Effect of inhaling 100% O2 on ventilation and acid-base balance in cerebrospinal fluid of neonates.

If 100% O2 produces hyperventilation by increasing central CO2 due to cerebral vasoconstriction or dimished reduction of oxyhemoglobin, then, there should be a parallel decrease in alveolar and CSF PCO2 during O2 breathing in neonates. To test this hypothesis, we measured ventilation, alveolar PCO2 and CSF PCO2, pH and HCO2 before and 10-20 min after infants began breathing 100% O2. With 100% O2, minute ventilation increased from 0.193 +/- (SE) 0.013 (n = 7) to 0.252 +/- 0.013 liter/min/kg (p less than 0.015), PACO2 decreased from 42 +/- 2 to 38 +/- 2 mm Hg (p less than 0.005), CSF PCO2 decreased from 51 +/- 1 to 44 +/- 1 mm Hg (p less than 0.015), and pH increased from 7.308 +/- 0.013 to 7.354 +/- 0.013 (p less than 0.05). CSF bicarbonate decreased, but not significantly. These findings, showing a trend toward alkalosis, suggest that the neonate, like the adult man, induces hyperventilation during hyperoxia via an increase in PCO2 at the central level.