Listed below are the co-oximetry data for two patients A & B. What would the pulse oximetry measured saturation be for patient A and patient B? Give reasons for your answer.
.
|
Patient A |
Patient B |
|
|
Oxyhaemoglobin (%) |
70 |
50 |
|
Reduced haemoglobin (%) |
10 |
10 |
|
Carboxyhaemoglobin (%) |
20 |
40 |
Patient A – 90%
Patient B - 90%
Pulse oximetry only uses 2 wavelengths and COHb is measured as OxyHb.
Well, this is a flaw of pulse oximetry. Both the oxygenated hemoglobin and the "carboxygenated" COHb will be measured as 100% saturated. Thus, in both patients, the oxygen saturation will read 90%.
Pulse oximetry is discussed at lengths in a fine article:
Mendelson, Yitzhak. "Pulse oximetry: theory and applications for noninvasive monitoring." Clinical chemistry 38.9 (1992): 1601-1607.
Co-oximetry is a fine thing indeed. LITFL has a nice summary.