Preemptive Mechanical Ventilation Based on Dynamic Physiology in the Alveolar Micro-environment: Novel Considerations of Time-Dependent Properties of the Respiratory System

The acute respiratory distress syndrome (ARDS) remains a serious clinical problem with the current treatment being supportive in the form of mechanical ventilation. However, mechanical ventilation can be a double-edged sword; if set properly, it can significantly reduce ARDS associated mortality but if set improperly it can have unintended consequences causing a secondary ventilator induced lung injury (VILI). The hallmark of ARDS pathology is a heterogeneous lung injury, which predisposes the lung to a secondary VILI. The current standard of care approach is to wait until ARDS is well established and then apply a low tidal volume (LVt) strategy to avoid over-distending the remaining normal lung. However, even with the use of LVt strategy, the mortality of ARDS remains unacceptably high at ~40%. In this review, we analyze the lung pathophysiology associated with ARDS that renders the lung highly vulnerable to a secondary VILI. The current standard of care LVt strategy is critiqued as well as new strategies used in combination with LVt to protect the lung. Using the current understanding of alveolar mechanics (i.e. the dynamic change in alveolar size and shape with tidal ventilation) we provide a rationale for why the current protective ventilation strategies have not further reduced ARDS mortality. New strategies of protective ventilation based on dynamic physiology in the micro-environment (i.e. alveoli and alveolar ducts) are discussed. Current evidence suggests that alveolar inflation and deflation is viscoelastic in nature, with a fast and slow phase in both alveolar recruitment and collapse. Using this knowledge, a ventilation strategy with a prolonged time at inspiration would recruit alveoli and a brief release time at expiration would prevent alveolar collapse, converting heterogeneous to homogeneous lung inflation significantly reducing ARDS incidence and mortality. Competing interest:PLA, GFN, MKS, and NMH have presented and received honoraria and/or travel reimbursement at event(s) sponsored by Dräger Medical Systems, Inc., outside of the published work. PLA, GFN and NMH have lectured for Intensive Care Online Network, Inc. (ICON). JV has received research grants from Maquet. NMH is the founder of ICON, of which PLA is an employee. NMH holds patents on a method of initiating, managing and/or weaning airway pressure release ventilation, as well as controlling a ventilator in accordance with the same, but these patents are not commercialized, licensed nor royalty-producing. The authors maintain that industry had no role in the design and conduct of the study; the collection, management, analysis, or interpretation of the data; nor the preparation, review, or approval of the manuscript. Corresponding Author: Joshua Satalin, 750 East Adams St, Syracuse, NY 13210, satalinj@upstate.edu © 2018 Lippincott Williams & Wilkins, Inc.

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