The Predictive Value of Initial Arterial Blood Gas Variations in Pneumonia Patients with Type I/II Respiratory Failure

There has not been much research into the relationship between early variations in the individual arterial blood gas (ABG) parameters- pH, PaO2, PaCO2 and HCO3- and treatment outcome in pneumonia patients with respiratory failure. If a statistically significant variation among the individual ABG values could be used as an early, accurate predictor of treatment success, it would allow for immediate active therapy of a patient with pneumonia who is in respiratory failure before a clinically obvious downward shift occurs. Pneumonia can also end in respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response.

This prospective trial included 42 patients who had clinical evidence of pneumonia and baseline clinical data, as well as two arterial blood samples for ABG analysis (one at baseline and another within 24 hours of the first). Patients were categorised as belonging to group 'A' with type I (hypoxemic) respiratory failure or group 'B' with type II (hypercapnic) respiratory failure based on the ABG findings. An investigation of binary logistic regression was carried out. In group A, the individual ABG parameters had a significant positive correlation with the treatment outcome: pH (p=0.034), HCO3- (p=0.034), PaO2 (p=0.035), PaCO2 (p=0.045), whereas in Group B, a non-significant positive correlation, pH (p=0.284), HCO3- (p=0.248), PaO2 (p=0.39), PaCO2 (p=0.240) was observed. In group B, a treatment failure rate of 40.91% was seen, as against 25% in Group A.

Individual ABG measurements can predict treatment outcome in pneumonia patients with type I respiratory failure, but not in type II respiratory failure patients.