Burn Wound Bacteriological Profiles, Patient Outcomes, and Tangential Excision Timing: A Prospective, Observational Study

Purpose: Because infection can thwart burn healing, microorganisms, their susceptibility patterns, and the effect of tangential excision timing on outcomes of burn patients were examined.Methods: A prospective, observational study was conducted that involved 318 patients with deep second-degree burns from a gas explosion treated in Xinxiang, Henan, China between January 2009 and December 2016. Patient demographic data, culture and antimicrobial susceptibility test results, and outcome variables (resuscitation fluid volume, signs of shock, body temperature, heart rate, and time to wound healing) were analyzed. Outcomes were compared among patients who had early (<24 hours), middle (2 to 7 days), and late (> 7 days) post burn excision. Results: Bacterial culture and drug sensitivity data were available for 314 of the 318 persons with burns >10% of total body surface area (TBSA). Of the 486 bacterial isolates, 330 (67.9%) were gram-negative and 156 (32.1%) were gram-positive. The number of isolates and resistance to third-generation cephalosporins increased over time. Patients having early tangential excision had significantly lower heart rate (P <.05) and reduced time to healing (P <.01) than patients in the middle or late excision group. Conclusion: Early tangential excision was found to be safe and to facilitate healing. 

Burns are one of the most common emergency events and global public health problems.¹ Resistance from the disruption of mechanical epithelial integrity can render patients with burns susceptible to the complications of infection.² Lipový et al³ investigated the prevalence of infection complications in burn patients; among 134 patients, 92 had infection complications. A prevalence study by Abbasi-Montazeri et al² regarding Staphylococcus aureus infection in a burn center highlighted the need for antibiotic susceptibility monitoring of methicillin-resistant S aureus. A retrospective study⁴ found infection remains the greatest danger for burn patients despite great advances in antimicrobial therapy over past decades. A prospective study⁵ indicated that infections in burn patients may lead to delays in wound healing, graft losses, and the development of sepsis. For example, Acinetobacter baumannii is an important pathogen causing infections in burn patients; multiple factors contribute to the multidrug resistance of A baumannii.⁶ A combination of an early diagnosis of wound infection, appropriate antimicrobial treatment, surgical debridement, and early wound closure may be effective in infection management.^7,8 

A retrospective study⁹ investigated visceral injuries, wound infection, and sepsis in 226 patients who sustained electrical burns. Mortality following burn injuries was shown to be likely due to infection; although a gradual decrease in mortality rates was observed over the last 5 years, mortality rates due to sepsis showed a slower decline. To support crucial treatment decisions, it is important to determine the bacterial microorganisms responsible for the infection of burn wounds, their prevalence, and their drug resistance state. Glik et al¹⁰ retrospectively analyzed the hospital notes of 388 patients with thermal injuries and found patients with sepsis caused by gram-negative bacteria are at higher risk of death than patients with infections caused by gram-positive bacteria. 

In the case study by Ma et al,¹¹ eschar formation was noted in burn injuries, which may be either superficial or deep. The presence of nonviable eschar not only serves as a physical barrier to wound healing, but it also is known to support significant bacterial growth.¹² Hence, per their prospective  study, Lawrence and Carney¹³ recommended surgical debridement of eschar. A retrospective study¹⁴ (N = 71) showed burns from a gas explosion, in which serious internal and combined injuries occur, have a higher prevalence of disseminated infection and mortality than other types of burns.

In contrast to excising burned skin down to fat or deep fascia, tangential excision involves first removing the necrotic tissue from the burn wound followed by covering with heterogeneous skin (irradiated pigskin) after excision.¹³ The bacterial profile of burn wounds and the safety and effectiveness of early tangential excision is unclear. The purpose of this study was to assess microorganisms and their antimicrobial susceptibility patterns from burn wounds of patients injured by gas explosion and to determine the most beneficial timing of tangential excision for these patients.

Study design and participants. A prospective, observational study was conducted among patients injured by gas explosion between January 2009 and December 2016. All patients with burn wounds injured by gas explosion who were admitted to the Research Center of Trauma and Orthopedics, Xinxiang Medical University, Henan, China, were considered eligible for participation regardless of age or diagnosis. This study was conducted in accordance with the Declaration of Helsinki and the approval of the Ethics Committee of Xinxiang Medical University. Written informed consent was obtained from all participants’ and/or their guardians. If consent was granted, the patient was enrolled. 

Bacterial identification. Samples isolated from wound, sputum, and blood to identify bacterial species and perform antimicrobial susceptibility testing were analyzed. Bacteria were cultured in an enrichment broth medium at 35˚ C for 4 days. When the medium became cloudy, bacteria were transferred onto blood agar for another 24 hours. Isolation was performed by conventional methods according to the National Clinical Test Operation Regulation.¹⁵ The isolates were identified with the Sceptor bacterial identification instrument (Becton Dickinson, Franklin, NJ).

Antimicrobial susceptibility test. Bacterial culture and drug sensitivity experiments were performed on persons with burns covering >10% total body surface area (TBSA). The Kirby-Bauer test was performed according to National Committee for Clinical Laboratory Standards criteria to determine antimicrobial susceptibility. Paper discs with different antimicrobial drugs (Oxoid; Thermo Fisher Scientific, Waltham, MA) were utilized. The rate of drug resistance was calculated as a percentage of drug-resistant bacteria. The wound bacterial culture and drug sensitivity tests were performed 6 to 14 days after the patient was burned.

Tangential excision. 

Grouping. Participants were divided into 3 groups depending on when tangential excision was performed in accordance with previous observational studies^16,17: group A received tangential excision during the early stage (<24 hours postburn), group B during the middle stage (2 to 7 days postburn), and group C during the late stage (>7 days postburn). All patients who had not received previous treatment were provided routine debridement once admitted to the study.

Additional treatment. Silver sulfadiazine cream was used topically and fluid resuscitation was applied according to the Ruijin formula^18,19 as follows: during the first 24 hours after injury, electrolytes were supplemented at 1.0 mL/kg/% TBSA and colloids at 0.5 mL/kg/% TBSA, with 2000–4000 mL basic water. During the second 24 hours, the amount of supplemented electrolytes and colloids was halved, with no change to the volume of basic water. The electrolytes comprised Ringer’s lactate solution, physiological saline, 50 g/L sodium bicarbonate injection, plasma, and 50 g/L glucose injection. According to accepted principles of administering electrolytes followed by colloids, electrolytes were administered quickly, followed by the slow administration of colloids.

Tangential excision procedure. Tangential excision involves removing the necrotic tissue from the burn wound and covering the wound with heterogeneous skin after excision. Methylene blue dye (5 g/L) was used to discern the necrotic tissue to remove. All patients received autologous skin grafts 5 to 7 days postoperation.

Clinical parameters. Five (5) clinical parameters were measured.

Resuscitation fluid volume. Resuscitation fluid volume was the amount of balanced blood supplemented during the first 3 days postburn according to the Ruijin rehydration formula.^18,19 The criteria for rehydration was judged as follows: urine volume >1 mL/kg/h, mean arterial pressure >65 mm Hg (1 mm Hg = 0.133 kPa), heart rate <120 times/minute, and central venous pressure of 0.8 to 1.2 kPa.

Signs of shock. Shock was considered to have occurred if the following were noted: weak pulse of the dorsalis pedis artery, abnormal peripheral circulation, heart rate >120/minute, and urine output <30 mL/hour.

Additional signs. Body temperature and heart rate were noted during the shock and rehydration phases, urine output was assessed during shock phase, and wound healing time was determined. 

Statistical analysis. The data were presented as mean ± SD and entered into and analyzed by SPSS, version 18.0 software (SPSS Inc, Chicago, IL). Differences between groups were analyzed by single-factor analysis of variance, and the t test was used for pairwise comparisons. Differences with P values <.05 were considered statistically significant.

Patient inclusion. Consent rate for participation was 91.0%. Of the 346 total cases, 318 patients (316 men, 2 women, age 31.1 + 2.1 years) were enrolled and underwent tangential excision at the General Hospital of Pingmerishenma Medical Group, which is affiliated with the Medical University of Xinxiang. The average burn area (% TBSA) was as follows: 136 patients <20%, 115 between 20% and 49%, and 16 with 80% to approximately 98%. The basic characteristics of patients are shown in Table 1. Bacterial culture and drug-sensitivity testing were performed on 314 patients with TBSA >10%. 

Identification of bacteria from wound samples. The culture from wound samples yielded 486 bacterial isolates, of which 330 (67.9%) were gram-negative and 156 (32.1%) were gram-positive. The top 10 isolates in each year are shown in Tables 2, 3, 4, and 5. Pseudomonas aeruginosa was the most common isolate followed by Klebsiella pneumoniae for gram-negative bacteria. S aureus was the most common isolate for gram-positive bacteria. A total of 38 fungal isolates was obtained from the burn wounds, most of which were of the Candida spp. These included 19 isolates of Candida albicans, 10 isolates of Candida tropicalis, 5 isolates of Torulopsis glabrata, and 4 isolates of other types.

Drug resistance. The rate of drug resistance was analyzed using the antimicrobial susceptibility test. The schedule was as follows: 83, 58, 39, 31, 29, 25, 20, 16, and 13 cases were cultured and tested at postburn days 6, 7, 8, 9, 10, 11, 12, 13, and 14, respectively. The drugs tested included ampicillin, amikacin, cefazolin, cefoperazone, ceftazidime, imipenem, piperacillin, vancomycin, and levofloxacin.

The most common isolated bacterial organisms with drug resistance included P aeruginosa, K pneumoniae, Enterobacter cloacae, Escherichia coli, A calcoaceticus, Proteus mirabilis, Citrobacter strains, S aureus, Enterococcus strains, and Streptococcus pyogenes. The drug exhibiting the highest drug resistance was cefazolin (1928 cases), followed by ampicillin (1784 cases) and amikacin (1269 cases). By contrast, the lowest number of cases of drug resistance was against imipenem, with 541 cases (see Table 6). 

Basic condition of postburn patients. Resuscitation fluid volume did not differ significantly at 1 to 3 days postburn among the 3 groups (P >.05). Urine output was higher in group A than in groups B and C, both at 1 day postburn (P <.05) and 3 days postburn (P <.01) (see Table 7). 

The incidence of shock was not significantly different among the 3 groups (21 cases in group A, 15 cases in group B, and 8 cases in group C; P >.05).

At 7, 10, and 14 days postburn, heart rate was significantly higher in groups B (116.4 ± 112.58, 104.52 ± 15.36, 100.33 ± 14.21, respectively) and C (119.6 ± 212.82, 110.38 ± 16.22, 104.67±13.58, respectively) than in group A (101.24 ± 12.36, 96.38 ± 14.66, 90.28 ± 8.92, respectively) (P <.05) (see Table 8). 

The wound healing time in group A was 19.08 ± 5.31 days, which was significantly shorter than that in groups B (29.36 ± 7.03 days; P <.01) and C (31.62 ± 7.18 days; P <.05).

Infection with multidrug-resistant organisms remains the leading cause of morbidity and mortality in burn patients; these organisms have been reported in prospective studies^20,21 as the frequent cause of nosocomial outbreaks of infection in hospital burn units or as colonizers of the wounds of burn patients. Prospective studies^22,23 also have shown several factors, including the presence of coagulated proteins, the avascularity of the burn wound, and the resultant absence of blood-borne immune factors make burn wounds susceptible to opportunistic colonization by bacteria and fungi.

In the present study, contamination of burn wounds also occurred at a high rate. The results showed gram-negative bacteria predominated (67.9%) in burn wounds of patients, compared to gram-positive bacteria (32.1%), which is consistent with a previous retrospective report.²⁴S aureus, Enterococcus strains, and S pyogenes were the main isolates of gram-positive bacteria before 2002, with S aureus exhibiting a progressive rise over the subsequent 4 years. P aeruginosa, K pneumoniae, and E cloacae were the main isolates of gram-negative bacteria. P aeruginosa, K pneumoniae, and E  cloacae were the main isolates of gram-positive bacteria in this study. The detection rate of E cloacae and A calcoaceticus was increased and both these species exhibited multidrug resistance.

The types of isolated species increased over the 8 years of the study. This could be related to the wide use of broad-spectrum antibiotics, which resulted in the inhibition of predominant sensitive bacteria, allowing the propagation of resistant bacteria that were previously disadvantaged. The predominance of P aeruginosa, K pneumoniae, and S aureus did not necessarily indicate the improper use of antibiotics²⁵ but was probably correlated with the widespread distribution of bacteria and increase in drug resistance. Bacteria in sputum samples were detected at the same rate as in wound samples, suggesting severe lung infection of patients burned by gas explosion, as noted in a prospective study.²⁶ This could be caused by respiratory tract burn when the patients cried out. The present study found the distribution of organisms was consistent with that of a cross-sectional study²⁰ and a prospective study.²⁸ 

An in vitro study by Sasidharan et al²⁸ found a variety of bacteria became resistant to third-generation cephalosporins. Although many third-generation cephalosporins were applied, no fundamental improvement was achieved. The ubiquitous occurrence of multidrug resistance could be due to the empirical use of broad-spectrum antibiotics; a retrospective study²⁹ has shown the mechanisms were proven to be based on β-lactamases, suggesting the importance of determining the predominant microorganisms and their antimicrobial susceptibility pattern in patients burned by gas explosion.

According to retrospective analysis^30,31 over 10 years, active removal of necrotic tissue and wound closure are basic principles of treatment for deep burns. Prospective analysis²⁶ showed deep second-degree burn wounds could heal with the rapid growth of residual epithelial tissues. According to a prospective study,³² infection tends to occur in patients with extensive deep second-degree burns during the removal of eschar, which may endanger life. Therefore, the treatment of deep second-degree burns is a problem. A retrospective study³³ indicated that delayed tangential excision to increase local interleukin 8 levels deepens the necrotic wound, thus converting deep second-degree burns to deep third-degree burns and preventing the healing process. Early tangential excision has the potential to resolve local inflammation and increase the level of epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor, which promote wound healing. A Cochrane review³⁴ recommended treatment with tangential excision 3 to 5 days after conventional dressing with pertrolatum-impregnated gauze. Early tangential excision has been recommended and adopted to retain viable deep dermis tissue.³⁵

In the current study, tangential excision was provided during the shock phase and shifted the excision time to 24 hours post-burn with no increase in complications noted. No significant difference was noted in the resuscitation fluid volume and the incidence of shock among the 3 groups. The patients who underwent early tangential excision exhibited better body temperature and heart rate, suggesting that tangential excision within 24 hours after burns was more beneficial than later excision. Urine output was higher in the early excision group than in the other groups; this could be because of the removal of necrotic tissue, reduction of wound exudate, and resolution of edema. The wound healing time was reduced by 10 days in the early tangential excision group.

The present study is prospective in nature, and the data may have inherent flaws unknown to the current researcher. Tangential excision was performed by different surgeons, which may have had an effect on the complication rates.

This prospective study investigated microorganisms and their susceptibility patterns found in the burn wounds of patients injured by gas explosion. Results showed early tangential excision (within 24 hours after the burn) was a safe and effective treatment. The majority of pathogens were found to be gram-negative bacteria. In this study, early tangential excision within 24 hours after burns was safe and effective for promoting the wound healing process of deep second-degree burns caused by gas explosion. Bacteria-sensitive antibiotics should be used early in the clinical treatment of patients with gas explosion injuries.

Potential Conflicts of Interest: none disclosed

Dr. Shao is a chief physician, Department of Cardiology, General Hospital of Pingmei Shenma Medical Group, Pingdingshan, China. Dr. Ren is a director, Research Center of Trauma and Orthopedic, Xinxiang Medical University, Xinxiang, Henan, China. Mr. Meng is an associate chief physician, Department of Cardiology, General Hospital of Pingmei Shenma Medical Group; and an associate professor, Research Center of Trauma and Orthopedic, Xinxiang Medical University. Ms. GZ Wang is an associate chief physician; and Dr. TY Wang is a professor, Research Center of Trauma and Orthopedic, Xinxiang Medical University.

Please address correspondence to: Wen-Jie Ren, PhD, and Tian-Yun Wang, PhD, Research Center of Trauma and Orthopedic, Xinxiang Medical University, Xinxiang, Henan, China; email: wtianyuncn@126.com