1. Using Blood Gases Dr. Jonathan R. Goodall M62 Coloproctology Meeting 2 nd April 2004

2. JRG Hope Hospital April 2004

3. Teaching Grandma to suck eggs…

4. JRG Hope Hospital April 2004 Introduction  The necessary basics  Clinical examples of ABG use in ICU  Newer considerations in interpretation of acid-base disturbances

5. JRG Hope Hospital April 2004 The Basics - Normal Values  pH 7.35 - 7.45 H + 35- 45 nmol.l -1  pCO 2 4.5 - 6 kPa  pO 2 11 -14 kPa  Actual HCO 3 22-26 mmol.l -1  Standard HCO 3 22-26 mmol.l -1  Base Excess +/- 2.0  SaO 2 ≥ 95 %

6. JRG Hope Hospital April 2004 The Basics - Interpretation Oxygenation  PaO 2  ? SaO 2 + Hb more important  Interpret only with knowledge of FiO 2

7. JRG Hope Hospital April 2004 The Basics - Interpretation Acid-Base Status  pH  pCO 2  HCO 3 (actual or standard)  Base Excess Oxygenation  PaO 2  SaO 2 + Hb more important?  Interpret only with knowledge of FiO 2

8. JRG Hope Hospital April 2004 H 2 O + CO 2 H 2 CO 3 H + + HCO 3 -

9. JRG Hope Hospital April 2004 H 2 O + CO 2 H 2 CO 3 H + + HCO 3 -

10. JRG Hope Hospital April 2004 The Basics - Standard Bicarbonate  The amount of bicarbonate that would be present if: PCO2 was 5.3 kPa Temp 37°C Blood fully oxygenated At sea level

11. JRG Hope Hospital April 2004 The Basics - Base Excess (Deficit)  The amount of base that needs to be added to or subtracted from each litre of blood (ecf) to return the pH to a value of 7.4 at: pCO2 5.3 kPa Temp 37°C

12. JRG Hope Hospital April 2004

13. Ivor Lewis Oesophagectomy  54 year old lady  No significant PMH  7 hour procedure  Initial post op period stable

14. JRG Hope Hospital April 2004

17. Date17/318/3 19/3 Time22:3008:0019:3010:45 FiO 2 0.40.61.0 pH7.407.437.367.35 pCO 2 4.74.444.714.74 pO 2 14.89.5916.49.9 BE-2.0-1.5-4.5-5.9

18. JRG Hope Hospital April 2004 Date17/318/3 19/3 Time22:3008:0019:3010:45 FiO 2 0.40.61.0 pH7.407.437.367.35 pCO 2 4.74.444.714.74 pO 2 14.89.5916.49.9 BE-2.0-1.5-4.5-5.9

19. JRG Hope Hospital April 2004 Date17/318/3 19/3 Time22:3008:0019:3010:45 FiO 2 0.40.61.0 pH7.407.437.367.35 pCO 2 4.74.444.714.74 pO 2 14.89.5916.49.9 BE-2.0-1.5-4.5-5.9

20. JRG Hope Hospital April 2004 Date17/318/3 19/3 Time22:3008:0019:3010:45 FiO 2 0.40.61.0 pH7.407.437.367.35 pCO 2 4.74.444.714.74 pO 2 14.89.5916.49.9 BE-2.0-1.5-4.5-5.9

21. JRG Hope Hospital April 2004

22. Date21/322/323/3 Time11:0019:4008:00 FiO 2 0.50.450.4 pH7.297.47.43 pCO 2 6.514.954.76 pO 2 11.316.810.8 BE-3.0-1.5-0.1

23. JRG Hope Hospital April 2004

24. Cellulitis (?)  75 year old lady  Established atrial flutter  Admitted with spreading cellulitis right calf  Hypotension unresponsive to fluids (and dobutamine!)

25. JRG Hope Hospital April 2004

26. Initial ABGs Date31/3 Time02:1504:4008:50 FiO 2 1.00.50.45 pH7.217.447.56 pCO 2 9.154.913.34 pO 2 10.816.016.8 BE-0.61.50.8

27. JRG Hope Hospital April 2004

28. Date31/3 Time02:1504:4008:50 FiO 2 1.00.50.45 pH7.217.447.56 pCO 2 9.154.913.34 pO 2 10.816.016.8 BE-0.61.50.8

29. JRG Hope Hospital April 2004 Date31/3 Time02:1504:4008:50 FiO 2 1.00.50.45 pH7.217.447.56 pCO 2 9.154.913.34 pO 2 10.816.016.8 BE-0.61.50.8

30. JRG Hope Hospital April 2004

32. Hyperchloraemic acidosis  Base deficit traditionally used as marker for metabolic acidosis  Appropriate fluid resuscitation should decrease base deficit  Chloride rich solutions (0.9% NaCl) can potentiate metabolic acidosis www.anaesthetist.com/icu/elec/ionz/Stewart  If base deficit persists despite ‘adequate’ fluids in an otherwise well patient, check [Cl - ]!

33. JRG Hope Hospital April 2004 Summary  Arterial blood gases can be used to guide therapy  Must be interpreted in the light of the clinical setting  Look at acid–base disturbances, then oygenation with FiO 2  Remember the possibility that treatment may cause problems!

34. JRG Hope Hospital April 2004