Pulse ox and hematocrit

sunnycalifRN · Nov 19, 2009

You don't mention his heart rate or blood pressure, but sounds like he's hypovolemic (dizzy when stands up). The SpO2 and Hct usually don't have much of a relationship. You can be 100% saturated even though your hct is 20%. But, the oxygen delivery to the tissues will be compromised since the oxygen carrying capacity is decreased. That's the "boxcars" analogy you mentioned, which is right on the money . . . so put him on O2 and he'll be less hypoxic.

sunnycalifRN · Nov 19, 2009

Ooops, forgot to mention . . . with poor perfusion, usually an ear or bridge of nose probe will pick up when the finger probe will not

WindwardOahuRN, RN · Nov 19, 2009

Here's a nice article that addresses the subject:

http://respiratory-care-sleep-medicine.advanceweb.com/Article/Pulse-Oximetry-Industry-Report.aspx?CP=2

SVO2 would be affected adversely by a low HCT...

meandragonbrett · Nov 21, 2009

Just don't forget that spO2 measures saturation of hemoglobin.....it doesn't determine if it's saturated with oxygen or CO2. Your oxyhemoglobin dissociation curve and Bohr's effect are your friends. Good luck!

danamobile · Dec 10, 2009

1) Full vitals would be good to know. You're asking if the crappy waveform can be from the hematocrit? Hematocrit is a number that is reflecting the % of RBCs in the blood. If its low, you have less cells=hypovolemia. If his BP low, HR up, and we can identify he's in any form of shock with poor perfusion, (specifically hypovolemic shock) then there could be an association with the hematocrit and the Sp02, more of a relationship (poor perfusion due to shock, caused by hypovolemia)

2) the sp02 is the saturation of oyxgen to the hemoglobin, if the saturation measurement is low, there is more room for more 02, therefore give it. There is no shame in giving a patient a few more liters 02, especially if they are having dyspnea, or are symptomatic. I've always been taught that if someone has a very low hemoglobin, even if they are showing high sp02 measurement, always place them on 02 for comfort and to ensure that there is as much oxygen as possible for every hemoglobin they absolutely have!!!

TemperStripe · Dec 10, 2009

Great info...since I work primarily in SICU (and also live at about 5000 feet), we have lots of patients with a low H&H. I am actually momentarily confused when I see someone with a crit higher than about 30.

danamobile · Dec 10, 2009

I work on a GI unit currently (and casually back in the ICU) and its weird to see people with a normal Hct. I mean, the patients are mostly dehydrated due to their diarrhea/alcoholism of sorts, but many have a GI bleed so we really don't look at it too much... also a lot are in hepatorenal failure and we don't push the fluids too often. I really don't know much about altitude and different levels in the blood. I'm going to read up on that now :)

Ok, so it appears that Hct increases with the altitude, and can be quite high for people that live there for a long time to accomodate for the lesser oxygen in the atmosphere, more RBCs are available.. but you said that you see only LOW Hcts?? What exactly is confusing you? Maybe all of your patients are all bleeding out? lol

Lets talk about this some more shall we? I'm at a fairly high altitude as well (going to see exactly now) as I live in Alberta, Canada.

TemperStripe · Dec 11, 2009

My mistake on the hct and altitude thing...I am clear on the other stuff (great info, too!) just apparently confused about that. :) Thanks for clearing it up!

Yes, we see lots of crits in the 20's. Surgical ICU...not necessarily bleeding out, though.

TakeBack · Dec 11, 2009

Doing some research on the relationship between pulse ox and crit. Just a couple of random questions if anyone has any info...
Example: A post-op patient with a crit of 20, they have ruled out that it's dilutional...
1. His pulse ox has been giving me a crappy wave form all day. He appears to be in the 90's when I do get a good read, but most of the time it's crap. Could this be related to the crit? (Also, cold hands, replaced the cord to the monitor, and gave him 2 new finger probes...still no luck.)
2. Asymptomatic most of the day, on room air and doing fine. Got up to walk and gets dizzy, pale, SOB, has to sit down...does giving him additional oxygen help saturate what low levels of hematocrit he DOES have, to help give him a little "boost" while waiting for the transfusion, or is that worthless, or am I confusing it with something else? Feels like the bottom line is, when your crit is that low, you don't have enough "boxcars" to transport the O's no matter how many liters you put him on...
I'm just thinking out loud and have actually managed to confuse myself in the process. Your thoughts are appreciated.

1. The waveform is from the measurement of pulsations; the value (%) comes from light absorbance by different states of hemoglobin. Your poor waveforms are due to peripheral vascular abnormality (vasoconstriction). Anemia does not influence the effectiveness of sat measurement.

2. Increasing the FiO2 (cannula/mask flow rate) will drive up the PaO2. Look at the high end of the Hb dissociation curve- it flattens out. The additional amount of saturation gained with this method of delivery will probably only raise the PO2 marginally.

Most of the O2 carried by blood is on Hb......a fraction of a percent is dissolved directly in the plasma. Driving the PO2 up higher will not add anything significant to blood O2 content.

Of course you won't deny a dyspneic pt O2, but know that it won't add a whole lot to tissue oxygen delivery.

Many postops can handle Hbs 6-8, but obviously the clinical picture is more important than raw numbers.

dmc_rrt · Dec 19, 2009

Hct is comprised of Hgb. If the pt's hgb is low, which could correspond to low hct, he can have 100% sats, but his oxygen carrying capacity is still crappy, and could still result in hypoxemia.

Look up the Oxygen carrying capacity (CaO2) equation. You will see that its all about the Hgb and O2 sats and very little about the PaO2.

morte, LPN, LVN · Dec 19, 2009

i have seen a patient that was so anemic that she was in air hunger, po was great ...100%