Count to 10 - Anaesthetic Primary Podcast EP15 - Pulse Oximetry | MiniPod | CT10
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Jul 18, 2023 Discover the fascinating world of pulse oximetry and how these devices measure oxygen saturation through light absorbance. Learn about common errors that can impact readings, as well as the importance of R values for accurate interpretation. Dive into past exam questions and uncover the types of tricky inquiries you might face. This episode demystifies a core clinical topic while preparing you for success in your assessments.
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How AC/DC Separates Arterial Signal
- The probe times red/infrared pulses (5–10ms) and measures AC (pulsatile) versus DC (static) components.
- The AC/DC ratio isolates arterial changes and feeds the R equation for saturation estimation.
Limits Of Calibration And Low SpO2 Accuracy
- R values are calibrated against healthy volunteers breathing hypoxic mixtures down to ~75% SaO2.
- Below ~75% SpO2 the device extrapolates and becomes increasingly unreliable.
Know Critical R-Value Anchors
- Memorize key R-to-SpO2 anchors: R=0.4 → 100%, R=1 → 85%, R=3.4 → 0% for exam answers.
- Practice writing the R (ratio of absorbance) equation to include in SAQs.