In Vivo Measurements of Respiratory Parameters during HFPV

High-frequency percussive ventilation (HFPV) is a non-conventional ventilatory modality which has proven effective and safe in patients with acute respiratory failure. HFPV associates the beneficial aspects of conventional mechanical ventilation with those of high-frequency ventilation. At the present time, HFPV ventilator provides only analog airway pressure waveform and digital output of peak and the mean airway pressures. Currently, the latter is the only parameter that allows an indirect comparison between conventional volume controlled ventilation (VCV) and HFPV treatment set up. The aim of this pilot study was to measure in vivo the main respiratory parameters, in order to use them for a new bedside monitoring of HFPV treatment. For such purpose pressure, flow and volume were measured in five patients undergoing HFPV. Lung resistance and compliance were estimated using multiple linear regression method on Dorkin high frequency pulmonary model, while endotracheal tube pressure drop was estimated using Blasius model. The results of this study showed that during the transition from conventional VCV to HFPV the tidal volume delivery can significantly change, although the same mean airway pressure was setup. Thus the volume measurement is clinically important during HFPV treatment. The validity of the Dorkin model during HFPV was confirmed in vivo. Moreover, the estimation of resistance, compliance and endotracheal tube pressure drop through non-invasive method represents an important step towards personalized HFPV treatment.