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Acid-Base Disturbances

Acid-Base Disturbances. Clinical Approach 2006 Pravit Cadnapaphornchai. Simple vs Mixed. Simple When compensation is appropriate Mixed When compensation is in appropriate. Simple Acid-Base Disturbances. When compensation is appropriate Metabolic acidosis ( ↓ HCO 3 , ↓ pCO 2 )

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Acid-Base Disturbances

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  1. Acid-Base Disturbances Clinical Approach 2006 Pravit Cadnapaphornchai

  2. Simple vs Mixed • Simple • When compensation is appropriate • Mixed • When compensation is inappropriate

  3. Simple Acid-Base Disturbances • When compensation is appropriate Metabolic acidosis (↓ HCO3, ↓ pCO2) Metabolic alkalosis (↑ HCO3, ↑ pCO2) Respiratory acidosis (↑ pCO2, ↑ HCO3) Respiratory alkalosis (↓ pCO2, ↓ HCO3)

  4. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  5. Organ dysfunction • CNS – respiratory acidosis (suppression) and alkalosis (stimulation) • Pulmonary – respiratory acidosis (COPD) and alkalosis (hypoxia, pulmonary embolism) • Cardiac – respiratory alkalosis, respiratory acidosis, metabolic acidosis (pulmonary edema) • GI – metabolic alkalosis (vomiting) and acidosis (diarrhea) • Liver – respiratory alkalosis, metabolic acidosis (liver failure) • Kidney – metabolic acidosis (RTA) and alkalosis (1st aldosteone)

  6. Organ Dysfunction • Endocrine • Diabetes mellitus – metabolic acidosis • Adrenal insufficiency – metabolic acidosis • Cushing’s – metabolic alkalosis • Primary aldosteronism – metabolic alkalosis • Drugs/toxins • Toxic alcohols – metabolic acidosis • ASA – metabolic acidosis and respiratory alkalosis • Theophylline overdose – respiratory alkalosis

  7. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  8. pH < 7.35 7.4 >7.45 Acidosis Metabolic Respiratory Mixed Alkalosis Metabolic Respiratory

  9. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  10. CO2 content LowNormalHigh Metabolic acidosis Normal Metabolic alkalosis Resp alkalosis Mixed Resp acidosis A normal CO2 content + high anion gap = metabolic acidosis + Metabolic alkalosis or metabolic ac + compensatory respiratory ac.

  11. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  12. Calculation of Anion Gap in Metabolic Acidosis Anion gap = Na – (Cl + HCO3) Normal 8 ± 2 Correction for low serum albumin Add (4-serum albumin g/dL) X 2.5 to the anion gap

  13. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  14. Compensations for Metabolic Disturbances • Metabolic acidosis • pCO2 = 1.5 x HCO3 + 8 ( ± 2) • Metabolic alkalosis • pCO2 increases by 7 for every 10 mEq increases in HCO3

  15. How does the kidney compensate for metabolic acidosis?

  16. How does the kidney compensate for metabolic acidosis? • By reabsorbing all filtered HCO3 • By excreting H+ as NH4+ (and H2PO4- ) Interpretations Urine pH < 5.5 Urine anion gap Negative

  17. Compensations for Respiratory Acidosis • Acute respiratory acidosis • HCO3 increases by 1 for every 10 mm increases in pCO2 • Chronic respiratory acidosis • HCO3 increases by 3 for every 10 mm increases in pCO2 If you don’t have kidneys, can you have chronic respiratory acidosis?

  18. Compensations for Respiratory Alkalosis • Acute respiratory alkalosis • HCO3 decreases by 2 for every 10 mm decrease in pCO2 • Chronic respiratory alkalosis • HCO3 decreases by 4 for every 10 mm decrease in pCO2 If you don’t have kidneys can you have chronic respiratory alkalosis?

  19. Mixed Acid-Base Disorders • Mixed respiratory alkalosis & metabolic acidosis • ASA overdose • Sepsis • Liver failure • Mixed respiratory acidosis & metabolic alkalosis • COPD with excessive use of diuretics

  20. Mixed Acid-Base Disorders • Mixed respiratory acidosis & metabolic acidosis • Cardiopulmonary arrest • Severe pulmonary edema • Mixed high gap metabolic acidosis & metabolic alkalosis • Renal failure with vomiting • DKA with severe vomiting

  21. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na - (Cl + CO2 content)} • Determine appropriate compensation • Determine the primary cause

  22. Generation of Metabolic Acidosis Loss of HCO3 diarrhea Administration of HCl, NH4+Cl, CaCl2, lysine HCl Exogenous acids ASA Toxic alcohol Endogenous acids ketoacids DKA starvation alcoholic Lactic acid L-lactic D-lactate H+ HCO3- Compensations Buffers Lungs Kidneys High gap Normal gap If kidney function is normal, urine anion gap Neg

  23. Loss of H+ from GI Vomiting, NG suction Congenital Cl diarrhea Loss of H+ from kidney 1st & 2nd aldosterone ACTH Diuretics Bartter’s, Gitelman’s, Liddle’s Inhibition of β – OH steroid deh H HCO3 Compensations Buffer Respiratory Forget the kidney Gain of HCO3 Administered HCO3, Acetate, citrate, lactate Plasma protein products

  24. CASE 1 A 24 year old diabetic was admitted for weakness. Serum Na 140, K 1.8, Cl 125, CO2 6, anion gap 9. pH 6.84 (H+ 144) pCO2 30, HCO3 5

  25. Interpretation of Case 1 Patient has normal gap metabolic acidosis

  26. Interpretation of Case 1 • Next determine the appropriateness of respiratory compensation • pCO2 = 1.5 x HCO3 + 8 ( ± 2) • pCO2 = 1.5 x 5 + 8 + 2 = 17.5 • The patient’s pCO2 is 30 • The respiratory compensation is inappropriate

  27. Interpretation of Case 1 • This patient has normal anion gap metabolic acidosis with inappropriate respiratory compensation • The finding does not fit DKA but is consistent with HCO3 loss from the GI tract or kidney

  28. How to differentiate normal gap acidosis resulting from GI HCO3 loss (diarrhea) vs dRTA?

  29. Diarrhea History Urine pH < 5.5 Negative urine anion gap dRTA History Urine pH > 5.5 Positive urine anion gap Diarrhea vs RTA

  30. Case 2 A 26 year old woman, complains of weakness. She denies vomiting or taking medications. P.E. A thin woman with contracted ECF. Serum Na 133, K 3.1, Cl 90, CO2 content 32, anion gap11. pH 7.48 (H+ 32), pCO2 43, HCO3 32. UNa 52, UK 50, UCl 0, UpH 8

  31. Interpretation of Case 2 • Determine the appropriateness of respiratory compensation • For every increase of HCO3 by 1, pCO2 should increase by 0.7 • pCO2 = 40 + (32-25) x 0.7 = 44.9 • The patient’s pCO2 = 43

  32. Interpretation of Case 2 • This patient has metabolic alkalosis with appropriate respiratory compensation

  33. Interpretation of Case 2 • Urine Na+ 52, UK+ 50, Cl- 0, pH 8 • Urine pH = 8 suggests presence of large amount of HCO3. The increased UNa and UK are to accompany HCO3 excretion. The kidney conserves Cl • The findings are consistent with loss of HCl from the GI tract • Final diagnosis = Self-induced vomiting

  34. Active vomiting ECF depletion Metabolic alkalosis High UNa, UK, low UCl Urine pH > 6.5 Remote vomiting ECF depletion Metabolic alkalosis Low UNa, high UK, low Cl Urine pH 6 Active diuretic ECF depletion Metabolic alkalosis High UNa, UK and Cl Urine pH 5-5.5 Remote diuretic ECF depletion Metabolic alkalosis Low UNa, high UK, low Cl Urine pH 5-6 Vomiting vs Diuretic

  35. Case 3 • A 40 year old man developed pleuritic chest pain and hemoptysis. His BP 80/50. pH 7.4, pCO2 25, HCO3 15 and pO2 50

  36. Interpretation of Case 3 • A normal pH suggests mixed disturbances

  37. Interpretation of Case 3 • His pCO2 is 25, his HCO315 • If this is acute respiratory alkalosis his HCO3 should have been 25-{(40-25) x 2/10}= 22 • If this is chronic respiratory alkalosis, his HCO3 should have been 25 – {(40-25) x 4/10} = 19 • If this is metabolic acidosis, his pCO2 should have been 1.5 x 15 + 8 = 30-31

  38. Interpretation of Case 3 • He has combined respiratory alkalosis and metabolic acidosis • The likely diagnosis is pulmonary embolism with hypotension and lactic acidosis or pneumonia with sepsis and lactic acidosis • Other conditions are ASA overdose, sepsis, liver failure

  39. Case 4 • A patient with COPD developed CHF. Prior to treatment his pH 7.35, pCO2 was 60 and HCO3 32. During treatment with diuretics he vomited a few times. His pH after treatment was 7.42, pCO2 80, HCO3 48.

  40. Interpretation of Case 4 • Pt’s data pH 7.35, pCO2 60 and HCO3 32 • For acute respiratory acidosis • For every 10 mm elevation of pCO2, HCO3 increases by 1, his HCO3 should have been 25 + (60-40) x 1/10 = 27 • He did not have acute respiratory acidosis

  41. Interpretation of Case 4 • Pt’s data pH 7.35, pCO2 60 and HCO3 32. • For chronic respiratory acidosis • For every 10 mm elevation of pCO2, HCO3 increases by 3 • His HCO3 should have been 25 + (60-40) x 3/10 = 31 • His HCO3 is 32 • He had well compensated chronic respiratory acidosis

  42. Interpretation of Case 4 • His pH is now 7.42, pCO2 80, HCO3 48 • If pCO2 of 80 is due to chronic respiratory acidosis, HCO3 should only be 32 +(80-60) x 3/10=38 and not 48 • He had combined metabolic alkalosis and respiratory acidosis after treatment of CHF

  43. Case 5 • A cirrhotic patient was found to be confused. Serum Na 133, K 3.3, Cl 115, CO2 content 14, anion gap 4 • pH 7.44 (H+ 36), pCO2 20, HCO3 13

  44. Interpretation of Case 5 • Determine the respiratory compensation • For chronic respiratory alkalosis, every 10 reduction in pCO2, HCO3 should decrease by 4 • HCO3 should be 25 - (40-20) x 4/10=17 • For acute respiratory alkalosis, HCO3 = 21 • Patient’s HCO3 is 13, suggesting a metabolic acidotic component is present • Anion gap is 4, even corrected for low albumin, is still low suggesting a normal gap metabolic acidosis • Patient had combined metabolic acidosis and respiratory alkalosis

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