Shunt, V/Q mismatch and venous admixture

By popular demand, here is the actual physiology and pharmacology viva that Stan was examined on for the part 1 ANZCA exam!

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Some links and formulas!

How does it measure cardiac output?

Using thermodilution and utilisation of Stewart Hamilton’s equation of:

(Tb-Ti)*Volume*k/intergration of change in T

What is venous admixture?

Venous admixture is the amount of mixed venous blood that needs to be added to end-capillary blood to account for the difference seen in pO2 between arterial blood and end-capillary blood.

It is calculated using the equation:

Qs/Qt = Cc’O2 – CaO2 / Cc’O2 – CvO2

Alveolar gas equation.

PAO2 = FiO2 (Patm – PH2O) – pCO2/R

 Is there anything else at the end?

Yes there is a correction factor (+F) which is FiO2 * pCO2 * (1-R)/R and this is normally less than 2mmHg.

O2 content = SaO2 * Hb * 1.34 (Huffner’s constant which ideally is 1.39) + pO2 * 0.003

the isoshunt diagram is figure 8 here:
https://erj.ersjournals.com/content/44/4/1023.figures-only

Please rate, post a review and subscribe!

Check out https://anaesthesiacollective.com/education/first-part-exam/ for general information and a collection of model answers

and 
sign up to the ABCs of Anaesthesia facebook group https://www.facebook.com/groups/2082807131964430

and check out the ABCs of Anaesthesia YouTube channel for more content
https://www.youtube.com/c/ABCsofAnaesthesia

If you have any questions, please email Lahiruandstan@gmail.com 

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