Cardiovascular and pulmonary consequences of airway recruitment in preterm lambs

Increases in positive end-expiratory pressure (PEEP) improve arterial oxygenation in preterm infants, but the effects on cardiopulmonary haemodynamics are understood poorly. We aimed to determine the effect of increased PEEP on cardiopulmonary haemodynamics and to compare measurements from indwelling flow-probes with Doppler echocardiography. Preterm lambs (129 +/- 1d) were ventilated initially with a tidal volume (VT) 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 to 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 shunting through the ductus arteriosus (DA), with a trend to an increased Oxygenation Index (OI) compared to controls (OI: 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 to Controls. Doppler echocardiography measurement of LPA flows correlated strongly with indwelling flow-probe (r(2)=0.73, p