Effect of ventilation style on cardiovascular and renal adaptation in preterm newborn lambs

Renal adaptive responses during the 24 h after delivery in term newborn lambs include marked increases in both glomerular filtration rate (GFR) and sodium reabsorption. This study investigated the effects of ventilation style on cardiovascular, renal, and endocrine adaptations in preterm newborn lambs. Lambs (n = 62) were delivered by cesarean section at 131 days gestation (term = 150 days), treated with surfactant, and randomized to one of three ventilation strategies: high-frequency oscillation (12 Hz), high rate (50 breaths/min; tidal volume = 8 ml/kg), or low rate (15 breaths/min; tidal volume = 15 ml/kg). Lambs (5 or 6/group) were ventilated for 2, 5, 10, and 24 h to maintain arterial PCO2 between 45 and 50 mmHg. Plasma vasopressin levels decreased to <25 pg/ml by 10 h, and fractional sodium excretion decreased to <1% by 16 h in all groups. However, cardiac output, renal plasma flow, and GFR values did not change over time for any of the groups. The style of ventilation employed had no measurable effects on overall cardiovascular, renal, or endocrine function. We conclude in ventilated preterm lambs that 1) the ventilation style does not affect the time course for postnatal adaptation, 2) adaptive changes in renal tubular sodium reabsorption are evident by 16 h after birth, and 3) changes in preterm newborn renal sodium reabsorption occur in the absence of postnatal changes in renal plasma flow or GFR.