Reference Study Description Findings/Comments
Obesity is associated with decreased incidence and/or severity of ARDS
O’Brien, 2006[20] Retrospective multi-center study comparing BMI with in-hospital mortality in mechanically ventilated adult patients with ALI/ARDS (n=1,488 patients between 1995 and 2001).
  • BMI was independently associated with in-hospital mortality. Survivors had greater average BMI and a higher proportion of the obese (BMI>30) patients were survivors
  • The risk of in-hospital mortality was significantly reduced in obese patients with BMI ranging from 30-39.9 compared to patients with normal or underweight BMIs, after adjusting for age, gender, race, SAPS II probability of survival, diagnosis or ICU-acquisition of renal or genitourinary diseases.
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    Morris, 2007[19] Prospective multi-center observational study analyzing the relationship between BMI at hospital admission and clinical outcomes in ALI patients (n=825 patients, 1999-2000).
  • Observed mortality was highest in underweight patients. Mortality decreased as BMI increased.
  • After adjusting for age, acute and chronic illness scores using the APACHE-III score and ALI etiology (sepsis, trauma or other), no statistically significant difference was found in mortality between obese and normal-weight patients.
  • ALI Patients with BMI>40 had longer adjusted hospital LOS, and ALI survivors had more prolonged adjusted ICU LOS and duration of mechanical ventilation than normal-weight patients.
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    Memtsoudis, 2012[15] Database study using the Nationwide Inpatient Sample (NIS) developed by the Agency for Healthcare Research and Quality (AHRQ) which compared the mortality in obese vs. non-obese patients with diagnoses of RI/ARDS after surgery (n=9,149,030 surgical admissions between 1998 and 2007).
  • Obese patients after surgery had a decreased incidence of RI/ARDS, need for mechanical ventilation when diagnosed with RI/ARDS, in-hospital overall mortality and mortality when intubated for RI/ARDS compared to non-obese patients after surgery.
  • Obesity was identified as an independent protective factor against in-hospital mortality after postoperative RI/ARDS (OR=0.31; CI=0.28-0.36) using multivariate regression analysis adjusted for age, gender, race, admission status, hospital characteristics, type of surgery, and comorbidity burden.
  • Prevalence of obesity diagnosis in the study population was 5.48%---a significantly lower percentage than the CDC national obesity estimate for adults, estimated to be 30%102. Possible explanations are surgical pre-selection bias and the use of billing-derived diagnosis codes, based on ICD-9-CM as used in Clinical Classification Software (CCS).
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    Obesity does not increase ARDS severity
    O’Brien, 2004[21] Retrospective multi-center study comparing BMI with in-hospital mortality in mechanically ventilated adult patients with ALI/ARDS (n=807).
  • Ventilator-free days and mortality were similar to those in normal-weight patients.
  • Underweight (BMI<18.5) and extremely obese patients (weight(kg)-to-height(cm)³1.0) were excluded from the analysis.
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    Gong, 2010[17] Prospective multi-center study analyzing BMI as risk factor for ARDS development and severity in patients at risk for ARDS at ICU admission (n=1,795, 1999-2007).
  • 30% of at-risk patients developed ARDS.
  • Patients who developed ARDS had greater average BMI, and BMI was positively correlated with ARDS development. ARDS development in obese patients occurred later in the ICU stay than in normal-weight patients. Authors suggested that the observed ventilatory settings might have played a role in the delayed ARDS development in obese patients.
  • Obesity was not associated with an increased ICU-mortality or with an increased 60-day mortality. Survivors had greater average BMI than non-survivors.
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    Anzueto, 2011[18] Secondary analysis of prospective observational multi-center study cohort of mechanically ventilated ICU patients designed to analyze the effect of BMI on outcomes of mechanical ventilation, including ARDS development (n=4,698, April 2004).
  • Obese and severely obese patients (BMI>30) had an increased incidence of ARDS development, higher tidal volumes per predicted body weight and higher PEEP levels.
  • Outcomes (duration of mechanical ventilation, weaning duration, ICU and hospital LOS and mortality) were not significantly different in obese compared to other BMI ranges. The authors observed a non-significant trend to lower mortality rates in patients with a BMI>30 compared to normal-weight patients.
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    Obesity is associated with lower inflammatory biomarkers during ARDS
    Stapleton, 2010[16] Retrospective analysis of the effect of BMI on plasma biomarkers and outcomes in ARDS patients evaluated in previous NHLBI ARDSNet trials
    (n=1,409).
  • BMI was not associated with increased mortality.
  • After adjusting for gender, APACHE III score, coexisting diabetes, and ALI risk factors, obese patients (BMI>30) had lower plasma IL-6, IL-8, and SP-D levels and higher plasma protein C and vWF levels, compared to normal-weight patients.
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    (ALI=Acute Lung Injury; ARDS=Acute Respiratory Distress Syndrome; ARDSNet= Acute Respiratory Distress Syndrome Network; BMI=Body Mass Index; ICU=Intensive Care Unit; LOS=Length of Stay; NHLBI=National Heart Lung and Blood Institute; RI=Respiratory Insufficiency; SAPS II=Simplified Acute Physiology Score II; SP-D=Surfactant Protein D; vWF=von Willebrand Factor)
    Table 1: Studies related to the Obesity-ARDS Paradox concept.