Biochemical changes associated with the use of haemodilution with 5 per cent dextrose in water and mannitol for open-heart surgery.

Many advantages are gained from the use of haemodilution in open-heart surgery. There is a lessened post-operative morbidity from bleeding, renal failure, and serum hepatitis. However, dilution with 5% dextrose in water is associated with a greater metabolic acidosis and a higher incidence of serious dysrhythmias than is pure blood. In order to elucidate the causes of these complications, 26 patients were studied using different degrees of haemodilution. The metabolic acidosis appeared to be mainly due to the dilution of blood buffer. Changes in electrolyte balance were more marked with greater dilution. The effects on serum sodium and chlorides were transient. The serum potassium level fell markedly during the post-operative phase and was associated with dysrhythmias. We believe that variation in potassium concentration is due to redistribution of potassium between the intracellular and extracellular phase as well as to an increased urinary excretion of potassium. The acidosis and hypokalaemia can be rapidly corrected by the administration of sodium bicarbonate and potassium. The changes in acid-base metabolism and electrolyte balance can possibly be prevented by suitably modifying the priming fluid.