# What is the max pao2 on 1.0 fio2?

#### koobs

10+ Year Member
7+ Year Member
Had an attending ask me this but I can't find the answer. He said to assume a 20ish healthy incubated patient. I have found the alveolar has equation, but can't finure what to use for arterial. Fick?

#### sigrhoillusion

7+ Year Member
PAO2 = ( FiO2 * (Patm – PH2O)) – (PaCO2 / RQ).

It depends on certain factors. Are you at sea level? Do they have a normal resp quotient? What's the PACO2.

If you are to assume everything is "normal" with a PaCO2 of 40 then it would be ~663mmHg

#### koobs

10+ Year Member
7+ Year Member
PAO2 = ( FiO2 * (Patm – PH2O)) – (PaCO2 / RQ).

It depends on certain factors. Are you at sea level? Do they have a normal resp quotient? What's the PACO2.

If you are to assume everything is "normal" with a PaCO2 of 40 then it would be ~663mmHg
Yeah that is what I thought. I said about 700 just doing the math in my head but he said no...

#### pgg

##### Laugh at me, will they?
Volunteer Staff
15+ Year Member
So -

He didn't follow that by telling you the answer and how he arrived at it?

That's some mighty fine teaching there, Lou.

7 users

10+ Year Member
So -

He didn't follow that by telling you the answer and how he arrived at it?

That's some mighty fine teaching there, Lou.

Ugh I used to have a few obnoxious attendings that would ask basic anesthesia physics-ish questions like this, give an answer and never explain. Very, very frustrating.

#### dhb

##### Member
10+ Year Member
Tiva or not? You also have to factor in the gas: 6% des will take a chunk off of that 660
Temperature of incubation is also a game changer.

#### Maverikk

7+ Year Member
PaO2 is measured. PAO2 can be calculated using the equation, quick and dirty way is to multiply the FiO2 by 6 and you'll get close assuming no extremes of elevation, normal pCO2

#### anbuitachi

10+ Year Member
PaO2 is measured. PAO2 can be calculated using the equation, quick and dirty way is to multiply the FiO2 by 6 and you'll get close assuming no extremes of elevation, normal pCO2

We multiply by 5 here

10+ Year Member
What's the highest number anyone on SDN has ever seen on an ABG for the PAO2? There is theoretical and then there is real world.

#### nimbus

##### Member
15+ Year Member
What's the highest number anyone on SDN has ever seen on an ABG for the PAO2? There is theoretical and then there is real world.

Off the top of my head, many 5xx. Don't think I've ever seen 600+.

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#### nimbus

##### Member
15+ Year Member
Off the top of my head, many 5xx. Don't think I've ever seen 600+.

I stand corrected. Young trauma patient from last night. I'm at sea level. FiO2 was 1.0. He even had a small left hemothorax.

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#### proman

##### Member
Moderator Emeritus
15+ Year Member
I guess I'm cheating but you can get PaO2 above 760 by going hypothermic. Our co-oximeters just give a blank result at around 24 degrees. I'll post a picture on Wednesday from my next circ arrest case. If you want to be pedantic, remind your attending that he didn't specify temperature or pressure.

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