MetabolicAcidosis

MetabolicAcidosis - Metabolic Acidosis Metabolic Acidosis A...

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Unformatted text preview: Metabolic Acidosis Metabolic Acidosis A Review by George B. Buczko MD FRCP(C) Case Presentation 1 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 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 Case Presentation 3 Arterial blood analysis: Arterial blood analysis: pH 6.95, paO2 337, paCO2 44, TCO2 10 H+102nM 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 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 Metabolic Acidosis Metabolic Acidosis Definition Acid­Base physiology Anion gap Differential diagnosis of metabolic acidosis with high anion gap Lactic acidosis Oxidative phosphorylation Types of Lactic acidosis Treatment of Lactic Acidosis Metabolic Acidosis (primary fall in serum bicarbonate) A condition that causes a primary fall in serum bicarbonate level H+ + HCO3­ H2CO3 H2O + CO2 Metabolic Acidosis Metabolic Acidosis (primary fall in serum bicarbonate) 1. 2. H+ + HCO3­ H2CO3 H2O + CO2 According to the above, a fall in HCO3­ will result from: Addition of H+ (shift right: in HCO ) Loss of bicarbonate (shift left: in H+) ­ 3 Increase in H+ occurs in both situations Metabolic Acidosis (primary fall in serum bicarbonate) Increase in H+: Increase in H Enzyme dysfunction which leads to Organ dysfunction Heart/Brain Metabolic Acidosis 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 Metabolic Acidosis 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 Metabolic Acidosis Metabolic Acidosis (primary fall in serum bicarbonate) The Anion Gap: The usual unmeasured anions that account for the “gap” are: Albumin Phosphates Sulphates Metabolic Acidosis 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 Metabolic Acidosis 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 Lactic Acidosis Lactic Acidosis Why do we need oxygen? For oxidative phosphorylation What is oxidative phosphorylation? ADP + P = ATP (requires energy) i The formation of ATP What does the oxygen do? Lactic Acidosis Lactic Acidosis Glycolysis: Glucose Pyruvate Acetyl CoA Kreb’s: Acetyl CoA NADH & FADH Electron transport chain (ETC) NADH & FADH ATP Lactic Acidosis The bulk of ATP is generated in the electron transport chain (ETC) in the mitochondrion The energy for creating the high­energy phosphate bond is generated at several points in the ETC. So are hydrogen ions High ­ Metabolic Acidosis Metabolic Acidosis (primary fall in serum bicarbonate) Oxygen allows for ATP formation in an electrically­neutral biologically safe manner Metabolic Acidosis Metabolic Acidosis (primary fall in serum bicarbonate) Lactic Acidosis Type A: failure of oxidative phosphorylation ( Type B: lactate production overwhelms lactate metabolism ) Pyruvate Lactate Lactic Acidosis Lactic Acidosis Type A (more severe) Failure of ETC: Decreased Oxygen delivery Shock of any type Severe hypoxemia Severe Anemia Inhibitors (CO, CN) Lactic Acidosis Type B (less severe) Lactate production overwhelms lactate Lactate production overwhelms lactate metabolism (not anaerobic) Malignancies (after chemotherapy) Hepatic failure Drugs (biguanides, AZT, INH) Back to original case Back to original case Arterial blood analysis: pH 6.95, paO2 337, paCO2 44, TCO2 10 H+102nM 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 Lactic Acidosis: Treatment Lactic Acidosis: Treatment Treat the underlying cause Lower the H+ concentration Lactic Acidosis: Treatment Underlying cause in this case: Underlying cause in this case: Profound rapid blood loss Transfusion of blood and products Circulatory support Lactic Acidosis: Treatment Lower the H+ concentration Lower the H H+ + HCO3­ H2CO3 H2O + CO2 Lower the paCO2 by increasing minute ventilation Lactic Acidosis: Treatment Lactic Acidosis: Treatment Lower the paCO2 by increasing minute ventilation Lactic Acidosis: Treatment For every 1meq/l drop in HCO3­ from 25, For every 1meq/l drop in HCO paCO2 should decrease by ~ 1 torr “Normal” paCO2 in the face of HCO3­ 10 is 25 (40 – 15) and not 40 torr Lactic Acidosis: Treatment Lactic Acidosis: Treatment Intravenous bicarbonate administration: Pro: lowers H+ concentration ( pH) improves pressor response improves myocardial function Con: worsens intracellular acidosis may worsen outcome hypertonic Lactic Acidosis: Treatment Lactic Acidosis: Treatment Bottom line: If there is adequate circulation and if minute ventilation is appropriate, some bicarbonate administration is warranted. Don’t aim for full correction, continue arterial blood analysis Metabolic Acidosis: Summary Definition Acid­Base physiology Anion gap Differential diagnosis of metabolic acidosis with high anion gap Lactic acidosis Oxidative phosphorylation Types of Lactic acidosis Treatment of Lactic Acidosis Lactic Acidosis Lactic Acidosis take­home points With hemodynamic instability: Severe acute bleed Sepsis Trauma Increase minute ventilation Analyze arterial blood Judicious intravenous NaHCO3­ ...
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This note was uploaded on 12/28/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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