Despite improvements in the care of critically-ill patients, hospital mortality for acute lung injury remains high at approximately 40%. We developed a classification rule to stratify mechanically ventilated patients with acute lung injury according to hospital mortality and compared this rule to the APACHE III prediction.
We used data of 2022 participants in ARDS Network trials to build a classification rule based on 54 variables collected prior to randomization.
We used a classification tree approach to stratify patients according to hospital mortality using a training subset of 1800 participants, and estimated expected prediction errors using tenfold cross validation. We validated our classification tree using a subset of 222 participants not included in model building, and calculated areas under the receiver operating characteristic curves (AUCs).
Measurements and Main Results
We identified combinations of age (>63 years), BUN (>15 mg/dl), shock, respiratory rate (>21 breaths/minute), and minute ventilation (>13.9 L/minute) as important predictors of hospital mortality at 90 days. The classification tree had a similar expected prediction error in the training set (28% versus 26%; p=0.18) and AUC in the validation set (0.71 versus 0.73; p=0.71) as did a model based on APACHE III.
Our tree-based classification rule performed similarly to APACHE III in stratifying patients according to hospital mortality, is simpler to use, contains risk factors that may be specific to acute lung injury, and identified minute ventilation as a potential novel predictor of death in patients with acute lung injury.