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

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Presentation on theme: "Approach to Acid Base Disorder By Dr. S. Shivakumar, M.D. Addl.Professor of Medicine, Stanley Medical College, Chennai."— Presentation transcript:

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 HCO 3 : 24 – 26 mEq/L (25)  pCo 2 : 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 1/10 7 ) = 100 x 10 – 9 = 100 nEq / L  Na & K : 10 – 3 = mEq

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

4 Estimating the H + ion from pH  Within narrow limits 0.01 change in pH ~ 1 m E q / L change of [H + ] = = = = 43 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 Suggestions Step I. Check validity : (Modified Henderson equation) H = 24 x Pco 2 Hco 3 H = 24 x = 40 nEq = pH = 7.4 eg:pH = 7.0 HC0 3 = 8 PCo 2 = 32 H = 24 x 32 8 = 96 nEq = pH 7.0

7 DisorderPrimary Change Secondary change Net effect M. Acidosis  Hco 3  Pco 2  pH (  H + ) M.Alkalosis  Hco 3  Pco 2  pH (  H + ) R. Acidosis  Pco 2  Hco 3  pH (  H + ) R. Alkalosis  Pco 2  Hco 3  pH (  H + ) Step II: Obtain minimum diagnosis  Look at pH - Acidosis / Alkalosis  Match the Pco 2 or Hco 3 - Metabolic / Respiratory

8 Examples of Simple Disorder DisorderpHHco 3 Pco 2 Metabolic Acidosis Respiratory Acidosis Metabolic Alkalosis Respiratory Alkalosis

9 Step III: Is it a simple or mixed Acid-base disorder? Simple Disorder : DisorderExample Metabolic acidosisDKA, Renal failure, Lactic acidosis, Methanol poisoning, Diarrhoea Metabolic alkalosisVomiting, Diuretics, Steroids Respiratory acidosis COPD Respiratory alkalosisPsychogenic hyperventilation, Hepatic Encephalopathy

10 Mixed Disorder SituationDisorder COPD + Vomiting Respiratory acidosis + Metabolic alkalosis COPD + Diarrhoea Respiratory acidosis + Metabolic acidosis Sepsis Metabolic acidosis + Respiratory alkalosis Cirrhosis + Diuretics Respiratory alkalosis + Metabolic alkalosis

11 Apply Compensation Metabolic Acidosis Pco 2 should  by 1.2 mm for each mEq  plasma Hco 3 Metabolic Alkalosis Pco 2 should  by 0.6 mm for each mEq  plasma Hco 3 Acute Resp.Acidosis Plasma Hco3  by 1 mEq / L for each 10 mm  P co 2 Chronic. Resp. Acidosis Plasma Hco3  by 4 mEq / L for each 10 mm  P co 2 Acute. Resp. Alkalosis Plasma Hco3  by 1 mEq / L for each 10 mm  P co 2 Chronic Resp Alkalosis Plasma Hco3  by 4 mEq / L for each 10 mm  P co 2

12 Example pH : 7.00Pco 2 = 32Hco 3  = 8 Fall in Hco 3 = 24 – 8 = 16 Compensatory Fall in Pco 2 = 16 x 1.2 = 19 Anticipated Pco 2 = 40 – 19 = 21 Estimated : Pco 2 = 32 (Pco 2  ) Diagnosis Mixed - Metabolic acidosis + Respiratory acidosis

13 Mixed acid base disorder DisorderCompensationPH Metabolic Acidosis + Respiratory Acidosis eg: COPD + DKA P Co 2  & Hco 3  for simple disturbance  pH = P Co 2  Hco 3  Metabolic Alkalosis+ Respiratory Alkalosis eg: Cirrhosis + Diuretics P Co 2  & Hco 3  for simple disturbance  pH = PCo 2  Hco 3 

14 Mixed acid base disorder DisorderCompensationPH Metabolic acidosis + Respiratory alkalosis eg : Sepsis PCo 2  & Hco 3  for simple disturbance Normal or slightly  or  (N) pH = PCo 2  Hco 3  Metabolic alkalosis + Respiratory acidosis PCo 2  & Hco 3  for simple disturbance Normal or slightly  or  (N) pH = PCo 2  Hco 3 

15 Examples of mixed acid base disorder Data Disorder pHHco 3 Pco 2 Po (30)9050 Respiratory acidosis + Metabolic acidosis (30)9050 Respiratory acidosis + Metabolic alkalosis (22)100 Metabolic acidosis + Respiratory alkalosis (43)100 Metabolic alkalosis + Respiratory alkalosis

16 Step IV: Determine the Anion gap AG = Na + – (Hco 3  + Cl  ) Normal = 12 ± 4 ( 8  16 ) Valuable in Metabolic acidosis – High gap / Normal gap Metabolic alkalosis – Evaluation of “Starting Hco 3 ” High gap acidosis : AG > 27 m E q /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 Hco 3 +  AG = Starting Hco 3  Starting Hco 3 > 29 suggests associated Metabolic Alkalosis in the presence of Metabolic Acidosis

18 Example Na + = 135 Hco 3  = 4 cl  = 90 pH = 6.8 AG = Na  ( Hco 3  + cl  ) = 135 – (4 + 90) = 41  High gap acidosis  AG = Calculated – AG Normal = 41 – 12 = 29 Starting Hco 3 = = 33 mEq / L Starting Hco 3 > 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 pH – 6.8pCo pO Hco Na+ 135k – 6.0Cl urea-110 S.Cr. – 3.0sugar-100

20 Approach with an Example(contd) Step 1 : Check Validity H = 24 X Pc0 2 = 24 X 22 = 155 nEq / L = pH 6.8 Hco Step 2: Obtain minimum diagnosis pH = 6.8 Pco 2 = 22 Hco 3 = 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 Pco 2 = 15.3, but Observed Pco 2 = 22 Mixed disorder  Metabolic Acidosis + Respiratory Acidosis

22 Approach with an Example (contd) Step 4: Determine Anion Gap Na = 135 Cl = 90 Hco 3 = 3.4 AG = 135 – ( ) = 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 = = 29.6 Starting Hc0 3 = Hco 3 +  AG = = 33 mEq /L (Metabolic alkalosis)

24 Diagnosis Triple Disorder = Metabolic acidosis + Resp.acidosis + Met.alkalosis  Metabolic acidosis – Renal failure  Respiratory acidosis – COPD  Metabolic alkalosis – Vomiting pH = 6.8 Pco 2 = 22Hco 3  = 3.4 Po 2 = 60 Na + = 135 k + = 6.0 Cl  = 90 Urea= 110 S.Cr = 3mg/dl Sugar = 100 mgs

25 Example –1  A 40 yr old man is admitted for diarrhoea & breathlesness for 2 days. pH - 7.2pCo pO Hco Na k - 2.9Cl urea-70 S.Cr sugar-110  Diagnosis: Normal AG Met.Acidosis (AG – 11)  Due to Diarrhoea + Hypokalemia,

26 Example –2  A 40 yr old man is admitted for diarrhoea of 1 week & breathlesness of 1 day pH - 7.1pCo pO Hco Na k Cl urea-120 S.Cr sugar-110  Diagnosis: High gap Acidosis (AG - 29)  Due to Renal failure + Hyperkalemia

27 Example –3  A 45 yr old female is admitted for high fever & breathlessness, diagnosed to have acute Cholecystitis pH - 7.3pCo pO Hco Na K + - 5Cl Urea-45 S.Cr Sugar-120  (Predicted pCo2 – 18, but observed pCo2 – 12)  Diagnosis: Metabolic acidosis + Respiratory Alkalosis Due to sepsis

28 Example –4  A 50 yr old Pt., a known case of COPD is admitted for severe diarrhoea pH - 6.9pCo pO Hco Na K + - 4Cl Urea-45 S.Cr Sugar  (Predicted pCo 2 – 25, but observed pCo2 – 40)  Diagnosis: Respiratory Acidosis (COPD ) + Metabolic acidosis (Diarrhoea)

29 Example –5  A 50 yr old, known COPD Pt. with Cor pulmonale on treatment with Frusemide and is admitted for severe vomitting. pH - 7.4pCo pO Hco Na K + - 4Cl Urea-45 S.Cr Sugar- 128  (Predicted pCo 2 – 54, but observed pCo2 – 80)  Diagnosis: Respiratory Acidosis (COPD ) + Metabolic Alkalosis (Vomiting + Diuretics)

30 Example –6  A 50 yr old Pt. with Cirrhosis Liver is admitted for coma & Vomitting. He has been treated with Frusemide recently for ascites. pH pCo pO Hco Na K Cl Urea - 45 S.Cr Sugar -110  (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

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