Mortality prediction to hospitalized patients with influenza pneumonia: PO2 /FiO2 combined lymphocyte count is the answer.

INTRODUCTION: Community-acquired pneumonia (CAP) severity scores perform well in predicting mortality of CAP patients, but their applicability in influenza pneumonia is powerless.

OBJECTIVES: The aim of our research was to test the efficiency of PO2 /FiO2 and CAP severity scores in predicting mortality and intensive care unit (ICU) admission with influenza pneumonia patients.

METHODS: We reviewed all patients with positive influenza virus RNA detection in Beijing Chao-Yang Hospital during the 2009-2014 influenza seasons. Outpatients, inpatients with no pneumonia and incomplete data were excluded. We used receiver operating characteristic curves (ROCs) to verify the accuracy of severity scores or indices as mortality predictors in the study patients.

RESULTS: Among 170 hospitalized patients with influenza pneumonia, 30 (17.6%) died. Among those who were classified as low-risk (predicted mortality 0.1%-2.1%) by pneumonia severity index (PSI) or confusion, urea, respiratory rate, blood pressure, age ≥65 year (CURB-65), the actual mortality ranged from 5.9 to 22.1%. Multivariate logistic regression indicated that hypoxia (PO2 /FiO2  ≤ 250) and lymphopenia (peripheral blood lymphocyte count <0.8 × 109 /L) were independent risk factors for mortality, with OR value of 22.483 (95% confidence interval 4.927-102.598) and 5.853 (95% confidence interval 1.887-18.152), respectively. PO2 /FiO2 combined lymphocyte count performed well for mortality prediction with area under the curve (AUC) of 0.945, which was significantly better than current CAP severity scores of PSI, CURB-65 and confusion, respiratory rate, blood pressure, age ≥65 years for mortality prediction (P < 0.001). The scores or indices for ICU admission prediction to hospitalized patients with influenza pneumonia confirmed a similar pattern and PO2 /FiO2 combined lymphocyte count was also the best predictor for predicting ICU admission.

CONCLUSION: In conclusion, we found that PO2 /FiO2 combined lymphocyte count is simple and reliable predictor of hospitalized patients with influenza pneumonia in predicting mortality and ICU admission. When PO2 /FiO2  ≤ 250 or peripheral blood lymphocyte count <0.8 × 109 /L, the clinician should pay great attention to the possibility of severe influenza pneumonia.