Multi-analyte calibration and verification of a multi-parameter laser-based pulse oximeter

Almost since its introduction pulse oximetry was known to overestimate oxygen saturation in cases of carbon monoxide poisoning or elevated methemoglobin (metHb) levels. To eliminate this dangerous behavior some manufacturers have added additional LED emitters to try to increase the number of measured hemoglobin species and to improve measurement accuracy, but have not been very successful. We hypothesized that the use of narrow-band laser light sources would make accurate and precise measurement of the four primary species of hemoglobin possible, even in cases of elevated levels of carboxyhemoglobin (COHb). Calibration and verification studies were performed on a tissue simulator that employed an artificial finger pulsating with whole human blood. This simulator allowed safe generation of 165 different combinations of the levels of oxyhemoglobin (O₂Hb), COHb, metHb, and reduced hemoglobin (RHb) for calibration of the laser-based pulse oximeter. A follow-on study used 56 mixed hemoglobin levels for verification and statistical analysis of the performance of this device. This laser-based pulse oximeter measured all four species of hemoglobin accurately and precisely (A_RMS ≤ 1.8%) for metHb levels in the clinically normal range. At elevated metHb levels the device continued to provide accurate and precise measurements of metHb and RHb (A_RMS ≤ 1.7%). The use of monochromatic laser light sources can create a new generation of highly accurate, multi-parameter, pulse oximeters.