Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 99, Issue 4, Pages 1453-1461Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00055.2005
Keywords
ventilation; pulmonary blood flow; fetus; preterm birth
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In mature lungs, elevated positive end-expiratory pressure (PEEP) reduces pulmonary blood flow (PBF) and increases pulmonary vascular resistance (PVR). However, the effect of PEEP on PBF in preterm infants with immature lungs and a patent ductus arteriosus is unknown. Fetal sheep were catheterized at 124 days of gestation (term similar to 147 days), and a flow probe was placed around the left pulmonary artery to measure PBF. At 127 days, lambs were delivered and ventilated from birth with a tidal volume of 5 ml/kg and 4-cmH(2)O PEEP; PEEP was changed to 0,,8, and 12 cmH(2)O in random order, returning to 4 cmH(2)O between each change. Increasing PEEP from 4 to 8 cmH(2)O and from 4 to 12 cmH(2)O decreased PBF by 20.5 and 41.0%, respectively, and caused corresponding changes in PVR; reducing PEEP from 4 to 0 cmH(2)O did not affect PBF. Despite decreasing PBF, increasing PEEP from 4 to 8 cmH(2)O and 12 cmH(2)O improved oxygenation of lambs. Increasing and decreasing PEEP from 4 cmH(2)O significantly changed the contour of the PBF waveform; at a PEEP of 12 cmH(2)O, end-diastolic flow was reduced by 82.8% and retrograde flow was reestablished. Although increasing PEEP improves oxygenation, it adversely affects PBF and PVR shortly after birth, alters the PBF waveform, and reestablishes retrograde flow during diastole.
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