[Reliability of transcutaneous PO2 measurements and ear oximetry at different levels of exercise]

Abstract

Measurement of transcutaneous PO2 (PtcO2) and of the saturation of hemoglobin by ear oximetry (StcO2) are two non-invasive methods which can be used when performing exercise tests in patients with respiratory failure. To evaluate their reliability, we have compared 18 patients recording the PtcO2 (Radiometer electrode TCM1) and of StcO2 (Biox II A) with arterial samples using a radial artery catheter at rest and at a level corresponding to 50% of the maximal predicted effort and at maximal power (Wmax) obtained at the time of a triangular exercise (increasing the charge at 15 watts/min). The PtcO2 was significantly lower than the PaO2 at rest and on exercise: the variation between PaO2 and PtcO2 was 1.85 kPa at rest (confidence interval -0.25 to 3.96 kPa) but decreased with exercise reaching 1.22 kPa at the last level of exercise (confidence interval -1.2 to 3.65 kPa). The relative raising of PtcO2 in relation to the PaO2 masks a fall in the observed PaO2 on average for the entire group (the PaO2 falls from 9.49 kPa to 8.62 kPa whereas the PtcO2 only falls from 7.64 kPa to 7.39 kPa). The mean StcO2 does not differ from th SaO2 at rest as on exercise. However, the confidence interval of the scatters between SaO2 and StcO2 increase considerably at maximal power: whereas it ranges between -5.5 and 3.5% at rest and in the middle range effort, and is between -13.4 and 11.1% at the last stage.(ABSTRACT TRUNCATED AT 250 WORDS)