Background Cerebral blood flow velocity (CBFv) in premature infants has been extensively studied due to the association between CBF disturbances and brain injury. Norms for CBFv in newborns 23–24 weeks’ gestation during the first week of life, however, have not been reported.

Objective Determine reference values for CBFv in healthy ventilated newborns 23–24 weeks’ gestation during the first week. Determine how CBFv norms are affected by CO2.

Methods Normotensive newborns at 23–24 weeks’ gestation without brain injury had Doppler ultrasound monitoring of middle cerebral artery CBFv twice daily during the first 3 days, and daily for the next 4 days. Baseline mean CBFv (approximately 15 min) was determined for each infant. A locally weighted regression technique was used; mean CBFv and 95% CIs were plotted for the population during the first week. Since CBFv increases 30% for every 7.5 mm Hg change in CO2, reference curves were also determined when CO2 was adjusted to 40, 50, and 60 mm Hg.

Results Eighteen newborns 23–24 weeks gestation had 74 baseline measurements during the first week. Birth weight was 612 85 grams. Mean CBFv increased from 10 to 21 cm/sec during the first week. Mean CBFv increased from 8 to 9, 12 to 15, and 16 to 23 cm/sec during the first week, respectively, when CO2 was adjusted to 40, 50, and 60 mm Hg.

Conclusions We present for the first time reference values for CBFv for normotensive newborns born at 23–24 weeks’ gestation and reference curves adjusted according to CO2.