I’m entering a few months prep for the UK and Ireland exit exam in Emergency Medicine: the FRCEM. I’ll be adding lots of little notes on pearls I’ve learned along the way. A lot of my revision is based around the Handbook of EM as a curriculum guide and review of contemporary, mainly UK guidelines. I also focus on the areas that I’m a bit sketchy on. With that in mind I hope they’re useful.
You can find more things on the FRCEM on this site here.
What is meant by DO2, VO2 and O2ER?
Mainly from LITFL
- DO2/VO2 relationships
- DO2 = oxygen delivery
- VO2 = oxygen consumption
- O2ER is oxygen extraction ratio and is ratio of VO2 to DO2 [O2ER = VO2 / DO2]
- Normally VO2 = 250ml/min and DO = 1000ml/min therefore O2ER = 25%. In other words oxygen delivery is usually well in excess of oxygen consumption
- the critical O2ER is about 70% and beyond this things don’t go well
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What is the Alveolar-arterial gradient?
- The Alveolar-arterial gradient
- Aa Gradient = PAO2-PaO2
- PAO2 comes from the alveolar gas equation
- PAO2 = PiO2 – PACO2/0.8
- remember PiO2 = 0.21 x (760 – 47) [at sea level]
- PaO2 comes from your ABG
- Normal Aa gradient increases with age.
- In a hypoxic patient a normal Aa gradient suggests hypoxia is due to 1) hypoventialtion (eg opiates) or 2) reduced FiO2
- Increased Aa gradient found in V/Q or shunt or increased O2ER or diffusion defect
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