Assessment of prognosis in patients with community-acquired pneumonia who require mechanical ventilation

Study objectives: Knowing that mortality is high in patients who require mechanical ventilation patients with community-acquired pneumonia (CAP), we hypothesized that the severity of acute lung injury could be used along with nonpulmonary factors to identify patients with the highest risk of death. We formulated a prediction model to quantitate the risk of hospital mortality in this population of patients, Design: Historical prospective study using data collected over the first 24 h of mechanical ventilation. We utilized a hypoxemia index-(1 - lowest [Pao(2)/PAo(2)) x (minimum fraction of inspired oxygen to maintain Pao(2) at > 60 mm Hg) x 100], where PAo(2) is the alveolar partial pressure of oxygen-to grade the severity of acute lung injury on a scale from 0 to 100. Setting: Tertiary care university hospital ICU. Patients: One hundred forty-four adult patients mechanically ventilated for respiratory failure caused by CAP. Measurements and results: Hospital mortality was 46% (n = 66). Multivariate logistic regression analysis revealed five independent predictors of hospital mortality: (1) the extent of lung injury assessed by the hypoxemia index; (2) the number of nonpulmonary organs that failed; (3) immunosuppression; (4) age > 80 years; and (5) medical comorbidity with a prognosis for survival < 5 years, At a 50% mortality threshold, the prediction model correctly classified outcome in 88% of cases. All patients with > 95% predicted probability of death died in hospital. Conclusions: Based on clinical parameters measured over the first 24 h of mechanical, ventilation, this model accurately identified critically ill, mechanically ventilated patients with CAP for whom prolonged intensive care may not be of benefit.