AIM To examine in vitro the effects of brief contact with various infusion solutions on red blood cells from newborn infants, as occurs in the “waste” syringe during routine blood sampling from umbilical artery catheters. The mixture of blood and solution in the “waste” syringe is usually reinfused into the baby. Reinfused red blood cells may be damaged by the infusion solution. It is hypothesised that an isotonic amino acid solution would cause no red blood cell agglutination and no more haemolysis than many commonly used solutions.

RESULTS A 0.25% normal saline solution caused 5.4% haemolysis, significantly more than all the other fluids tested. There was less haemolysis with 0.25% normal saline when there was complete mixing of blood and solution within the “waste” syringe. Normal saline and isotonic sodium acetate solutions caused < 0.1% haemolysis, significantly less than all the other fluids tested. The isotonic amino acid solution caused 0.8% haemolysis, which is similar to that caused by the remaining solutions tested. Agglutination was seen with isotonic dextrose and with the two isotonic amino acid solutions containing cysteine.

CONCLUSIONS Isotonic amino acid solution (without added cysteine) caused no agglutination and the same or less haemolysis than many commonly used solutions and may offer advantages in nutrition and fluid balance.