To me anesthesia is cool

[Narcotized]

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and pharm isn't.

Just throwing that out there since it seems a common theme is you have to like physio and pharm (physiology is very cool, by the way). I force myself to learn the pharm, but I've never been crazy about pharm and am sure I never will be. But I still dig anesthesia.

 

[n2b8r]

Me too!! I LOVE physiology, but pharm is more bleh. Autonomic pharm is a little more interesting, but I'm not crazy about it.

and pharm isn't.

Just throwing that out there since it seems a common theme is you have to like physio and pharm (physiology is very cool, by the way). I force myself to learn the pharm, but I've never been crazy about pharm and am sure I never will be. But I still dig anesthesia.

 

[PistolPete]

Makes me feel a bit better... love physiology, not so much a pharm fan. Looking forward to my elective!

 

[MikeTheGipper]

Makes me feel a bit better... love physiology, not so much a pharm fan. Looking forward to my elective!

I think the pharm will be a lot more interesting and exciting when you are applying it and seeing it work in action. I just read a few days ago posts about attendings that hated pharm in med school and went on to love anesthesiology.

 

[Idiopathic]

you cant separate them, fortunately (or unfortunately, depending on your perspective). in the operating room, EVERYONE gets at least three medicines, and they all affect the physiology of the patient, so they are inexorably linked. that makes it a little easier, i think, since you can appreciate the system as a whole (patient needs more "tone" rather than phenylephrine, or needs more "cardiac output", instead of dobutamine).

 

[Narcotized]

you cant separate them, fortunately (or unfortunately, depending on your perspective). in the operating room, EVERYONE gets at least three medicines, and they all affect the physiology of the patient, so they are inexorably linked. that makes it a little easier, i think, since you can appreciate the system as a whole (patient needs more "tone" rather than phenylephrine, or needs more "cardiac output", instead of dobutamine).

I agree the physiology of pharm can often be very cool, but nothing is more painful to me than reviewing pharmacology of anesthesia. Takes me forever and it's like having root canal. The structure is blah blah blah, protein bound blah blah percent, excreted blah blah. Everything else about anesthesia is so much easier to read for me. Others love pharm. I just wanted to throw it out there that you don't have to enjoy pharm to enjoy anesthesia (but you do have to know it, of course).

 

[badasshairday]

Since this thread is about Physiology, thought I would ask you guys this question.

In room air conditions with 21% inspired oxygen, the PO2 arterial is ~100mmHg and the PO2 of the mixed venous blood is ~40mmHg.

When a patient breathes 100% inspired oxygen, the PO2 in the arterial blood is ~600mmHg. What would the PO2 of the mixed venous blood be in this case?




My answer: I don't think it would be a similar drop of 60mmHg as it is on room air. Nor would it be several hundred. Does the POz remain ~40mmHg in this scenario?

Any help would be greatly appreciated. I'm trying to get a basic handle on physio topics in anesthesiology.

 

[michigangirl]

Completely agree, Narcotized. Especially as a med student, it's hard to have any context and base everything on whether you like pharm or physiology. I hated pharm and I actually didn't really care too much for physio. But I didn't have a context. Once I was able to apply the stuff, it all made sense, and was exciting (the physio anyway, the pharm only so so)- now i'm a peds anesthesiologist and intensivist. If I had based my future specialty only on whether I loved physio and pharm in med school-- I'd be in a VERY different place today.

 

[countingdays]

Since this thread is about Physiology, thought I would ask you guys this question.

In room air conditions with 21% inspired oxygen, the PO2 arterial is ~100mmHg and the PO2 of the mixed venous blood is ~40mmHg.

When a patient breathes 100% inspired oxygen, the PO2 in the arterial blood is ~600mmHg. What would the PO2 of the mixed venous blood be in this case?




My answer: I don't think it would be a similar drop of 60mmHg as it is on room air. Nor would it be several hundred. Does the POz remain ~40mmHg in this scenario?

Any help would be greatly appreciated. I'm trying to get a basic handle on physio topics in anesthesiology.

It would drop several hundred. Your reasoning seems to based on the misconception that pO2 is dropping because dissolved oxygen is being used up at the tissue level, and that with constant oxygen consumption, the drop in pO2 should be the same. Dissolved oxygen is usually insignificant beside bound O2. Think about the hemoglobin saturations that correspond to those pO2s and it'll make more sense. The sat is 100% at pO2 100 or 600, so the extra O2 is hardly changing O2 content. Look up the O2 carrying capacity of blood formula. It'll make more sense.

 

[proman]

Agree with above. Less than 3% of tissue oxygen consumption is from dissolved oxygen, so PaO2 results in minimal effect on mixed venous oxygen content. This is, of course, assuming that you have normally behaving and adequate hemoglobin and aren't at altitude or pressure.

I loved pharm. I view what we do as applied pharmacology.

 

[Narcotized]

It would drop several hundred. Your reasoning seems to based on the misconception that pO2 is dropping because dissolved oxygen is being used up at the tissue level, and that with constant oxygen consumption, the drop in pO2 should be the same. Dissolved oxygen is usually insignificant beside bound O2. Think about the hemoglobin saturations that correspond to those pO2s and it'll make more sense. The sat is 100% at pO2 100 or 600, so the extra O2 is hardly changing O2 content. Look up the O2 carrying capacity of blood formula. It'll make more sense.

Calling Dr. Fick, Calling Dr. Fick.

CaO2 = Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 + PaO2 x (.003 ml O2/mm Hg/dl).

Arterial O2 content:
=15 x 1.34 x 1.0 + (100 x .003) = 20.4 cc/dl
=15 x 1.34 x 1.0 + (600 x .003) = 21.9 cc/dl

Venous O2 content roughly:
=15x 1.34 x .75 + (40 x .003) = 15.2 cc/dl

In the first situation O2 consumption is 5.2cc/dl x 50dl/min = 260cc/min; sounds about right.

To keep the second situation with constant O2 consumption, CvO2 would need to be 1.5 cc/dl higher at 16.7 cc/dl. Sat would be in the low 80's with a PaO2 somewhere around 50's. As stated PaO2 is a minimal contributor of O2 content, and venous PaO2 remains fairly stable dispite the 500 difference in arterial PaO2.

 

[fakin' the funk]

To keep the second situation with constant O2 consumption, CvO2 would need to be 1.5 higher at 16.7, Sat would be in the low 80's with a PaO2 somewhere around 50's. As state PaO2 is a minimal contributor of O2 content, and venous PaO2 remains fairly stable dispite the 500 difference in arterial PaO2.

Nice post.

In people who are having pretty marginal O2 delivery+demand matching (shock), increasing FiO2 and therefore PO2 and therefore CaO2 can actually improve CvO2 and thereby SvO2 enough for you to detect it (in this case SvO2 of 70s -> 80s). I would argue that in shock states, 1.5 ml O2/dl blood is a lot.