The effect of metabolic acidosis upon autoregulation of cerebral blood flow in newborn dogs.

The radioactive microsphere technique was used in 13 newborn dogs to determine the effect of a metabolic (lactic)acidosis upon cardiac output (CO), cerebral blood flow (CBF), and autoregulation of cerebral blood flow. The animals were mechanically ventilated with supplemental oxygen to ensure normocarbia and hyperoxia throughout the experiments. Baseline cardiac output and cerebral blood flow measurements were made, followed by a lactic acid infusion to maintain pH less than 7.25. Metabolic acidosis produced a 27% fall in cardiac output and no change in cerebral blood flow (19 ml/100 g/min). Autoregulation was tested in 6 of the acidemic puppies by acute volume depletion to reduce blood pressure by 30% of baseline, followed by rapid volume re-expansion of the withdrawn blood. With volume depletion, CO decreased by 38%, and with volume re-expansion CO returned to baseline. The CBF remained at baseline levels with volume depletion but was slightly increased after rapid volume re-expansion. Five acidemic controls maintained CO and CBF constant with time. Thus cerebral autoregulation is preserved in the newborn dogs during metabolic acidosis, although cerebral blood flow was slightly increased following volume re-expansion.