Metabolic Acidosis

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Metabolic Acidosis

• A Review by
• George B. Buczko MD FRCP(C)

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Case Presentation 1

• 54 year old man with fever and abnormal liver
  function for liver biopsy
• Biopsy well tolerated until 3 hours afterwards
  when he developed abdominal distension , with
  systolic BP 40 and Hg 4.6

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Case Presentation 2

• Vasopressin and bicarbonate infusions and blood
  transfusion restored BP to 85/40
• The patient was rushed to the OR for exploratory
  laparotomy

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Case Presentation 3

• Arterial blood analysis
• pH 6.95, paO2 337, paCO2 44, TCO2 10 H102nM
• Na 142, K 6.3, Cl 106 anion gap 26
• Albumin 1.2g/dl
• Expected anion gap 6 because of low albumin
• Anion gap 20 above expected
• Lactate 18.3meq/l
• Minute ventilation 6.4 liters

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Case Presentation 4

• The problem high H
• Cerebral enzyme dysfunction
• Cardiac enzyme dysfunction
• Myocardial dysfunction in the face of hemorrhagic
  shock
• Downward spiral from more than just blood loss

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Metabolic Acidosis

• Definition
• Acid-Base physiology
• Anion gap
• Differential diagnosis of metabolic acidosis with
  high anion gap
• Lactic acidosis
• Oxidative phosphorylation
• Types of Lactic acidosis
• Treatment of Lactic Acidosis

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• A condition that causes a primary fall in serum
  bicarbonate level
• H HCO3- ? H2CO3 ? H2O CO2

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• H HCO3- ? H2CO3 ? H2O CO2
• According to the above, a fall in HCO3- will
  result from
• Addition of H (shift right ? in HCO3- )
• Loss of bicarbonate (shift left ? in H)
• Increase in H occurs in both situations

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• Increase in H
• Enzyme dysfunction which leads to
• Organ dysfunction
• Heart/Brain

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• Increase in H
• H is accompanied by an anion in order to
  maintain electrical neutrality
• The anion may be Cl- (HCl administration)
• The anion may be LACTATE, a KETONE, PHOSPHATE,
  SULPHATE, or an ingested anion

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• The Anion Gap
• In the body
• cations anions
• Not all of the anions are measured in routine
  laboratory analysis
• Na (Cl- HCO3-) 12

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• The Anion Gap
• The usual unmeasured anions that account for the
  gap are
• Albumin
• Phosphates
• Sulphates

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• The Anion Gap
• ?anion gap in the presence of ?H is a marker
  for the presence of anions that accompany H but
  are not routinely measured

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Metabolic Acidosis(primary fall in serum
bicarbonate)

• High Anion Gap Acidosis
• Type Anion
• Lactic lactate
• Diabetic ketones
• Uremia sulphate/phosphate
• ASA salicylate
• Methanol formate
• E. Glycol oxalate

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Lactic Acidosis

• Why do we need oxygen?
• For oxidative phosphorylation
• What is oxidative phosphorylation?
• ADP Pi ATP (requires energy)
• The formation of ATP
• What does the oxygen do?

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Lactic Acidosis
Glycolysis Glucose?Pyruvate?Acetyl
CoA Krebs Acetyl CoA?NADH FADH Electron
transport chain (ETC) NADH FADH?ATP
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Lactic Acidosis

• The bulk of ATP is generated in the electron
  transport chain (ETC) in the mitochondrion
• The energy for creating the high-energy phosphate
  bond is generated at several points in the ETC.
  So are hydrogen ions

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Metabolic Acidosis(primary fall in serum
bicarbonate)
High -
Oxygen allows for ATP formation in an
electrically-neutral biologically safe manner
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Metabolic Acidosis(primary fall in serum
bicarbonate)

• Lactic Acidosis
• Type A failure of oxidative phosphorylation
  (Pyruvate?Lactate)
• Type B lactate production overwhelms lactate
  metabolism

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Lactic AcidosisType A (more severe)

• Failure of ETC
• Decreased Oxygen delivery
• Shock of any type
• Severe hypoxemia
• Severe Anemia
• Inhibitors (CO, CN)

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Lactic AcidosisType B (less severe)

• Lactate production overwhelms lactate metabolism
  (not anaerobic)
• Malignancies (after chemotherapy)
• Hepatic failure
• Drugs (biguanides, AZT, INH)

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Back to original case

• Arterial blood analysis
• pH 6.95, paO2 337, paCO2 44, TCO2 10 H102nM
• Na 142, K 6.3, Cl 106 anion gap 26
• Albumin 1.2g/dl
• Expected anion gap 6 because of low albumin
• Anion gap 20 above expected
• Lactate 18.3meq/l
• Minute ventilation 6.4 liters

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Lactic Acidosis Treatment

• Treat the underlying cause
• Lower the H concentration

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Lactic Acidosis Treatment

• Underlying cause in this case
• Profound rapid blood loss
• Transfusion of blood and products
• Circulatory support

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Lactic Acidosis Treatment

• Lower the H concentration
• H HCO3- ? H2CO3 ? H2O CO2
• Lower the paCO2 by increasing minute ventilation

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Lactic Acidosis Treatment
Lower the paCO2 by increasing minute ventilation
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Lactic Acidosis Treatment

• For every 1meq/l drop in HCO3- from 25, paCO2
  should decrease by 1 torr
• Normal paCO2 in the face of HCO3- 10 is 25 (40
  15) and not 40 torr

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Lactic Acidosis Treatment
Intravenous bicarbonate administration Pro lowe
rs H concentration (?pH) improves pressor
response improves myocardial function Con wors
ens intracellular acidosis may worsen
outcome hypertonic
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Lactic Acidosis Treatment
Bottom line If there is adequate circulation and
if minute ventilation is appropriate, some
bicarbonate administration is warranted. Dont
aim for full correction, continue arterial blood
analysis
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Metabolic Acidosis Summary

• Definition
• Acid-Base physiology
• Anion gap
• Differential diagnosis of metabolic acidosis with
  high anion gap
• Lactic acidosis
• Oxidative phosphorylation
• Types of Lactic acidosis
• Treatment of Lactic Acidosis

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Lactic Acidosistake-home points
With hemodynamic instability Severe acute
bleed Sepsis Trauma Increase minute
ventilation Analyze arterial blood Judicious
intravenous NaHCO3-