The impact of low body mass index on postoperative outcomes in pancreatectomy patients: a retrospective analysis of Japanese administrative data

To comparatively examine in-hospital mortality among different underweight body mass index (BMI) categories in pancreatic cancer patients after pancreatectomy in Japan. We conducted a large-scale multi-center retrospective cohort study of adult patients with pancreatic cancer who underwent pancreatectomy between April 1, 2010 and March 31, 2016. Patients were classified according to BMI as follows: normal BMI (18.50-24.99 kg/m(2)), mild thinness (17.00-18.49 kg/m(2)), moderate thinness (16.00-16.99 kg/m(2)), and severe thinness (< 16.00 kg/m(2)). A multivariable logistic regression analysis was performed with in-hospital mortality as the dependent variable and BMI groups as the main independent variable of interest. We analyzed 6173 patients from 332 hospitals. The results showed that the severe thinness group had a longer postoperative hospital stay (34.4 +/- 25.6 days) and higher incidence of postoperative pneumonia (5.5%) than the other groups. The generalized estimating equations accounted for patient demographics, surgical procedure, anesthetic technique, activities of daily living score, and Charlson comorbidity index as covariates. Relative to the normal BMI group, the odds ratios for in-hospital mortality were 0.57 (95% confidence interval: 0.26-1.24; P = 0.16) in the mild thinness group, 1.49 (0.64-3.48; P = 0.36) in the moderate thinness group, and 2.54 (1.05-6.08; P = 0.04) in the severe thinness group. Severe thinness was significantly associated with a higher risk of mortality, and extremely low BMI should be considered a risk factor in pancreatectomy patients.