Kim Richard Y, Glick Connor, Furmanek Stephen, Ramirez Julio A, Cavallazzi Rodrigo
University of Louisville School of Medicine, Dept of Medicine, Division of Pulmonary, Critical Care, and Sleep Disorders Medicine, Louisville, KY, USA.
University of Louisville School of Medicine, Dept of Medicine, Division of Infectious Diseases, Louisville, KY, USA.
ERJ Open Res. 2021 Mar 22;7(1). doi: 10.1183/23120541.00736-2020. eCollection 2021 Jan.
The obesity paradox postulates that increased body mass index (BMI) is protective in certain patient populations. We aimed to investigate the association of BMI and different weight classes with outcomes in hospitalised patients with community-acquired pneumonia (CAP). This cohort study is a secondary data analysis of the University of Louisville Pneumonia Study database, a prospective study of hospitalised adult patients with CAP from June, 2014, to May, 2016, in Louisville, KY, USA. BMI as a predictor was assessed both as a continuous and categorical variable. Patients were categorised as weight classes based on World Health Organization definitions: BMI of <18.5 kg·m (underweight), BMI of 18.5 to <25 kg·m (normal weight), BMI of 25.0 to <30 kg·m (overweight), BMI of 30 to <35 kg·m (obesity class I), BMI of 35 to <40 kg·m (obesity class II), and BMI of ≥40 kg·m (obesity class III). Study outcomes, including time to clinical stability, length of stay, clinical failure and mortality, were assessed in hospital, at 30 days, at 6 months and at 1 year. Clinical failure was defined as the need for noninvasive ventilation, invasive ventilation or vasopressors within 1 week of admission. Patient characteristics and crude outcomes were stratified by BMI categories, and generalised additive binomial regression models were performed to analyse the impact of BMI as a continuous variable on study outcomes adjusting for possible confounding variables. 7449 patients were included in the study. Median time to clinical stability was 2 days for every BMI group. There was no association between BMI as a continuous predictor and length of stay <5 days (chi-squared=1.83, estimated degrees of freedom (EDF)=2.74, p=0.608). Clinical failure was highest in the class III obesity group, and higher BMI as a continuous predictor was associated with higher odds of clinical failure. BMI as a continuous predictor was significantly associated with 30-day (chi-squared=39.97, EDF=3.07, p<0.001), 6-month (chi-squared=89.42, EDF=3.44, p<0.001) and 1-year (chi-squared=83.97, EDF=2.89, p<0.001) mortalities. BMI ≤24.14 kg·m was a risk factor whereas BMI ≥26.97 kg·m was protective for mortality at 1-year. The incremental benefit of increasing BMI plateaued at 35 kg·m. We found a protective benefit of obesity on mortality in CAP patients. However, we uniquely demonstrate that the association between BMI and mortality is not linear, and no incremental benefit of increasing BMI levels is observed in those with obesity classes II and III.
肥胖悖论假定，在某些患者群体中，体重指数（BMI）升高具有保护作用。我们旨在调查BMI及不同体重类别与社区获得性肺炎（CAP）住院患者预后的关联。这项队列研究是对路易斯维尔大学肺炎研究数据库的二次数据分析，该数据库是对2014年6月至2016年5月在美国肯塔基州路易斯维尔住院的成年CAP患者进行的一项前瞻性研究。BMI作为预测指标，既作为连续变量也作为分类变量进行评估。根据世界卫生组织的定义，患者被分为不同体重类别：BMI<18.5 kg·m²（体重过轻）、BMI为18.5至<25 kg·m²（正常体重）、BMI为25.0至<30 kg·m²（超重）、BMI为30至<35 kg·m²（I级肥胖）、BMI为35至<40 kg·m²（II级肥胖）以及BMI≥40 kg·m²（III级肥胖）。研究结局包括达到临床稳定的时间、住院时间、临床治疗失败及死亡率，分别在住院时、30天、6个月及1年时进行评估。临床治疗失败定义为入院1周内需要无创通气、有创通气或使用血管升压药。患者特征及粗结局按BMI类别进行分层，并采用广义相加二项回归模型分析BMI作为连续变量对研究结局的影响，同时对可能的混杂变量进行校正。7449例患者纳入本研究。每个BMI组达到临床稳定的中位时间均为2天。BMI作为连续预测指标与住院时间<5天之间无关联（卡方值=1.83，估计自由度（EDF）=2.74，p=0.608）。临床治疗失败在III级肥胖组中最高，BMI作为连续预测指标越高，临床治疗失败的几率越高。BMI作为连续预测指标与30天（卡方值=39.97，EDF=3.07，p<0.001）、6个月（卡方值=89.42，EDF=3.44，p<0.001）及1年（卡方值=83.97，EDF=2.89，p<0.001）死亡率显著相关。BMI≤24.14 kg·m²是1年死亡率的危险因素，而BMI≥26.97 kg·m²对1年死亡率具有保护作用。BMI升高的增量获益在35 kg·m²时趋于平稳。我们发现肥胖对CAP患者的死亡率具有保护作用。然而，我们独特地证明了BMI与死亡率之间的关联并非线性，在II级和III级肥胖患者中未观察到BMI水平升高带来的增量获益。
