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Abstract
Concentrations of urea, creatinine, uric acid, sodium, potassium, chloride, and osmolality were determined in cerebrospinal fluid and serum before and 4-30 hours after start of 14 hemodialyses carried out with equipment of high efficiency. After 3-4 hours dialysis average serum urea was reduced from 347-76 mg per cent, whereas CSF urea was only reduced to 80 per cent of predialytic values. Osmotic equilibrium between serum and CSF was found after hemodialysis, and could be accounted for by the reduction of the contributions of sodium and chloride to the total osmolality of CSF.
It is suggested that an essential part of the fall in concentration of the non-protein nitrogen compounds in CSF during dialysis was due to dilution of CSF with water dragged into the subarachnoid space by the osmotic gradient between serum and CSF caused by urea.
It is suggested that the re-establishment of the predialytic steady state between the concentrations of urea, creatinine, and uric acid in serum and CSF, which requires 18-24 hours, takes place by bulk absorption of CSF.