Figure 30-34 Hemoglobin extinction curves. Pulse oximetry uses the wavelengths of 660 and 940 nm because they are available in solid-state emitters (not all wavelengths are able to be emitted from diodes). Unfortunately, HbCO and HbO₂ absorb equally at 660 nm. Therefore, HbCO and HbO₂ both read as SaO₂ to a conventional pulse oximeter. In addition, Hbmet and reduced Hb share absorption at 660 nm and interfere with correct SaO₂ measurement. (Courtesy of Susan Manson, Biox/Ohmeda, Boulder, Colorado, 1986.)