Lung cancer pulse oximetry and capnography in lung function laboratories.

OBJECTIVE: To compare values reflecting oxyhemoglobin saturation obtained by pulse oximetry (SpO2) and values for end-tidal carbon dioxide pressure (PETCO2) obtained by capnography with direct measures of gas saturation values and pressures (PaO2 and PaCO2) in arterial blood gas samples.

PATIENTS AND METHODS: We studied 57 consecutive patients ranging in age from 34 to 83 years--16 of whom were smokers--who presented for lung function testing.

RESULTS: The mean (SD) SpO2 was 95% (2.4%), and oxygen saturation measured directly in arterial blood samples was 95.1% (2.3%) (P=NS). The mean PETCO2 was 37.9 (5.3) mm Hg and PaCO2 by arterial blood gas analysis was 40.6 (5.4) mm Hg (P<.0001). The correlation between the 2 measurements of oxygen saturation (SpO2 and direct assessment) was 0.806 (P<.0001), and the correlation between PETCO2 and PaCO2 was 0.845 (P<.0001). The mean difference between the 2 expressions of oxygen saturation was 0.08% (1.46%) and between PETCO2 and PaCO2 was 2.7 (2.9) mm Hg.

CONCLUSION: Both measurement devices (pulse oximeter and capnograph) are appropriate for use in a lung function laboratory. The difference between PETCO2 and the PaCO2 should be kept in mind.