Plasma, red cell and cerebrospinal fluid concentrations of mannitol and sorbital in patients with severe chronic renal failure.

The concentrations of mannitol and sorbitol in plasma, red cells, cerebrospinal fluid and urine were determined in 24 patients with chronic renal failure; 10 of them were on conservative treatment and 14 were haemodialysed three times weekly. The mannitol concentration was significantly increased in the plasma and the cerebrospinal fluid of the uraemic patients compared with the controls. In six out of ten uraemic patients mannitol clearance values exceeded creatinine clearance values. The plasma concentration of sorbitol was undetectable or very low in all patients and control subjects. Red-cell and cerebrospinal fluid concentrations of sorbitol showed a large individual variation in the uraemic patients on conservative treatment and did not correlate with kidney function. During dialysis the mannitol concentration decreased, leading to a small osmotic gradient between the plasma and the red cells. The changes in the concentration of mannitol during dialysis showed no connection with the symptoms of central nervous disturbance which appeared during dialysis treatment. The red cell sorbitol concentration during dialysis increased by about 20%. There was a correlation (p less than 0.05) between t,e increase in sorbital in cereemic patients.