Cardiovascular effects of carbon dioxide in ventilated preterm infants.

Sick preterm infants may, under certain conditions, demonstrate blood pressure passive cerebral blood flow in response to changes in arterial carbon dioxide tension. Blood pressure in turn depends on cardiac output and peripheral resistance. A Doppler technique for assessing cardiac output compared favourably in terms of reproducibility to a thermodilution technique in a group of infants undergoing cardiac catheterization for congenital heart disease. Doppler was subsequently used to monitor changes in cardiac output following an increase in arterial carbon dioxide tension of 1 kPa in 25 ventilated preterm infants. Blood pressure increased significantly (p = 0.006). However, heart rate did not change significantly (p = 0.16) and, in addition, both stroke and minute volume decreased (p = 0.023, p = 0.02, respectively). This suggests that accompanying changes in components of peripheral resistance exert important effects on blood pressure in the preterm neonate in response to changes in arterial carbon dioxide tension.