O2 sat and Pulse Oximetry (Strong Exam)

A discussion of the principles and limitations of pulse oximetry, the normal range of oxygen saturation, and general etiologies of a reduced O2 sat (i.e. hypoxemia).
0:00 Introduction
0:28 General principles of pulse oximetry
2:23 Comparison between pulse ox and ABGs
4:02 Limitations of pulse oximetry
10:06 The normal range of O2 sat
11:41 Etiologies of hypoxemia (low O2 sat)
12:43 Common pitfalls/mistakes with measuring & interpreting O2 sats
References:
Sinex JE. Pulse oximetry: principles and limitations. Am J Emerg Med. 1999; 17:59-67.
Jensen LA, Onyskiw LE, Prasad NG. Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults. 1998; 27:387-408.
Sjoding MW, Iwashyna TJ, Valley TS. Change the Framework for Pulse Oximeter Regulation to Ensure Clinicians Can Give Patients the Oxygen They Need. Am J Respir Crit Care Med. 2023; 207:661-664.
Sjoding MW, et al. Racial Bias in Pulse Oximetry Measurement. NEJM. 2020. 383;2477-2478.
Shi C. et al. The accuracy of pulse oximetry in measuring oxygen saturation by levels of skin pigmentation: a systematic review and meta-analysis. BMC Medicine. 2022; 20:267.
Louw A, et al. Accuracy of pulse oximetry in the intensive care unit. 2001; 27:1606-1613.
Enright PL, Sherrill DL. Reference Equations for the Six-Minute Walk Test in Healthy Adults. Am J Respir Crit Med. 1998; 158:1384-1387.
Rodriguez-Molinero A, Narvaiza L, Ruiz J, et al. Normal respiratory rate and peripheral blood oxygen saturation in the elderly population. J Am Geriatr Soc. 2013; 61:2238-40.
Ceylan B, et al. Evaluation of oxygen saturation values in different body positions in healthy individuals. J Clin Nurs. 2016; 25:1095-1100.
#physicalexam #osce #hypoxemia

[@ehiggins7476]

From an RT"s point of view, always look at the patient clinical presentation when in doubt of the pulse oximetry value.

[@rickshay4656]

on more than one occasion i’ve been called to a patients room for hypoxia. The patient is sleeping and the waveform is terrible. I find where the patients probe is and ensure there is no pressure on that point (i.e, reposition their hand) and boom, hypoxia cured. Thank you for the video!

[@lakeis3]

Thank you so much for mentioning pulse oximetry and black skin. I feel like this isn't talked about enough.

[@fjs1111]

Absolutely awesome Doctor Strong, awesome!!

[@user-zr6vn8ok5d]

Essential information for any medical professional brilliantly explained. Thank you.

[@Will-yz7oi]

Excellent information and insights! Much appreciated.

[@Macsooder]

I absolutely love this video. Beautifully and simply explained. This one goes into my must watch playlist :)

[@aconcretemoth9382]

this underscores the need for nurse rounding to observe the patient and not rely on the monitor for any patient who has a condition WORTH monitoring.

[@waelfadlallah8939]

I wish you can upload more 🙏

[@user-fi4ep5yo7z]

Thank You So Much.... Circulating Haemoglobin .... have much better understanding now...

[@bxxxl9447]

A great lecture, it would be helpful if there's a lecture about supplemental O2 therapy

[@StrongMed]

Here's an old one about the impact of supplemental O2 on the ABG: kzbin.info/www/bejne/b5zPo3d5ltGfb68

[@dr.siddharthm.dgeneralmedicine]

Wonderful videos.please make videos on General Practioner's Daily OPD patients.dealing with common problems.

[@asdfasdf-xk3hb]

What’s the mechanism for hypoxia in PE? V/Q mismatch doesn’t quite make sense to me that even a large infarct could cause enough hypoxia to cause a measurable change in the O2sats

[@LucasdaMatta]

sometimes the PE causes a degree of reactive pulmonary hypertension that is enough to back up into the RA and open a PFO, causing shunting and mixing of deoxygenated blood into the left heart.

[@StrongMed]

When a large pulmonary vessel is occluded, two things happen: - The portion of the lung that is downstream from the occlusion continues to be ventilated, but now has zero perfusion - The blood that normally would have gone to that portion of the lung is redirected elsewhere. Some of it gets redirected to portions of the lung which do not receive good ventilation. While the lung has a natural mechanism to vasoconstrict vessels going to areas with poor ventilation, it does not have an adaptation to deal with the opposite problem (i.e. bronchioles going to areas with poor perfusion). Your instinct is correct though that it would need to be a relatively large PE to cause hypoxemia via this mechanism in the sense that many relatively small PEs do not cause low O2 sats. There are a number of studies showing that the presence or absence of hypoxemia has minimal to no impact on the probability a patient with suspected PE or presenting with dyspnea actually has a PE. Here's just one that isn't non-paywalled: www.atsjournals.org/doi/10.1164/ajrccm.162.6.2004204

[@Admiration9]

id like to add shunts are not exclusively intracardiac. patients with small airway pathologies like pulmonary edema and ARDS have pulmonary shunts where blood flow to diseased portions of the lungs that are not ventilating are preserved, leading to admixing of non-oxygenated ang oxygenated blood.

[@garyjsimm]

Doc, as far as hypoxia and hypoxemia, can you have one without the other?

[@StrongMed]

Unless mild, hypoxemia otherwise always leads to hypoxia. However, a number of situations exist in which hypoxia occurs without hypoxemia. Oxygen delivery to peripheral tissues is approximately equal to the product of cardiac output, O2 sat, and hemoglobin concentration. So for example, in cardiogenic shock where the cardiac output is markedly reduced, or in profound anemia resulting in very low hemoglobin concentration, patients can experience hypoxia despite no hypoxemia. Cyanide poisoning can have the same end result by interfering with cells' ability to utilize oxygen. And hypoxia can occur more locally due to a focal obstruction of blood flow from an embolus or from compartment syndrome.

[@alirezazakaie1106]

Your last video isn't accessible...it is somehow private

[@StrongMed]

Sorry, it's a scheduled release for Sunday morning. I do this so I don't need to worry about uploading it and entering in all of the information (including references) Saturday night. This also allows colleagues to vet them ahead of time if it's something that I'd like more feedback on.

[@alirezazakaie1106]

Waiting for new videos😫

[@StrongMed]

I know, I'm sorry. The CV exam videos are taking a while to edit. I've got a one-off, general interest video coming in 2 days, hopefully followed by weekly CV exam videos for the next 4 weeks after that.