Metabolic AcidosisMetabolic Acidosis

Bonnie CramerBonnie Cramer

December 11, 2008December 11, 2008

What is normal?What is normal?

Serum pH: 7.35-7.45Serum pH: 7.35-7.45 Serum bicarbonate: 22-29 Serum bicarbonate: 22-29 PCO2: 35-45PCO2: 35-45 Anion gap: 7-16Anion gap: 7-16

How do we maintain this How do we maintain this normal state?normal state?

BuffersBuffers Dissolved CO2  +  H2O  <—>  H2CO3   <—>   Dissolved CO2  +  H2O  <—>  H2CO3   <—>  

HCO3-  +  H+ HCO3-  +  H+

Types of Metabolic AcidosisTypes of Metabolic Acidosis

Metabolic acidosis = low pH and low Metabolic acidosis = low pH and low serum bicarbonate.serum bicarbonate.

Non-anion gapNon-anion gap Anion gapAnion gap

Measured cations – measured anionsMeasured cations – measured anions Na – (Cl+HCO3)Na – (Cl+HCO3)

Causes of Metabolic Causes of Metabolic AcidosisAcidosis

Increased acid generationIncreased acid generation Loss of bicarbonateLoss of bicarbonate Decreased renal acid excretionDecreased renal acid excretion

CausesCauses Increased acid productionIncreased acid production

Increased anion gapIncreased anion gap Lactic acidosisLactic acidosis KetoacidosisKetoacidosis Diabetes mellitusDiabetes mellitus StarvationStarvation AlcoholAlcohol IngestionsIngestions MethanolMethanol Ethylene glycolEthylene glycol ASAASA Toluene (if early)Toluene (if early)

Normal anion gapNormal anion gap Toluene (if late)Toluene (if late)

CausesCauses

Loss of bicarbonateLoss of bicarbonate Normal anion gapNormal anion gap

Diarrhea or other intestinal losses (tube Diarrhea or other intestinal losses (tube drainage)drainage)

Type 2 (proximal) renal tubular acidosisType 2 (proximal) renal tubular acidosis Posttreatment of ketoacidosisPosttreatment of ketoacidosis Carbonic anhydrase inhibitorsCarbonic anhydrase inhibitors Ureteral diversion (i.e. ileal loop)Ureteral diversion (i.e. ileal loop)

CausesCauses

Decreased renal acid excretionDecreased renal acid excretion Increased anion gapIncreased anion gap

Chronic Kidney DiseaseChronic Kidney Disease Normal anion gapNormal anion gap

Some cases chronic kidney diseaseSome cases chronic kidney disease Type 1 (distal) RTAType 1 (distal) RTA Type 4 RTA (hypoaldosteronism)Type 4 RTA (hypoaldosteronism)

Anion gap causesAnion gap causes

M: methanolM: methanol U: uremiaU: uremia D: diabetic ketoacidosisD: diabetic ketoacidosis P: paraldehydeP: paraldehyde I: INHI: INH L: lactic acidosisL: lactic acidosis E: ethanol, ethylene glycolE: ethanol, ethylene glycol S: salicilatesS: salicilates

If you’re really into this…If you’re really into this…

Compensatory responseCompensatory response Respiratory compensation results in 1.1-Respiratory compensation results in 1.1-

1.2mmHg fall in PCO2 for ever 1meq/L 1.2mmHg fall in PCO2 for ever 1meq/L reduction in plasma bicarbonate (use reduction in plasma bicarbonate (use 24)24)

Happens within 1 hourHappens within 1 hour Example: A bicarb of 14 should be Example: A bicarb of 14 should be

associated with a PCO2 of 28.associated with a PCO2 of 28.

CasesCases

If you want to cheat…If you want to cheat…

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