Cerebrospinal fluid buffering during acute experimental respiratory acidosis

¹ Division of Neurology, University of Washington School of Medicine, Seattle, Washington

Cerebrospinal fluid (CSF) in vitro has less buffering capacity than blood since it lacks serum protein and cellular hemoglobin buffers. However, during acute respiratory acidosis CSF pH falls less than blood pH, indicating a significant in vivo spinal fluid buffering capacity. The nature of this buffering capacity was studied in anesthetized and artificially ventilated cats. Carbon dioxide tensions of 70–75 mm Hg were induced by 7% CO₂ breathing. Simultaneous arterial blood and cisternal CSF samples were drawn at 0, 15, 30, 60, and 120 min. pCO₂ and bicarbonate were measured with a radiometer AME-1 pH meter and tonometer, using the Astrup technique. A rapid increase in CSF bicarbonate maintained spinal fluid significantly more alkaline than blood throughout CO₂ breathing, even though CSF and blood CO₂ tensions were nearly equal. Intravenous bicarbonate did not alter CSF bicarbonate significantly during 2 hr. It is postulated that the buffering capacity of spinal fluid increases as a result of diffusion of preformed bicarbonate from brain cells.