title: Positive end-expiratory pressure differentially alters pulmonary hemodynamics and oxygenation in ventilated, very premature lambs.
abstract: 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 approximately 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.
authors.affiliation: Fetal and Neonatal Research Group, Department of Physiology, Monash University, Australia. gpolglase@obsgyn.uwa.edu.au
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Polglase
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Morley
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Crossley
authors.forename: Peter
authors.initials: P
authors.lastname: Dargaville
authors.forename: Richard
authors.initials: R
authors.lastname: Harding
authors.forename: David L
authors.initials: DL
authors.lastname: Morgan
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Hooper
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D005333:Fetus / Q000502:physiology; D005865:Gestational Age; D006439:Hemodynamics / Q000502:physiology; D010101:Oxygen Consumption; D011175:Positive-Pressure Respiration; D011651:Pulmonary Artery / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D012121:Respiration, Artificial; D012756:Sheep; D014655:Vascular Resistance