THE EFFECTS OF RAPID HEMODIALYSIS ON BRAIN TISSUES AND CEREBROSPINAL FLUID OF DOGS

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Abstract
The effects of hemodialysis on cerebral tissue and cerebrospinal fluid constituents and on intracranial pressure were investigated in dogs. It was shown that the potassium content of the cerebral cortical gray matter is decreased in uremic brain. In uremic animals the urea concentration of cerebral tissues was found to be in equilibrium with that of plasma whereas the urea concentration of cerebrospinal fluid was significantly lower. Hemodialysis for 60 minutes with a Kolff twin-coil artificial kidney rapidly decreased the urea concentration in the plasma and caused a considerable but slower decrease in the urea content of cerebral tissues. The urea level in cerebrospinal fluid was only slightly altered. Consequently, a significant transient difference developed between the urea concentrations in brain and plasma. The difference between the concentration of urea in cerebrospinal fluid and plasma was always more pronounced and of longer duration after hemodialysis. Swelling of cortical gray matter was demonstrated in 50% of dialyzed uremic animals and of white matter in 75%. A rapid rise in cerebrospinal fluid pressure occurred during dialysis in all cases. Similar effects were observed when a concentration gradient for sodium between plasma and the central nervous system was produced in normal animals by dialysis against a hyposmotic, low-sodium bath fluid. It was concluded that, in experimental uremia, hemodialysis results in increased cerebrospinal fluid pressure owing to an osmotically induced increase in cerebrospinal fluid volume and, to a variable extent, to osmotically induced cerebral tissue swelling. Osmotically induced cerebral swelling was shown to be a different phenomenon from cerebral edema associated with trauma.