MetHb Detection Accurate Using 'Pulse CO-Oximeter'

Unlike earlier model, noninvasive finger monitor readings precise even with hypoxemia

FRIDAY, Nov. 19 (HealthDay News) -- A newly introduced "pulse CO-oximeter" device used by anesthesiologists can accurately measure both arterial oxygen saturation and methemoglobin (MetHb) levels, even in the setting of hypoxemia, according to research published in the November issue of Anesthesia & Analgesia.

John R. Feiner, M.D., and Philip E. Bickler, M.D., of the University of California in San Francisco, conducted a study comparing a pulse CO-oximeter, which measures both arterial oxygen saturation (Spo2) and MetHb concentration (%MetHb), to direct measurement of arterial oxygen saturation (Sao2) and arterial MetHb. The device (Masimo Rainbow SET Radical-7) had recently been modified by its manufacturer for better accuracy over a range of arterial oxygen saturations. Twelve healthy volunteers were given sodium nitrite to artificially raise MetHb levels and hypoxia was induced by altering fractional inspired oxygen.

The researchers found that the reading bias and precision of the Masimo MetHb over the entire Sao2 span (74 to 100 percent) were 0.16 and 0.83 percent, respectively, and were similar across the span; Masimo Spo2 readings were biased −1.93 percent across the 70 to 100 percent Sao2 range.

"In conclusion, the current Masimo Rainbow pulse CO-oximeter demonstrated a high level of accuracy for measuring MetHb up to %MetHb of 14.4 percent, which did not degrade during hypoxia. Methemoglobinemia also does not impair the ability of the Rainbow pulse CO-oximeter to detect hypoxemia, although, as with most pulse oximeters, elevated MetHb levels create lower Spo2 readings during normoxia," the authors write.

This study was supported by funds established from testing pulse oximetry accuracy for various pulse oximeter device manufacturers. The authors received research funding from Masimo Inc., which also provided probes and oximeters.

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