Airway pressure release ventilation (APRV) delivers continuous positive airway pressure with periodic releases to facilitate CO₂ removal. It has been proposed both as an early intervention to reduce ventilator-induced lung injury (VILI) and as a rescue strategy for acute respiratory distress syndrome (ARDS). APRV may improve lung homogeneity, alveolar recruitment, and gas exchange, with some studies suggesting better outcomes. However, its clinical use remains limited due to ongoing concerns about safety, efficacy, and lack of standardised settings. Measuring key lung-protective parameters like driving pressure and VILI-related indices is challenging with APRV, making direct comparisons with standard modes difficult.
A new study addresses this gap by using digital twins—computational models of ARDS patients—to compare VILI indices between pressure-controlled ventilation (PCV) and various APRV settings, aiming to clarify APRV’s impact on lung injury risk. Data from 98 ARDS patients receiving PCV were used, including paired ventilator settings and arterial blood gases. VILI indices were computed for each PCV datapoint and for simulated APRV settings (fixed and time-controlled adaptive modes) within the same digital twins. More than 4.8 million parameter variations were tested using global optimisation algorithms to identify the lowest achievable VILI indices while maintaining adequate gas exchange.
In the digital twin simulations, APRV settings with an inspiratory pressure of 25 cm H₂O, low pressure of 0 cm H₂O, inspiration time of 5 s, and expiration time adjusted to achieve 75% of peak expiratory flow (mean 0.5 s) reduced mean mechanical power by 32% and tidal alveolar recruitment/de-recruitment by 34% compared with PCV. These benefits were accompanied by moderate hypercapnia (mean PaCO₂ 58.5 mm Hg, pH 7.32 vs. PaCO₂ 45.6 mm Hg, pH 7.37). Mean driving pressure, tidal volume, and lung stress/strain remained similar between modes. Computational optimisation confirmed these APRV settings were near-optimal for minimising both mechanical power and tidal recruitment/de-recruitment.
This study provides new evidence that APRV can achieve VILI indices comparable to PCV while offering potential lung-protective benefits. Adjusting the Thigh/Tlow ratio could further reduce VILI while preserving normocapnia, potentially benefiting patients in whom hypercapnia must be avoided, such as those with right ventricular failure, pulmonary hypertension, or traumatic brain injury.
The study suggests that carefully applied APRV can reduce mechanical power and tidal alveolar recruitment/de-recruitment compared with PCV in ARDS patients. When moderate hypercapnia is acceptable, effective settings may include Phigh = 25 cm H₂O, Plow = 0 cm H₂O, Thigh = 5 s, and Tlow set to achieve 75% of peak expiratory flow. Optimisation in digital twin simulations indicated these settings are near-optimal for minimising lung injury while maintaining gas exchange. These findings could inform future randomised controlled trials comparing APRV with standard ventilation modes.
Source: Critical Care Medicine
Image Credit: iStock
