Oxygen saturation versus concentration

[cfdavid]

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Dudes,

We're in pulmonary physiology right now. I now know that a patient could have normal arterial P02 and normal Hb/O2 saturation WITH polycythemia and anemia.

Thus, the point was made that we need to look at O2 "content" (total concentration), which involves knowing what their Hb levels are.

I know that "pulse oxymeters" are used in the OR. I was under the impression that they were only measuring Hb saturation. Is this the case?

If so, then do you routinely measure for Hb levels to make sure the person will not require special attention (as in the case of someone that's anemic)??

 

[Mman]

f so, then do you routinely measure for Hb levels to make sure the person will not require special attention (as in the case of someone that's anemic)??

I have yet to take care of a patient that was healthy enough and having that minor of a procedure that they didn't have a CBC sent pre-op.

 

[toughlife]

Dudes,

We're in pulmonary physiology right now. I now know that a patient could have normal arterial P02 and normal Hb/O2 saturation WITH polycythemia and anemia.

Thus, the point was made that we need to look at O2 "content" (total concentration), which involves knowing what their Hb levels are.

I know that "pulse oxymeters" are used in the OR. I was under the impression that they were only measuring Hb saturation. Is this the case?
yes

If so, then do you routinely measure for Hb levels to make sure the person will not require special attention (as in the case of someone that's anemic)??

It's part of pre-op eval.

 

[Monty Python]

I have yet to take care of a patient that was healthy enough and having that minor of a procedure that they didn't have a CBC sent pre-op.

Interesting .... in the private sector, the vast majority of healthy same-day surgeries are done with no labs unless indicated by medical condition - which would usually rule them out from same-day in the first place.

I've put hundreds of hernias, bunions, plastics, etc, to sleep with no labs.

 

[jwk]

Interesting .... in the private sector, the vast majority of healthy same-day surgeries are done with no labs unless indicated by medical condition - which would usually rule them out from same-day in the first place.

I've put hundreds of hernias, bunions, plastics, etc, to sleep with no labs.

Ditto - there are NO routine labs or pre-op tests, only those that are indicated for a specific reason.

 

[Mman]

Ditto - there are NO routine labs or pre-op tests, only those that are indicated for a specific reason.

I agree completely. I just haven't had the chance to take care of those healthy patients and minor procedures yet as a resident at a large academic center. I would guesstimate that fewer than 5% of my cases thus far have been patients that were even candidates to go home the same day.

 

[cfdavid]

So, are there special concerns relative to anesthesia that must be addressed if someone is anemic???

Just curious. What would you do? It seems that a higher PO2 (i.e. if you gave pure O2) would not help someone that's anemic given that their Hb sat was high (98% or above as measured by the pulse ox).

 

[militarymd]

So, are there special concerns relative to anesthesia that must be addressed if someone is anemic???

Just curious. What would you do? It seems that a higher PO2 (i.e. if you gave pure O2) would not help someone that's anemic given that their Hb sat was high (98% or above as measured by the pulse ox).

that is correct....

 

[toughlife]

So, are there special concerns relative to anesthesia that must be addressed if someone is anemic???

Just curious. What would you do? It seems that a higher PO2 (i.e. if you gave pure O2) would not help someone that's anemic given that their Hb sat was high (98% or above as measured by the pulse ox).

To understand this issue better you need to remember the O2 content equation:

CaO2: (1.34 x Hb x O2sat) + (0.003 x PaO2)

By thinking of it this way you can see, in fact, that Hb is the major determinant of
O2 content rather than the PaO2.

OK?

 

[cfdavid]

To understand this issue better you need to remember the O2 content equation:

CaO2: (1.34 x Hb x O2sat) + (0.003 x PaO2)

By thinking of it this way you can see, in fact, that Hb is the major determinant of
O2 content rather than the PaO2.

OK?

Absolutely, that was the point, and the basis for my original question. But, how would you manipulate someone's Hb levels that is anemic? I'd think you couldn't.

Thus, what kind of risks would an anemic patient face under anesthesia given their low O2 concentration/content?? Perhaps I should have phrased my question better.

 

[toughlife]

Absolutely, that was the point, and the basis for my original question. But, how would you manipulate someone's Hb levels that is anemic? I'd think you couldn't.

Thus, what kind of risks would an anemic patient face under anesthesia given their low O2 concentration/content?? Perhaps I should have phrased my question better.

Not much except to xfuse them.

Lactic acidosis and ischemia

 

[EV-Stentor]

Not much except to xfuse them.

Lactic acidosis and ischemia

Agree with above but if want to get a little more in depth i would say play with O2 dissociation curve: maintain ambient temp, pH, PO4-, 2,3 BPG, etc and minimize O2 consumption: avoid tachcardia, full muscle relaxation, etc and most importantly: tell surgeon to go easy on the blood letting and consider cell saver

 

[cfdavid]

Agree with above but if want to get a little more in depth i would say play with O2 dissociation curve: maintain ambient temp, pH, PO4-, 2,3 BPG, etc and minimize O2 consumption: avoid tachcardia, full muscle relaxation, etc and most importantly: tell surgeon to go easy on the blood letting and consider cell saver

So, ischemia due to lack of tissue perfusion, and likewise lactate buildup via the same (more anaerobic metabolism).... That makes sense.

But, Stentor, you say to minimize 02 comsumption....???

It seems that the decrease in pH (from lactate build up) would enhance 02 unloading, but is it common to drip some 2,3 BPG? Can you really "exogenously" manipulate the Hb dissociation curve?? Again, just curious.

 

[LostTommyGuns]

In my experience an important part of the pre-op labs is to get a feel for where your boundaries are. If you have a good hemoglobin and you hear some sucking going on you might glance at the canister to see how much blood is being spilled. If you Hemoglobin is bordering on unacceptable, you'll have units in the room and when you hear that sucking the units go up...

Like much of medicine is an indicator or a factor not a problem with a solution... 🙂

 

[jetproppilot]

Absolutely, that was the point, and the basis for my original question. But, how would you manipulate someone's Hb levels that is anemic? I'd think you couldn't.

Thus, what kind of risks would an anemic patient face under anesthesia given their low O2 concentration/content?? Perhaps I should have phrased my question better.

Anytime an organ system is not receiving enough oxygen for whatever reason (coronary artery blockage, anemia, whatever) it is at risk of damage or death. So you could see a stroke, a heart attack, kidney dysfunction, etc.

But it is simply amazing how much the human body will tolerate anemia (most of the time) without postoperative problems.

In the early nineties, CF, it was common to feel comfortable with patients having heart surgery with hematocrits of 18, 19, 20, somewhere in there, during the pump run. You'd think intuitively that most patients with multi-vessel coronary artery disease wouldnt be able to tolerate an anemic state like that, but most did.

That trend is changing though. Hematocrits are being maintained a little higher during CABGs since (I believe) CVA incidence was found to be lower....