Effect of craniotomy on regional brain blood flow and ECF pH changes during isocapnic hypoxia.

Regional cerebrovascular responses to 30 min of isocapnic hypoxia were examined in anesthetized rabbits. In some of the animals, a left-side craniotomy was performed and cortical ECF pH was measured either 1 mm or 2-3 mm below the surface. In the animals with open cranium, the increase in blood flow during hypoxia was greater in the right cortex than in the left cortex. In animals with closed cranium, the increases in blood flow were equal in both right and left crania. ECF pH measured 1 mm below the cortical surface decreased throughout the entire 30 min of exposure, while pH measured 2-3 mm below the surface was increased for the first 6 min, after which it began to decrease. Our results indicate that craniotomy reduces the local vasodilation in response to hypoxia which in turn favors a decrease in local ECF pH.