(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)
|Obesity is associated with decreased incidence and/or severity of ARDS
||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.
||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.
||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).
|Obesity does not increase ARDS severity
||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.
||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.
||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.
|Obesity is associated with lower inflammatory biomarkers during ARDS
||Retrospective analysis of the effect of BMI on plasma biomarkers and outcomes in ARDS patients evaluated in previous NHLBI ARDSNet trials
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.