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

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

Methods: 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 measurements. The occlusion maneuver was performed on the ventilator, and a corresponding reference P was recorded from the ASL5000 breathing simulator simultaneously. Hamilton-C6, Hamilton-G5, and Servo-U ventilators were used to obtain sustained P measurements (continuous P). The reference P measured with the simulator was analyzed by using a Bland-Altman plot.

Results: The 2 lung mechanical models capable of measuring occlusion P yielded values equivalent to reference P (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 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 for the Servo-U was underestimated only in the obstructive model (bias and precision values were -0.86 and 1.76, respectively). Continuous P for the Hamilton-G5 was mostly similar to but less accurate than occlusion P (bias and precision values were 1.62 and 2.06, respectively).

Conclusions: The accuracy of continuous P 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.