A Question from the senior

[Salah]

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Hello there..

An anesthesia resident is talkin to you from here, Egypt . 🙂

Apart from the huge effort we "anesthesia residents" perform here in my hospital for none interrupted hours or even days, I find the anesthesiology is a very interesting field and I like it . 🙂


Well, yesterday my senior in job asked me a question and told me to search for the answer so I thought to share you all the question asked 😛 , the question was :-

Why the intubated anesthetized patient is in need for 100% Oxygen while all the awake ppl can live with a good Oxygen saturation on the room air Oxygen ??!!

In another way, why if we replaced the 100% Oxygen in the anesthesia machine with a normal air mixture the anesthetized patient will begin to get a low O2 saturation in the puls oximeter 🙄

WHY ............... ?? 😕

 

[Noyac]

Hello there..

An anesthesia resident is talkin to you from here, Egypt . 🙂

Apart from the huge effort we "anesthesia residents" perform here in my hospital for none interrupted hours or even days, I find the anesthesiology is a very interesting field and I like it . 🙂


Well, yesterday my senior in job asked me a question and told me to search for the answer so I thought to share you all the question asked 😛 , the question was :-

Why the intubated anesthetized patient is in need for 100% Oxygen while all the awake ppl can live with a good Oxygen saturation on the room air Oxygen ??!!

In another way, why if we replaced the 100% Oxygen in the anesthesia machine with a normal air mixture the anesthetized patient will begin to get a low O2 saturation in the puls oximeter 🙄

WHY ............... ?? 😕

Well first of all, this is not true. I typically run the O2 conc well below 100% even down to 30%. But what your senior is looking for deals with respiratory mechanics. Look to the zones of respiration and how mechanical ventilation differs from normal respiration for your answer. It has something to do with alveoli ventilated and alveoli perfused, VQ mismatch.

 

[Salah]

Thanx Noyac for the reply 🙂

He "my senior" meant by 100% O2 the O2 delivered to the ventilator/anesthesia machine from the pipe lines, I think we can't replace it with air or reduce its conc to be 30%, can we? 😕

 

[cchoukal]

Sure we can. While it is true that the wall source for exygen is purely 100% oxygen (+/- a few %), there is also a wall source for air. The anesthesia machine can mix these (along with nitrous oxide, anesthetic gases, and, sometimes, carbon dioxide). The anesthesiologist can "dial in" whatever concentration they want. There seems to be some evidence that in certain situations, a higher FiO2 is associated with better tissue oxygenation and, presumably, a lower rate of wound infections. On the other hand, a lower FiO2 probably reduces that formation of atelectasis in underventilated lung segments. These are just a couple of quick examples of when/why we might choose a certain concentration of oxygen

 

[Planktonmd]

Thanx Noyac for the reply 🙂

He "my senior" meant by 100% O2 the O2 delivered to the ventilator/anesthesia machine from the pipe lines, I think we can't replace it with air or reduce its conc to be 30%, can we? 😕

I think you misunderstood the question and are trying to fill the gabs with your own interpretation.
He most likely wanted to ask you: why would people under general anesthesia require more oxygen to maintain the same saturation? and the answer would be what Noyac implied:
VQ mismatch caused by many things: Supine position, Loss of physiological PEEP, Atelectasis, Decreased FRC and the change from negative pressure to positive pressure ventilation.

 

[VentdependenT]

I think you misunderstood the question and are trying to fill the gabs with your own interpretation.
He most likely wanted to ask you: why would people under general anesthesia require more oxygen to maintain the same saturation? and the answer would be what Noyac implied:
VQ mismatch caused by many things: Supine position, Loss of physiological PEEP, Atelectasis, Decreased FRC and the change from negative pressure to positive pressure ventilation.

what he said.

Remeber that just putting someone to sleep in the supine position drops the FRC greatly. Throw in all that V/Q junk and kaboom. You lost plenty of lung to move air with.

Now in a healthy non-obese person you could easily run em on 21% and have em sat in the 90's.

SO why run em on higher concentrations? Gives you a buffer if something goes wrong. Gets more 02 to the wound to oxidize those bugs. Cuts down on PONV.

 

[Noyac]

Will 100% O2 generate more O2 free radicals? Should we care?

 

[VentdependenT]

Will 100% O2 generate more O2 free radicals? Should we care?

Good question. I'd imagine that it wouldnt unless the body was having a reaction (like to the stress of surgery) in which the immune cells where creating tons of free-radicals to kill stuff. The higher O2 might, just might, provide a teeny bit more substrate. But only by .003XFio2. Not much eh?

The toxicity is from the high 02 itself I believe.


Should we care?

Not for the surgery. Or the first arbitrary first 24hours (yes atelectasis can be a problem but thats what PEEP is for).

Other times I'd avoid high O2 is neonates, premature infants, and people taking bleomycin.

 

[Noyac]

Not for the surgery, unless its a lung transplant I guess.

Other times I'd avoid high O2 is neonates, premature infants, and people taking bleomycin.

Airway cases as well.

 

[coprolalia]

Airway cases as well.

Yeah, fire in the airway is not so nice.

-copro

 

[huktonfonix]

Does anyone know if there is any actual data supporting worse outcome in lung transplants with higher FiO2? I've seen some data showing no difference in outcome (can't remember source right now), but I've never actually seen data showing the reverse. Having said that we still use the lowest FiO2 we can on our transplants, but I still wonder if it has any merit or if its more voodoo.

 

[SleepIsGood]

Sure we can. While it is true that the wall source for exygen is purely 100% oxygen (+/- a few %), there is also a wall source for air. The anesthesia machine can mix these (along with nitrous oxide, anesthetic gases, and, sometimes, carbon dioxide). The anesthesiologist can "dial in" whatever concentration they want. There seems to be some evidence that in certain situations, a higher FiO2 is associated with better tissue oxygenation and, presumably, a lower rate of wound infections. On the other hand, a lower FiO2 probably reduces that formation of atelectasis in underventilated lung segments. These are just a couple of quick examples of when/why we might choose a certain concentration of oxygen

Hey cchoukal.

apparently this business of "absorption atelectasis" is not true. The author's name is Myles and he has a paper in Anesthesiology (Aug 2007) where he discusses not using Nitrous at all. As you know one of the arguments against this was the incr in absorption atelectasis d/t high O2. He actually makes a case and shows how using N2O actually increases atelectasis.

 

[fakin' the funk]

Does anyone know if there is any actual data supporting worse outcome in lung transplants with higher FiO2? I've seen some data showing no difference in outcome (can't remember source right now), but I've never actually seen data showing the reverse. Having said that we still use the lowest FiO2 we can on our transplants, but I still wonder if it has any merit or if its more voodoo.

That would be a hell of a project - randomizing lung transplant recipients to high vs. low FiO2 and following their long or short-term outcomes...😱

 

[epidural man]

SO why run em on higher concentrations? Gives you a buffer if something goes wrong.

Good point.

However, one reason I like to run low O2 is because I like to see a change sooner - so if the A-a gradient is increasing, you will know right away. If you are running on 100%, 80%, even 50%, you will never really know most of the time until it is really bad.

 

[Noyac]

Sometimes I run 100% and other times I get the conc down as low as possible. It depends on the case and the pt. If they have a tight coronary profile then they get more O2. If I want to know of any changes earlier then I cut it down. I don't think we can sit here and say that one is better than the other in every circumstance. Not that any of you are saying that. We need to take every case into account at that time. This is what differentiates us from other providers. We know the physiology and we know how to BEST deal with it.

 

[Salah]

A good discusion over here and I really find it useful for me so thanks all for your comments .

I think you misunderstood the question and are trying to fill the gabs with your own interpretation.
He most likely wanted to ask you: why would people under general anesthesia require more oxygen to maintain the same saturation? and the answer would be what Noyac implied:
VQ mismatch caused by many things: Supine position, Loss of physiological PEEP, Atelectasis, Decreased FRC and the change from negative pressure to positive pressure ventilation.

This is actually wat I was lookin for, so its related to the VQ mismatch that may be happened during anesthesia . I'll try to get more info about this title thanks for the guide :>