Abstract
Background: Very preterm newborns with respiratory distress at birth demonstrate increased end-expiratory lung volumes when ventilated with positive end-expiratory pressure (PEEP). However, the regional distribution of ventilation is unknown, especially if PEEP is not held constant but altered as occurs during face mask removal.
Aim: To determine the how the distribution of ventilation changes between different PEEPs
Method: Rabbit pups (28dGA) were delivered by c-section and mechanically ventilated with a peak inflation pressure of 35cmH2O and a sequence of PEEP. The PEEP sequences were (A) 0-5-10-5-0cmH2O, (B) 5-10-0-5-0cmH2O and (C) 10-5-0-10-0cmH2O. Phase contrast X-ray imaging was used to image and analyse the distribution of aeration.
Results: In sequence A and B, upper lobes (U) were more aerated than lower lobes (L) at functional residual capacity (FRC) throughout the ventilation period (A: 10PEEP U vs L - 70.5±2.9% vs 55.7±3.3%, p<0.05; B: 10PEEP U vs L - 70.9±1.5% vs 56.8±2.8%, p<0.05). Tidal volume (VT) aerated U and L similarly until the volume of the lungs at peak inflation (VPIP) achieved >70% of maximal lung volume (p>0.05). Once VPIP was >70%, VT aerated L more than U (A: U vs L; 22.3±3.7% vs 30.3±3.6%, p<0.05; B: U vs L; 20.4±1.6% vs 26.9±1.7%, p<0.05). Sequence C ventilated differently; FRC was only different between lobes at 0PEEP (p>0.05) and VT lacked difference at 10PEEP despite VPIP >70% (p<0.05).
Conclusion: At FRC, U are better aerated than L at different PEEP levels. During inflation, the VT was distributed more to lower lobes than upper lobes after the lungs were fully aerated. This is not observed if lungs were initially aerated with a very high PEEP.
- © 2011 ERS
