Effect of carboxyhemoglobin on measured oxygen saturation by pulse oximetry

SpO₂ and cooximetry versus carboxyhemoglobin (COHb) at FiO₂ = 1.0. SpO₂ consistently overestimates O₂ saturation in the presence of COHb. At COHb = 70 percent, SpO₂ is still roughly 90 percent, while oxyhemoglobin has fallen to 30 percent.