The Validity of PO2Measurement in Capillary Blood as a Substitute for Arterial PO2

Abstract

PO₂ in capillary blood was compared with arterial PO₂ under different conditions. PO₂ in capillary blood from the hyperemic earlobe at rest and during exercise compares favorably with arterial PO₂, while discrepancy is rather large when capillary blood at rest is sampled from the warmed finger-tip. For PCO₂, good accordance was found regardless of the site of sampling. In circulatory collapse, PO₂ in capillary blood does not accurately reflect arterial PO₂, even if sampled at the earlobe. At oxygen tensions above 200 mm Hg accordance is very poor and the capillary method is thus unsuitable for determining true anatomic shunt.