Describe the principles of measurement of arterial haemoglobin O2 saturation using a pulse oximeter (60% marks). Outline the limitations of this technique (40% marks).
Most candidates provided a reasonable structured sequence of how a pulse oximeter generates a value. Nearly all candidates described the Beer-Lambert laws correctly, but few specifically described the basic principles of absorption spectrophotometry. Most candidates had a reasonable list of extrinsic factors that can interfere with pulse oximeter performance, but few described the intrinsic/inherent limitations of the device that can cause SpO2 to be different to SaO2, such as functional versus fractional saturation.
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