Increase in P50 with the use of bicarbonate hemodialysis

We studied the effect of bicarbonate and acetate on oxygenation during dialysis in ten male chronic dialysis patients. The dialysis delivery system and dialysate constituents were identical except for the use of either bicarbonate or acetate. We found no hemodynamic differences between the two kinds of dialysis. Blood PO2 fell by a similar amount, but blood PCO2 was higher during bicarbonate dialysis. The blood pH became alkalotic by the second hour of bicarbonate dialysis and remained so throughout the dialysis, whereas blood pH became alkalotic only at the end of acetate dialysis. The P50 increased significantly only during bicarbonate dialysis, but 2.3 DPG concentration did not change. Red cell volume, assessed by the mean corpuscular hemoglobin concentration, was unchanged. Without changes in the red cell volume we cannot explain the observed changes in P50 in the absence of concomitant changes in 2.3 DPG concentration.