Bias and Precision of Continuous P_0.1 Measurement by Various Ventilators: A Simulation Study

Most ventilators measure airway occlusion pressure (occlusion P_0.1) by occluding the breathing circuit; however, some ventilators can predict P_0.1 for each breath without occlusion. Nevertheless, few studies have verified the accuracy of continuous P_0.1 measurement. The aim of this study was to evaluate the accuracy of continuous P_0.1 measurement compared with that of occlusion methods for various ventilators using a lung simulator.

A total of 42 breathing patterns were validated using a lung simulator in combination with 7 different inspiratory muscular pressures and 3 different rise rates to simulate normal and obstructed lungs. PB980 and Dräger V500 ventilators were used to obtain occlusion P_0.1 measurements. The occlusion maneuver was performed on the ventilator, and a corresponding reference P_0.1 was recorded from the ASL5000 breathing simulator simultaneously. Hamilton-C6, Hamilton-G5, and Servo-U ventilators were used to obtain sustained P_0.1 measurements (continuous P_0.1). The reference P_0.1 measured with the simulator was analyzed by using a Bland-Altman plot.

The 2 lung mechanical models capable of measuring occlusion P_0.1 yielded values equivalent to reference P_0.1 (bias and precision values were 0.51 and 1.06, respectively, for the Dräger V500, and were 0.54 and 0.91, respectively, for the PB980). Continuous P_0.1 for the Hamilton-C6 was underestimated in both the normal and obstructive models (bias and precision values were -2.13 and 1.91, respectively), whereas continuous P_0.1 for the Servo-U was underestimated only in the obstructive model (bias and precision values were -0.86 and 1.76, respectively). Continuous P_0.1 for the Hamilton-G5 was mostly similar to but less accurate than occlusion P_0.1 (bias and precision values were 1.62 and 2.06, respectively).

The accuracy of continuous P_0.1 measurements varies based on the characteristics of the ventilator and should be interpreted by considering the characteristics of each system. Moreover, measurements obtained with an occluded circuit could be desirable for determining the true P_0.1.