1. A&E(VINAYAKA) Blood Gas Analysis Dr. Prakash Mohanasundaram Department of Emergency & Critical Care medicine Vinayaka Missions University

2. A&E(VINAYAKA) Primary & Compensatory changes Primary change Compensation Respiratory acidosis PaCO 2 [HCO 3 ] Respiratory alkalosis PaCO 2 [HCO 3 ] Metabolic acidosis [HCO 3 ]PaCO 2 Metabolic alkalosis [HCO 3 ]PaCO 2

3. A&E(VINAYAKA) THE SIX STEP APPROACH

4. A&E(VINAYAKA) The 6 step approach 1)Acidemic or Alkalemic 2)Is the primary disturbance respiratory or metabolic 3)If Respiratory, is it acute or chronic 4)If Metabolic, is there an anion gap?

5. A&E(VINAYAKA) The 6 step approach 5)Are there any other metabolic disturbances with the anion gap acidosis? 6)Assess normal respiratory compensation for a metabolic disturbance.

6. A&E(VINAYAKA) Step - 1 Acidemic or Alkalemic Acidemic : pH < 7.35 Alkalemic : pH > 7.45

7. A&E(VINAYAKA) Step - 2 Is the primary disturbance Respiratory or Metabolic Respiratory disorder will alter the PaCO 2 High CO 2 in acidosis, Low CO 2 in alkalosis Go to Step – 3

8. A&E(VINAYAKA) Step - 2 Metabolic disorder will alter the [HCO3] HCO 3 < 22, metabolic acidosis “Go to Step-4” HCO 3 >26,metabolic alkalosis

9. A&E(VINAYAKA) Step - 3 RESPIRATORY ACUTECHRONIC

10. A&E(VINAYAKA) Step - 3 Respiratory Acidosis Acute pH = 0.08 x (PaCO 2 – 40 ) /10 Chronic pH = 0.03 x (PaCO 2 – 40 ) /10

11. A&E(VINAYAKA) Step - 3 Respiratory Alkalosis Acute pH = 0.08 x (PaCO 2 – 40 ) /10 Chronic pH = 0.03 x (PaCO 2 – 40 ) /10

12. A&E(VINAYAKA) Respiratory Acidosis Hypoventilation : PaCO 2 CNS depression : Sedatives, CNS disease Lung disease : Asthma, Chronic lung disease Musculoskeletal disorders : GBS, Myasthenia

13. A&E(VINAYAKA) Respiratory Alkalosis Hyperventilation : PaCO 2 CNS events ( hemorrhage) Drugs ( salicylates) Anxiety

14. A&E(VINAYAKA) Step - 4 METABOLIC ACIDOSIS CHECK ANION GAP

15. A&E(VINAYAKA) Step - 4 Anion Gap = Na- (Cl + HCO 3 ) Usually 12 +- 2  Anion Gap Metabolic acidosis : AG > 12  Non Anion Gap acidosis : AG < 12

16. A&E(VINAYAKA) Anion Gap Metabolic Acidosis HCO 3 & AG Methanol Uremia DKA Paraldehyde Infection Lactic acid Ethylene glycol Salicylates

17. A&E(VINAYAKA) Non-Anion Gap Metabolic acidosis Loss of HCO 3, or external acid infusion Low HCO 3 but AG < 12 GI loss of HCO 3 (Diarrhea) Renal losses Renal tubular necrosis Carbonic anhydrase inhibitors Ureteral diversion

18. A&E(VINAYAKA) Step - 5 Is there another metabolic disturbance co-existing with an anion gap acidosis Corrected HCO 3 = HCO 3 + (AG – 12) Corrected HCO 3 > 24 : Additional metabolic alkalosis Corrected HCO 3 < 24 : Non AG acidosis co-exists.

19. A&E(VINAYAKA) Example Anion Gap Metabolic acidosis HCO 3 10, AG 26 Corrected HCO 3 = 1O + (26-12) =24 No additional disturbance HCO 3 15, AG 26 Corrected HCO 3 = 15 + (26-12) =29 Co-existing metabolic alkalosis

20. A&E(VINAYAKA) Step-6 Assess normal respiratory compensation for a metabolic acidosis Winter’s formula Expected PaCO 2 = (1.5 X HCO 3 ) + (8 +- 2) If HCO 3 is 10, PaCO 2 should be 21-25 If PaCO 2 < 21, additional respiratory alkalosis If PaCO 2 > 25, additional respiratory acidosis

21. A&E(VINAYAKA) Step - 6 Assess normal respiratory compensation for a metabolic disturbance In metabolic Alkalosis winters formula not applicable PaCO 2 will rise, but not over 50-55

22. A&E(VINAYAKA) Case 1 Measured pH 7.24 PCO 2 60 mm Hg PO 2 56 mm Hg Calculated HCO 3 24mmol/L BE +2 SaO 2 85 % 5 Month old baby with Bronchiolitis FiO 2 70%

23. A&E(VINAYAKA) Case 1 Step-1 Acidemia or Alkalemia ? Acidemia Step-2 Primary disturbance Respiratory Step-3 Acute or Chronic pH = 0.08 x (60-40) / 10 = 0.16 7.4 – 0.16 = 7.24 Acute Respiratory Acidosis Uncompensated pH 7.24 PCO2 60 mm Hg PO2 56 mm Hg HCO3 24mmol/L

24. A&E(VINAYAKA) Case 2 Measured pH 7.10 PCO 2 20 mm Hg PO 2 87 mm Hg Calculated HCO 3 8 mmol/L BE - 15 SaO 2 96% 3 year old with severe diarrhea, diminished urine output, lethargy, Na-135, Cl- 115 FiO 2 24%

25. A&E(VINAYAKA) Case 2 Step-1 Acidemia or Alkalemia ? Acidemia Step-2 Primary disturbance Metabolic Step-4 What is the Anion Gap ? Na- (Cl + HCO 3 ) 135-(115 + 8) = 12 Step-6 What is the expected CO 2 ? Expected PaCO 2 = (1.5 x HCO 3 ) +( 8 +- 2 ) =( 1.5 x 8 ) + ( 8 +- 2 ) = 18 – 22 Compensated metabolic acidosis pH 7.10 PCO2 20 mm Hg PO2 87 mm Hg HCO3 8 mmol/L Na-135, Cl- 115

26. A&E(VINAYAKA) Case 3 Measured pH 7.1 o PCO 2 60 mm Hg PO 2 60 mm Hg Calculated HCO 3 10 mmol/L BE - 15 SaO 2 87 % 50 Year old resuscitated after a cardiac arrest. Na-142, Cl- 108 FiO 2 100%

27. A&E(VINAYAKA) Case 3 Step-1 Acidemia or Alkalemia ? Acidemia Step-2 Primary disturbance Metabolic Step-4 What is the Anion Gap ? Na- (Cl + HCO 3 ) 142-(108 + 10) = 24 pH 7.1o PCO2 60 mm Hg PO2 60 mm Hg HCO3 10 mmol/L Na-142, Cl- 108

28. A&E(VINAYAKA) Case 3 Step – 5 What is the corrected HCO 3 C orrected HCO 3 = HCO 3 + (AG – 12 ) 10 + ( 24 – 12 ) = 22 Step – 6 What is the expected CO 2 ? Expected PaCO 2 = (1.5 x HCO 3 ) +( 8 +- 2 ) ( 1.5 x 10 ) + ( 8 +- 2 ) = 21 – 25 Mixed metabolic and respiratory acidosis

29. A&E(VINAYAKA) Case 4 Measured pH 7.52 PCO 2 26 mm Hg PO 2 112mm Hg Calculated HCO 3 22 mmol/L BE +2 SaO 2 99% 4 year girl with lethargy, irritability, jaundice FiO 2 33 %

30. A&E(VINAYAKA) Case 4 Step-1 Acidemia or Alkalemia ? Alkalemia Step-2 Primary disturbance Respiratory Step-3 Acute or Chronic pH = 0.08 x (26-40) / 10 = 0.11 7.4 + 0.11 = 7.51 Acute Respiratory Alkalosis Uncompensated pH 7.52 PCO2 26 mm Hg PO2 112mm Hg HCO3 22 mmol/L

31. A&E(VINAYAKA) THANK YOU