination of dye were quantified at 5-minute intervals with the fiberoptic perfusion fluorometer. Analysis of dye delivery clearly identified six hypofluorescent flaps presumed to be ischemic. In five of these flaps, revision was attempted. Three evidenced improved fluorescein uptake and elimination on reinjection of dye. These flaps survived, whereas the other two necrosed. Of the 54 flaps deemed patent after the first injection, two evidenced poor fluorescence on reinjection 3 hours later. These flaps necrosed and evidenced venous thrombosis (which probably occurred during the 3 hours between the first and second injections). Fiberoptic fluorometry can be employed to assess a free flap immediately after vascular anastomosis and throughout the critical hours postoperatively. Assessment of uptake and elimination after single or serial injections reflects flap perfusion and predicts viability with a high degree of accuracy.     

Closing the burn wound.

With recent advances in supportive therapy and surgical care, closure of the burn wound now can be accomplished earlier and more effectively than previously. Only by keeping the patient in a state of positive nitrogen balance, immunologically competent, and in equilibrium with the bacteria colonizing the burn wound can early wound closure be carried out with a minimal number of postburn complications.     

烧伤创面与糖尿病溃疡创面的比较

目的比较烧伤创面与糖尿病溃疡创面的差异，初步分析糖尿病患者溃疡创面难愈的机制。方法分别切取非糖尿病烧伤患者的足部创面（对照组）和糖尿病患者的足部溃疡创面（试验组）组织，行组织块培养。用酶联免疫吸附测定（ELISA）法、反转录-PCR法分别检测创面组织释放的成纤维细胞生长因子2（FGF2）、血管内皮生长因子（VEGF）蛋白质及其mRNA水平；免疫组织化学法检测创面微血管密度（MVD）的变化。人脐静脉内皮细胞分别在含5mmol／L葡萄糖的培养液（正常培养液组）、含30mmol／L葡萄糖的培养液（高糖组）、含30mmol／L甘露醇的培养液（甘露醇组）中培养7d，以ELISA法测定VEGF蛋白质水平。结果对照组患者FGF2、VEGF蛋白质水平分别为（59±3）ng／ml、（56±7）pg／ml，试验组2种蛋白质水平分别为（89±6）ng／ml、（108±5）pg／ml，组间比较差异均有统计学意义（P〈0．05或P〈0．01），mRNA比较结果与蛋白质相似；2组的MVD水平，差异亦有统计学意义（P〈0．05）。体外细胞培养时当培养液含FGF2，高糖组与正常培养液组的VEGF蛋白质水平相近（P〉0．05）；移去FGF2后2、5d，正常培养液组该指标明显高于高糖组（P〈0．05或P〈0．01）。结论糖尿病患者溃疡创面难愈与血管化受到抑制以及调控血管生长的因子低表达密切相关。     

Primary excision of the burn wound

Early excision of burn eschar and wound closure significantly improves survival following major burn injury. Immediate primary excision performed by burn-experienced surgeons in dedicated burn care facilities can reduce further morbidity and mortality, length of hospital stay and medical costs. Burn care at the millennium is evolving rapidly into a subcategory of trauma surgery, with burn patients increasingly being viewed as victims of major trauma who benefit most from immediate and definitive surgical correction of their injuries.     

Fungal infection of the burn wound

Six of 92 patients with invasive mycotic infection of the burn wound survived. These patients demonstrate the value of prompt diagnosis and expeditious debridement of the infected tissue in successfully managing this dangerous infection.     

Burn wound coverage and burn wound closure

Early excision and grafting changed dramatically topical wound treatment, but are restricted by difficulty in diagnosing burn depth, by limited donor sites and by technical skills to excise special areas (perineum, face). In addition to the extent of burn and the age of the patient the depth is determinant of mortality, morbidity and of patient's quality of life. It results from the time-temperature relation and is further influenced by local and systemic causes of conversion: dehydration, edema, infection and shock hypoxia, metabolic derangements, peripheral vessels diseases may contribute do deepening of burn wound. Superficial burn on day one appears deep dermal by day three, where spontaneous epithelization lasts much longer than 21 days and results in hypertrophic scarring. To prevent this sequelae deep dermal burn may be treated like full-thickness injury with excision and autografting. Another way is removal of dead layers of corium and using biological or synthetic cover. We have found a more effective way to reach wound closure (not only cover) in the method of "upside-down" application of recombined human/pig skin (RHPS), composed of allogeneic human keratinocytes cultured on cell-free pig dermis. The allogeneic epidermal cells temporarily "take", "close" the excised wound and simultaneously encourage epithelization from adnexa remnants in the wound bed. Thus definitive closure is achieved.     

Dermal ischemia in the burn wound

Rats receiving full-thickness burns were studied by postmortem angiography of the burn wound. Immediately postburn, the circulation was found to be patent and unchanged from unburned controls. Vascular compromise was found to be progressive over 24 hr, with the first evidence of disruption between 2 and 4 hr postburn. Animals were then given heparin postburn with no change in the pathologic process. However, when animals were pretreated with heparin, the vascular integrity was spared up to 72 hr postburn. The authors speculate that some tissues in the burn wound are not irreversibly destroyed at the time of injury but die later as a result of an ongoing pathologic process. They further speculate that there is a prepathologic period during which this process may be reversed or prevented by pharmacologic manipulation. The prepathologic period may last up to 4 hr postburn.     

Evaluation of a bi-layer wound dressing for burn care I. Cooling and wound healing properties

Severe burns remain a significant cause of morbidity and mortality despite the availability of numerous therapies. We assessed the wound healing and skin-cooling properties of a DRDC hydrogel/polyurethane wound dressing using different pre-clinical models. Our results show that 85% of partial-thickness, non-contaminated porcine wounds treated with our dressing healed within 6 days. In contrast, 85% of the wounds treated with commercial dressings healed within 8 days. Application of a moist DRDC dressing (to simulate a condition of exudate absorption) on a scald burn covering 25% of the dorsal area in rats reduced skin temperature by 1.70 +/- 0.14 degrees C for 5 min, the skin temperature being comparable to that of control burned rats after 20 min. The application of a moist DRDC dressing did not induce significant differences in body temperatures compared with that of burned animals without dressing coverage throughout the 90-min experiment. While no change in body temperatures were observed when standard dressings (i.e., not pre-moistened) were applied, skin temperature increased gradually. These data show that our dressing is effective in promoting faster healing of the treated wound; and providing a transient, but beneficial cooling effect to the skin contact-site, without the adverse effect of inducing whole-body hypothermia.     

Bacterial control in the burn wound

The goal in the treatment of septic burn wounds, as in any infection, is to reestablish the normal balance between the bacteria and the host defense. This is readily done by controlling the numerical level of bacteria while expending all efforts to remove irreversibly damaged tissue and obtaining a closed wound by autograft with the patient's own skin as rapidly as possible.     

Excision of the burn wound in patients with large burns

The known major determinants of survival for patients with burn injury are age, burn size, inhalation injury, and infection. The clinical courses of 210 patients with burns of 30% of the body surface or greater treated from Jan 1, 1983, through Dec 31, 1985, were reviewed to determine whether excision of the burn wound could be identified as a factor in survival after massive burn injury. The predominant site of infection changed from the burn wound to the lung, with pneumonia being the most common bacterial infection in patients whose wounds were treated as described. Effective topical control of bacterial proliferation and excision of the burn wound have resulted in replacement of invasive bacterial wound infection by nonbacterial burn wound infection. The apparent advantages of excision, particularly in large burns, may reflect only patient selection, since only those patients who are considered to be physiologically stable and able to tolerate the physiologic stress of excision are considered for operation.     

Débridement of the burn wound with sutilains ointment

Twenty-one patients with fresh full-thickness burns received a course of two daily applications of sutilains ointment to an area of their burn wound not exceeding 9 per cent of the body surface. Twelve had a mirror-image control burn site of equivalent depth and extent, which was treated identically except sutilains applications were omitted. Good débridement, defined as a wound free of adherent eschar, was observed in 9 patients (43 per cent). The remaining patients' wounds had adherent eschar at the end of the test, or demonstrated equal débridement of both the test and control site. Good débridement was not promoted by increasing the frequency of wet dressings between sutilains applications. Débridement was better in patients receiving more than 8 days of applications. A higher percentage of patients receiving silver sulphadiazine demonstrated good débridement than those receiving gentamicin or no topical antibacterial agent. Burn wound bacterial colonization pattern in sutilainstreated patients did not vary from that observed in those patients receiving only topical antibacterial agents alone.Histological examination revealed that areas with good débridement showed an intense inflammatory cell response and dissolution of the elastic fibres. Control sites and areas with poor débridement showed a lesser inflammatory response and preservation of elastic fibres. No explanation for the variable response to sutilains was apparent histologically. Because of pain associated with application, cost and the unpredictability, sutilains should not be used indiscriminately without monitoring its response carefully and should be used only in conjunction with a topical antibacterial.     

Aspergillus infection of the burn wound.

During a 15-year period, 18 patients with major burns developed a wound infection due to Aspergillus. Ages averaged 28 years, extents of burn were 54% (14-97%) BSA for total surface involvement and 42% (14-85%) BSA for full-thickness injury. Pseudomonas sepsis preceded Aspergillus infection in 16 cases. Thirteen of the episodes occurred in three epidemics, each apparently related to contaminated air-conditioner ducts and filters. Treatment was based upon wound excision in all 18 patients, with recurrence initially in each. Topical and parenteral antifungal agents were never individually successful in controlling the infection. Whenever fungal sepsis involved an extremity alone and thus amputation could rid the body of the entire infected site, survival could then be achieved. The overall mortality rate was 78%. Protection of the wound from Aspergillus colonization appeared to be the only reliable method of preventing this often lethal fungus infection.