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The modified 5-item frailty index (mFI-5) as a measure of frailty and biological age has been shown to be a reliable predictor of complications and mortality in a variety of surgical specialties. However, its role in burn care remains to be fully elucidated. We, therefore, correlated frailty with in-hospital mortality and complications following burn injury. The medical charts of all burn patients admitted between 2007 and 2020 with an affection of ≥ 10 % of the total body surface area (TBSA) were retrospectively reviewed. Clinical, demographic, and outcome parameters were collected and evaluated, and the mFI-5 was calculated based on the data obtained. Univariate and multivariate regression analyses were used to investigate the association between mFI-5 and medical complications and in-hospital mortality. 617 burn patients were included in the present study. Increasing mFI-5 scores were significantly associated with increased in-hospital mortality (p < 0.0001), myocardial infarction (p = 0.03), sepsis (p = 0.005), urinary tract infections (p = 0.006), and perioperative blood transfusions (p = 0.0004). They were also associated with an increase in the length of hospital stay and the rate of surgical procedures, albeit without statistical significance. An mFI-5 score ≥ 2 was a significant predictor of sepsis (OR = 2.08, 95% CI: 1.03 to 3.95; p =0.04), urinary tract infection (OR = 2.82, 95% CI: 1.47 to 5.19; p =0.002), and perioperative blood transfusions (OR = 2.61, 95% CI: 1.61 to 4.25; p =0.0001). Multivariate logistic regression analysis revealed that an mFI-5 ≥ 2 was not an independent risk factor for in-hospital mortality (OR = 1.44, 95% CI: 0.61 to 3.37; p =0.40). The mFI-5 is a significant risk factor for only a few select complications in the burn population. It is not a reliable predictor of in-hospital mortality. Therefore, its utility as a risk stratification tool in the burn unit may be limited. Yet, it holds the potential to improve the accuracy and prognostic value of established burn scores.
Burn injuries are considered one of the most devastating forms of trauma and are associated with severe morbidity and mortality. Globally, 11 million burn injuries and nearly 200,000 burn-related deaths are recorded annually.
Accordingly, burn injuries have a substantial health economic impact. High mortality rates and frequent perioperative complications remain a major concern in severely burned patients, leading to prolonged length of hospital stay, increased healthcare costs, and the suspension of early clinical and social rehabilitation.
Therefore, the prediction of mortality and adverse events has become an essential component in clinical burn care, with continuous efforts being dedicated to establish objective and accurate proxies for the risk of complications after severe burn injuries. In this context, throughout the last decades, various prognostic indices and scores have been proposed, aiming to identify high-risk patients preemptively.
Bagheri M, Fuchs PC, Lefering R, et al. The BUrn Mortality Prediction (BUMP) Score – An improved mortality prediction score based on data of the German burn registry. Burns. Published online February 2022:S0305417922000274. doi:10.1016/j.burns.2022.02.007
Such models commonly classify elderly patients as a particularly vulnerable subpopulation.
In recent years, the concept of frailty has additionally been implemented as a surrogate for biological age to enhance mortality prediction. Briefly, frailty describes a loss in physiological function and reserves beyond normal aging, causing a state of susceptibility and diminished resistance to systemic or external stressors such as surgical procedures.
Several frailty indices have been developed to facilitate the assessment of perioperative risk factors for postoperative adverse events and mortality. One of the earliest and most extensive risk assessment tools was the 70-item scale frailty index (CSHA-FI), which was based on the Canadian Study of Health and Aging and has shown high prognostic value in predicting adverse surgical outcomes.
Accordingly, a similar 11-item frailty index (mFI-11) was created based on the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, which was further reduced to a 5-factor index (mFI-5).
This simplified version has been shown to yield consistent predictions of postoperative complications and mortality and has been validated in different cohorts undergoing various surgical procedures.
Despite this well-documented role of mFI-5 as an accurate risk stratification tool, its applicability and utility for predicting outcomes in patients with severe burns have yet to be determined. Therefore, we aimed to assess the predictive value of the mFI-5 for complications and in-hospital mortality in a single-center burn population and to evaluate its potential role in burn-related risk stratification.
METHODS
Study design and data extraction
In this retrospective analysis all data were retrieved from the records of burn patients admitted to the burn unit at Hannover Medical School, from March 2007 to December 2020. All patients aged 16 years and older who presented with a total body surface area (TBSA) affected ≥ 10% were included. All included patients were stratified according to mFI-5, which yielded 3 cohorts: mFI-5 = 0, mFI-5 = 1, and mFI-5 ≥ 2.
Clinical and demographic variables including age, gender, TBSA, abbreviated burn severity index (ABSI) score, burn location, inhalation injury, burn severity, comorbidities, and the cause of the burn accident at the time of the burn injury were analyzed. Similarly, outcome parameters such as medical complications, in-hospital mortality, date, and cause of death, blood transfusions, number of surgical procedures, total and intensive unit care (ICU) length of stay (LOS) and mechanical ventilation were also evaluated. To calculate the mFI-5, the following comorbidities were considered: hypertension requiring medication, chronic obstructive pulmonary disease, congestive heart failure, diabetes mellitus, and total or partial dependent functional health status (Table 1). Consistent with previous literature,
Risk Analysis Index and Its Recalibrated Version Predict Postoperative Outcomes Better Than 5-Factor Modified Frailty Index in Traumatic Spinal Injury.
Frailty predicts worse outcomes for spine surgery patients with interhospital transfer status: Analysis of 295,875 patients from the National Surgical Quality Improvement Program (NSQIP) 2015-2019.
the mFI-5 score was calculated by dividing the sum of all positive variables by the total number of input variables in the database, with a higher mFI-5 score indicating a higher degree of frailty. This research was approved by the Ethics Committee of Hannover Medical. It was conducted according to the STROBE guidelines.
Table 1Variables included in the Modified Frailty Index-5 (mFI-5).
Hypertension requiring medication
History of chronic obstructive pulmonary disease
History of congestive heart failure
Diabetes mellitus
Total or partial dependent functional health status
All data were processed and saved using Microsoft Excel (Version 16, Microsoft Corporation, Redmond, WA). All statistical analyses were performed using GraphPad Prism 9 (GraphPad Software Inc., San Diego, CA). Categorical variables were expressed as numbers and percentages and their differences were measured by χ2 or binomial test. Continuous variables were expressed as means and standard deviation and their differences were assessed by one-way ANOVA. All complications were evaluated by univariate logistic analysis to decipher the independent effect of an mFI-5 ≥ 2 on complications as outcome parameters. Multivariate logistic regression analysis was conducted to evaluate potential risk factors, including the mFI-5, on in-hospital mortality. These were reported as adjusted odds ratio (OR) with 95% confidence intervals. Kaplan–Meier curves were plotted to show the survival probabilities of the patient cohorts. Statistical difference was calculated by log-rank (Mantel–Cox) test. A p-value of <0.05 was considered significant for all statistical purposes.
RESULTS
617 patients admitted to our burn center for burn injuries during the aforementioned study period were included. The detailed descriptive statistics of the patients’ demographic and burn variables are shown in Tables 2 and 3.
Table 2Descriptive statistics of demographic and clinical parameters.
Stratification by mFI-5 revealed that the majority of the included patients presented with an mFI-5 of 0 (65.6 %). 21.9% of all patients presented with a score of 1 and 12.5% showed an mFI-5 of ≥ 2. With increasing mFI-5 score, patients were more likely to suffer from domestic burn injuries (p < 0.001), whereas work-related burns and injuries during recreational activities were mostly observed in patients with an mFI-5 of 0. Our results demonstrated a progressive increase in the age range and proportional incidence of most comorbidities with increasing mFI-5 score. While the mean TBSA was highest in patients with an mFI-5 of 1 (27.2), the ABSI score showed an increase with higher mFI-5 scores (p < 0.001). Accordingly, the number of full-thickness burns (p = 0.04) increased with higher mFI-5 scores (see Table 4).
Table 4Perioperative outcomes.
Variable
mFI-5 = 0 (n = 405)
mFI-5 = 1 (n = 135)
mFI-5 ≥ 2 (n = 77)
p-value
LOS (days) (mean ± SD)
24.9 (25.0)
26.1 (20.9)
28.9 (17.2)
0.37
LOS on ICU (days) (mean ± SD)
14.8 (20.8)
16.6 (19.9)
20.4 (16.9)
0.07
Surgical intervention rate (mean ± SD)
3.5 (3.9)
3.4 (3.3)
3.6 (2.9)
0.93
Mechanical ventilation
131 (32.3)
63 (46.7)
33 (42.9)
0.04
Mechanical ventilation (hours) (mean ± SD)
58.6 (221.8)
119.8 (352.2)
71.5 (181.4)
0.05
Complications
Myocardial infarction
5 (1.2)
6 (4.4)
4 (5.2)
0.03
Pneumonia
44 (10.9)
19 (14.1)
13 (16.9)
0.31
Pulmonary embolism
3 (0.7)
2 (1.5)
1 (1.3)
0.72
Thrombosis
15 (3.7)
3 (2.2)
4 (5.2)
0.53
Sepsis
28 (6.9)
20 (14.8)
13 (16.9)
0.005
Urinary tract infection
33 (8.1)
13 (9.6)
16 (20.8)
0.006
In-hospital mortality
36 (8.9)
32 (23.7)
21 (27.3)
<0.0001
Perioperative blood transfusions
110 (27.2)
54 (40.0)
41 (53.2)
0.0004
Red cells (units) (mean ± SD)
3.0 (7.8)
4.4 (8.9)
4.2 (6.4)
0.14
Platelets (units) (mean ± SD)
0.2 (1.8)
0.2 (0.7)
0.1 (0.4)
0.86
Fresh frozen plasma (units) (mean ± SD)
1.7 (8.2)
2.5 (7.2)
1.5 (4.8)
0.52
Abbreviations: mFI-5, Modified Frailty Index-5; LOS, length of stay; ICU, intensive care unit; SD, standard deviation. n (%), unless otherwise stated.
Similarly, medical complications such as myocardial infarction, pneumonia, pulmonary embolism, thrombosis, sepsis, and urinary tract infection were observed more frequently with higher frailty scores. Significant differences in the occurrence of complications among the cohorts were noted for myocardial infarction (p = 0.03), sepsis (p = 0.005), urinary tract infection (p = 0.006), and perioperative blood transfusions (p = 0.0004).
Regarding the outcome parameters, the total and ICU LOS, as well as the surgical intervention rate were higher with an increasing mFI-5 score. Yet, this correlation showed no statistical significance (see Table 4). In-hospital mortality analysis revealed a significant decline in overall survival probability in patients with increasing frailty (p < 0.001). Figure 1 demonstrates the corresponding Kaplan-Meier curves of the stratified patient cohorts up to 80 days after admission (p < 0.0001, log-rank test).
Fig. 1Kaplan–Meier survival analysis of overall in-hospital survival following burn unit admission.
A univariate analysis was performed to assess the predictive value of an mFI-5 ≥ 2 regarding the occurrence of any complications (Table 5). Significant results were found for sepsis (OR = 2.08, 95% CI: 1.03 to 3.95; p =0.04), urinary tract infection (OR = 2.82, 95% CI: 1.47 to 5.19; p =0.002), and perioperative blood transfusions (OR = 2.61, 95% CI: 1.61 to 4.25; p =0.0001).
Table 5Univariate regression analysis of mFI-5 ≥ 2 with complications.
When adjusted for confounders, multivariate regression analysis identified age (OR = 1.05, 95% CI: 1.02 to 1.09; p =0.005), renal insufficiency (OR = 9.39, 95% CI: 4.26 to 21.44; p < 0.0001), TBSA (OR = 1.08, 95% CI: 1.03 to 1.14; p =0.002) and full-thickness burns (OR = 4.07, 95% CI: 1.53 to 11.54; p =0.006) as independent risk factors with significantly higher odds of in-hospital mortality (Table 6). An mFI-5 score ≥ 2 was not an independent predictor of in-hospital mortality (OR = 1.44, 95% CI: 0.61 to 3.37; p =0.40).
Table 6Multivariate regression analysis of risk factors with in-hospital mortality.
Yet, as life expectancy increases, so does the incidence of comorbidities and functional impairments. As such, the burden of age-related pathologies may become a growing public health concern in the future years. In this context, burn units will face the challenge of admitting increasing numbers of elderly burn patients with complex comorbidity profiles. Strikingly, in the field of burn care, senescence is widely linked to poor outcomes.
Multimorbidity, immobility, and polypharmacy, all common phenomena that befall in particular elderly patients, have traditionally been hypothesized to underlie this observation.
Historically, age has been considered an integral pillar of survival prediction in burn care, linking advanced age with a decline in survival probability. Along with burn injury severity, it has been included as a mono-perspective physiologic variable in the most commonly used burn scores.
Even though differences in overall health status may significantly impact the capacity to recover from a burn wound, to date, most prognostic scores do not take into account medical impairments that might interfere with the patient's physiologic reserves and their ability to adequately respond to stressors. Accordingly, profound discrepancies between a patient's chronological age and biological health status of a patient are not reflected in the aforementioned scores. Due to this non-consideration of the mismatch between biological and chronological age, the prognostic value of commonly applied scores may be limited. Although it may not be surprising that advanced age is associated with poor outcomes, previous reports have indicated that the burden of frailty exceeds that of chronologic age alone by more than twenty-eightfold.
Frailty Is a Better Predictor than Age of Mortality and Perioperative Complications after Surgery for Degenerative Cervical Myelopathy: An Analysis of 41,369 Patients from the NSQIP Database 2010–2018.
To date, the concept of frailty remains elusive and has, therefore, been the subject of controversy in the scientific literature over the past three decades, with a fluid boundary between physiologic and pathological aging.
Still, the concept of frailty has gained popularity in recent years and has gradually been included in the preoperative evaluation of various surgical fields as a holistic alternative to chronologic age.
In Germany, the impact of frailty on overall health, morbidity, and survival probability has been recognized by the national Study on Adult Health in Germany (DEGS1) conducted by the Robert Koch Institute on behalf of the Federal Ministry of Health.
DEGS: Studie zur Gesundheit Erwachsener in Deutschland: Bundesweite Quer- und Längsschnittstudie im Rahmen des Gesundheitsmonitorings des Robert Koch-Instituts.
The report emphasizes that the assessment of frailty helps identify high-risk cohorts, thereby providing an avenue to initiate preventative measures to counteract the further loss of functional abilities. These conclusions are reiterated in studies, finding an association between frailty and perioperative complications, higher rates of mortality, dependency, and prolonged hospital stay.
being the most frequently used. In principle, frailty measure tools should provide evidence-based predictions whilst being easy to use and reliable in their application.
In the present study, we employed the validated mFI-5 due to its previously documented wide and broad applicability and aimed to evaluate the prognostic value of the score on perioperative outcomes in severely burned patients. We found that patients were significantly more likely to experience myocardial infarction, sepsis, urinary tract infection, and perioperative blood transfusions with increasing frailty during hospitalization. In addition, higher mFI-5 scores were associated with a significant increase in mortality rates. Interestingly, we found that our most frail cohort experienced the lowest TBSA rates in the study population. Nonetheless, the effects of the patient's comorbidity profile and burn characteristics appeared to outweigh the impact of the TBSA affected given the higher mortality rates observed in this cohort.
In our burn population, an mFI-5 ≥ 2 seemed to be a valid outcome predictor of sepsis, urinary tract infection and perioperative blood transfusions, which may render it a surrogate parameter for potential clinical resource strain. In contrast to renal insufficiency, TBSA, or full-thickness burns, an mFI-5 ≥ 2 was not found to be an independent risk factor of in-hospital mortality in our cohort. Likewise, it was also not found to be a reliable predictor of myocardial infarction, pneumonia, pulmonary embolism, or thrombosis, thus limiting its utility as an overall outcome and complication predictor in the burn population. Therefore, our findings suggest that the physiologic reserve quantified by the mFI-5 cannot be considered a major determinant of significant complications or in-hospital mortality in burn patients, underscoring that risk stratification in acute burn care is much more complex.
To the best of our knowledge, this is the second study on the utility of the mFI-5 in a burn unit population. Previously, Sen et al. performed a secondary analysis of the Transfusion Requirement in Burn Care Evaluation (TRIBE) study and similarly assessed the predictive value of the mFI-5.
Modified Frailty Index is an Independent Predictor of Death in the Burn Population: A Secondary Analysis of the Transfusion Requirement in Burn Care Evaluation (TRIBE) Study.
They included a total of 347 patients with a TBSA of ≥ 20%. The authors reported that an mFI-5 ≥ 2 was not independently associated with in-hospital mortality in their analysis, which is in line with our results. A further analysis of medical complications was not performed. Interestingly, they found an mFI-11 score >1 independently associated with in-hospital mortality.
Regarding the predictive value of complications, our observations are consistent with the findings of previous studies which have evaluated large-scale datasets to assess the predictive value of the mFI-5 with regard to selected perioperative complications, particularly in the field of orthopedic surgery.
We acknowledge that the simplified mFI-5 score may be convenient to assess in various elective surgical populations given its straightforward composition and easy calculation. Accordingly, we anticipate that the mFI-5 will be increasingly adopted as a risk stratification tool in elective surgical procedures. However, in the acute setting, where the necessary parameters cannot be evaluated in a timely manner due to unavailability, inability to verify, or lack of patient responsiveness, it may serve as a suboptimal assessment tool. As such, the utility of the mFI-5 score for clinical decision-making may be limited in the burn unit. This may also explain why the scoring of frailty in burn patients has not yet been implemented in the standardized outcome assessments.
Further large-scale studies investigating a potential improvement of the prognostic value of established burn severity scores by integrating frailty assessments are required.
In addition to frailty, other facets may play a crucial role in patient stratification in elderly burn patients and, therefore, warrant further research. For instance, Sgonc et al. found that elderly patients – despite the absence of frailty – may present with severe age-related skin alterations.
Such changes in dermal (micro)structure may manifest as loss of collagen, increase in inflammatory cells, and reduced microvascularization, ultimately affecting wound healing and depth of burn wound. Several biomarkers have been suggested as objective measures of skin aging, e.g. inflammatory or apoptosis markers, hormonal measures, and length assessment of the telomeres.
Therefore, the consideration of biological age using quantifiable biomarkers may be of interest for future studies, possibly providing a more universal tool for patient stratification in burn care.
Limitations
Our study has several limitations. First, all data including the frailty assessment were analyzed retrospectively. As a result, the impact of confounding factors or bias cannot be ruled out. Second, all results are based on in-hospital data, limiting our conclusions to short-term observations. Accordingly robust long-term conclusions cannot be drawn. In addition, the present analysis only evaluated the association between frailty and in-hospital mortality and selected complications. The effects of burn patient frailty on further outcome parameters such as readmission rates, functional levels following discharge and costs of health burden might be an imperative avenue for future research.
CONCLUSION
The mFI-5 as a frailty assessment tool seems to reliably identify burn patients at risk for sepsis, urinary tract infection, and perioperative blood transfusions. However, it was not found to be an independent risk factor for in-hospital mortality and other serious medical complications. Its utility as an overall outcome and complication predictor in the burn population is, therefore, limited. Despite its limitations in the acute setting, it may help improve the accuracy and prognostic value of established burn scores, particularly for elderly and frail patients. As an acquired deficit model, which accounts for functional ability and medical comorbidities, further studies on the possible incorporation in established burn prognostication tools are warranted.
Data Availability Statement
The data presented in this study are available on request from the corresponding author.
Ethical Approval
Not required
Declaration of Competing Interest
None.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Bagheri M, Fuchs PC, Lefering R, et al. The BUrn Mortality Prediction (BUMP) Score – An improved mortality prediction score based on data of the German burn registry. Burns. Published online February 2022:S0305417922000274. doi:10.1016/j.burns.2022.02.007
Risk Analysis Index and Its Recalibrated Version Predict Postoperative Outcomes Better Than 5-Factor Modified Frailty Index in Traumatic Spinal Injury.
Frailty predicts worse outcomes for spine surgery patients with interhospital transfer status: Analysis of 295,875 patients from the National Surgical Quality Improvement Program (NSQIP) 2015-2019.
Frailty Is a Better Predictor than Age of Mortality and Perioperative Complications after Surgery for Degenerative Cervical Myelopathy: An Analysis of 41,369 Patients from the NSQIP Database 2010–2018.
DEGS: Studie zur Gesundheit Erwachsener in Deutschland: Bundesweite Quer- und Längsschnittstudie im Rahmen des Gesundheitsmonitorings des Robert Koch-Instituts.
Modified Frailty Index is an Independent Predictor of Death in the Burn Population: A Secondary Analysis of the Transfusion Requirement in Burn Care Evaluation (TRIBE) Study.
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