A study of experimental acute lung injury in pigs on zero end-expiratory pressure

Abstract

ObjectivesTidal expiratory flow limitation (EFL) has been reported in humans with acute lung injury (ALI) and assumed to be associated with small airway closure. Detection of EFL is important because by selecting positive end-expiratory pressure at such a level that EFL is no longer present in the tidal breath, the repeated opening and closure of small airways can be prevented. The objective of this study was to investigate the occurrence of EFL in two experimental models of ALI. AnimalsTen female piglets. MethodsAnimals were anaesthetized, tracheotomized and mechanically ventilated on zero end-expiratory pressure. Acute lung injury was induced by oleic acid (OA) (n = 5) or saline lavage (SL) (n = 5). Tidal EFL was assessed by the negative expiratory pressure test. Lung and chest wall mechanics were partitioned using an oesophageal balloon. Resistance and static elastance were assessed by a rapid airway occlusion technique at baseline ventilatory settings. ResultsThere was no EFL at any time before and after ALI in both models. This may be due to an increased elastance which promoted higher expiratory flow after ALI and to a decreased chest wall to lung static elastance ratio which could favour small airways patency. The similar increase in total lung resistance, in the two models, after ALI was mostly due to an increased airway resistance in the OA model and to the lung tissue resistance in the SL model. Conclusions and clinical relevanceTidal EFL was not detected in experimental ALI. This finding casts some doubt about the usefulness of some experimental models of ALI to mimic some reported findings in human ALI.