Describe the principles of measurement of arterial haemoglobin oxygen saturation using a pulse oximeter. Outline the limitations of this technique.
The main points expected for a pass included a brief description of the following:
· The system components
· The principles of light absorbance and the Beer-Lambert Law
· The differential absorbance of Hb species in red/infrared spectrum, and their use to
calculate the amount of reduced and oxygenated Hb present
· LED emitting 660/940/off cycles at 450-900Hz, averages data over several cycles to
eliminate ambient light, and detect pulsatile and non pulsatile elements
· Pulse added absorption of each cycle compared as ratio “R” at different wavelengths
· Calibration curve to compare “R” to SaO2 data from healthy volunteers
· The limitations of the technique including:
- quality of product, bias, precision and accuracy
- insensitivity to PaO2
- false readings and their causes
Diagrams gained marks only with sufficient labelling and explanation
Of all the possible college examiner comments, none is more useful than a solid breakdown of what was expected for a pass, making this an outstanding effort. One is puzzled by the rarity of such things, as all examiners must surely be provided with some sort of marking grid, and so it should be quite effortless to reproduce some parts of it in their comments.
Sinex, James E. "Pulse oximetry: principles and limitations." The American journal of emergency medicine 17.1 (1999): 59-66.
Jubran, Amal. "Pulse oximetry." Critical care 3.2 (1999): R11.
Jubran, Amal. "Pulse oximetry." Applied Physiology in Intensive Care Medicine 1. Springer, Berlin, Heidelberg, 2012. 51-54.
Jubran, Amal. "Pulse oximetry." Critical Care 19.1 (2015): 272.
Kamat, Vijaylakshmi. "Pulse oximetry." Indian J Anaesth 46.4 (2002): 261-8.
Kyriacou, Panayiotis, Karthik Budidha, and Tomas Y. Abay. "Optical techniques for blood and tissue oxygenation." Encyclopedia of Biomedical Engineering, ed R. Narayan (Oxford: Elsevier) (2019): 461-472.
Severinghaus, John W., and Shin O. Koh. "Effect of anemia on pulse oximeter accuracy at low saturation." Journal of clinical monitoring 6.2 (1990): 85-88.
Fluck, Robert R., et al. "Does ambient light affect the accuracy of pulse oximetry?." Respiratory care 48.7 (2003): 677-680.
Amar, David, et al. "Fluorescent light interferes with pulse oximetry." Journal of clinical monitoring 5.2 (1989): 135-136.
Block, Frank E. "Interference in a pulse oximeter from a fiberoptic light source." Journal of clinical monitoring 3.3 (1987): 210-211.
American Association for Respiratory Care. AARC Clinical Practice Guideline: Pulse oximetry. Respir Care 1991;36(12):1406–1409
Ralston, A. C., R. K. Webb, and W. B. Runciman. "Potential errors in pulse oximetry: I. Pulse oximeter evaluation." Anaesthesia 46.3 (1991): 202-206.
Webb, R. K., A. C. Ralston, and W. B. Runciman. "Potential errors in pulse oximetry: II. Effects of changes in saturation and signal quality." Anaesthesia 46.3 (1991): 207-212.
Singh, Anupam Kumar, et al. "Comparative evaluation of accuracy of pulse oximeters and factors affecting their performance in a tertiary intensive care unit." Journal of clinical and diagnostic research: JCDR 11.6 (2017): OC05.
Severinghaus, J. W. "Pulse oximetry uses and limitations." ASA Convention. 1989.
Ralston, A. C., R. K. Webb, and W. B. Runciman. "Potential errors in pulse oximetry III: effects of interference, dyes, dyshaemoglobins and other pigments." Anaesthesia 46.4 (1991): 291-295.
Severinghaus, John W. "Takuo Aoyagi: discovery of pulse oximetry." Anesthesia & Analgesia 105.6 (2007): S1-S4.
Tremper, Kevin K. "Pulse oximetry." Chest 95.4 (1989): 713-715.
Feiner, John R., John W. Severinghaus, and Philip E. Bickler. "Dark skin decreases the accuracy of pulse oximeters at low oxygen saturation: the effects of oximeter probe type and gender." Anesthesia & Analgesia 105.6 (2007): S18-S23.
Pologe, Jonas A. "Pulse oximetry: technical aspects of machine design." International anesthesiology clinics 25.3 (1987): 137-153.
Webster, John G. Design of pulse oximeters. CRC Press, 1997.