1. In patients with acute strokes entering a large ongoing randomised double-blind controlled trial of intravenous glycerol therapy, the extent and pathogenesis of any ensuing haemolysis were evaluated using standard clinical investigations and in vitro techniques. 2. Twenty patients received 10% glycerol in saline (500 ml over 4 h on 6 consecutive days) and 15 received corresponding control treatment with saline. 3. Intravascular haemolysis was evident after the first infusion; compared with the controls the glycerol group had i) a greater mean reduction in serum haptoglobin concentration (P less than .05), and ii) a greater proportion exhibiting haemoglobinaemia (P = 0.03). 4. After 6 days of glycerol treatment, the mean reduction in haemoglobin concentration was only 0.8 g more than in controls; this difference being neither clinically nor statistically significant. 5. Glycerol therapy was not associated with haemoglobinuria, renal insufficiency or disseminated intravascular coagulation. 6. Exposure of red blood cells to 1-10% glycerol in vitro did not induce haemolysis per se; on re-exposure to lower concentrations lysis ensued provided a minimum osmotic gradient was present. 7. Whilst taking standard dosage regimes of glycerol, the stroke patients we studied manifested a degree of intravascular haemolysis but its consequences were not clinically significant; lysis probably ensued after venous blood acquiring high glycerol concentrations mixed with blood containing little or no glycerol.
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