Impact of Inspiratory Pressure Rise Time on Lung-Emptying in Time Controlled Adaptive Ventilation.

Abstract

Background: The airway pressure release ventilation (APRV)-based time controlled adaptive ventilation (TCAV) protocol can potentially minimize ventilator-induced lung injury (VILI). Inspiratory pressure rise time (IPRT) is a parameter available in pressure-controlled ventilation modes, yet its role within TCAV remains unclear. We hypothesized that varying IPRTs impact lung emptying and associated ventilatory parameters (driving pressure [ΔP], intrinsic PEEP [PEEPi], exhaled tidal volume [V_Te]). Methods: This single-center, prospective exploratory study included 10 intubated subjects ventilated utilizing the TCAV protocol. Subjects underwent consecutive experimental trials with IPRTs of 500 and 1,000 ms, each preceded by a baseline (BL) with an IPRT of 0 ms. Analyzed parameters were ventilator-derived ΔP (ΔP_vent), PEEPi, and V_Te. Elastance (E_RS = ΔP_vent/V_Te) and elastance-derived ΔP (ΔP_elast = E_RS × V_Te) were calculated. End-expiratory lung volume (EELV) and end-inspiratory lung volume were assessed through electrical impedance tomography (EIT). Results: Prolonged IPRT increased ΔP_elast compared with ΔP_vent in each baseline/trial combination (ΔP_vent 13.5 ± 1.5 cm H₂O vs ΔP_elast 18.4 ± 2.7 cm H₂O at 1,000 ms IPRT, P < .001) through a loss of PEEPi. Conventional PEEPi measurements did not detect these changes. The EIT data showed a reduction in EELV during the trials. Conclusions: IPRT prolongation under TCAV reduced EELV/PEEPi, therefore increasing ΔP. Conventional PEEPi measurement methods are misleading in this context. We therefore suggest adding the recommendation to set IPRT to 0 ms for the TCAV protocol.