Lethal area 50 percent (LA50) or standardized mortality ratio (SMR): Which one is more conclusive?

BACKGROUND: Burn injuries impose a considerable burden on healthcare systems. It is among the top ten causes of mortality and a major cause of disability. This study aimed to calculate and compare the lethal area fifty percent (LA50) and standardized mortality ratio (SMR) in patients with burns.

METHODS: This is a five-year cross-sectional study. The study population consisted of 3284 patients with acute burns who were admitted to the Burn Department of Imam Reza Hospital in Mashhad, Iran, from 2010 to 2015. LA50 and SMR were calculated. SPSS 16 was used for logistic regression analysis.

RESULTS: The mean percentage of burn total body surface area (TBSA%) was 37.0 (25.5), and deceased patients with burns had a significantly higher burn TBSA% than alive discharged patients (70.3 (24.2) vs. 28.1 (17.1), p<0.001). The most common cause of burn was fire (71.7%). The total case fatality rate was 21.2%. However, this index was more than double in females than in males (31.9% vs. 14.3%, p<0.001). The SMR, based on the abbreviated burn severity index (ABSI), increased from 61% to 80% during the 5-year period. LA50 for total admitted patients was 63.8% (95% confidence interval [CI]=60.4-67.7). LA50 for scalds was the highest (72.1%) compared to those of other types of mechanisms of burn injuries. TBSA, age, and gender were found to be mutually independent predictors of death.

CONCLUSION: The trend of LA50 in these five years declined by 12%, whereas the SMR was below 100%. Improvement in burn management quality in high-risk groups including the elderly, females, and patients with extensive burns may improve LA50 in burn units. However, LA50 alone is not a conclusive index for the performance of a burn department, and it should be interpreted alongside with SMR.