Pulmonary homogenicity changes during recruitment maneuvers and positive end-expiratory pressure in dogs with acute respiratory distress syndrome

Introduction

The objective of the study was to investigate pulmonary homogenicity changes during recruitment maneuvers (RM) and positive end-expiratory pressure (PEEP) in dogs with pulmonary acute respiratory distress syndrome (ARDSp) or extrapulmonary acute respiratory distress syndrome (ARDSexp).

Methods

After induction of saline lavage-injured ARDS (ARDSp, n = 8) or oleic-acid-injured ARDS (ARDSexp, n = 8), PEEP was set at 20 cmH₂O and RM were performed (40/30-maneuver). RM were repeated every 5 minutes until reaching sufficient alveolar recruitment (PaO₂/FiO₂ > 400 mmHg), and then the tidal volume was set at 10 ml/kg and PEEP was lowered by 2 cmH₂O in every 10 minutes. Optimal PEEP was defined at 2 cmH₂O above the PEEP where PaO₂/FiO₂ dropped below 400 mmHg. Computed tomography (CT) scans were done before and after induction of ARDS and at each pressure level. By the changes in the CT values, the lung was divided into hyperinflated, normally aerated, poorly aerated and nonaerated regions. Lung volumes were calculated by Pulmo software.

Results

After RM, the total lung volume and air volume were significantly increased before and after induction of ARDS in the two models (P < 0.05). At optimal PEEP, poorly aerated and nonaerated lung areas decreased and normally aerated lung areas increased sharply but were accompanied by significant alveolar hyperinflation in the two models (P < 0.05). Compared with ARDSexp models, the changing of hyperinflated lung areas was markedly greater in ARDSp models at optimal PEEP (P < 0.05). After three-dimensional renderings of CT scans, alveolar hyperinflation occurred mainly in nondependent lung regions, whereas alveolar recruitment occurred in dependent regions.

Conclusion

The alveolar hyperinflation increase and pulmonary heterogeneity climb during RM and at optimal PEEP. A focal distribution of lung injury in ARDSp may be more susceptible to alveolar hyperinflation with optimal PEEP.