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. Author manuscript; available in PMC: 2023 Aug 3.
Published in final edited form as: Shock. 2022 Aug 3;58(2):103–110. doi: 10.1097/SHK.0000000000001965

Evaluating sepsis criteria in detecting alterations in clinical, metabolic and inflammatory parameters in burn patients

Carly M Knuth 1, Sarah Rehou 3,4, Dalia Barayan 1, Marc G Jeschke 1,2,3,4,*
PMCID: PMC9529909  NIHMSID: NIHMS1822525  PMID: 35953463

Abstract

Sepsis has become the leading cause of death in burn patients. Furthermore, sepsis and septic complications result in significant morbidities and longer hospitalization, which has profound impacts on the healthcare system. Despite this, sepsis in burn patients is surprisingly poorly understood and characterized. This retrospective, single-institution cohort study aimed to increase our understanding of the septic response after burns. We hypothesized that different sepsis definitions will results in distinctive septic trajectories and biochemical patterns after injury. Sepsis was defined by our burn centre-specific prospective definition, the American Burn Association criteria, Sepsis-3 criteria, and the Mann-Salinas criteria. Applying these definitions, we compared clinical, metabolic, and inflammatory markers in septic and non-septic burn patients. We found that the Sepsis-3 criteria is the most reliable screening tool used prior to clinical diagnoses for detecting sepsis trajectories and biochemical patterns. Moreover, we characterized distinct temporal alterations in biomarkers during the pre-and post-septic periods in burn patients, which may be incorporated into future sepsis definitions to improve the accuracy of a sepsis diagnosis in burn patients.

Keywords: Burns, Sepsis, Inflammation, Metabolism

Introduction

Despite overall improvements in the survival rate of burn patients in recent decades, the number of deaths attributed to sepsis remains unacceptably high. During sepsis, a dysregulated host response to infection invokes a series of systemic complications, such as lean and fat mass catabolism, tachycardia, and profound whole-body inflammation, ultimately leading to life-threatening organ dysfunction 19. Sepsis in burn patients poses a significant diagnostic challenge as the symptoms of severe burns parallel that of sepsis in the general population 10. All patients with burns encompassing over 20% of total body surface area (TBSA) exhibit persistent systemic inflammatory response syndrome (SIRS), which is often used to define classical sepsis. This is due to the unique hypermetabolic response triggered by severe burns, which persists long after wound closure and may be present for up to 3 years 15. Given that the presence of SIRS criteria would indicate sepsis at baseline, burn patients have been historically excluded from study populations that have described sepsis definitions. As a result, the diagnosis and management of sepsis in burn patients remain poorly understood and inadequately characterized.

The current study aims to increase our knowledge and understanding of sepsis and its pathophysiologic response in burn patients. Based on previous work 33, we hypothesize that different sepsis definitions will result in distinctive septic trajectories and biochemical patterns after injury. Moreover, we propose that identifying biochemical markers will not only help provide insight into the pathological changes underlying sepsis in burns, but will also validate the clinical pattern of different diagnostic definitions. To test this, we identified septic burn patients based on the main definitions that are currently being used clinically: the American Burn Association (ABA; 11) sepsis criteria, the Mann-Salinas et al. Novel Predictors of Sepsis (Mann-Salinas; 22), and the Third International Consensus Definition for Sepsis and Septic Shock (Sepsis-3; 29), which was updated in 2016 to utilize the Sequential Organ Failure Assessment (SOFA) rather than SIRS criteria (Table 1). Additionally, we incorporated our burn center-specific definition that prospectively identifies septic patients. Subsequently, we compared septic burn patients according to each definition in terms of demographics, clinical and biochemical markers.

Table 1:

Sepsis Definitions.

American Burn Association (ABA) Sepsis Criteria Mann-Salinas et al. Novel predictors of sepsis Sepsis-3 Consensus Definition for Sepsis and Septic Shock
Includes at least three of the following triggers:  1. Tachycardia, >130bpm qSOFA ≥2:
 I. Temperature, >39° or <36.5°  2. Mean Arterial Pression <60mm Hg  1. Altered mental state
 II: Progressive tachycardia, >110bpm  3. Base deficit <−6mEq/L  2. Respitory rate ≥22 breath/min
 III: Progressive tachypnea, >25bpm not ventilated  4. Temperature <36°  3. Systolic blood pressure ≤100mm Hg
 IV: Thrombocytopenia, 3d post-initial resuscitation, <100,000/uL  5. Use of vasoactive medications SOFA ≥2:
 V: Hyperglycemia without pre-existing Type II diabetes  6. Blood glucose >150mg/dL  1. PaO2/FiO2 Ratio
 VI: Inability to continue enteral feeding >24h  2. Glasgow Coma Scale
Additionally, a documented infection of at least one of the following:  3. MAP
 1. Culture positive  4. Vasopressin requirements
 2. Pathologic tissue source identified  5. Serum creatinine or urine output
 3. Clinical response to antimicrobial drug  6. Bilirubin
 7. Platelet count
Septic Shock:
1. Vasopressors required to maintain MAP ≥65mm Hg, AND
2. Serum lactate concentration >2mmol/L
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MAP: Mean arterial pressure; SOFA: Sequential organ failure assessment; qSOFA: quick SOFA

Methods

Study Design and Participants

This was a retrospective, single-institutional cohort study involving burn patients admitted to the Ross Tilley Burn Centre at Sunnybrook Health Sciences Centre over a span of 10-years. The study protocol was approved by the Sunnybrook Research Ethics Board (Approval #194–2010). Subjects were selected using the following inclusion criteria: adult patients (≥18 years), ≥10% TBSA burns, and patients that survived ≥72-hours post-admission. From this, we identified a total of 316 patients who met these criteria. Further, 64 patients (20%) were diagnosed with sepsis during the acute hospitalization period.

As described previously 33, the Ross Tilley Burn Centre clinical diagnoses of sepsis (RTBC) were prospectively identified by a team of burn care specialists and physicians while considering the patient’s complete medical profile. The parameters used to indicate sepsis diagnosis included tachycardia, hyperglycemia/ hypoglycemia, enteral feeding intolerance, wound infections, alterations in temperature, radiologic or microbiological features of infectious source, vasopressor dependency, hemodynamic instability, need for active resuscitation, and administration or response to systemic antibiotics. Prospective clinical diagnoses served as a reference standard for this study. Subsequently, medical records were screened to retrospectively identify whether RTBC-diagnosed septic patients met the criteria for ABA, Mann-Salinas, and Sepsis-3 definitions of sepsis (Table 1). Diagnosis with these criteria occurred within 48-hours from the time of clinical diagnosis to avoid any potentially concealing effects of treatment relative to symptoms of sepsis.

All non-septic clinically diagnosed septic patients were first stratified by burn severity into moderate (10—19.5% TBSA) and severe (≥20% TBSA) burns, whereby demographics and clinical outcomes were compared within their respective burn severity groups. Clinical outcomes of non-septic patients were compared with RTBC-diagnosed septic patients with severe burns, and from those, patients who met the criteria for ABA, Sepsis-3 and Mann-Salinas definitions. A cut-off for septic onset of >50-days was used to limit any temporal-dependent variation in sepsis prognosis following burns.

Clinical Outcomes

Demographics such as age and biological sex were obtained with patient consent. Clinical outcomes were prospectively recorded by the burn care team during acute hospitalization. Clinical outcomes included mortality, length of stay (LOS), full TBSA, TBSA with 3rd-degree burns (TBSA-3), and presence or absence of inhalation injury.

Inflammatory Responses

Circulating inflammatory cytokines were detected in the serum of burn patients collected at several timepoints during acute hospitalization. Cytokine profiling of select mediators were determined with the Milliplex MAP human cytokine/chemokine/growth factor panel A (cat# HCYTA-60K) using the Luminex 200 instrument (EMD Millipore, Massachusetts, USA). We analyzed the following cytokines: epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2), granulocyte colony-stimulating factor (GCSF), interferon-γ (IFN-γ), interferon gamma-produced protein-10 (IP-10), interleukin-1β, IL-4, IL-6, IL-8, IL-10, macrophage chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1β (MIP-1β), tumour necrosis factor-α (TNF-α), and vascular endothelial growth factor (VEGF).

Metabolic Responses

Resting energy expenditure (REE) was measured under a steady-state using a Sensor Medics 2900 metabolic measurement cart, as previously described 16,17. Predicted REE (pREE), calculated using the Harris-Benedict equation, and measured REE (mREE) were both used for these analyses.

Statistical Analysis

Statistical analyses were conducted using: Two-tailed Student’s t-tests (demographics and clinical outcomes); Mann-Whitney U non-parametric tests (cytokine/chemokine responses); two-way ANOVA (LOS; non-septic vs. septic); survival probability with log-ranked Mantel-Cox test (survival curves) and Chi-squared tests for statistical comparisons; and simple linear regressions (correlations). Data are presented as mean ± standard error of the mean (SEM) in figures. Statistical comparisons were conducted using GraphPad Prism software 9.3. Statistical significance was set at p<0.05.

Results

Patient Cohorts

A total of 316 burn patients met the eligibility criteria for this study. Out of this population, 16 (5%) moderately burned patients and 48 (15%) severely burned patients were clinically diagnosed with sepsis (Table 2). The average sepsis onset occurred at 10 ± 0.8 days and 13 ± 1.6 days post-burn in moderate and severe burn patients, respectively. When comparing non-septic and septic patients with moderate burn sizes, there were no differences in age (p=0.14), biological sex (p=0.14), total (p=0.54) and 3rd degree %TBSA burns (p=0.70). We observed a significant increase in LOS (p=0.03) and LOS per %TBSA burn (p=0.02) in septic patients. Further, moderately burned septic patients displayed an increased incidence of inhalation injury (p=0.0031) and mortality (13%; n=2) compared to non-septic patients (1%; n=1) (p=0.0006).

Table 2:

Patient demographics of non-septic and septic burn patients with 10–19.5% TBSA and ≥20% TBSA.

  10–20% TBSA ≥20% TBSA
  Non-Septic Septic p-value Non-Septic Septic p-value
n 155 16   97 48  
Sepsis Onset (days post-burn) n/a 10 ± 0.8 n/a n/a 13 ± 1.6 n/a
Age (y) 49 ± 1.5 57 ± 5.2 0.14 47 ± 1.8 48 ± 2.4 0.56
Biological sex (%male) 74% 56% 0.14 72% 75% 0.72
TBSA (%) 14 ± 0.2 14 ± 0.8 0.54 33 ± 1.3 38 ± 2.1 2.00E-02
TBSA-3 (%) 5.0 ± 0.4 5.5 ± 1.6 0.70 17 ± 1.7 28 ± 2.5 8.00E-04
LOS (d) 20 ± 0.9 26 ± 2.7 3.00E-02 34 ± 2.8 54 ± 4.1 1.00E-04
LOS/TBSA 1.5 ± 0.1 2.0 ± 0.2 2.00E-02 1.1 ± 0.2 1.8 ± 1.4 9.52E-07
Inhalation Injury (%) 11% 38% 3.10E-03 37% 60% 7.90E-03
Mortality (%) 1% 13% 6.00E-04 8% 25% 5.90E-03
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TBSA: Total body surface area; TBSA3: 3rd degree TBSA; LOS: Length of stay

Significant differences are denoted by bolded p-values

Data is presented as mean ±SD

Similarly, no significant differences in age (p=0.56) or biological sex (p=0.72) were observed between severely burned non-septic and septic patients. However, septic patients had significantly larger total (p=0.02) and 3rd degree (p=0.0008) %TBSA burns, an increased LOS (p=0.0079), and a greater incidence of inhalation injury (p=0.0004). Additionally, we observed an 8% (n=8) mortality rate in non-septic severe burn patients in comparison with 25% (n=12) mortality in septic severe burn patients (p=0.0059). Severely burned septic patients displayed the lowest probability of survival (70.8%) when compared to all non-septic (moderate, 87.5%; severe, 88.7%) and moderately burned septic patients (87.5%) (Figure 1A). Further, severely burned septic patients had a significantly greater LOS when compared to all groups (p<0.0001) (Figure 1B).

Figure 1: Survival probability and duration of acute hospitalization in non-septic and septic burn patients.

Figure 1:

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A) Kaplan-Meier survival curve and B) LOS among non-septic and septic burn patients with 10–19.5% and ≥20% TBSA burn size. C) Kaplan-Meier survival curve and D) LOS among non-septic and septic burn patients with severe burns (≥20% TBSA), as identified by RTBC, ABA, and Sepsis-3 criteria. Significance denoted by *p<0.05, **p<0.01, ***p<0.001, and ****p<0.0001.

Survival and Septic Onset

We further stratified the RTBC septic burn cohort into three groups based on meeting the criteria for ABA, Sepsis-3, and Mann-Salinas sepsis definitions. Of all 48 severely burned septic patients (RTBC), 58% (n=28) met the criteria for ABA, 90% (n=43) for Sepsis-3, and 29% (n=14) for Mann-Salinas (Table 3). No significant differences in age or biological sex were observed. However, RTBC, ABA, and Sepsis-3-diagnosed septic patients had significantly greater total %TBSA (p<0.05) relative to non-septic severe burn patients, while those who met Mann-Salinas criteria did not differ significantly (Table 3).

Table 3:

Patient demographics of non-septic and septic patients who were clinically diagnosed septic and met sepsis criteria.

  Non-Septic RTBC ABA Sepsis-3 Mann-Salinas
n 97 48 28 43 14
Sepsis Onset (days post-burn) n/a 13 ± 1.6 11 ± 1.8 13 ± 1.7 6.8 ± 1.3 #
Age (y) 47 ± 1.8 48 ± 2.4 45 ± 3.0 49 ± 2.6 52.8 ± 50.2
Biological sex (%male) 72% 75% 79% 74% 71%
TBSA (%) 33 ± 1.3 38 ± 2.1 * 42 ± 3.0 * 38 ± 2.3 * 39 ± 5.1
TBSA-3 (%) 17 ± 1.7 28 ± 2.5 *** 32 ± 3.7 *** 29 ± 2.7 *** 27 ± 5.0*
LOS (d) 34 ± 2.8 54 ± 4.1 *** 50 ± 4.7 ** 54 ± 4.2 *** 44 ± 6.9
LOS/TBSA 1.1 ± 0.2 1.8 ± 1.4 **** 1.6 ± 0.1 *** 1.9 ± 1.5 **** 1.7 ± 0.2 **
Inhalation Injury (%) 37% 60% ** 50% 63% ** 43%
Mortality (%) 8% 25% ** 21% 26% ** 50% ****
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LOS: Length of stay; TBSA: Total body surface area; TBSA3: 3rd degree TBSA

Significant differences between non-septic and septic criteria are denoted as:

*

p<0.05

**

p<0.01

***

p<0.001

****

p<0.0001

Data is presented as mean ±SD

Sepsis-3, but not ABA criteria, detected a similar increase in mortality (26%; p<0.01) and incidence of inhalation injury (63%; p<0.01) to that of the RTBC diagnosis (mortality: 25%, p<0.01; inhalation injury: 60%, p<0.01) (Table 3; Figure 1C). All septic patients exhibited a significant increase in LOS (RTBC, Sepsis-3, p<0.0001; ABA, p<0.01) compared with non-septic patients (Figure 1D).

The pattern of septic onset was similar between RTBC and Sepsis-3 diagnosed patients, primarily occurring within 10—16 days post-burn (Figure 2A). The average onset of sepsis in the ABA criteria occurred at 11 ± 1.8 days (p=0.37) and at 13 ± 1.7 days post-burn (p=0.90) in Sepsis-3 (Figure 2B). In all criteria, we observed a dramatic drop in sepsis diagnoses following 16 days post-burn, which was followed by a slight increase at >31 days post-burn. When comparing RTBC and Mann-Salinas criteria, 50% of septic burn patients diagnosed by the Mann-Salinas criteria died during hospitalization (n=7; p<0.0001). Additionally, the onset of sepsis occurred significantly earlier in Mann-Salinas (6.8 ± 1.3 days) compared to RTBC. Given these profound differences in burn sepsis progressions and other confounding factors (i.e. low sample size), the Mann-Salinas sepsis criteria was omitted from further analyses.

Figure 2: Septic onset in burn patients diagnosed by sepsis criteria.

Figure 2:

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A) Time-course of the number of patients developing sepsis following a severe burn injury, according to sepsis criteria. B) Average onset of the first septic episode in severe burn patients.

Metabolic Responses

There were no clear associations between absolute pREE and increasing days post-burn in non-septic (p=0.39) and septic patients diagnosed by RTBC (p=0.56), ABA (p=0.75), and Sepsis-3 (p=0.93) (Supplementary Figure 1A-D). When comparing pre-septic and post-septic REE values, we did not detect any significant differences for pREE (Supplementary Figure 1E-F) or mREE (Supplementary Figure 1G-H) within sepsis criteria.

Systemic Inflammatory Responses

Lastly, we compared the expression patterns of circulating mediators between non-septic and septic patients. Among growth factors, EGF was significantly decreased at 0–3 (RTBC, p<0.001; ABA p<0.05; Sepsis-3, p<0.01) and increased at 4–9 days post-burn in ABA septic patients (p<0.05; Figure 3A). There were no differences in VEGF or FGF-2 at any timepoints, with the exception of a slight yet non-significant (p=0.16) increase in VEGF at 4–9 days post-burn in ABA patients, as well as a significant difference in FGF-2 expression at 10–16 days post-burn between NS and ABA (p<0.05; Figure 3B—C). GCSF increased in all septic patients (p<0.01) at 10–16 days post-burn (Figure 3D). MCP-1 increased at >31 days post-burn in ABA and Sepsis-3 septic patients (p<0.05; Figure 3E) and MIP-1β decreased at 17–30 days in Sepsis-3 patients (p<0.05; Figure 3F).

Figure 3: Circulating growth factors and macrophage attractants in non-septic and septic burn patients.

Figure 3:

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Plasma concentrations of growth factors from non-septic and septic burn patients, including A) EGF, B) VEGF and C) FGF2, and macrophage attractants, such as D) G-CSF, E) MCP-1, and F) MIP-1β. Significant differences (p<0.05) compared with non-septic groups at specified timepoint: a denotes significance difference from RTBC; b denotes significant difference from ABA; c denotes significant difference from Sepsis-3.

Among inflammatory mediators, IL-6 expression significantly increased in all septic burn patients (p<0.01) at 0–3 days post-burn and at 10–16 days post-burn in RTBC and Sepsis-3 (p<0.05), but not ABA patients. Additionally, RTBC septic patients displayed prolonged increase in IL-6 at 17–30 days post-burn (p<0.05; Figure 4A). TNF-α was significantly elevated in all septic patients at 10–16 days (RTBC; Sepsis-3, p<0.01; ABA, p<0.05) and at >31 days post-burn in ABA (p<0.05) and Sepsis-3 (p<0.01) patients (Figure 4B). Moreover, IL-1β expression increased at 4–9 (RTBC and Sepsis-3, p<0.0001; ABA p<0.001) and at 10–16 (p<0.05) days post-burn in all sepsis criteria relative to non-septic counterparts. IL-1β remained elevated at 17–30 days post-burn in RTBC septic patients (p<0.01), followed by a significant increase at >31 days post-burn for all sepsis criteria (p<0.01; Figure 4C). While IFN-γ substantially decreased immediately until 30 days post-burn in all sepsis criteria (0–3 and 4–9days: RTBC and Sepsis-3, p<0.0001, 0–3, ABA, p<0.001; 10–16days: all, p<0.05; 17–30 days: all, p<0.0001; Figure 4D), IP-10 increased at 4–9 days post-burn in Sepsis-3 patients (p<0.05) and at 10–16 days for all septic patients (RTBC, p<0.001; ABA and Sepsis-3, p<0.01; Figure 4E). Further, IL-10 expression increased in all septic patients at 4–9 (p<0.0001), 10–16 (p<0.01) and >31 days post-burn (RTBC, ABA, p<0.05; Sepsis-3, p<0.01). An increase in IL-4 was detected at 0–3 (RTBC, Sepsis-3, p<0.001; ABA, p<0.01) and 4–9 (RTBC, Sepsis-3, p<0.01; ABA, p<0.001) days post-burn (Figure 4F—G). Finally, IL-8 expression significantly increased in all criteria at 0–3 days post-burn (p<0.05) and in ABA criteria at 10–16 days post-burn (p<0.05; Figure 4H).

Figure 4: Circulating inflammatory mediators in non-septic and septic burn patients.

Figure 4:

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Plasma concentrations of inflammatory mediators from non-septic and septic burn patients., including A) IL-6, B) TNF-α, C) IL-1β, D) IFN-γ, E) IP-10, F) IL-10, G) IL-4, and H) IL-8. Significant differences (p<0.05) compared with non-septic groups at specified timepoint: a denotes significance difference from RTBC; b denotes significant difference from ABA; c denotes significant difference from Sepsis-3.

Discussion

Sepsis is the leading cause of mortality in severe burn patients 18, which is largely due to the complexity of the septic burn pathophysiology and the absence of reliable diagnostic criteria. In support of our hypothesis, we determined that the three sepsis criteria examined in this study (ABA, Sepsis-3, and Mann-Salinas) revealed distinct septic trajectories when compared to non-septic patients. Moreover, we identified a combination of biochemical patterns in septic burn patients that may be applied clinically to more accurately diagnose and treat sepsis post-burn.

We first compared the clinical demographics between non-septic and septic burn patients in our centre, regardless of sepsis criteria. As expected, we found that septic patients with either a moderate (10–19.5% TBSA) or severe (>20% TBSA) burn size experienced a greater duration of hospitalization and higher mortality rate when compared with their non-septic counterparts. These findings are well-documented in the literature 18,27,32. However, as the clinical presentation of a severe burn patient without infection is similar to a septic patient in the general population, we focused on comparing septic and non-septic severe burn patients.

The current study is in line with our previous findings 33, which determined that the Sepsis-3 criteria was most predictive and outperformed two burn-specific sepsis criteria in detecting sepsis in burn patients. Here, we found that the Sepsis-3 criteria identified 90% of clinically diagnosed patients and most closely matched the pattern of clinical outcomes. Moreover, the average septic onset was nearly identical between RTBC and Sepsis-3 criteria.

The ABA criteria was unsuccessful in identifying sepsis in nearly half of the clinically diagnosed patients. This discrepancy also resulted in an earlier average septic onset and non-significant differences in mortality compared to non-septic burn patients. While the ABA criteria was intended to address burn-specific predictors of sepsis, the findings from the current study and previous work 12,33 suggest that the ABA definition would benefit from a reassessment. For example, the addition of septic shock, which was incorporated into the Sepsis-3 criteria as a more severe subset of sepsis, may improve the accuracy of predicting sepsis in burn patients.

The Mann-Salinas burn sepsis criteria was initially developed to improve upon the inadequacies of the ABA criteria 22. Here, however, the Mann-Salinas criteria failed to identify a substantial portion of clinically diagnosed septic patients, resulting in the average septic onset occurring at a considerably earlier timepoint. Additionally, the overly selective nature of the Mann-Salinas criteria, which limited the patient population and skewed the diagnostic period, increased mortality. Given these findings, we suggest that the Mann-Salinas criteria lacks diagnostic value and is not currently suitable for use in the septic burn patient population.

In our cohort, we found that sepsis onset is somewhat biphasic, for which case rates peak at 10—15 days post-burn followed by a modest increase after 31 days post-burn. This pattern was best reflected by the Sepsis-3 criteria, and to a lesser extent by the ABA criteria. This timeline is in accordance with previous studies demonstrating that sepsis typically occurs during later periods (weeks-to-months) rather than within the immediate days following severe burns 2,8,35. However, it is interesting to note that sepsis can occur as early as 72-hours post-burn. This early sepsis incidence was reflected in all definitions, and it seems therefore a valid but also important observation. Currently, many burn care providers observe signs of stress and inflammation as an early response post-burn rather than a septic response. We would like to raise awareness that sepsis can occur early post-burn and adequate anti-septic treatments, surgery, nutrition, and antibiotics are paramount for survival.

Among the sepsis criteria, the RTBC clinical diagnosis and the Sepsis-3 criteria were most valuable in detecting significant alterations in established septic biomarkers when compared with non-septic burn patients. Significant increases in classical pro-inflammatory (IL-6, IL-1β) and anti-inflammatory (IL-10, IL-4, IL-8) cytokines and a significant decrease in EGF and IFN-γ concentrations were detected during the pre-septic acute phase (within 9 days) of burns. These biomarkers may serve as early indicators of sepsis in severe burn patients.

Many studies have highlighted the potential role of IL-6 as a prognostic biomarker for sepsis 13,30. However, there is limited information on its predictive value for septic burn patients. A recent study by Gille et al. reported that serum IL-6 concentrations were significantly higher at the time of suspected sepsis in burn patients with bloodstream infections compared with those without 9. In our study, we did not detect significant differences during the period of septic onset, rather immediate increases in IL-6. This temporal discrepancy in IL-6 expression may be explained by differences in septic onset, whereby Gille et al. report a median of approximately 5 days to suspected sepsis 9, a much earlier occurrence compared with our patient cohort. In a murine model of burns and endotoxemia-induced sepsis, a combinational treatment blocking IL-6 and the soluble IL-6 receptor improved systemic inflammation and mortality when administered before and after endotoxemia 25. This indicates that pre-emptively antagonizing IL-6 prior to suspected infection may improve outcomes.

We have previously identified IL-1β and IL-10 as potent indicators of sepsis in burn patient samples collected within 96-hours post-injury 5. IL-1β+ cells were prominently detected at the site of injury in burn patients who developed sepsis compared with those who remained non-septic. Concomitantly, plasma concentrations of IL-10 were significantly elevated acutely post-burn, which is consistent with the present report. Moreover, the persistent elevation of IL-10 has been previously correlated with sepsis occurrence and risk of mortality in burn patients 6,26. This may be due to the release of IL-10 from regulatory T (T-reg) cells, which may invoke systemic immunosuppression 14. Further, early interventions targeting IL-10 may be of use, as treatment with anti-IL-10 antibodies was shown to improve outcomes in a two-hit model of burn sepsis 21.

Intriguingly, septic burn patients (in all criteria) lacked EGF and IFN-γ expression immediately post-burn. EGF expression was also absent during the period of sepsis onset, while IFN-γ concentrations remained significantly low throughout the study period. EGF promotes wound healing and it is suggested that sustained exposure is required to facilitate proper re-epithelization of burned skin 28. Treatment with EGF has shown efficacy in patients with either burn injury or sepsis 4,20,36. However, there have been no reports on the role of EGF in septic burn patients. Thus, future studies should address the potential importance of circulating EGF. On the other hand, the absence of IFN-γ expression in septic burn patients, perhaps due to immunosuppression 14, has been demonstrated. A phase III multicenter trial in burn patients revealed that IFN-γ administration over 90-days failed to prevent septic onset and did not improve survival 31. However, these results were criticized due to study design flaws 7. Therefore, a clear role of IFN-γ and efficacy of IFN-γ therapy in septic burn patients remains to be fully elucidated.

Three biochemical markers displayed significant elevations in expression solely during the period of sepsis onset at 10—16 days post-burn: TNF-α, IP-10, and GCSF. TNF-α is one of the most well-studied cytokines as it is considered one of the key initiators of the host response to infection. TNF-α concentrations have been shown to significantly increase in septic burn patients 1,34. This may be regulated by the actions of IL-10 produced by T-reg cells, which induces macrophage activation and secretes TNF-α 24.

Despite these intriguing findings, some limitations should be addressed. First, the authors acknowledge that the ABA and Mann-Salinas sepsis criteria were not designed to predict the trajectory of septic outcomes, rather to diagnose sepsis. However, these data generated from prospective septic diagnoses of each criteria could be implemented into current definitions to improve the detection of sepsis and clinical outcomes for septic burn patients. Furthermore, given that our burn centre-specific criteria most closely resembles the Sepsis-3 criteria, we acknowledge that a potential bias may exist with regards to outcomes. However, RTBC criteria served as a reference standard and we maintain that a comprehensive clinical diagnosis is superior to any current sepsis criteria 33. Thus, we believe our findings demonstrating the value of Sepsis-3 criteria, rather than ABA or Mann-Salinas, in detecting sepsis in burn patients remains valid.

Lastly, this was a single-institutional cohort study, therefore sample size may be a limitation. Of the 316 eligible burn patients enrolled in this study, there were 16 moderately burned and 48 severely burned septic patients. Despite detecting significant alterations in biomarkers, our study was not adequately powered, which may explain the lack of significant differences in REE between septic criteria. We encourage further studies with larger cohorts to expand upon our findings.

Taken together, our study validates the superiority of a prospective clinical diagnosis as well as the non-burn-specific Sepsis-3 criteria to use as a screening tool prior to clinical diagnosis in identifying sepsis in severe burn patients. Given that the condition of septic burn patients quickly deteriorates post-infection, effective screening tools are essential to mitigate complications. Therefore, the induction of the SOFA score, as used in the Sepsis-3 definition, should be considered for future burn-specific sepsis criteria, as supported by previous work 3,23,27. Additionally, we have established the trajectory of biomarkers that are significantly altered prior to and during sepsis onset. Pre-septic mediators (IL-4, IL-8, IL-6, IL-10, IL-1β, and EGF) as well as septic onset mediators (TNF-α, IP-10, GCSF, and IL-10) may be used as temporal indicators for burn patients at risk of developing sepsis. Given the complete lack of response of IFN-γ in septic burn patients, this may be a valuable tool to detect sepsis at any given timepoint during hospitalization in burn patients, although further work is needed. Nonetheless, the biomarkers identified here may be incorporated into existing sepsis criteria to improve diagnosis and prognosis of septic burn patients.

Supplementary Material

Supplemental Data File (.doc, .tif, pdf, etc.)

Supplementary Figure 1: Lack of differences in resting energy expenditures among patients in distinguish sepsis criteria. A) Absolute percent pREE during pre-septic and post-septic periods. B) Change in percent pREE from pre-septic to post-septic levels among sepsis criteria. C) Absolute mREE during pre-septic and post-septic periods. D) Change in mREE from pre-septic to post-septic levels among sepsis criteria. E—H) Correlation between pREE and days post-burn in non-septic and septic burn patients identified by RTBC, ABA, and Sepsis-3 criteria.

Acknowledgements

We would like to thank the Ross Tilley Burn Centre staff for their support and patients for their participation.

Funding/Support:

Dr. Marc Jeschke is currently receiving a grant (#R01GM133961) from the National Institutes of Health

Footnotes

Conflicts of Interest:

Disclosure summary: The authors have no disclosures to report.

References

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Supplementary Materials

Supplemental Data File (.doc, .tif, pdf, etc.)

Supplementary Figure 1: Lack of differences in resting energy expenditures among patients in distinguish sepsis criteria. A) Absolute percent pREE during pre-septic and post-septic periods. B) Change in percent pREE from pre-septic to post-septic levels among sepsis criteria. C) Absolute mREE during pre-septic and post-septic periods. D) Change in mREE from pre-septic to post-septic levels among sepsis criteria. E—H) Correlation between pREE and days post-burn in non-septic and septic burn patients identified by RTBC, ABA, and Sepsis-3 criteria.

NIHMS1822525-supplement-Supplemental_Data_File___doc___tif__pdf__etc__.tiff (1.3MB, tiff)

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