Oxygen saturation determination by photoplethysmographic and electrochemical methods: comparison of results in adult patients with pulmonary diseases

Abstract

Pulse oximetry is widely introduced to determine ox-ygen saturation of the blood. For patients with pulmonary diseases oxygen saturation is a major parameter used for the assessment of pulmonary gas exchange. The objec-tive of our study was to compare the results of oxy gen saturation measured by photoplethysmographic and elec-trochemical methods in patients with pulmonary disea-ses. Materials and methods. The authors studied 252 pa-tients with pulmonary diseases of different etiology. All the patients underwent pulse oximetry (SpO2) and blood gas analysis (SaO2) for oxygen saturation measurement, as well as spirometry. Results. We have established high direct correlations (R=0.869) between oxygen saturation levels determined by different methods. The mean abso-lute value of the difference between SpO2 and SaO2 was 0.74±2.35 pp. The value of the difference was influenced by the value of partial pressure of oxygen in the blood: if РаО2 was higher than 80 mm Hg, the mean va lue of the dif-ference (Md) was 0.1 pp (percentage points), and the con-sistency limit ranged from –2.6 to 2.8 pp; as РаО2 lo wered, the results increased to the maximum at РаО2 ofless than 60 mm Hg (Md=0.8 pp; the consistency limit could reach±±8.0 pp). The saturation value measured by pulse oxime-try with supposed hypoxemia of less than 60 mm Hg was possible at SpO2 of less than 93%. The difference between SpO2 and SaO2 beyond 3.0 pp was detec ted in 47 (18.7%) patients with pulmonary diseases. It was more frequent-ly determined in patients with interstitial lung diseases (34.0%) than patients with other pulmonary diseases (12.5–16.6%). Conclusion. Oxygen saturation determina-tion by pulse oximetry adequately shows pulmonary gas exchange in patients with pulmonary diseases and can be used in practical pulmonology. Though, blood gas analysis results should be specified if SpO2 is 93% or lower.