Association between body mass index and short-term mortality in patients with intra-abdominal infections: a retrospective, single-centre cohort study using the Medical Information Mart for Intensive Care database

Objectives: This study aimed to determine the relationship between the body mass index (BMI) and short-term mortality of patients with intra-abdominal infection (IAI) using the Medical Information Mart for Intensive Care (MIMIC-III) database.

Design: Retrospective cohort study.

Setting: Adult intensive care units (ICUs) at a tertiary hospital in the USA .

Participants: Adult IAI ICU patients from 2001 to 2012 in the MIMIC-III database.

Interventions: In univariate analysis, we compared the differences in the characteristics of patients in each BMI group. Cox regression models were used to evaluate the relationships between BMI and short-term prognosis.

Primary and secondary outcome measures: 90-day survival.

Results: In total, 1161 patients with IAI were included. There were 399 (34.4%) patients with a normal BMI (<25 kg/m²), 357 (30.8%) overweight patients (25-30 kg/m²) and 405 (34.9%) obese patients (>30 kg/m²) who tended to be younger (p<0.001) and had higher Sequential Organ Failure Assessment scores (p<0.05). The mortality of obese patients at 90 days was lower than that of patients with a normal BMI (20.74% vs 23.25%, p<0.05), but their length of stay in the ICU was higher (4.9 days vs 3.6 days, p<0.001); however, their rate of mechanical ventilation utilisation was higher (61.48% vs 56.86%, p<0.05). In the Cox regression model, we also confirmed that BMI was a protective factor in patients with IAIs, and the adjusted mortality rate of patients with a higher BMI was 0.97 times lower than that of patients with a lower BMI (p<0.001, HR=0.97, 95% CI 0.96 to 0.99).

Conclusions: IAI patients with an overweight or obese status might have lower 90-day mortality than patients with a normal BMI.