Effects of end-inspiratory and end-expiratory pressures on alveolar recruitment and derecruitment in saline-washout-induced XXXX -- a computed tomography study.

@entity742 @entity12906 @entity651 @entity2507 @entity9239 @entity647
BACKGROUND: Lung protective ventilation using low end-inspiratory pressures and tidal volumes (VT) has been shown to impair alveolar recruitment and to promote derecruitment in @entity647 . The aim of the present study was to compare the effects of two different end-inspiratory pressure levels on alveolar recruitment, alveolar derecruitment and potential overdistention at incremental levels of positive end-expiratory pressure. METHODS: Sixteen adult @entity742 were randomized to be ventilated with a peak inspiratory pressure of either 35 cm @entity2507 (P35, low VT) or 45 cm @entity2507 (P45, high VT) after saline washout-induced @entity651 . Positive end-expiratory pressure ( @entity9239 ) was increased in a stepwise manner from zero (ZEEP) to 7, 14 and 21 cm of @entity2507 in hourly intervals. Tidal volume, initially set to 12 ml kg(-1), was reduced according to the pressure limits. Computed tomographic scans during end-expiratory and end-inspiratory hold were performed along with hemodynamic and respiratory measurements at each level of @entity9239 . RESULTS: Tidal volumes for the two groups (P35/P45) were: 7.7 +/- 0.9/11.2 +/- 1.3 ml kg(-1) (ZEEP), 7.9 +/- 2.1/11.3 +/- 1.3 ml kg(-1) ( @entity9239 7 cm @entity2507 ), 8.3 +/- 2.5/11.6 +/- 1.4 ml kg(-1) ( @entity9239 14 cm @entity2507 ) and 6.5 +/- 1.7/11.0 +/- 1.6 ml kg(-1) ( @entity9239 21 cm @entity2507 ); P < 0.001 for differences between the two groups. Absolute nonaerated lung volumes during end-expiration and end-inspiration showed no difference between the two groups for given levels of @entity9239 , while tidal-induced changes in nonaerated lung volume (termed cyclic alveolar instability, CAI) were larger in the P45 group at low levels of @entity9239 . The decrease in nonaerated lung volume was significant for @entity9239 14 and 21 cm @entity2507 in both groups compared with ZEEP (P < 0.005). Over-inflated lung volumes, although small, were significantly higher in the P45 group. Significant @entity12906 was noted in the P35 group despite increases in the respiratory rate. CONCLUSION: Limiting peak inspiratory pressure and VT does not impair alveolar recruitment or promote derecruitment when using sufficient levels of @entity9239 .
