The section, EDAIC MCQ (Multiple Choice Question) and answer, covers a different topic each day with the intent that candidates can prepare one small topic each day, making steady progress in their exam preparation.
Question: Identify the correct statements regarding pulse oximetry
- It calculates oxygenated haemoglobin as a percentage of total haemoglobin in arterial blood
- Oxygenated Hb absorbs more light at 940 nm than Hb
- Oxygenated Hb absorbs more light at 660 nm than Hb
- It is reliable and accurate (+/- 2%) between 50% and 100% saturation in sinus rhythm.
- Red nail polish can interfere with reading
Answers:
-
- True
- True
- false
- false
- false
Pulse oximeters calculate the amount of oxyhaemoglobin (HbO) as a percentage of the total haemoglobin in arterial blood.
Pulse oximetry provides a continuous reading of plethysmographic oxygen saturation (SpO2), in other words, the oxygen saturation of pulsatile blood. The display the tracing of pulsatility against time, known as a plethysmograph.
Light at 940 nm and 660 nm is absorbed by both HbO and deoxyhaemoglobin (Hb), but with differing efficiency. HbO absorbs more light at 940 nm than Hb, whereas the situation is reversed at 660 nm.
The ratio of absorption at 660 nm to the absorption at 940 nm is calculated and used to derive the oxygen saturation using an algorithm.
Reliable and accurate (+/- 2%) between 70% and 100% saturation in sinus rhythm. Accuracy significantly decreases below 70%.
black, green or blue nail polish colours may interfere with the reading.
Cardiovascular physiology module by targetedaic
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‘EDAIC MCQ (Multiple Choice Question) and answer’ covers a different topic each day with the intent that candidates can prepare one small topic each day, making steady progress in their exam preparation.
