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

Body mass index (BMI) has been correlated with complications and outcome in surgical patients at the two extremes of the nutrition spectrum.

To study the relationship between BMI, outcome, hospital length of stay, and complications in patients admitted to the surgical intensive care unit (SICU).

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.

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.

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.