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Approach to Acid Base Disorder

Approach to Acid Base Disorder. By Dr. S. Shivakumar, M.D. Addl.Professor of Medicine, Stanley Medical College, Chennai. Normal Values. pH : 7.36 – 7.44 (7.40) plasma HCO 3 : 24 – 26 mEq/L (25) pCo 2 : 39 – 43 (40) plasma (H + ) : 36 – 44 nEq / L (40 nEq / L)

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Approach to Acid Base Disorder

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  1. Approach to Acid Base Disorder By Dr. S. Shivakumar, M.D. Addl.Professor of Medicine, Stanley Medical College, Chennai.

  2. Normal Values • pH : 7.36 – 7.44 (7.40) • plasma HCO3: 24 – 26 mEq/L (25) • pCo2 : 39 – 43 (40) • plasma (H+) : 36 – 44 nEq / L (40 nEq / L) • pH < 7.2 : Severe Acidosis • pH > 7.6 : Severe Alkalosis • pH : 7.0 = 1 x 10 – 7 (1 x 1/107) = 100 x 10 – 9 = 100 nEq / L • Na & K : 10 – 3 = mEq

  3. Correlation between H+ ion & pH Change in 0.3 pH  Double or Halve the H+

  4. Within narrow limits 0.01 change in pH ~ 1 mEq / L change of [H+] Estimating the H+ ion from pH X 0.8  1.25

  5. Approach • Step I : Check validity • Step II : Obtain Minimum diagnosis • Step III: Is it a Simple or Mixed acid base disorder • Step IV : Determine Anion gap • Step V : Is it a Triple disorder

  6. SuggestionsStep I. Check validity : (Modified Henderson equation) H = 24 x Pco2 Hco3 H = 24 x 40 24 = 40 nEq = pH = 7.4 eg:pH= 7.0 HC03= 8 PCo2 = 32   H = 24 x 32 8 = 96 nEq = pH 7.0

  7. Step II:Obtain minimum diagnosis • Look at pH - Acidosis / Alkalosis • Match the Pco2 or Hco3 - Metabolic / Respiratory

  8. Examples of Simple Disorder

  9. Step III:Is it a simple or mixed Acid-base disorder? Simple Disorder :

  10. Mixed Disorder

  11. Apply Compensation

  12. Example pH : 7.00 Pco2 = 32 Hco3 = 8 Fall in Hco3 = 24 – 8 = 16 Compensatory Fall in Pco2 = 16 x 1.2 = 19 Anticipated Pco2 = 40 – 19 = 21 Estimated : Pco2 = 32 (Pco2  ) Diagnosis Mixed - Metabolic acidosis + Respiratory acidosis

  13. Mixed acid base disorder

  14. Mixed acid base disorder

  15. Examples of mixed acid base disorder

  16. Step IV: Determine the Anion gap AG = Na+– (Hco3 + Cl ) Normal = 12 ± 4 ( 8  16 ) Valuable in Metabolic acidosis – High gap / Normal gap Metabolic alkalosis – Evaluation of “Starting Hco3” High gap acidosis : AG > 27 mEq /L 17  26 Suggestive Eg.– Ketoacidosis, Lactic acidosis, Methanol intoxication, Renal failure Normal gap acidosis – Diarrhoea, RTA

  17. AG in metabolic alkalosis • Valuable in diagnosis of Triple disorder (Metabolic acidosis,Met.alkalosis & Resp. acidosis) • Delta () AG = Calculated Anion gap – Normal Anion gap Hco3 +AG = Starting Hco3 • Starting Hco3 > 29 suggests associated Metabolic Alkalosis in the presence of Metabolic Acidosis

  18. Example Na+ = 135 Hco3 = 4cl = 90 pH = 6.8 AG = Na  ( Hco3 + cl ) = 135 – (4 + 90) = 41  High gap acidosis AG = Calculated – AG Normal = 41 – 12 = 29 Starting Hco3 = 4 + 29 = 33 mEq / L Starting Hco3 > 29 suggests associated Metabolic Alkalosis in the presence of Metabolic Acidosis

  19. Approach with an Example A 50 year old male suffering from COPD & vomiting is admitted for breathlessness. Biochemical parameters

  20. Approach with an Example(contd) Step 1 :Check Validity H = 24 X Pc02 = 24 X 22 = 155 nEq / L = pH 6.8 Hco3 3.4 Step 2:Obtain minimum diagnosis pH = 6.8 Pco2 = 22 Hco3= 3.4  Metabolic acidosis

  21. Approach with an Example(contd) Step 3: Is it a Simple or Mixed Acid base disturbance By applying compensation (24  3.4 = 20.6 ; 20.6  1.2 = 24.7; 40  24.7 = 15.3) Predicted Pco2 = 15.3, butObserved Pco2= 22 Mixed disorder Metabolic Acidosis + Respiratory Acidosis

  22. Approach with an Example (contd) Step 4: Determine Anion Gap Na = 135 Cl = 90 Hco3 = 3.4 AG = 135 – (3.4 + 90) = 41.6 • High Gap acidosis

  23. Approach with an Example (contd) Step 5: Is it a triple disorder Look for metabolic acidosis with AG AG = Calculated AG - AG normal = 41.6 - 12.0 = 29.6 Starting Hc03 = Hco3+ AG = 3.4 + 29.6 = 33 mEq /L (Metabolic alkalosis)

  24. Diagnosis pH= 6.8 Pco2 = 22 Hco3 = 3.4 Po2 = 60 Na+ = 135 k += 6.0 Cl= 90 Urea= 110 S.Cr= 3mg/dl Sugar = 100 mgs Triple Disorder = Metabolic acidosis + Resp.acidosis + Met.alkalosis • Metabolic acidosis – Renal failure • Respiratory acidosis – COPD • Metabolic alkalosis – Vomiting

  25. A 40 yr old man is admitted for diarrhoea & breathlesness for 2 days. Example –1 • Diagnosis: Normal AG Met.Acidosis (AG – 11) • Due to Diarrhoea + Hypokalemia,

  26. A 40 yr old man is admitted for diarrhoea of 1 week & breathlesness of 1 day Example –2 • Diagnosis:High gap Acidosis (AG - 29) • Due to Renal failure + Hyperkalemia

  27. A 45 yr old female is admitted for high fever & breathlessness, diagnosed to have acute Cholecystitis Example –3 • (Predicted pCo2 – 18, but observed pCo2 – 12) • Diagnosis: Metabolic acidosis + Respiratory Alkalosis Due to sepsis

  28. A 50 yr old Pt., a known case of COPD is admitted for severe diarrhoea Example –4 • (Predicted pCo2 – 25, but observed pCo2 – 40) • Diagnosis: Respiratory Acidosis (COPD ) + Metabolic acidosis (Diarrhoea)

  29. A 50 yr old, known COPD Pt. with Cor pulmonale on treatment with Frusemide and is admitted for severe vomitting. Example –5 • (Predicted pCo2 – 54, but observed pCo2 – 80) • Diagnosis: Respiratory Acidosis (COPD ) + Metabolic Alkalosis (Vomiting + Diuretics)

  30. A 50 yr old Pt. with Cirrhosis Liver is admitted for coma & Vomitting. He has been treated with Frusemide recently for ascites. Example –6 • (Predicted Hco3– 20, but observed Hco3– 40) • Diagnosis: Respiratory Alkalosis (Cirrhosis ) + Metabolic Alkalosis (Vomitting + Diuretics)

  31. Summary • Suspect the diagnosis from history • Suspect the disturbance from physical symptoms • Evaluate routine laboratory date : Sugar, RFT, LFT, Na+, K+ • Establish the cause of Acid Base disorder (Utilize thoughtful differential diagnosis), • Direct management of underlying disorder, unless pH is in a dangerous range

  32. Thank You

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