Acid-base changes in blood and cerebrospinal fluid during altered ventilation.

Abstract

Functional abnormalities of the central nervous system are observed with hypo- and hyperventilation. This study correlates changes of pH, carbon dioxide tension and carbon dioxide content in arterial and cerebral venous blood and cerebrospinal fluid during altered ventilation. With the experimental design in which ventilation was controlled and the sagittal sinus, femoral artery, and cisterna magna were cannulated, a slight metabolic acidosis was found. With 10% CO2 inhalation acidosis occurred in both blood and spinal fluid and early in the period of inhalation, the usual cerebrospinal-arterial fluid pCO2 gradient was reversed. With hyperventilation, pH and pCO2 changes were more pronounced in the arterial blood but, as hyperventilation was continued, the arterial-cerebrospinal fluid difference decreased. It appeared likely that brain tissue acts as an important buffer, absorbing and releasing CO2 during states of altered ventilation. CO2 diffuses rapidly across cell boundaries, whereas bicarbonate crosses more slowly, thus providing an explanation for the differences noted between blood and cerebrospinal fluid. The particular clinical importance of these observations is that arterial pH, pCO2, and CO2 content may not accurately reflect changes within the cerebrospinal fluid or brain when ventilation is altered. Submitted on May 1, 1961