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Positive end-expiratory pressure enhances development of a functional residual capacity in preterm rabbits ventilated from birth

¹Department of Physiology, ³School of Physics, ⁴Monash Centre for Synchrotron Science, and ⁵Division of Biological Engineering, Monash University, Melbourne; and ²Neonatal Research, Royal Women's Hospital, Parkville, Victoria, Australia; and ⁶SPring-8/JASRI, Sayo, Hyogo, Japan

Submitted 2 December 2008 ; accepted in final form 21 March 2009

The factors regulating lung aeration and the initiation of pulmonary gas exchange at birth are largely unknown, particularly in infants born very preterm. As hydrostatic pressure gradients may play a role, we have examined the effect of a positive end-expiratory pressure (PEEP) on the spatial and temporal pattern of lung aeration in preterm rabbit pups mechanically ventilated from birth using simultaneous phase-contrast X-ray imaging and plethysmography. Preterm rabbit pups were delivered by caesarean section at 28 days of gestational age, anesthetized, intubated, and placed within a water-filled plethysmograph (head out). Pups were imaged as they were mechanically ventilated from birth with a PEEP of either 0 cmH₂O or 5 cmH₂O. The peak inflation pressure was held constant at 35 cmH₂O. Without PEEP, gas only entered into the distal airways during inflation. The distal airways collapsed during expiration, and, as a result, the functional residual capacity (FRC) did not increase above the lung's anatomic dead space volume (2.5 ± 0.8 ml/kg). In contrast, ventilation with 5-cmH₂O PEEP gradually increased aeration of the distal airways, which did not collapse at end expiration. The FRC achieved in pups ventilated with PEEP (19.9 ± 3.2 ml/kg) was significantly greater than in pups ventilated without PEEP (–2.3 ± 3.5 ml/kg). PEEP greatly facilitates aeration of the distal airways and the accumulation of FRC and prevents distal airway collapse at end expiration in very preterm rabbit pups mechanically ventilated from birth.

phase contrast X-ray imaging; plethysmography; resuscitation

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