Literature Mentioned
- Chan, Edward D., Michael M. Chan, and Mallory M. Chan. “Pulse Oximetry: Understanding Its Basic Principles Facilitates Appreciation of Its Limitations.” Respiratory Medicine 107, no. 6 (June 1, 2013): 789–99. https://doi.org/10.1016/j.rmed.2013.02.004.
- Sami, H. M., B. S. Kleinman, and V. A. Lonchyna. “Central Venous Pulsations Associated with a Falsely Low Oxygen Saturation Measured by Pulse Oximetry.” Journal of Clinical Monitoring 7, no. 4 (October 1991): 309–12. https://doi.org/10.1007/BF01619351.
- Shelley, Kirk H., Marc Dickstein, and Steven M. Shulman. “The Detection of Peripheral Venous Pulsation Using the Pulse Oximeter as a Plethysmograph.” Journal of Clinical Monitoring 9, no. 4 (September 1, 1993): 283–87. https://doi.org/10.1007/BF02886699.
- Stewart, K. G., and S. J. Rowbottom. “Inaccuracy of Pulse Oximetry in Patients with Severe Tricuspid Regurgitation.” Anaesthesia 46, no. 8 (1991): 668–70. https://doi.org/10.1111/j.1365-2044.1991.tb09720.x.
- Influence_of_Arterial_Dissolved_Oxygen_Level_on.7
- Anaesthesia – 2004 – Secker – Accuracy of pulse oximetry in patients with low systemic vascular resistance
- https://emcrit.org/pulmcrit/central-venous-saturation/
- https://journals.sagepub.com/doi/pdf/10.1177/175114370700800304
Additional Resources
Now on to the Podcast
- EMCrit 373 – Mike Weinstock with another Critical Care Bounceback: “Asymptomatic Hypertension” - April 18, 2024
- EMCrit Wee – Ross Prager on 10 Heuristics for the New ICU Attending - April 13, 2024
- EMCrit 372 – FoundStab Intubation SOP - April 5, 2024
My newborn daughter has spent the last 5 months in hopsital after being born premature. She has continual pulse oximetry and likes to be settled by patting, and I observe on a daily basis that rhythmic movements, such as patting or those generated by muscular contractions with transcutaneous pacing, absolutely can mimic a reliable waveform pulse oximetry trace.
Quite fascinating. Would be interesting to know how the morphology of the artifactual pulse ox waveform compared to the true waveform (which should have been running in the background at 15-20 bpm).
In any case, this would make me wanna confirm mechanical capture with US, if an A-line is not in place, while setting up to do an A-line for continuous monitoring, finally following it up by a TVP.
-Aman Thind
I’m surprised that you’re expecting pulse-ox to correlate with transcutaneous pacing – that’s one of the two cases were I’ve always taught to NOT trust the pulse-ox (CPR being the other). The optical sensor is very sensitive to movement, and the rhythmic movement of the arm will generally create a much higher amplitude than the pulse. I have had success taping down the arm during TC pacing temporarily… For a practical (and fun) demonstration, take an unconscious patient, and tap their finger at a set rate , and watch the pulse-ox rate match your tapping (and almost completely lose the… Read more »
I just tried an inflatert bp cuff to suprasystolic pressures, put on an SpO2 probe and tapped my hand. Nice tracings….
nice work!!!
A quick thought from a prehospital perspective. Our training assumes that we lack U/S and art lines which would be the ideal indicators. Given the unreliability of carotid and upper extremity pulses during TCP, and the apparent lack of reliability of pulse oximetry, the we’re left with three useful indicators to confirm capture: clinical improvement, femoral pulses (as demonstrated by Dr Brunet’s colleague), and ETCO2. Invariably, capture will cause a significant spike in cardiac output, which will noticeably increase ETCO2.
yep, agree with all of that
Absolutely fascinating. The morphology of the fake pulse ox waveform compared to the real one (which should have been going at 15-20 bpm in the background) would be fascinating to learn about drive mad.
“The basic assumption of a pulse oximeter is that anything that pulses and absorbs red and infrared light between the light source and the light detector must be arterial blood.” https://doi.org/10.1378/chest.95.4.713 A pulse oximeter is actually an oximeter AND a photo-plethysmograph (PPG), the latter being the interesting part here: It detects stable DC-signals (tissue, venous and non-pulsatile arterial blood) and pulsatile AC-signals (assumed to be pulsatile arterial blood) and INTERPRETS and DISPLAYS them as a pulse/heart rate. This also explains the limitations of a pulse oximeter to detect a weak pulse and to calculate SpO2 and HR. The TC-pacing/muscle… Read more »
fantastic Kai!