Despite an epidemic of obesity among adults and increasing use of intensive care unit resources, the effect of excess body weight on outcomes from critical illness is understudied. We examined the role of excess body weight as an independent risk factor for poorer outcomes in patients with acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS).
A retrospective cohort study involving the 902 mechanically ventilated patients enrolled in randomized, controlled trials for the treatment of ALI/ARDS. We used the body mass index (BMI) as an indicator of excess body weight with categories of normal (BMI 18.5 – 24.9 kg/m2), overweight (BMI 25 – 29.9 kg/m2) and obese (BMI ≥30 kg/m2). We conducted multivariate analyses of subjects with calculable BMIs to determine independent factors associated with clinical outcome from ALI/ARDS.
Unadjusted analyses showed that indirect causes of lung injury, including trauma, were more common in obese subjects. Overweight and obese subjects also had higher pre-enrollment peak and plateau airway pressures due to higher set tidal volumes. After risk adjustment, excess body weight was not independently associated with mortality, achieving unassisted ventilation, or number of ventilator-free days. These findings persisted with continuous and categorical measures of BMI. We found no significant interaction between ventilator protocol assignment and obese BMI.CONCLUSIONS: We could not demonstrate that excess body weight was independently associated with poorer outcome from ALI/ARDS. Lower tidal volume assignment (6 mL/kg predicted body weight) showed superior outcomes for all BMI groups.
Overweight and obese patients with ALI/ARDS have outcomes similar to those with normal BMIs, even after risk-adjustment. The lack of interaction between the ventilator protocol assignment and obesity suggests that the benefit of lower tidal volume ventilation for ALI/ARDS extends to patients of all BMIs.
J.M. O’Brien, Eli Lilly, have given educational presentations for company.