How to survive a gas attack

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Slides for a short talk on some tips and tricks for trainees when interpreting ABGs (arterial blood gases). Talk given at the free registrar's day at Bedside Critical Care 2013 in the Whitsunday Islands.

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  • Photo by Misserion
  • Normal Aa gradient increases 5-7 mmHG for every 10% increase in FiO2 due to the overcoming of hypoxic vasoconstriction opening blood flow to poorly ventilated lung areas.
  • Adams et al. included all ED patients over a seven month time period in whom a lactate level was measured for any reason. They considered an AG >12 abnormal and conducted sensitivity analyses of the AG for detecting the presence of a lactate >2.5 mmol/L. The AG was 52.8% sensitive, 81.0% specific with a negative predictive value of 89.7% for the prediction of lactic acidosis.(Adams BD, Bonzani TA, Hunter CJ. The anion gap does not accurately screen for lacticacidosis in emergency department patients. Emerg Med J. 2006;23(3):179-182.)
  • How to survive a gas attack

    1. 1. How to Survive ain 10 minutes… A Talk by Chris Nickson
    2. 2. No $ Photo by Misserion
    3. 3. Overview A-a GradientCompensation Strong Ions Anion Gap
    4. 4. All aboutA-a gradients(not really…)
    5. 5. A-a gradient = PAO2 – PaO2
    6. 6. PAO2 = FiO2 (PB – PH20) – (PaCO2/R)
    7. 7. Quick check:expected PaO2 = %FiO2 x 5
    8. 8. Caveats: high PaCO2A-a gradient varies with age and FiO2
    9. 9. Rule of thumb:expected A-a gradient = (age/4) + 4
    10. 10. Be aCompensation King (or Queen)
    11. 11. Respiratory compensation = rapidMetabolic compensation = slow
    12. 12. Metabolic compensation The 1-2-3-4-5 Rule
    13. 13. 1
    14. 14. 12
    15. 15. HCO312
    16. 16. HCO31 42
    17. 17. HCO31 42 5
    18. 18. HCO31 42 5acute chronic
    19. 19. HCO310 mmHg  1 4PaCO2  2 5 acute chronic
    20. 20. Respiratory compensation
    21. 21. PaCO2 = 1.5 x HCO3 + 8 (+/-2) if metabolic acidosisPaCO2 = 0.7 x HCO3 + 20 (+/-5) if metabolic alkalosis
    22. 22. Rule of thumb:If pH = 7.xy then PaCO2 ≈ xy
    23. 23. Strong ions… WTF?
    24. 24. The real determinants of pH are: Strong ions Weak acids [ATOT] PCO2
    25. 25. Strong Ion difference: Na – Cl <38 = NAGMA>38 = metabolic alkalosis
    26. 26. EMCrit by Scott Weingarthttp://emcrit.org/podcasts/acid-base-i/ Acid-Base Physiology by Kerry Brandishttp://www.anaesthesiamcq.com/AcidB aseBook/ABindex.php
    27. 27. High Lactate withNormal Anion Gap… WTF?
    28. 28. Anion gap Na – (HCO3+Cl)Normal = 8-12 mM LTKR
    29. 29. Anion gap is only ~50% sensitivefor lactic acidosis
    30. 30. What causes alow anion gap?
    31. 31. Low Anions: Albumin High Cations Bromism Analytical error
    32. 32. Correcting for low albumin is essentialAGadj = AGobs + 0.25 x (42 - Albobs)
    33. 33. THE ENDhttp://lifeinthefastlane.com/education /clinical-cases/http://lifeinthefastlane.com/exams/fac em-fellowship/vaq-subject/http://lifeinthefastlane.com/exams/cic m-fellowship/saq-keyword/
    34. 34. THE END http://lifeinthefastlane.com/education/clinical-cases/http://lifeinthefastlane.com/exams/facem-fellowship/vaq-subject/http://lifeinthefastlane.com/exams/cicm-fellowship/saq-keyword/

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