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a simple question about sats.

MICU   (2,644 Views 10 Comments)
by hyhero89 hyhero89 (Member)

1,923 Visitors; 16 Posts

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Hi. I am a nurse on ward.

straight to the subject, I am looking through

books to study o2 saturation and this thought

just popped up in my head.

a pulse oximetry is used to measure SaO2, while the clip is applied to the patient's fingertip,right?

So the question is,how the pulse oxi measures arterial blood gas when there's no artery at fingertips?

quite a dumb question huh? Help

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loveofrn has 2 years experience.

2 Likes; 6,887 Visitors; 346 Posts

wrist_anatomy_arteries01.jpg

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Mavrick has 30+ years experience and works as a Certified Post-Anesthesia Nurse (CPAN).

4 Likes; 23,631 Visitors; 1,576 Posts

It's an artery until it turns into a capillary.

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1,923 Visitors; 16 Posts

then this statement is false?

SpO2 stands for Peripheral capillary oxygen saturation. It is an estimation of the oxygen saturation level.

I think it can be said that p stands for pulse oximetry

(Just for convenience maybe?)

not peripheral capillary...

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1,923 Visitors; 16 Posts

still struggling here. but thanks for the link.

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FlyingScot has 28 years experience and works as a Oncological Clinic/Port Draw Queen.

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Reviewing the anatomy of the vessels will help tremendously in understanding how pulse oximetry measures arterial saturation. Understanding how the pulse ox actually does this and does it indirectly is actually quite interesting.

The arterial side of anatomy goes: artery to arterioles to capillary bed.

The venous side goes: vein, venules, capillary bed

[ATTACH]18285[/ATTACH]

So you see there IS arterial blood in the fingertips.

The linked article does an excellent job of explaining how the actual machine works. It's important to know that pulse oximeters, unlike saO2 monitors only read ON the pulse when there is a surge of arterial blood into the capillary bed. The diode is further engineered to be able to differentiate between the oxygenated blood vs the de-oxygenated blood by using both infra-red and red light sources.

Oximetry | Johns Hopkins Medicine Health Library

Pretty amazing actually.

Hope this helps.

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50 Likes; 14,524 Visitors; 850 Posts

I found a link from Philips Medical (one of the many manufacturers of pulse oximeters) that you may find helpful. It includes some of the same information that has already been provided by PPs, but has some graphics that may be helpful, and it goes into further detail. It can be found here: http://incenter.medical.philips.com/doclib/enc/fetch/586262/586457/Understanding_Pulse_Oximetry.pdf%3Fnodeid%3D586458%26vernum%3D2

a pulse oximetry is used to measure SaO2, while the clip is applied to the patient's fingertip,right?

Also, take care not to confuse SpO2 with SaO2. SpO2 is the measurement obtained via pulse oximetry, while SaO2 is the measurement obtained by arterial blood gas analysis (venous blood can also be analyzed, yielding an SvO2 measurement). There is a glossary of terms on p. 13 of the linked manual that explains more precisely the difference between SpO2 and SaO2.

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1,923 Visitors; 16 Posts

thank you first. will read anyminute!

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1,923 Visitors; 16 Posts

God.. thanks you two flyingscot and vanilla bean. haven't thought of functional hemo and non functional hemo... it was really helpful! Oh and flyingscot, link 18285 attachment doesn't work :crying2:

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