Repeated endo-tracheal tube disconnection generates pulmonary edema in a model of volume overload: an experimental study

Background: An 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. Methods: Yorkshire pigs (similar to 12 weeks) were studied in three series. First, we compared PEEP abruptly deflated from 26 cmH(2)O or from PEEP 5 cmH(2)O to zero. Second, pigs were randomly crossed over to receive rapid versus gradual PEEP removal from 20 cmH(2)O. Third, pigs with relative volume overload, were ventilated with PEEP 15 cmH(2)O 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. Results: As compared to PEEP 5 cmH(2)O, abrupt deflation from PEEP 26 cmH(2)O increased PVR, lowered oxygenation, and increased lung wet-to-dry ratio. From PEEP 20 cmH(2)O, 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. Conclusion: Single 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.

Automated summary

The experiment conducted on a large animal model showed that single abrupt deflation from high positive end-expiratory pressure (PEEP) or repeated short deflations from moderate PEEP can cause pulmonary edema, impaired oxygenation, and increased pulmonary vascular resistance (PVR), consistent with previous findings in rodents. Rapid deflation may therefore be a clinically relevant cause of impaired lung function, which can be attenuated by gradual pressure release.