A pg’s guide to abg

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Step by step to cracking that cryptic sheet !

All credits to Dr Tiny Nair MD,DM, Consultant cardiologist, PRS Hospital, Thiruvananthapuram.

Published in: Health & Medicine, Technology
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A pg’s guide to abg

  1. 1. A PG’S GUIDE TO ABG
  2. 2. CAN YOU TRUST THE REPORT? Henderson-Hasselbalch shortcut:-  80 – Last two digits of pH = (24 X pCO2)/HCO3 Balanced equation = Correct ABG.
  3. 3. pA(lveolar)O2 SHENANIGANS pAO2 = 150 – (pCO2 X 1.25) [@ room air] If pa(rterial)O2 is low, calculate:-  pAO2 – paO2 = dO2 = >15 or <15.
  4. 4. dO2 REVELATIONS I dO2 > 15 › COPD › ILD › Pneumonia › Pulmonary edema › Right to left shunt
  5. 5. dO2 REVELATIONS II dO2 < 15 › Low FiO2 › CNS diseases › High altitude › Respiratory muscle disease › Upper airway obstruction
  6. 6. PRIMARY DISORDER Resp and Metab are on opposite sides of acidosis and alkalosis. Easy :- Primary disorder tallies with pH.
  7. 7.  (Resp + Metab) acidosis/alkalosis. Calculate (Δ Value/Normal value) for pCO2 and HCO3. Larger value is the primary.
  8. 8. COMPENSATION Resp Metabolic Acidosis Alkalosis HCO3 pCO2 X 0.7 X 0.1 X 0.4 I N C a/c R c/c EpCO2 A HCO3 S HCO3 I X 0.2 N pCO2 X 1.2 X 0.5 G Alkalosis Acidosis
  9. 9. JUMPING THE ANION GAP Always calculated for metabolic acidosis. AG = Na – (Cl + HCO3) = <10 normally. High AG ≥ 10 ΔAG = Excess anions = AG – 10 (Anions neutralized by HCO3) Original HCO3 = ΔAG + HCO3
  10. 10. ΔAG REVELATIONS ΔAG = ΔHCO3; All is well. ΔAG > ΔHCO3 = HAG Met Acid + Meta Alk. ΔAG < ΔHCO3 = HAG Met Acid + NAG Met Acid.
  11. 11. NAGMA – SO WHAT? Calculate Urine AG = (Na + K) – Cl Normal UAG = 0 ≈ GI loss (diarrhoea) UAG > 0 ≈ Urinary loss (RTA)
  12. 12. APPENDIX High RBS needs corrected Na. Corrected Na = Na + [(RBS-100)/100] X 1.4.
  13. 13. HCO3 THERAPY pH < 7.2 and HCO3 < 5 – 10 mEq/l Inadequate ventilatory compensation Elderly on β-blockers in severe acidosis with compromised cardiac function Concurrent severe AG and NAGMA Severe acidosis with renal failure/intoxication
  14. 14. HOW MUCH HCO3 HCO3 deficit = (ideal – actual) X 0.5 X lean body wt.
  15. 15. NOW GO AND BREAK THAT CRYPTIC ABG!

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