Effect of PaCO2 and Haemoglobin Concentration on Day to Day Variation of CBF in Preterm Neonates

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Abstract
The CBF was measured on the first three days of life in 22 mechanically ventilated, preterm neonates (mean gestational age 29.5 weeks) with simultaneous recordings of arterial carbon dioxide tension (PaCO2), arterial oxygen tension (PaO2), haemoglobin concentration (Hgb), haemoglobin oxygen saturation and mean arterial blood pressure (MABP). CBF.infin. tended to increase slightly with age. The intra-individual variation of CBF.infin. was positively related to changes in PaCO2 (p = 0.0004) and inversely related to changes in Hgb (p = 0.029). Neither PaO2 nor MABP achieved a significant relation to changes in CBF.infin.. Thus, the mean CBF.infin.-CO2 reactivity was calculated to 22.1% per kPa whereas CBF.infin. increased by a mean of 11.9% per mM decrease of Hgb thereby providing a constant oxygen delivery to the brain. It is concluded that PaCO2 and Hgb have the expected effect on CBF.infin. in preterm neonates even during respiratory distress shortly after birth.