Airway occlusion pressure (P0.1)
P0.1, or "airway occlusion pressure", is the pressure generated in the airways during the first 0.1s of an inspiratory effort against an occluded airway.
P0.1 is a good measure of respiratory drive. It increases proportionally to increased pCO2. During the occlusion maneuvre, airway pressure reflects the pressure generated by the respiratory muscles. Without actual volume displacement (due to occlusion), respiratory mechanics do NOT influence the value. The occlusion does not modify the muscle effort because there is no conscious or unconscious reaction to the occlusion (due to the short timeframe).
Monitoring Respiratory Drive and Inspiratory Effort
Respiratory drive is the intensity of the neural stimulus to breath. Currently, there is no method to directly measure the activity of the respiratory centers, therefore respiratory drive is inferred based on their output. Each measure of output entails limitations as an estimate of drive:
- breathing pattern (tidal volume and respiratory rate): influenced by respiratory mechanics independently of the status of respiratory drive.
- electrical activity of the diaphragm: requires catheter insertion, there is no reference value to follow, and represents the activity of only one muscle
- inspiratory effort (esophageal pressure and diaphragm ultrasound): in patients with respiratory muscle weakness, despite a high respiratory drive inspiratory effort might be low (risk of underestimation of repiratory drive)
- P0.1 as described here
Measuring P0.1
Most modern ventilators can measure P0.1. Some estimate the value based on the trigger phase of each breath; some require activation of a short end-expiratory occlusion and subsequent respiratory effort against the occlusion.
Breath to breath variability: generally should average 3-5 measurements. iPEEP can introduce a very small error in the measurement (generally less than 1 cm H2O).
Interpreting P0.1
The value of P0.1 is in detecting an excessive or low respiratory drive and inspiratory effort, and to use these interpretations in guiding management of patient-ventilatory asynchrony.
| Population | Reference Values |
|---|---|
| Healthy adults, spontaneous breathing | 1 cm H2O |
| Ventilated patients, excessive effort | >3.5 cm H2O |
| Ventilated patients, decreased effort | <1.5 cm H2O |