Short-term studies on the use of glycerol as an osmotic agent in continuous ambulatory peritoneal dialysis (CAPD)

The use of glycerol as an osmotic agent in two different concentrations (92 mmol/l and 272 mmol/l) in peritoneal dialysis fluid was investigated over 3 days in six patients on continuous ambulatory peritoneal dialysis and compared with two concentrations of glucose (76 mmol/l and 215 mmol/l) in the same patients. The calorific value of the absorbed osmotic agent was lower, by 19% with isotonic and 22% with hypertonic solutions, when glycerol was used in place of glucose. However, glycerol provided significantly lower total ultrafiltration than glucose at each concentration, despite a higher initial osmotic pressure of the glycerol-based solutions. Thus, the higher concentration of glycerol required to provide equal ultrafiltration may offset any calorific advantage. Equilibration of creatinine and urea was slower and creatinine clearance lower with glycerol. Solutions containing glycerol were initially less acid (pH 6.5) than those containing glucose (pH 5.1). Blood glycerol levels, which were in the physiological range with glucose as the osmotic agent, reached a peak 80-fold greater at 4.3 +/- 0.8 mmol/l during dialysis with fluid containing glycerol at 272 mmol/l and eightfold higher at 0.42 +/- 0.09 mmol/l with glycerol at 92 mmol/l. There was no evidence of haemolysis or other toxic effect despite these levels. The rise in blood glucose and insulin noted during the use of glucose-based solutions was not found with glycerol. Circulating levels of lactate, pyruvate, alanine, non-esterified fatty acids and the ketone bodies were similar with the two agents. Although these short-term studies have shown no conclusive advantage of glycerol over glucose, long-term effects of glycerol, particularly on circulating lipid levels, will determine its future role as an osmotic agent in continuous ambulatory peritoneal dialysis.