Background: Sodium bicarbonate (NaHCO3) is often used for correction of metabolic acidosis in preterm infants. The effects of NaHCO 3 administration on cerebral hemodynamics and oxygenation are not well known. Furthermore, there is no consensus on infusion rate of NaHCO 3. Objectives: To evaluate the effects of rapid versus slow infusion of NaHCO3 on cerebral hemodynamics and oxygenation in preterm infants. Methods: Twenty-nine preterm infants with metabolic acidosis were randomized into two groups (values are mean ± SD): In group A (GA 30.5 ± 1.7 weeks, b.w. 1,254 ± 425 g) NaHCO3 4.2% was injected as a bolus. In group B (GA 30.3 ± 1.8 weeks, b.w. 1,179 ± 318g) NaHCO3 4.2% was administered over a 30-min period. Concentration changes of oxyhemoglobin (cO2Hb) and deoxyhemoglobin (cHHb) were assessed using near infrared spectrophotometry. Changes in HbD (= cO2Hb - cHHb) represent changes in cerebral blood oxygenation and changes in ctHb (= cO2Hb + cHHb) reflect changes in cerebral blood volume. Cerebral blood flow velocity was intermittently measured using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models (SAS procedure MIXED), to account for the fact that the repeated observations in each individual were correlated. Results: Administration of NaHCO3 resulted in an increase of cerebral blood volume which was more evident if NaHCO3 was injected rapidly than when infused slowly. HbD and cerebral blood flow velocity did not show significant changes in either group. Conclusion: To minimize fluctuations in cerebral hemodynamics, slow infusion of sodium bicarbonate is preferable to rapid injection. Copyright © 2006 S. Karger AG.