Sir.—In the February 1990 issue of AJDC, Courtney et al1 described the correlation between simultaneously obtained capillary and umbilical artery catheter blood gas levels. Their study demonstrated r values of .79, .72, and .42 for pH, PCO2, and PO2, respectively, for capillary blood gases from warm, wrapped heels. Analysis of variance revealed that the major source of variation in pH was intersubject, while PCO2 and PO2 variance was accounted for by differences in arterial and capillary methods.
The article described potential sources of variation in blood gas measurements. This discussion does not address the systematic difference in heparin volume between sampling techniques. Capillary specimens were collected in standard heparinized capillary tubes. These tubes are typically 100 ΜL and contain 5 to 8 U of lyophilized heparin (no volume of heparin). In contrast, arterial samples in this
ZUERLEIN TJ. Heparin's Effect on Blood Gas Analysis. Am J Dis Child. 1990;144(12):1287-1288. doi:10.1001/archpedi.1990.02150360009005