Atelectrauma Versus Volutrauma: A Tale of Two Time-Constants
Jason H. T. Bates, Donald P. Gaver, Nader M. Habashi, Gary F. Nieman
Abstract
Objectives: Elucidate how the degree of ventilator-induced lung injury due to atelectrauma that is produced in the injured lung during mechanical ventilation is determined by both the timing and magnitude of the airway pressure profile. Design: A computational model of the injured lung provides a platform for exploring how mechanical ventilation parameters potentially modulate atelectrauma and volutrauma. This model incorporates the time dependence of lung recruitment and derecruitment, and the time-constant of lung emptying during expiration as determined by overall compliance and resistance of the respiratory system. Setting: Computational model. Subjects: Simulated scenarios representing patients with both normal and acutely injured lungs. Measurements and Main Results: Protective low-tidal volume ventilation (Low-V t ) of the simulated injured lung avoided atelectrauma through the elevation of positive end-expiratory pressure while maintaining fixed tidal volume and driving pressure. In contrast, airway pressure release ventilation avoided atelectrauma by incorporating a very brief expiratory duration ( JOURNAL/ccex/04.03/02107256-202012000-00019/inline-graphic1/v/2023-10-20T231948Z/r/image-jpeg ) that both prevents enough time for derecruitment and limits the minimum alveolar pressure prior to inspiration. Model simulations demonstrated that JOURNAL/ccex/04.03/02107256-202012000-00019/inline-graphic2/v/2023-10-20T231948Z/r/image-jpeg has an effective threshold value below which airway pressure release ventilation is safe from atelectrauma while maintaining a tidal volume and driving pressure comparable with those of Low-V t . This threshold is strongly influenced by the time-constant of lung-emptying. Conclusions: Low-V t and airway pressure release ventilation represent markedly different strategies for the avoidance of ventilator-induced lung injury, primarily involving the manipulation of positive end-expiratory pressure and JOURNAL/ccex/04.03/02107256-202012000-00019/inline-graphic3/v/2023-10-20T231948Z/r/image-jpeg , respectively. JOURNAL/ccex/04.03/02107256-202012000-00019/inline-graphic4/v/2023-10-20T231948Z/r/image-jpeg can be based on exhalation flow values, which may provide a patient-specific approach to protective ventilation.