Setting Positive End-Expiratory Pressure During Jet Ventilation to Replicate the Mean Airway Pressure of Oscillatory Ventilation

BACKGROUND: High-frequency ventilation can be delivered with either oscillatory ventilation (HFOV) or jet ventilation (HFJV). Traditional clinician biases may limit the range of function of these important ventilation modes. We hypothesized that (1) the jet ventilator can be an accurate monitor of mean airway pressure (P̄_aw) during HFOV, and (2) a mathematical relationship can be used to determine the positive end-expiratory pressure (PEEP) setting required for HFJV to reproduce the P̄_aw of HFOV.

METHODS: In phase 1 of our experiment, we used a differential pressure pneumotachometer and a jet adapter in-line between an oscillator circuit and a pediatric lung model to measure P̄_aw, PEEP, and peak inspiratory pressure (PIP). Thirty-six HFOV setting combinations were studied, in random order. We analyzed the correlation between the pneumotachometer and HFJV measurements. In phase 2 we used the jet as the monitoring device during each of the same 36 combinations of HFOV settings, and recorded P̄_aw, PIP, and ΔP. Then, for each combination of settings, the jet ventilator was placed in-line with a conventional ventilator and was set at the same rate and PIP as was monitored during HFOV. To determine the appropriate PEEP setting, we calculated the P̄_aw contributed by the PIP, respiratory rate, and inspiratory time set for HFJV, and subtracted this from the goal P̄_aw. This value was the PEEP predicted for HFJV to match the HFOV P̄_aw.

RESULTS: The correlation coefficient between the pneumotachometer and HFJV measurements was r = 0.99 (mean difference 0.62 ± 0.30 cm H₂O, p < 0.001). The predicted and actual PEEP required were highly correlated (r = 0.99, p < 0.001). The mean difference in these values is not statistically significantly different from zero (mean difference 0.25 ± 1.02 cm H₂O, p > 0.15).

CONCLUSIONS: HFJV is an accurate monitor during HFOV. These measurements can be used to calculate the predicted PEEP necessary to match P̄_aw on the 2 ventilators. Replicating the P̄_aw with adequate PEEP on HFJV may help simplify transitioning between ventilators when clinically indicated.