Novel Time-Controlled Adaptive Ventilation Method to Minimize VILI

The current ARDS Network (ARDSNet) Acute Respiratory Management Approach (ARMA) follows a Protect the Lung Approach (PLA) strategy, aiming to prevent overdistension of the normal tissue (“baby lung”) while ventilating a heterogeneously injured lung with regional alveolar instability and collapse. However, the low tidal volume (VT) and airway pressures in ARMA facilitate the progressive loss of end-expiratory lung volume (EELV), pushing the lung into the ventilator-induced lung injury (VILI) vortex (Fig. 2.4 ). The Open Lung Approach (OLA) attempts to prevent the lung from entering the VILI vortex using recruitment maneuvers (RM), and higher positive end-expiratory pressure (PEEP) but, unfortunately, has not effectively reestablished durable recruitment. To address this, an alternative strategy is the Time-Controlled Adaptive Ventilation (TCAV) method, which employs the Stabilize the Lung Approach (SLA) method to set and adjust the airway pressure release ventilation (APRV) mode. This method represents a paradigm shift in lung-protective mechanical ventilation, designed to immediately stabilize alveoli and prevent progressive loss of EELV, thereby removing the lungs’ progression into the VILI vortex. Over hours or days, TCAV allows for gradual safe lung reopening, ultimately reestablishing homogeneous ventilation. The Mechanical Breath Profile (MBP), encompassing all airway volumes, pressures, flows, rates, and the time they are applied during inspiration and expiration, plays a crucial role in TCAV efficacy. The significant difference between the SLA method with TCAV and the ARMA, PLA, or OLA methods lies in using the MBP component of time. TCAV utilizes inspiratory and expiratory time as ‘tools’ in the ventilator toolbox to protect the acutely injured lung. Understanding that ARDS pathophysiology renders the lung time- and pressure-dependent (Chap. 5 ) is critical in designing a physiologically based lung-protective mechanical breath using both inspiratory and expiratory time (Figs. 5.3 , 5.4 , 5.6 , 5.7 , and 5.8 , Videos 5.1, 5.2, and 5.3). The extended time at inspiration with TCAV (CPAP Phase) facilitates recruitment, while a brief time at expiration (Release Phase) helps minimize alveolar re-collapse. TCAV is personalized and adaptive, where the expiratory time is adjusted based on changes in respiratory system compliance (CRS). The TCAV method couples VT with CRS. A low CRS results in a decreased VT and vice versa. This prevents delivering a high VT into a collapsed, stiff lung, keeping driving pressure low, or a low VT to a more compliant lung that could result in loss of EELV. The extended inspiratory time gradually reopens collapsed viscoelastic lung tissue over hours or days, depending on the severity of ARDS. Lung reopening during the extended CPAP phase is assisted by an “inflate and brake” method, ratcheting open small volumes of lung tissue with each breath. Thus, the TCAV method is similar to the “inflate and brake” mechanism by which the newborn gradually ratchets open their fluid-filled lungs at birth. While literature demonstrates the TCAV efficacy in various animal injury models, case studies, small prospective clinical studies, and meta-analyses, the main obstacle preventing its widespread adoption as a primary ventilation mode is the lack of a large randomized controlled trial (RCT) similar to the ARMA method.