Spontaneous breathing promotes lung injury in an experimental model of alveolar collapse

Abstract

Vigorous spontaneous breathing has emerged as a promotor of lung damage in acute lung injury, an entity known as “patient self-inflicted lung injury”. Mechanical ventilation may prevent this second injury by decreasing intrathoracic pressure swings and improving regional air distribution. Therefore, we aimed to determine the effects of spontaneous breathing during the early stage of acute respiratory failure on lung injury and determine whether early and late controlled mechanical ventilation may avoid or revert these harmful effects. A model of partial surfactant depletion and lung collapse was induced in eighteen intubated pigs of 32 ±4 kg. Then, animals were randomized to (1) SB‐group: spontaneous breathing with very low levels of pressure support for the whole experiment (eight hours), (2) Early MV-group: controlled mechanical ventilation for eight hours, or (3) Late MV-group: first half of the experiment on spontaneous breathing (four hours) and the second half on controlled mechanical ventilation (four hours). Respiratory, hemodynamic, and electric impedance tomography data were collected. After the protocol, animals were euthanized, and lungs were extracted for histologic tissue analysis and cytokines quantification. SB-group presented larger esophageal pressure swings, progressive hypoxemia, lung injury, and more dorsal and inhomogeneous ventilation compared to the early MV-group. In the late MV-group switch to controlled mechanical ventilation improved the lung inhomogeneity and esophageal pressure swings but failed to prevent hypoxemia and lung injury. In a lung collapse model, spontaneous breathing is associated to large esophageal pressure swings and lung inhomogeneity, resulting in progressive hypoxemia and lung injury. Mechanical ventilation prevents these mechanisms of patient self-inflicted lung injury if applied early, before spontaneous breathing occurs, but not when applied late.

Failure of First Transition to Pressure Support Ventilation After Spontaneous Awakening Trials in Hypoxemic Respiratory Failure: Influence of COVID-19

“…However, assisted ventilation led to profound hypoxemia in most of the patients who failed, which albeit hypothetical in nature, could have modified the patient’s clinical course. Bachmann et al observed persistent severe hypoxemia in ARDS models undergoing PSV even after 4 hours of a recovery period under protective MV ( 41 ). Similarly, we observed wide NMBAs and prone requirements after failure due to severe hypoxemia, which unfaithfully delayed ventilator weaning and prolonged MV.…”

Acinar micromechanics in health and lung injury: what we have learned from quantitative morphology

“…In a healthy lung, however, the pulmonary surfactant system not only reduces but also harmonizes surface tension in the alveoli, so that alveoli of different sizes can co-exist and stress concentration is avoided ( Schürch, 1982 ; Schirrmann et al, 2010 ). Low volume mechanical ventilation or spontaneous breathing in presence of stress concentrations, such as microatelectases or flooded alveoli, results in injury of the blood-gas barrier and degradation of lung mechanics, despite no increase in strain at the organ level ( Wu et al, 2014 ; Albert et al, 2020 ; Krischer et al, 2021 ; Bachmann et al, 2022 ). High tidal volume ventilation with low positive end-expiratory pressure produces progressive ventilation-induced lung injury with severe damage of the blood-gas barrier in mice ( Hamlington et al, 2018 ).…”

Patient Self-Inflicted Lung Injury—A Narrative Review of Pathophysiology, Early Recognition, and Management Options

“…Although evidence from experimental and clinical studies suggests that P-SILI is a severe and life-threatening clinical condition, intensivists have no consensus on when to intubate a patient with excessive respiratory effort. In animal studies with artificially induced lung injury, early use of mechanical ventilation eventually led to less severe lung injury than leaving them to ventilate spontaneously with vigorous effort, and mechanical ventilation prevented self-inflicted lung injury if applied early but not when applied late [6,7,67,68]. Some authors, therefore, advocate that in the context of high respiratory drive and vigorous respiratory effort, mechanical ventilation with lung-protective parameters might be considered a protective therapy to minimize P-SILI [5,69].…”