High-Frequency Percussive Ventilation: Pneumotachograph Validation and Tidal Volume Analysis

INTRODUCTION: High-frequency percussive ventilation (HFPV) is an increasingly used mode of mechanical ventilation, for which there is no proven real-time means of measuring delivered tidal volume (V_T).

OBJECTIVE: To validate a pneumotachograph for HFPV and then exploit flow-sensor data to describe the behavior of both low-frequency and high-frequency breaths.

METHODS: Sensor performance was gauged during changes in high-frequency (4–12 Hz) and low-frequency rate and ratio, mean airway pressure, oxygen concentration, heated or heated-humidified gas flow, and endotracheal tube diameter. Glass bottle (adiabatic V_T) and test lung (adiabatically derived low-frequency V_T) based adiabatic conditions provided both an initial source for analog-signal calibration and an accepted standard comparator to flow-sensor measurement of high-frequency and low-frequency (flow-sensor-derived) V_T), respectively.

RESULTS: Pneumotachography proved accurate and precise over an array of tested settings and conditions when analyzing both high-frequency (difference between mean ± SD high-frequency V_T and adiabatic V_T was –0.2 ± 1.8%, 95% confidence interval –0.5 to 0.9%) and low-frequency breaths (mean ± SD difference between flow-sensor-derived low-frequency V_T and adiabatically derived low-frequency V_T was 0.6 ± 2.4%, 95% confidence interval 0.1–1.1%). High-frequency V_T and frequency exhibited an exponential relationship. During HFPV, flow-sensor-derived low-frequency V_T had a mean ± SD of 1,337 ± 700 mL, 95% confidence interval 1,175–1,499 mL.

CONCLUSIONS: Readily available pneumotachography provided accurate measurements of low-frequency and high-frequency V_T during HFPV. In the setting of acute lung injury, typical HFPV settings may deliver injurious V_T.