Oxygen indexes as predictors of mechanical ventilation in pneumonia at 2600 meters above sea level

Abstract

Background: the values of the difference of alveolar arterial oxygen D(A-a)O2 and ratio of the alveolar oxygen pressure and fraction of inspired oxygen (PaO2/FiO2) are poorly known at high altitude to predict mechanical ventilation (MV) in patients over 65 years with community-acquired pneumonia (CAP).

Objective: to know the values of D(A-a)O2 and PaO2/FiO2 in CAP patients requiring ventilatory support.

Methods: prospective cohort study where D(A-a)O2 y PaO2/FiO2 were obtained from arterial blood gases at entrance to the emergency room, with calculation of sensitivity (S), specificity (E), positive predictive value (PPV), negative predictive value (NPP) and area under the ROC curve for MV requirement within the first 72 hours.

Results: 247 patients were followed; 37 (15%) required MV. No differences were found in age, gender and comorbidities between the groups of MV and no MV. The area under the ROC curve for D(A-a) O2 as a predictor of MV was 0.84 (95% CI: 0.77 to 0.92), for the la PaO2/FiO2 of 0.85 (95% CI: 0.78 to 0.92) (p <0.0001). For a D(A-a)O2 in 55 patients was obtained a sensibility to predict MV in 70.27%, specificity 86.19%, PPV 47%, NPV 94%, positive likelihood ratio (LR +): 5.1, negative likelihood ratio (LR -): 0.3. A PaO2/FiO2 of 180 has a sensitivity to predict MV of 86.65%, specificity: 70.27%, PPV 34%, NPV 97%, LR +: 2.9, LR: 0.2. Overall mortality was 3.2%.

Conclusion: the values of D(A-a)O2 and PaO2/FiO2 relate to the requirement of MV in patients older than 65 with CAP