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Approach to metabolic acidosis

Approach to metabolic acidosis. Waleed Talal Alotaibi MBBS. objectives. Definitions How to approach? Differential diagnosis Anion gap VS. non-anion gap metabolic acidosis Treatment of severe metabolic acidosis. Definitions. Normal pH 7.36 to 7.44 HCO3 22 to 28 meq /L PCO2 36 to 44 mmHg

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Approach to metabolic acidosis

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  1. Approach to metabolic acidosis WaleedTalalAlotaibi MBBS

  2. objectives • Definitions • How to approach? • Differential diagnosis • Anion gap VS. non-anion gap metabolic acidosis • Treatment of severe metabolic acidosis

  3. Definitions • Normal pH 7.36 to 7.44 • HCO3 22 to 28 meq/L PCO2 36 to 44 mmHg • Acidemia • Alkalemia • Acidosis • Alkalosis • Metabolic acidosis • Metabolic alkalosis • Respiratory acidosis • Respiratory alkalosis • Simple acid-base disorder • Mixed acid-base disorder

  4. How to approach? • In simple 4 steps: • First: determine the primary diagnosis • Second: assess the degree of compensation • Third: calculate anion gap (if elevated, caculate delta delta ratio) • Fourth: clinical diagnosis

  5. Primary diagnosis • Metabolic acidosis: • Low arterial pH, and low serum HCO3

  6. Compensation • Respiratory compensation begins within 30 min and complete within 12 to 24 hrs • Expected compensation: • Decrease in PCO2 = 1.2 ×ΔHCO3 • PCO2 = 1.5 × HCO3 + 8 ± 2 • PCO2 = serum HCO3 + 15 • PCO2 = decimal digits of pH

  7. Anion gap • Why anion gap? • Normal serum AG 7 to 13 meq/L • Serum AG = measured cations – measured anions • Serum AG = (Na + k) – (Cl + HCO3) • Serum AG = unmeasured anions – unmeasured cations

  8. Anion gap • If AG is elevated then calculate delta delta (ΔAG/ΔHCO3) why? • (calculated AG-expected AG)/(24-HCO3) • Expected AG = 2.5 × albumin (g/dL)

  9. Clinical diagnosis • AG metabolic acidosis VS. non-AG metabolic acidosis

  10. AG metabolic acidosis • MUDPILERS • Methanol • Uremia • DKA • Paraldehyde • INH • Lactic acidosis • Ethanol/ethylene glycol • Rhabdomyolysis, renal failure • Salicylate

  11. AG metabolic acidosis • Work up for ketonuria, if negative do renal function, lactate and osmolal gap (OG) • OG = measured osmoles – calculated osmoles • Calculated osmoles = (2 × Na) + (glucose/18) + (BUN/2.8) • If OG > 10 --- ingestion? Do toxin screen

  12. Non-AG metabolic acidosis • HARD UPS • Hyperalimentation • Acetazolamide • Renal Tubular Acidosis • Diarrhea • Uretero-Pelvic Shunt • Post-Hypocapnia • Spironolactone

  13. Non-AG metabolic acidosis • Workup: urine AG = (U Na + U K) – U Cl • If negative: appropriate renal response to acidemia • If positive: the kidneys failed to secrete NH4

  14. Treatment • Usually according to the underlying cause • Severe metabolic acidosis (pH < 7.2): • The goal is to achive pH >7.20 and HCO3 >8 • NaHCO3 • 8- HCO3 × wt. × 0.5 = mmol of HCO3

  15. References • Uptodate • The Massachusetts General hospital Handbook of Internal Medicine, 4th edition

  16. Thank you

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