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Abstract

Introduction: Although an increased body mass index (BMI) is associated with an elevated risk of chronic health diseases such as diabetes and hypertension, it is unclear whether patients with high BMIs fare worse when they are admitted to an intensive care unit (ICU) for an acute disorder. Some studies have instead described an "obesity paradox" where obese patients (BMI>30 kg/m2) have a lower ICU mortality rate, particularly when diagnosed with acute infections and septic shock. However, most studies have not addressed the outcomes of patients with more extreme obesity, defined as "super obesity" (BMI > 50), who may have outcomes that are different from patients whose BMI are below this threshold. Methods: A retrospective analysis of patients admitted to the MICU at LAC+USC Medical Center from 2008 to 2013 was performed. Patients were divided into 3 groups: BMI of 30-39, 40-49 and >50. In this pilot study, the first 55 patients reviewed in each BMI set were assigned to their respective group. Variables assessed included age, sex, APACHE II score, reason for ICU admission, use of non-invasive and invasive mechanical ventilation, need for dialysis, tracheostomy, use of a pulmonary artery catheter, mortality, and hospital and ICU length of stay (LOS). Analysis of variance was used to detected differences in means of continuous data and a chi square test was used to evaluate categorical data among the three groups. A p<0.05 was considered significant. Results: The mean age for super obese patients (BMI >50) was younger (44 + 2.7 SEM) than either of the BMI 30-39 and BMI 40-49 groups at 49 + 2.7 and 51 + 3.1 years, respectively (p<0.05). There was no significant difference among APACHE II scores or ICU length of stay. However, the mean hospital LOS was 7 + 2.1 days longer for patients with BMI > 50 than those with a BMI = 30-39, and 4 + 1.5 days longer than those with a BMI = 40-49. Mortality was similar among the three groups. Although there was no difference in the need or duration of invasive mechanical ventilation, there was a higher proportion of noninvasive mechanical ventilation used in the BMI>50 cohort (p<0.05), in that 34 (62%) of the super obese patients used noninvasive ventilation compared with 16 (29%) in the 40-49 group and 6 (11%) in the 30-39 group. Although there was a trend toward higher rates of tracheostomy or pulmonary artery catheter placement in the super obese patients, this did not achieve statistical significance. Super obese patients did not have a higher propensity to require hemodialysis than did the other groups (p>0.05). Indications for admission were different among the groups, with the BMI>50 patients being admitted to the ICU more frequently for cardiopulmonary indications (arrhythmias, heart failure, dyspnea, hypoxia) than were patients in the other groups (p<0.05). Conclusions: Super obese patients with a BMI >50 who are admitted to the MICU were younger in comparison to less obese patients. While there was no difference in use or duration of invasive mechanical ventilation in the 3 groups, patients with BMI >50 more often required non-invasive ventilation. Patients at the higher extremes of obesity were admitted to the ICU for cardiopulmonary issues more so than patients with BMI 30-50. Despite these differences, crude mortality rates were similar among these 3 groups of obese patients.