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Cardiovascular and pulmonary consequences of airway recruitment in preterm lambs

¹School of Women's and Infants' Health, The University of Western Australia, Crawley, Western Australia; ²Department of Physiology, Monash University, Clayton, Victoria; and ³Department of Neonatal Medicine, Royal North Shore Hospital, and University of Sydney, Sydney, New South Wales, Australia

Submitted 3 November 2008 ; accepted in final form 12 February 2009

Increases in positive end-expiratory pressure (PEEP) improve arterial oxygenation in preterm infants, but the effects on cardiopulmonary hemodynamics are understood poorly. We aimed to determine the effect of increased PEEP on cardiopulmonary hemodynamics and to compare measurements from indwelling flow probes with Doppler echocardiography. Preterm lambs (129 ± 1 days) were ventilated initially with a tidal volume of 7 ml/kg and 4 cmH₂O of PEEP. In ramp lambs (n = 7), PEEP was increased by 2-cmH₂O increments to 10 cmH₂O and then in decrements back to 4 cmH₂O. PEEP was unchanged in controls (n = 6). Doppler echocardiographic flow measurements in the left pulmonary artery (LPA) and ductus arteriosus (DA) were correlated with flow probe measurements. Compared with controls, high PEEP reduced LPA flow from baseline (10-cmH₂O PEEP: 43 ± 8% vs. control: 83 ± 21%; P = 0.029). High PEEP increased the proportion of right-to-left (R-L) shunting through the DA, with a trend to an increased oxygenation index compared with controls (oxygenation index: 44.5 ± 13.5 at 10-cmH₂O PEEP vs. 19.4 ± 4.5 in controls; P = 0.07). Increasing PEEP decreased heart rate (17 beats/min; P = 0.03) and tended to lower systolic arterial pressure (5.0 mmHg; P = 0.052) compared with controls. Doppler echocardiography measurement of LPA flows correlated strongly with indwelling flow probe (r² = 0.73, P < 0.001), except during highly turbulent flows. Increases in PEEP have significant cardiopulmonary consequences in preterm lambs, including reduced LPA flow and increased R-L shunt through the DA. These changes are likely due to the concomitant increase in downstream pulmonary vascular resistance and increased cardiovascular constraint induced by PEEP.

pulmonary hemodynamics; Doppler echocardiography; waveform analysis; preterm; cardiovascular

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