The Effects of Acute Total Asphyxia and Metabolic Acidosis on Cerebrospinal Fluid Bicarbonate Regulation in Newborn Puppies

Abstract

Summary: We evaluated CSF [HCO₃-] regulation in lightly anesthetized newborn puppies following: (1) acute total asphyxia; (2) metabolic acidosis; and (3) metabolic acidosis induced after acute asphyxia. Five and one-half min of total asphyxia resulted in a 4.4 mM/liter decrease in mean CSF [HCO₃-]. During 65 min of recovery with mechanical ventilation mean CSF [HCO₃-] increased 1.7 mM/liter. Mean plasma [HCO₃-] decreased 7 mM/liter and recovered 4.5 mM/liter in the same period. We produced a stable metabolic acidosic for 4 hr using a peritoneal dialysis technique with PaCO₂ maintained at the normal value. With acidosis in nonasphyxiated control puppies, CSF [HCO₃-] decreased steadily. At 4 hr, the ratio, ΔCSF [HCO₃-]/Δplasma [HCO₃-], was 0.43, a value close to that observed in adults of many species with metabolic acid-base disturbances, 0.41. With acidosis in asphyxiated puppies allowed 1 hr of recovery, the time course and mean values of plasma and CSF [HCO₃-] were indistinguishable from those of the nonasphyxiated acidotic controls. Newborn puppies appear to regulate CSF [HCO₃-] in response to acute asphyxia or metabolic acidosis, and acute asphyxia does not impair the puppy's ability to regulate CSF [HCO₃-] in metabolic acidosis.

Speculation: The puppy can regulate CSF [HCO₃-] in two stresses which occur commonly in the newborn period, birth asphyxia, and metabolic acidosis. This ability would help to preserve normal acid-base balance in the central nervous system during these stresses.

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