Validity of arterialized earlobe blood gases at rest and exercise in normoxia and hypoxia

The purpose of this study was to compare arterial and arterialized blood gases during normoxic and hypoxic exercise. In the same conditions, earlobe pulse oximetry O2 saturation (SpO2SpO2) was compared to arterial oxygen saturation (SaO2SaO2). Ten men performed incremental cycle ergometer tests, in normoxia and hypoxia (FIO2=0.127FIO2=0.127). Blood samples were drawn simultaneously from the radial artery and pre-warmed earlobe capillary blood of subjects at rest, submaximal and near maximal exercise. R2 between the two samples were 0.99 for PO2PO2 and SO2SO2, 0.86 for PCO2PCO2 and 0.97 between SpO2SpO2 and SaO2SaO2. Earlobe PO2PO2 mean was 4.4 ± 3.6 mmHg lower than PaO2PaO2 in normoxia but in hypoxia only 1.1 ± 2.2 mmHg low. The mean difference were low in normoxia between SaO2SaO2 and SpO2SpO2 and increased in hypoxia, were acceptable for PCO2PCO2, SO2SO2, pH in all conditions. In conclusion, except for PO2PO2 in normoxia, pre-warmed earlobe capillary blood is a good substitute to arterial blood to allow measurement of blood gas values in normoxia and hypoxia at rest and exercise.