1. Metabolic Acidosis Bonnie Cramer December 11, 2008

2. What is normal? Serum pH: 7.35-7.45 Serum pH: 7.35-7.45 Serum bicarbonate: 22-29 Serum bicarbonate: 22-29 PCO2: 35-45 PCO2: 35-45 Anion gap: 7-16 Anion gap: 7-16

3. How do we maintain this normal state? Buffers Buffers Dissolved CO2 + H2O H2CO3 HCO3- + H+ Dissolved CO2 + H2O H2CO3 HCO3- + H+

4. Types of Metabolic Acidosis Metabolic acidosis = low pH and low serum bicarbonate. Metabolic acidosis = low pH and low serum bicarbonate. Non-anion gap Non-anion gap Anion gap Anion gap Measured cations – measured anions Measured cations – measured anions Na – (Cl+HCO3) Na – (Cl+HCO3)

5. Causes of Metabolic Acidosis Increased acid generation Increased acid generation Loss of bicarbonate Loss of bicarbonate Decreased renal acid excretion Decreased renal acid excretion

6. Causes Increased acid production Increased acid production Increased anion gap Increased anion gap Lactic acidosis Lactic acidosis Ketoacidosis Ketoacidosis Diabetes mellitus Diabetes mellitus Starvation Starvation Alcohol Alcohol Ingestions Ingestions Methanol Methanol Ethylene glycol Ethylene glycol ASA ASA Toluene (if early) Toluene (if early) Normal anion gap Normal anion gap Toluene (if late) Toluene (if late)

7. Causes Loss of bicarbonate Loss of bicarbonate Normal anion gap Normal anion gap Diarrhea or other intestinal losses (tube drainage) Diarrhea or other intestinal losses (tube drainage) Type 2 (proximal) renal tubular acidosis Type 2 (proximal) renal tubular acidosis Posttreatment of ketoacidosis Posttreatment of ketoacidosis Carbonic anhydrase inhibitors Carbonic anhydrase inhibitors Ureteral diversion (i.e. ileal loop) Ureteral diversion (i.e. ileal loop)

8. Causes Decreased renal acid excretion Decreased renal acid excretion Increased anion gap Increased anion gap Chronic Kidney Disease Chronic Kidney Disease Normal anion gap Normal anion gap Some cases chronic kidney disease Some cases chronic kidney disease Type 1 (distal) RTA Type 1 (distal) RTA Type 4 RTA (hypoaldosteronism) Type 4 RTA (hypoaldosteronism)

9. Anion gap causes M: methanol M: methanol U: uremia U: uremia D: diabetic ketoacidosis D: diabetic ketoacidosis P: paraldehyde P: paraldehyde I: INH I: INH L: lactic acidosis L: lactic acidosis E: ethanol, ethylene glycol E: ethanol, ethylene glycol S: salicilates S: salicilates

10. If you’re really into this… Compensatory response Compensatory response Respiratory compensation results in 1.1- 1.2mmHg fall in PCO2 for ever 1meq/L reduction in plasma bicarbonate (use 24) Respiratory compensation results in 1.1- 1.2mmHg fall in PCO2 for ever 1meq/L reduction in plasma bicarbonate (use 24) Happens within 1 hour Happens within 1 hour Example: A bicarb of 14 should be associated with a PCO2 of 28. Example: A bicarb of 14 should be associated with a PCO2 of 28.

11. Cases

12. If you want to cheat… www.medcalc.com www.medcalc.com www.medcalc.com