Certified Respiratory Therapist Practice Exam

Which test of lung mechanics can best detect auto-PEEP in a patient receiving ventilatory support?

1. Alveolar Gas Exchange Measurement

2. Flow-Volume Loop

3. Lung Compliance Test

4. Blood Gas Analysis

The correct answer is: Flow-Volume Loop

The determination of auto-PEEP, or intrinsic positive end-expiratory pressure, is best accomplished using the flow-volume loop. This graphical representation allows for the analysis of airflow and lung volumes during forced expiration and inspiration. When auto-PEEP is present, the expiratory flow will show a characteristic downward slope that does not return to the baseline, indicating that air remains in the lungs at the end of expiration. This pattern provides clear visual evidence of trapped air, making it an effective tool for detecting auto-PEEP in patients receiving mechanical ventilation. Other tests mentioned, such as alveolar gas exchange measurement, lung compliance tests, and blood gas analysis, do not provide the specific flow dynamics that reveal the presence of auto-PEEP as effectively as the flow-volume loop does. Alveolar gas exchange can indicate overall lung function and gas exchange capability, but it lacks the detailed flow measurement. Similarly, lung compliance tests assess the elastic properties of the lungs but may not directly indicate the presence of trapped air. Blood gas analysis primarily evaluates oxygenation and acid-base status but does not directly assess lung mechanical properties related to auto-PEEP.