Arterial blood gas analysis: potential errors due to the addition of heparin.

The effect of sodium heparin on the determination of the major arterial blood gas parameters was studied. The addition of heparin produced errors in all three parameters tested, i.e. PO2, PCO2 and pH. The PCO2 determination was most affected, a 12% decrease being introduced into a 1.5 ml blood sample by the volume of heparin which fills the deadspace of a syringe and needle. Small but statistically significant errors were also produced in PO2 and pH by this heparin concentration. The clinical implications of these findings are discussed and certain measures outlined to avoid such errors.