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Using Blood Gases

Using Blood Gases. Dr. Jonathan R. Goodall M62 Coloproctology Meeting 2 nd April 2004. Teaching Grandma to suck eggs…. Introduction. The necessary basics Clinical examples of ABG use in ICU Newer considerations in interpretation of acid-base disturbances. The Basics - Normal Values.

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Using Blood Gases

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

  2. JRG Hope Hospital April 2004

  3. Teaching Grandma to suck eggs… JRG Hope Hospital April 2004

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

  5. The Basics - Normal Values • pH 7.35 - 7.45 H+ 35- 45 nmol.l-1 • pCO2 4.5 - 6 kPa • pO2 11 -14 kPa • Actual HCO3 22-26 mmol.l-1 • Standard HCO3 22-26 mmol.l-1 • Base Excess +/- 2.0 • SaO2 ≥ 95 % JRG Hope Hospital April 2004

  6. Oxygenation PaO2 ? SaO2 + Hb more important Interpret only with knowledge of FiO2 The Basics - Interpretation JRG Hope Hospital April 2004

  7. Acid-Base Status pH pCO2 HCO3 (actual or standard) Base Excess Oxygenation PaO2 SaO2 + Hb more important? Interpret only with knowledge of FiO2 The Basics - Interpretation JRG Hope Hospital April 2004

  8. H2O + CO2 H2CO3 H+ + HCO3- JRG Hope Hospital April 2004

  9. H2O + CO2 H2CO3 H+ + HCO3- JRG Hope Hospital April 2004

  10. 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 JRG Hope Hospital April 2004

  11. 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 JRG Hope Hospital April 2004

  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 JRG Hope Hospital April 2004

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  24. Cellulitis (?) • 75 year old lady • Established atrial flutter • Admitted with spreading cellulitis right calf • Hypotension unresponsive to fluids (and dobutamine!) JRG Hope Hospital April 2004

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  26. Initial ABGs JRG Hope Hospital April 2004

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  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-]! JRG Hope Hospital April 2004

  33. 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 FiO2 • Remember the possibility that treatment may cause problems! JRG Hope Hospital April 2004

  34. JRG Hope Hospital April 2004

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