CSF acid-base regulation and ventilation during acute hypercapnia in the newborn dog.

We studied the response of blood, cerebrospinal fluid (CSF), and brain ionic composition and acid-base status as well as ventilation to acute respiratory acidosis (FICO2 0.08) in lightly anesthetized newborn puppies. Control puppy plasma ions and CSF-plasma ionic distribution ratios were essentially adultlike while in blood a mild, compensated respiratory acidosis was present, and in CSF, PCO2 and [HCO3-] were slightly higher than in adults. Brain tissue water content was higher in puppy vs. adult; the Cl- space was greater; the content of [Na+], [Cl-], and [HCO3-] were higher and [K+] lower. During respiratory acidosis, CSF [HCO3-] increased 2.0 mmol/l by 15 min and 6.2 mmol/l by 3 h, a response quantitatively like that observed in the adult. The quantity, CSF [Na+] -- [Cl-], increased stoichiometrically with CSF [HCO3-], indicating the mechanistic involvement of these ions in the CSF [HCO3-] response. In brain tissue, water content, [Cl-], and the [Cl-] space were unchanged, but by 3 h [Na+] and [HCO3-] were increased. Ventilation was stimulated but the response expressed as ml.min-1.Torr-1.body wt-1 was less in puppy than in adult.