Burned patients who die from causes other than the burn affect the model used to predict mortality: a national exploratory study

Abstract

Introduction: The Baux score – the sum of age and total body surface area burned (TBSA %) – is a good predictor of mortality has a high specificity but low sensitivity. Our aim was to examine the causes of death in patients who die with Baux scores of <100, which may explain the lower sensitivity and possibly affect the prediction of mortality. Methods: All patients admitted to our centre for burn care from 1993 to 2015 (n = 1946) were included in this retrospective, descriptive, exploratory study. The study group comprised those patients who died with Baux scores of <100 (n = 23), and their medical charts were examined for the cause of death and for coexisting diseases. Results: Crude mortality was 5% (93/1946) for the overall cohort, and a quarter of the patients who died (23/93) had Baux scores of less than 100 (range 64–99). In this latter group, flame burns were the most common (18/23), the median (10th–90th centile) age was 70 (46–86) years and for TBSA 21 (5.0–40.5) %, of which 7 (0–27.0) % of the area was full thickness. The main causes of death in 17 of the 23 were classified as “other than burn”, being cerebral disease (n = 9), cardiovascular disease (n = 6), and respiratory failure (n = 2). Among the remaining six (burn-related) deaths, multiple organ failure (predominantly renal failure) was responsible. When we excluded the cases in which the cause of death was not related to the burn, the Baux mortality prediction value improved (receiver operating characteristics area under the curve, AUC) from 0.9733 (95% CI 0.9633–0.9834) to 0.9888 (95% CI 0.9839–0.9936) and the sensitivity estimate increased from 45.2% to 53.9%. Conclusion: Patients with burns who died with a Baux score <100 were a quarter of all the patients who died. An important finding is that most of these deaths were caused by reasons other than the burn, usually cerebrovascular disease. This may be the explanation why the sensitivity of the Baux score is low, as factors other than age and TBSA % explain the fatal outcome