Value and accuracy of dual oximetry during pulmonary resections

During thoracic surgery, one-lung ventilation (1LV) is often required. The purpose of this prospective study was to examine the usefulness and accuracy of dual-oximetry during 1LV. Prior to the induction of anesthesia, 30 patients had a radial artery and a fiberoptic pulmonary artery catheter (15 Edwards, 15 Spectramed by randomization) inserted. Arterial O2 saturation (SpO2) was monitored by pulse oximetry, and mixed venous O2 saturation (SvO2) by oximetry (Edwards or Spectramed). Arterial and mixed venous blood gases were obtained and immediately analyzed by an OSM3-Hemoximeter. Measurements, including hemodynamics and blood gases, were obtained before induction, during two-lung ventilation (2LV) in the supine and lateral decubitus positions, during 1LV, and following extubation. The change from 2LV to 1LV was associated with significant increases in cardiac index (CI) and oxygen delivery index (DO2I), whereas PaO2 and arterial and mixed venous oxygen saturation decreased. The ratio of oxygen consumption to delivery remained stable. Continuous oximetry when compared with in vitro measurements yielded a correlation coefficient for arterial oxygen saturation of r = 0.794 (P less than or equal to 0.001) and a value of bias and precision of -0.5% +/- 1.7%; for mixed venous oxygen saturation of r = 0.874 (P less than or equal to 0.001) and -1.3% +/- 2.8% for the two-wavelength Edwards catheter; and, r = 0.862 (P less than or equal to 0.001) and -0.1% +/- 3.2% for the two-wavelength Spectramed catheter. These findings demonstrate that dual-oximetry is an on-line, reliable method to measure SpO2 and SvO2. SpO2 less than 95% reflects hypoxygenation and hypoxia (PaO2 less than or equal to 70 mm Hg). SvO2 is determined primarily by oxygenation (r = 0.005; P less than or equal to 0.05) rather than by CI (r = 0.001, ns). Since DO2I increased during 1LV to maintain the oxygen supply and demand balance, SvO2 monitoring might be useful as an early indicator in identifying high-risk patients with compromised DO2I resulting from decreased CI.