Certified Transport Registered Nurse Certification Practice Exam

What does a decrease in the P/F ratio indicate?

1. Improved oxygenation

2. Worsening lung function

3. Normal respiratory health

4. Enhanced oxygen therapy

The correct answer is: Worsening lung function

A decrease in the P/F ratio, which stands for the PaO2/FiO2 ratio, signifies worsening lung function or increased impairment in oxygen exchange within the lungs. This ratio is commonly used to assess the severity of acute respiratory distress syndrome (ARDS) and to gauge how effectively the lungs are transferring oxygen to the bloodstream. When the P/F ratio declines, it indicates that either the partial pressure of oxygen in arterial blood (PaO2) is diminishing or the fraction of inspired oxygen (FiO2) is relatively unchanged, which could be a result of multiple factors such as fluid accumulation, inflammation, or a significant decrease in lung compliance. Hence, a low P/F ratio reflects a compromised ability of the lungs to maintain adequate oxygenation and, therefore, suggests that lung function is deteriorating. Monitoring this ratio is crucial for the timely management of respiratory distress and can provide essential insights into the patient's respiratory status.