Which of the following is more compatible with heparin contamination of blood gas analysis?
A. Lower pH, higher pO2, higher pCO2
B. Normal pH, higher pO2, lower pCO2
C. Lower pH, lower pO2, higher pCO2
D. No regular pattern
Answer: B
Many a time, we encounter blood gas results that are incompatible with clinical findings. Most commonly, for example, pO2 is high even if the patient is on room air, and pCO2 low but the patient does not seem to be hyperventilating. One of the possibilities is excessive heparin for blood gas syringe preparation.
The pH will not change because of the vast buffering capacity of oxyhemoglobin and plasma protein. The pCO2 is more afftected than pO2. PO2 will rise while pCO2 decreases sharply, both changes are in proportion to the relative differences in partial pressure of these gases between blood and heparin.
See Table 1 of the following reference for the results of a very nice experiment of arterial blood dilution by heparin sodium and normal saline.
Reference
M D Dake, J Peters, and R Teague. The effect of heparin dilution on arterial blood gas analysis. West J Med. 1984 May; 140(5): 792–793. (Free fulltext available at the website of PubMed Central here.