Cerebrospinal fluid acid-base balance in newborns.

In adults, cerebrospinal fluid (CSF) acid-base balance is an important determinant of cerebral blood flow, ventilatory drive, and state of consciousness. Sixteen lumbar punctures were performed on newborns (mean gestational age, 33.8 weeks; range, 26 to 44 weeks). The mean CSF pH was 7.366 units, 0.036 less than the mean capillary blood pH (NS). The mean CSF arterial carbon dioxide tension (PCO2) was 40.3 mm Hg, 6.7 greater than the mean blood PCO2 (p less than 0.01). The mean bicarbonate ion concentration in CSF was 21.8 mEq/L, 1.2 greater than that in blood (NS). Acid-base determinations in CSF of neonates with intraventricular hemorrhage did not differ significantly from those of neonates with otherwise normal CSF. These acid-base values are similar to those found in adults and did not vary with gestational age, suggesting that mechanisms to establish this acid-base gradient are developed by 26 weeks' gestation.