The effect of low body mass index on outcome in critically ill surgical patients.

BACKGROUND: Body mass index (BMI) has been correlated with complications and outcome in surgical patients at the two extremes of the nutrition spectrum. OBJECTIVE: To study the relationship between BMI, outcome, hospital length of stay, and complications in patients admitted to the surgical intensive care unit (SICU). DESIGN: Review of prospectively acquired data in SICU patients. Data acquired included weight, height, age, gender, Acute Physiology and Chronic Health Evaluation (APACHE) II-III scores, Simplified Acute Physiology II (SAPS II) scores, and morbidity and mortality. Patients who stayed in the unit <24 hours were excluded. RESULTS: Of 793 patients, 706 had a normal BMI (NBMI; mean 22.12 kg/m²) and 87 were underweight (UBMI; mean 16.81 kg/m²). There was no statistically significant difference in APACHE II-III and SAPS scores. The NBMI group had more infections, and the UBMI group had more pulmonary complications (χ(2), P < .0087). There was no significant difference in acute respiratory distress syndrome, atrial fibrillation, myocardial infarction, septicemia, or ventilator- associated pneumonia (Fisher exact test, P = 0.38; χ(2), P = .41). The ICU length of stay between the 2 groups was not significantly different (6.7 vs 5.8 days; P = .64). Overall, there was 11.1% (88/793) SICU mortality; 74 of 706 (10.5%) patients expired in the NBMI group, and 14 of 87 (16.1%) patients expired in the UBMI group. CONCLUSIONS: Low BMI is associated with increased mortality in SICU patients. A BMI <18.5 kg/m² is an independent factor affecting outcome in surgical critical care patients.