Chest
Volume 117, Issue 2, February 2000, Pages 503-512
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Clinical Investigations in Critical Care
Assessment of Prognosis in Patients With Community-Acquired Pneumonia Who Require Mechanical Ventilation

https://doi.org/10.1378/chest.117.2.503Get rights and content

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[Pao2/PAo2]) × (minimum fraction of inspired oxygen to maintain Pao2 at> 60 mm Hg) × 100], where PAo2 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.

Section snippets

Patient Selection

We reviewed chart data from 144 consecutive admissions of adult patients with severe CAP requiring mechanical ventilation. The study was approved by our institution's committee on human research. The patients were admitted to the ICU of Moffitt-Long Hospital between July 1994 and July 1997. Nine patients were excluded because of misplaced records. The main outcome measure was hospital mortality. Thirty-five predictive variables and antibiotic use, assessed over the first 24 h of mechanical

Subject Characteristics

The study population consisted of 144 patients; overall hospital mortality was 46% (n = 66). All data were obtained during the first 24 h of mechanical ventilation, except where noted. Table 1, Table 2 show baseline characteristics of the study population. An etiologic organism was identified in 30% of patients, with Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus being the most common isolates (Table 3). Table 4 details antibiotic use at the start of mechanical

Discussion

We have found that the extent of lung injury as well as other nonpulmonary factors are important independent markers of prognosis in patients with CAP requiring mechanical ventilation. These predictors were incorporated into a model that shows good discriminative ability (88% accuracy in outcome classification) in our study. Furthermore, the model identified patients with the poorest prognosis (> 95% probability of death in hospital) without misclassifying survivors. Importantly, the model

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