When using a conventional pulse oximeter, presence of which of the following substances in the blood will produce the GREATEST difference between measured and actual SpO2?

Conventional pulse oximeters operate by transmitting light energy at 660 and 940 nm through perfused tissues. The absorption at these two wavelengths is used to calculate the percentage of hemoglobin that is bound to oxygen. Any substances present in the blood that have absorptions near 660 or 940 nm may interfere with the accuracy of readings. In addition, hemoglobin in confirmations other than hemoglobin A (adult) may cause inaccurate readings.

Carboxyhemoglobin will result in an overestimation of the actual SpO2. Methemoglobin will produce an underestimation of actual SpO2, with measured values tending toward 85 percent. Fetal hemoglobin has very little effect on measured SpO2. The presence of sickle cell hemoglobin has unpredictable results.

There are several...

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