What am I missing?

[redy]

Basic physiology question I guess.

Oxygen content= 1.34 x hemoglobin concentration x SaO2 + 0.0031 x PaO2.

Obviously the PaO2 isn't a major factor. So now a guy whose Hb is say 8 already has half the oxygen as a regular dude. That's fifty percent or so less. Now if the guy with Hb of 15 has saturation of 85 everybody freaks out when his Oxygen content is only 15% less. If we know why he is 85 or 88 or whatever it is, cuz of PNA or PE or COPD what does it matter? Ofcourse thats if his CO enables adequate delivery to prevent anaerobic metabolism and his lactate is normal.

The reason I ask is I have a guy with PNA (bacterial vs PCP) had BAL and after BAL his sat went down to 88-89 on 50% FiO2 and 5 PEEP (from 95%). I was fine with it. But the nurses kept bugging me for 2 hours until I had enough and went up to 60% and his sat was 91-92. His lactate is normal. His PaO2 was 60 at the time. I explained everything but they still wouldn't let go.

I am asking if any of my understanding or rationale is wrong? As long as I have a reason why you are sats are low I don't care if you are 88 or 95 or 99. And why 88? I am not entirely sure other than my previous pulm chief had taught me that.

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[jdh71]

Basic physiology question I guess.

Oxygen content= 1.34 x hemoglobin concentration x SaO2 + 0.0031 x PaO2.

Obviously the PaO2 isn't a major factor. So now a guy whose Hb is say 8 already has half the oxygen as a regular dude. That's fifty percent or so less. Now if the guy with Hb of 15 has saturation of 85 everybody freaks out when his Oxygen content is only 15% less. If we know why he is 85 or 88 or whatever it is, cuz of PNA or PE or COPD what does it matter? Ofcourse thats if his CO enables adequate delivery to prevent anaerobic metabolism and his lactate is normal.

The reason I ask is I have a guy with PNA (bacterial vs PCP) had BAL and after BAL his sat went down to 88-89 on 50% FiO2 and 5 PEEP (from 95%). I was fine with it. But the nurses kept bugging me for 2 hours until I had enough and went up to 60% and his sat was 91-92. His lactate is normal. His PaO2 was 60 at the time. I explained everything but they still wouldn't let go.

I am asking if any of my understanding or rationale is wrong? As long as I have a reason why you are sats are low I don't care if you are 88 or 95 or 99. And why 88? I am not entirely sure other than my previous pulm chief had taught me that.

You are correct. The nurses are wrong, but you can't tell a nurse ****, so it's just easier to turn up the gorram oxygen and then they'll leave you alone.

EDIT: To be fair a good nurse will listen, but you have to really explain it to them. They are very concrete about these things though and sometimes they just don't give a ****, a sat of 88 is a sat of 88 as far as they concerned, now help the patient (dick).

 

[Hernandez]

Pop quiz...... What happens to 2,3-Bisphosphoglycerate levels in sepsis?

 

[redy]

Go up? I would imagine so cuz that would shift the curve to the right so that for the same PaO2 the sat is lower meaning easier to unload at the tissue level. Right?

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[Bostonredsox]

You are correct. The nurses are wrong, but you can't tell a nurse ****, so it's just easier to turn up the gorram oxygen and then they'll leave you alone.

EDIT: To be fair a good nurse will listen, but you have to really explain it to them. They are very concrete about these things though and sometimes they just don't give a ****, a sat of 88 is a sat of 88 as far as they concerned, now help the patient (dick).

I tell them and the RT my goal Spo2 is 90 quite frequently, obviously pt dependent. They know not to ask me any questions unless it's below the goal I set. And even then, RT will just adjust the fio2 if they drop below unless they are in the vent, then they ask me what changes I want prior to initiating a change as it's often an increase in peep not fio2.

You have needy nurses bro.

 

[deleted547339]

Pop quiz...... What happens to 2,3-Bisphosphoglycerate levels in sepsis?

no. bad attending. you cannot pimp me at home. pimp me at work? fine. pimp me at home? shame on you. lol

 

[redy]

I tell them and the RT my goal Spo2 is 90 quite frequently, obviously pt dependent. They know not to ask me any questions unless it's below the goal I set. And even then, RT will just adjust the fio2 if they drop below unless they are in the vent, then they ask me what changes I want prior to initiating a change as it's often an increase in peep not fio2.

You have needy nurses bro.

Well the patient is/was a doctor himself here. So the nurses are kind of giving him the VIP treatment, which is no problem in itself. This of course isn't helping the patient. So was driving me crazy.

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[redy]

You are correct. The nurses are wrong, but you can't tell a nurse ****, so it's just easier to turn up the gorram oxygen and then they'll leave you alone.

EDIT: To be fair a good nurse will listen, but you have to really explain it to them. They are very concrete about these things though and sometimes they just don't give a ****, a sat of 88 is a sat of 88 as far as they concerned, now help the patient (dick).

Thanks jdh71...I have been preaching the same forever to residents and nurses. Just needed reaffirmation that my rationale was right.

 

[Hernandez]

Go up? I would imagine so cuz that would shift the curve to the right so that for the same PaO2 the sat is lower meaning easier to unload at the tissue level. Right?

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Nope, septic shock tends to decrease 2,3 DPG levels which shift the curve which direction kids?

Moral of the story....clinically you don't know where the oxy-dissociation curve is on a pt, so is 60% FIO2 going to hurt someone? Who knows....he who tells me they know what a safe level of oxygen is in a critically I'll pt...is probably full of it. I can tell you it is somewhere betwen 19% and 110%.....so why quibble with nurses over a few degrees SaO2 when despite your learned status, you can't tell me what exactly is going on on the cellular and mitochondrial level other than to say you don't see any significant signs of tissue hypoxia (I.e lactic acidosis).....so meet them half way....55% FIO2!

Or, here is another question.....why did the guys sat drop after a BAL? Was the fellow who did the procedure incompetent? Did he change the physiology while he was down there? Did he need a whole liter of saline to get a sample?


....but yes, back to your initial question....your's is the answer a Pulmonologist should give.....

 

[redy]

Nope, septic shock tends to decrease 2,3 DPG levels which shift the curve which direction kids?

Moral of the story....clinically you don't know where the oxy-dissociation curve is on a pt, so is 60% FIO2 going to hurt someone? Who knows....he who tells me they know what a safe level of oxygen is in a critically I'll pt...is probably full of it. I can tell you it is somewhere betwen 19% and 110%.....so why quibble with nurses over a few degrees SaO2 when despite your learned status, you can't tell me what exactly is going on on the cellular and mitochondrial level other than to say you don't see any significant signs of tissue hypoxia (I.e lactic acidosis).....so meet them half way....55% FIO2!

Or, here is another question.....why did the guys sat drop after a BAL? Was the fellow who did the procedure incompetent? Did he change the physiology while he was down there? Did he need a whole liter of saline to get a sample?



....but yes, back to your initial question....your's is the answer a Pulmonologist should give.....

Ha ha....I didnt do the BAL....My attending (who is the chief) did it. We used no more than 250 cc and got about 100 ml back. Maybe his condition is worsening.

While I do not know the level at which oxygen is toxic, I would guess 60% is more toxic than 50%. In any case I didn't want to do it cuz there was no need to do it.

 

[jdh71]

Nope, septic shock tends to decrease 2,3 DPG levels which shift the curve which direction kids?

Moral of the story....clinically you don't know where the oxy-dissociation curve is on a pt, so is 60% FIO2 going to hurt someone? Who knows....he who tells me they know what a safe level of oxygen is in a critically I'll pt...is probably full of it. I can tell you it is somewhere betwen 19% and 110%.....so why quibble with nurses over a few degrees SaO2 when despite your learned status, you can't tell me what exactly is going on on the cellular and mitochondrial level other than to say you don't see any significant signs of tissue hypoxia (I.e lactic acidosis).....so meet them half way....55% FIO2!

Or, here is another question.....why did the guys sat drop after a BAL? Was the fellow who did the procedure incompetent? Did he change the physiology while he was down there? Did he need a whole liter of saline to get a sample?


....but yes, back to your initial question....your's is the answer a Pulmonologist should give.....

I've seen sats drop all the time after BALs, even by "non-****-ups". I think the argument about why the sats drop after the BAL and anyone who can tell me why is akin to your argument about knowing the safe oxygen levels and why during sepsis.

 

[Hernandez]

Ha ha....I didnt do the BAL....My attending (who is the chief) did it. We used no more than 250 cc and got about 100 ml back. Maybe his condition is worsening.

While I do not know the level at which oxygen is toxic, I would guess 60% is more toxic than 50%. In any case I didn't want to do it cuz there was no need to do it.

Or maybe the bronch decreased the peep to the point you dropped the guy below FRC and de-recruited him? Or he has bad COPD and the elevated peep + cough dropped a lung? Etc etc. the point isn't oh his sats drop, think about what's happening and is there anything else that can help. For instance, if he happened to not be spontaneously breathing look at the pressure/volume loops, look at the waveforms, listen to the cat.

I've seen sats drop all the time after BALs, even by "non-****-ups". I think the argument about why the sats drop after the BAL and anyone who can tell me why is akin to your argument about knowing the safe oxygen levels and why during sepsis.

too bad my group isn't hiring, we'd get along great. I can't prove it, but i I will argue the most common reason is likely dropping the lung volumes below FRV due to suctioning.

 

[redy]

Or maybe the bronch decreased the peep to the point you dropped the guy below FRC and de-recruited him? Or he has bad COPD and the elevated peep + cough dropped a lung? Etc etc. the point isn't oh his sats drop, think about what's happening and is there anything else that can help. For instance, if he happened to not be spontaneously breathing look at the pressure/volume loops, look at the waveforms, listen to the cat.



too bad my group isn't hiring, we'd get along great. I can't prove it, but i I will argue the most common reason is likely dropping the lung volumes below FRV due to suctioning.

Interesting idea makes physiologic sense. They did go up on his PEEP to 8 overnight to maintain his oxygenation. His PCP came back +, now on IV bactrim maintaining pretty much at the same status. Will see if/when he improves.

 

[DeadCactus]

Regardless of left or right shift, the oxygen dissociation curve is generally regarded as getting much sharper bellow about 88%. Just eyeballing a chart, but at 90% you'd be at a slope of about 10 mm Hg of O2 to a 1% change in oxygen saturation.

So a 10 mmHg drop in PaO2 at an SpO2 of 90% would decrease oxygen delivery by roughly (1.34*Hgb + 0.031).

At an SpO2 of 80%, the slope is about 1 mmHg O2 to 1% SpO2. So that same 10 mmHg drop in PaO2 at an SpO2 of 80% is now a decrease in oxygen delivery of roughly (13.4*Hgb + 0.031) or essentially a 10 times greater drop in oxygen delivery for the same change in PaO2.

The concern isn't the difference in oxygenation as you drop into the 80's but rather the stability of the system. Keeping the SpO2 in the low 90's buffers the system and gives you more time to react and adjust to changes where as once you start treading into 80's SpO2 and oxygenation can start dropping much more rapidly...

That's how it was always taught and sold to me. Makes sense as far as I can tell. Maybe others have different opinion. Whether the difference between 88% and 92% large enough to warrant higher oxygen toxicity is probably a more difficult question.