Lung aeration and volumes following alveolar recruitment maneuvers with three airway pressures in healthy anesthetized and mechanically ventilated Beagle dogs

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ObjectiveTo compare the effects of three recruitment airway pressures (RPaw) on lung aeration and volumes in mechanically ventilated dogs during propofol anesthesia. Study designProspective, crossover randomized experimental study. AnimalsA total of eight healthy anesthetized experimental Beagle dogs in dorsal recumbency. MethodsDogs were mechanically ventilated with a tidal volume of 15 mL kg–1 and zero positive end-expiratory pressure and 100% oxygen. Three maneuvers consisting of a 30 second inspiration at RPaws of 15 (RPaw15), 25 (RPaw25) and 35 (RPaw35) cmH2O were performed randomly, 15 minutes apart. Changes in lung aeration and lung deformation were compared with end-expiratory baseline (before the application of each RPaw) and between-RPaws using computed tomography scans and calculations of global lung strain. Between-group comparisons were performed with one-way anova for repeated measures followed by Tukey test for multiple comparisons. A p value < 0.05 was considered significant. ResultsThe amount of nonaeration was minimal (<1%) at baseline and not different with the application of the RPaws. The amount of hypoaeration and normoaeration during baseline decreased with all RPaws (p < 0.001). There was no difference between RPaws regarding hypoaeration (all p > 0.999), whereas normoaeration was higher at RPaw15 than RPaw25 and RPaw35 (p < 0.009). Compared with baseline, the fraction of hyperaerated alveoli increased with each RPaw (p < 0.001) and was lower during RPaw15 than RPaw25 and RPaw35 (both p ≤ 0.007). Global lung strain was lower during RPaw15 than at higher RPaw (p < 0.001). Conclusions and clinical relevanceA RPaw of 15 cmH2O for 30 seconds was the recommended RPaw because it was as effective at reversing hypoaeration as RPaws of 25 and 35 cmH2O but with less hyperaeration and potential for overdistension of the lungs in this particular population of dogs with negligible atelectasis.