Differences by age in the obesity paradox in severe burns

Many studies show a "obesity paradox", which seems to protect against death. Whether an obesity paradox space is present in severe burn patients remains a matter of great debate. Most research on the obesity paradox of burn injuries is classified by body mass index (BMI) rather than by age.

To investigate whether the obesity paradox exists in severe burn patients stratified by age.

Retrospective analysis was performed on 490 patients with severe burns who were ≥ 18 years of age and were admitted to Fujian Medical University Union Hospital from January 2005 to December 2020. Demographic and clinical characteristics were collected, including age, BMI, total body surface area (TBSA), presence of inhalation injury, abbreviated burn severity index (ABSI) score, diabetes comorbidities, hypertension comorbidities, and in-hospital mortality. The patients were divided into the younger group (18 ≤ age<65 years) and the older group (age ≥ 65 years). The important variables of the two groups were compared. The predictive value of BMI stratified by age on in-hospital mortality was evaluated by binary logistic regression analysis and the Cochran's and Mantel-Haenszel statistics.

A total of 490 patients were selected for this study, and were divided into the younger group (413) and the elderly group (77) according to their ages. In the younger group, logistic regression analyses indicated that high BMI remained significantly and independently associated with decreased in-hospital mortality (P = 0.021). That is, in-hospital mortality decreased by 17.8% when BMI increased by 1 kg/m². In the older group, BMI was not associated with in-hospital mortality (P = 0.808). In the younger group, the results of Pearson's chi-square test was less than 0.05, indicating a correlation between BMI and prognosis. In the older group, the conclusion was contrary with, no correlation between BMI and prognosis. If the confounding factors of age were not considered, this results in no correlation between BMI and prognosis. In the younger group, the survival/death ratio of patients with overweight and obesity was 2.078 times that of patients with normal weight.

In this study of patients with severe burns, overweight and obesity had protective effect on burn injury in the younger group (18 ≤ age<65 years), but not in the older group (age ≥ 65 years). Investigating the obesity paradox in burn patients needs to consider age differences. However, multicentre clinical trials are needed to verify the results.