Elsevier

Burns

Volume 35, Issue 2, March 2009, Pages 201-209
Burns

A model for predicting mortality among critically ill burn victims

https://doi.org/10.1016/j.burns.2008.07.019Get rights and content

Abstract

Objective

To develop a model for predicting mortality among burn victims.

Methods

All casualties admitted to our intensive care burn unit (ICBU) with a diagnosis of thermal or inhalation injury were studied. Age, total and full-thickness body surface area (BSA) burned, presence of inhalation injury, gender, mechanism of injury, delay to ICBU admission and mechanical ventilation during the first 72 h were recorded. The 851 participants were randomly divided into derivation (671) and validation (180) sets. From univariate and multivariate logistic regression analyses a mortality predictive equation was derived.

Results

Mortality was 17.6%. In univariate analysis, all variables were significantly associated with mortality except mechanism of injury and delay to ICBU admission. In multivariate analysis, age, total and full-thickness BSA burned, female gender and early mechanical ventilation were independently associated with mortality.

Conclusions

We propose a mortality predictive equation for burned victims. In this model, MV and not inhalation injury is a mortality risk factor.

Introduction

The outcome of thermal trauma is closely associated with variables such as presence of inhalation injury, body surface area (BSA) burned and age [1]. However, inhalation injury is difficult to quantify [2] and, although generally accepted as a prognostic factor, some studies have failed to show a relationship between inhalation injury and outcome [3], [4]. Also, the relative prognostic significance of full-thickness BSA (FTBSA) versus total (TBSA) BSA burned remains unsettled. Finally, regression models generally used to study the association between different variables and mortality prognosis often assume a linear relationship, but an analysis that took into consideration a more complex relationship might be more appropriate.

In this study we analysed the relationship between demographic variables and outcome among people admitted to an intensive care burn unit (ICBU). Our objectives were, first, to clarify the relationship between the requirement of mechanical ventilation after trauma and mortality. We observed that some individuals might have mild inhalation injury and yet do well without mechanical ventilation, whereas others might require mechanical ventilation early after admission without having had inhalation injury. Therefore, we hypothesised that the early requirement of mechanical ventilation could be more strongly associated with mortality than inhalation injury itself. Second, we aimed to compare the relative impact of TBSA versus FTBSA burned. Our third aim was to elucidate the non-linear relationship between mortality and other variables such as age and BSA burned.

Section snippets

Participants

Data were obtained from the Hospital Universitario de Getafe Burn Registry, and every person admitted to our ICBU from April 1992 to December 2005 was prospectively included in our database. People are admitted to our ICBU with ≥20% BSA burned, inhalation injury, or less extensive burns depending on age and comorbidities. We excluded from the analysis burns due to non-thermal injury (such as chemical or electrical burns), associated non-burn trauma, admission based on non-burn-related diagnoses

Unadjusted and adjusted mortality risk factors

In this study population mean age was 46.2 ± 20.6 years, and 70.4% were men. Median TBSA and FTBSA were 20% and 9%, respectively. Mean mortality was 17.6% with a 95% confidence interval (CI) of 15.1–20.4%; mean mortality decreased from 23.8% in 1992–1995 to 12.3% in 2001–2005. The LA50% was 65%.

The derivation and validation sets were not significantly different in any of the analysed variables, except that in the derivation set a higher proportion of participants were admitted early after injury (

Effect of age

Ageing is associated with decreased ability of the respiratory and cardiovascular systems to cope with demands imposed by injury. Thus, a relationship between age and mortality after burn is anticipated and has been reported by many studies [10], [11], [12], [13]. Moreau et al. [14] developed an age-risk score after burn, and showed that age is not linearly related to mortality if the group includes children. Our finding of a linear relationship between age and mortality is probably explained

Conclusions

This study confirms and expands previous knowledge on the relationship between injury-associated factors and mortality among burn victims. Our predictive model performs in our validation set comparably or even better than other models previously published. We describe the relative contribution to mortality of TBSA and FTBSA burned, as well as the non-linear relationship between BSA burned and outcome. In line with recent studies, we did not find an independent relationship between inhalation

Conflicts of Interest

José A. Lorente-Balanza, on behalf of all the authors of the article entitled “Mortality prediction in critically ill burn patients”, states that there is not any conflict of interest to declare.

Acknowledgement

This research was partially supported by grants FIS 07/1275 and FIS 06/1664.

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