Heterogeneity in the association between inhalation injury and outcomes in inpatients with burns: A nationwide study using the Japanese Burn Registry

Inhalation injury is a major prognostic factor in burn care; however, its impact may vary with patient age and burn size. This study aimed to evaluate how its association with in-hospital mortality varies by age and percentage of total body surface area burned (%TBSA) among inpatients with burns. This retrospective cohort study used data from the Japanese Society of Burn Injuries Burn Registry 2011, enrolling 24,065 patients hospitalized for acute burn care between 2011 and 2023. After the exclusion of cases with missing data, 20,982 patients were finally analyzed. The association between inhalation injury and in-hospital mortality was assessed using multivariate logistic regression models with interaction terms between inhalation injury and the categories of %TBSA and age. Additionally, the adjusted predicted mortality and average marginal effects (AMEs) were calculated to quantify the difference in the predicted mortality between patients with and without inhalation injury across the age and %TBSA categories. Of the 20,982 patients included, 4823 (23.0 %) had clinically documented inhalation injury, while 16,159 (77.0 %) did not. Patients with inhalation injury had higher crude in-hospital mortality than those without (22.0 % vs. 5.5 %; p < 0.001). Furthermore, patients with 70 %–79 % TBSA had the greatest difference in adjusted predicted mortality between those with and without inhalation injury (AME: 34.2 %; 95 % confidence interval [CI], 15.8 %–52.5 %). This difference began to increase from the age of 50 years (AME: 3.5 %; 95 % CI, 2.1–4.9), reaching 24.0 % (95 % CI, 12.5–35.5) at the age of 90 years and above. The association between inhalation injury and mortality in patients with burns differs according to patient age and burn size, demonstrating significant heterogeneity. These findings highlight that the prognostic impact of inhalation injury is not uniform across all patients but varies by individual characteristics. Clinicians should consider these variations when interpreting inhalation injury and making individualized treatment decisions. • Inhalation injury was present in 23 % of hospitalized burn patients. • Inhalation injury increased in-hospital mortality (22.0 % vs. 5.5 %). • The greatest mortality gap occurred in patients with 70 %–79 % TBSA burns. • Mortality impact of inhalation injury increased from age 50 onward. • Prognostic effect of inhalation injury varies by age and burn size.