The human central nervous system discharges carbon dioxide and lactic acid into the cerebrospinal fluid

The central nervous system was previously thought to draw oxygen and nutrition from the arteries and discharge carbon dioxide and other metabolic wastes into the venous system. At present, the functional role of cerebrospinal fluid in brain metabolism is not fully known.

In this prospective observational study, we performed gas analysis on venous blood and cerebrospinal fluid simultaneously acquired from 16 consecutive preoperative patients without any known neurological disorders.

The carbon dioxide partial pressure (pCO₂) (p < 0.0001) and lactic acid level (p < 0.001) in the cerebrospinal fluid were significantly higher than those in the peripheral venous blood, suggesting that a considerable proportion of metabolic carbon dioxide and lactic acid is discharged from the central nervous system into the cerebrospinal fluid. The oxygen partial pressure (pO₂) was much higher in the cerebrospinal fluid than in the venous blood, corroborating the conventional theory of cerebrospinal fluid circulatory dynamics. The pCO₂ of the cerebrospinal fluid showed a strong negative correlation with age (R = - 0.65, p = 0.0065), but the other studied variables did not show significant correlation with age.

Carbon dioxide and lactic acid are discharged into the circulating cerebrospinal fluid, as well as into the venules. The level of carbon dioxide in the cerebrospinal fluid significantly decreased with age.