Effect of heparin on umbilical arterial blood gases.

Arterial blood gas analysis was performed utilizing different heparin volumes and concentrations on 20 umbilical cord blood samples. A significant decrease in the bicarbonate concentration and base excess was found when 10,000 instead of 1,000 U/mL heparin was used to coat the syringe. When 0.2 mL of 1,000 U/mL heparin was added to 0.8 mL of blood, significant decline in the PCO2, base excess and bicarbonate concentration occurred. When 0.2 mL of 10,000 U/mL heparin was added to 0.8 mL of blood, a significant decline in the pH, PCO2, bicarbonate concentration and base excess was noted. Increasing the dilution and/or quantity of heparin in an umbilical arterial blood specimen may result in a significant misinterpretation of the fetal acid-base status by indicating a more significant chronic metabolic acidosis component than really exists.