2. Bloedgas Workshop Laura Kater
Emergency Physician Rode Kruis Ziekenhuis, Beverwijk
ROD

3. What will we discuss Warming up Aa gradient
Arterial vs venous blood gas

4. 1kPa = 7.5 mmHg

5. Warming up

6. 35 yo female Dyspnea FiO2 100% ABG: pH 6.76 pCO2 72 Bic 10 BE -26.0
pO2 24
Sat 94

7. 31 yo male Dyspnea FiO2 100% ABG: pH 6.72 pCO2 87 Bic 11 BE -28.7
pO2 301
Sat 97

8. 94 yo female Dyspnea FiO2 4 ltr O2 = ongeveer 30%? ABG: pH 7.15
pCO2 55
Bic 19 BE
pO2 62
Sat 83

9. Aa
Gradient

10. Aa gradient = alveolar minus arterial oxygen pressure pAO2 – paO2

11. pAO2: calculation paO2: measurement in arterial blood gas

12. Why is this important?

13. pAO2
pAO2 (mmHg) = 7x %O2 – paCO2 – 10 So at room air: 7x21 – 40 – 10 = 97 mmHg

14. Example 65 yo, room air (FiO2 21%) ABG 7.44 / 29 / 88 / 19 / -3 / 95%
pAO2 = 7x21 – 29 – 10 = 108 mmHg
paO2 in ABG = 88 mmHg
Difference = Aa gradient = 20 mmHg

15. Is that normal???

16. Aa gradient
Aa max = age / 3 + pAO2 / 5 – 23 Our pt: 65 / / 5 – 23 = – 23 = Calculated gradient was 20.

17. Another one 61 yo, FiO2 30% ABG 7.02 / 22 / 146 / 6 / -24 / 98%
pAO2 = 7x30 – 22 – 10 = 178 mmHg
paO2 = 146
Aa gradient = 32
Aa max for this age:
61/ /5 – 23 =
– 23 = 32.9
Conclusion: normal Aa gradient

18. En nu?
30 yo, non rebreather (FiO2 +/-80%) ABG: 7.40 / 40 / … / 25 / 0 / 100% What pO2 do you expect? pAO2 = 7x80 – 40 – 10 = 510 mmHg Max Aa gradient = 30/ / 5 – 23 = – 23 = 89 Expected paO2 in ABG is about 421 mmHg

19. Last…
74 yo, room air ABG: 7.42 / 39 / 62 / 25 / 1 / 90% pAO2 = 7x21 – 39 – 10 = 98 mmHg paO2 = 62 Aa gradient = 36 Aa max = 74/3 + 98/5 – 23 = – 23 = 21 Aa gradient 15 mmHg to high = low paO2 Pulm.problem?, shunt / VQ mismatch?

20. Lifeinthefastlane.com

21. Arterial or Venous

22. Use bloodgas in ED acid-base status pH, bicarbonaat
respiratory function
pCO2, sometimes pO2

23. Why venous? Painful arterial punction Hematoma after art.punction
Easy to sample a venous one when you’re already drawing blood for standard labs

24. BUT
Is a venous bloodgas clinical equivalent to arterial?????

25. EMRAP june 2008 summarizes a few publications:(

26. A few publications in:
Annals of EM april 1998 In diabetic ketoacidosis in adults the venous blood gas measurements accurately demonstrate the degree of acidosis. Mean difference between arterial and venous pH was 0.03 (range )

27. EM Journal sept 2001
strong correlation between arterial and venous
pH, difference 0.4.

28. Journal EM jan 2002
Very good agreement in pH with venous samples being -/-34 units lower than arterial samples.
pCO2 on average 5.8 mmHg higher in venous samples

29. Canadian Journal EM 2002
pH art an venous difference 0.36
pCO2 6 mmHg
HCO3- 1.5

30. Annals of EM 2005 very good correlation between arterial and venous pH and HCO3-

31. EM Australasia feb 2006
in pts with DKA the weighted average differences between arterial and venous
pH was 0.02
bic -1.88

32. For details look at the studies

33. Resus.me Cliff Reid:

34. Professor Anne-Maree Kelly, June 2009
pH - Close enough agreement for clinical purposes in DKA, isolated metabolic disease; more work needed in shock, mixed disease
Bicarbonate - Close enough agreement for clinical purposes in most cases; more work needed in shock, mixed disease, calculated vs measured gap
pCO2 – NOT enough agreement for clinical purposes; potential as a screening test
Base excess – Insufficient data

35. Lim and Kelly
Eur J of EM 2010 Available evidence suggests that there is good agreement for pH and HCO3 values between arterial and pVBG results in patients with COPD, but not for pO2 or pCO2. Widespread clinical use is limited because of the lack of validation studies on clinical outcomes

36. Questions???

38. Take home message
When in doubt of a pulmonary problem causing hypoxia, use the Aa gradient to calculate if the oxygen you give your patiënt correlates with the paO2 in the ABG
Think before you ask for an ABG. What do you need to know, will a venous blood gas do?
When in need of an ABG: local anesthesia.

39. Thank you!