Regional Cerebral Blood Flow and Cerebral Metabolic Rate of Oxygen during Hyperventilation in the Newborn Dog

Abstract

Cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO₂) were measured during normocarbia and during both moderate and severe hypocarbia. Eighteen newborn mongrel dogs, 1 to 7 days of age, were given pancuronium and ventilated with 70% N₂O and 30% O₂. The respirator was adjusted to achieve a PaCO₂ of 15 torr, all subsequent changes to 25 and 40 torr were made by adjusting the inspired concentration of CO₂. The sequence of PaCO₂ levels was randomized. CBF was measured by microsphere technique and CMRO₂ calculated as arterial-sagittal sinus O₂ content difference times hemispheric blood flow. AH measurements were made after 30 min at each PaCO₂. Total CBF was reduced at a PaCO₂ of 25 torr (P2 to 15 torr resulted in a significant decrease in total CBF (P 2. All regional cerebral blood flows were reduced at a PaCO₂ of 25 torr (p2 of 15 torr. CMRO₂ was 1.28 ± 0.47 ml/ 100 g/min at a PaCO₂ of 40 torr and fell to 1.09 ± 0.34 (PP2 values of 25 and 15 torr, respectively. Cardiac output was calculated to be 169 ± 71 ml/kg/min at a PaCO₂ of 40 torr and fell to 135 ± 27 (PP2 values of 25 and 15 torr, respectively. Regression analysis of the relationship between PaCO₂ and CBF for values of PaCO₂ between 10 and 50 torr was nonlinear (In CBF=a + b-PaCO₂). A series of regression curves for regional CBF are presented with R values between 0.69 and 0.81 (P2 values of 25 and 15 torr results in significant decreases in total as well as regional cerebral blood flows. CMRO₂ and cardiac output also show significant decreases at PaCO₂ values of both 25 and 15 torr compared to normocarbia. A nonlinear relationship is demonstrated between regional CBF and PaCO₂ between 10 and 50 torr.