Abstract
BackgroundAn abrupt lung deflation in rodents results in lung injury through vascular mechanisms. Ventilator disconnections during endo-tracheal suctioning in humans often cause cardio-respiratory instability. Whether repeated disconnections or lung deflations cause lung injury or oedema is not known and was tested here in a porcine large animal model.MethodsYorkshire pigs (~ 12 weeks) were studied in three series. First, we compared PEEP abruptly deflated from 26 cmH2O or from PEEP 5 cmH2O to zero. Second, pigs were randomly crossed over to receive rapid versus gradual PEEP removal from 20 cmH2O. Third, pigs with relative volume overload, were ventilated with PEEP 15 cmH2O and randomized to repeated ETT disconnections (15 s every 15 min) or no disconnection for 3 h. Hemodynamics, pulmonary variables were monitored, and lung histology and bronchoalveolar lavage studied.ResultsAs compared to PEEP 5 cmH2O, abrupt deflation from PEEP 26 cmH2O increased PVR, lowered oxygenation, and increased lung wet-to-dry ratio. From PEEP 20 cmH2O, gradual versus abrupt deflation mitigated the changes in oxygenation and vascular resistance. From PEEP 15, repeated disconnections in presence of fluid loading led to reduced compliance, lower oxygenation, higher pulmonary artery pressure, higher lung wet-to-dry ratio, higher lung injury score and increased oedema on morphometry, compared to no disconnects.ConclusionSingle abrupt deflation from high PEEP, and repeated short deflations from moderate PEEP cause pulmonary oedema, impaired oxygenation, and increased PVR, in this large animal model, thus replicating our previous finding from rodents. Rapid deflation may thus be a clinically relevant cause of impaired lung function, which may be attenuated by gradual pressure release.
Highlights
An abrupt lung deflation in rodents results in lung injury through vascular mechanisms
Newer mechanisms of Ventilator-induced lung injury (VILI) are being recognised; recently, using an in-vivo rat model, we have identified a form of lung injury that is caused by an abrupt decrease in airway pressure following sustained inflation [4]
Series I: Deflation from High versus Low PEEP Six pigs were subjected to incremental PEEP from 5 to 26 cmH2O, followed by abrupt release to zero end-expiratory pressure (ZEEP) (High PEEP group); and 4 pigs underwent ventilation at PEEP 5 cmH2O followed by deflation to ZEEP (Low PEEP group)
Summary
An abrupt lung deflation in rodents results in lung injury through vascular mechanisms. Newer mechanisms of VILI are being recognised; recently, using an in-vivo rat model, we have identified a form of lung injury that is caused by an abrupt decrease in airway pressure following sustained inflation (i.e. acute lung deflation) [4]. Attention to acute lung deflation is Katira et al Critical Care (2022) 26:47 important since deflation events resulting from endotracheal tube disconnects during suctioning or transport may occur several times a day in the care of critically ill ventilated patients. Such deflations result in altered respiratory mechanics [5] and reduced oxygenation, alveolar de-recruitment and reduced lung volume [6, 7]. Such deflations, can potentially contribute to altered respiratory function, and may add injury or oedema, thereby impacting outcomes [9,10,11]
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