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Metabolic disorders

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Melissa Davis

Acid Base disorders, this is a break down on how to determine acid base disorders. Somewhat unfinished but may still be useful.

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Metabolic Disorders Melissa Davis, MSIV
Arterial Blood Gas pH/PaCo2/PaO2/ HCO俗 /O2 Sat 7.4/40/95/24/98 First determine if the patient is Oxygenating by determining the Pa02/FiO2 PaFi >300 is normal
Primary Disorder Start at HCO俗 HCO俗 Normal HCO俗 21-27mEq/L Normal pH 7.35-7.45 Decreased pH Low Metabolic Acidosis High Respiratory Alkalosis Elevated pH Low Respiratory Acidosis High Metabolic Alkalosis
Metabolic Acidosis Always Calculate Anion Gap Normal AG 12 賊2 Normal Osmolal Gap <10 Normal Urine AG 30-50 Anion Gap Elevated Osmolal gap Elevated Consider Ethylene Glycol or Methanol Normal Consider Ketoacidosis, Lactic Acidosis, Renal Failure, ASA Toxicity Normal Urine Anion Gap Negative Extra Renal Cause Positive Renal Cause
Anion Gap Anion Gap= [Na+] [Cl- + HCO俗 ] Cations Na+ Anions Unmeasured Anions HCO俗 Cl-
Low Anion Gap Most unmeasured anions consist of albumin Hypoalbuminemia may cause a low AG Serum AG falling by 2.5meq/L for every 1 g/dL (10 g/L) reduction in the serum albumin concentration Increased Light Chains (Multiple Myeloma)is an unmeasured cation This results in a Low Anion Gap
Methanol MUDPILES Uremia Diabetic Ketoacidosis Paraldehyde Isoniazid or Iron tablets Lactic Acidosis Ethylene Glycol Salicylate Toxicity
Osmolal Gap Osmolal Gap = [Measured Osmolality] [Calculated Osmolality] Normal Osmolality: 280 mosmol/kg Calculated Osmolality = 2 + 18 + ( 牛 2.8) Reasons for Increased Osmolal Gap: The presence of an additional solute or solutes ( i.e. Ethanol, Methanol, or Ethylene Glycol The measured sodium concentration may be spuriously reduced (called pseudohyponatremia) with marked hyperlipidemia or hyperproteinemia.
Urine Anion Gap Urine AG= ([UNa+] + [UK+]) [UCl-] Normal Urine AG: 30-50mEq/L Indirect estimate of urinary ammonium (NH4+) excretion, which is not measured directly in clinical practice. Extrarenal causes have an increase in NH4+ excretion because they kidneys are responding appropriately to the acidosis and attempting to rid the body of H+. NH4+ is excreted in the form of NH4Cl thereby making the UAG negative. Urine Renal Cell Blood NH4+ NH4+ Cl- NH4Cl NH3 H+
Positive Urine Anion Gap Renal Causes Renal Tubular Acidosis Urine Renal Cell Blood NH4+ NH4+ Cl- NH4Cl NH3 H+
RTA Type 2 (proximal) RTA Type 1 (distal) RTA Type 4 H+
Mixed Disorders Is there a compounding metabolic or respiratory disorder? Determine what the HCO俗 would be if there were no Anion Gap by calculating the Corrected [HCO俗 ]. Determine if the change is PCO2 is appropriate compensation for the primary metabolic acidosis. Corrected [HCO俗 ] = measured [HCO俗 ] + [AG 12] Expected Respiratory Compensation Acute = . HCO俗 + Chronic 躯2 = HCO俗 + 15 Quick Check PCO2 value should approximate last 2 digits of pH If PCO2 is not equal to expected compensatory value consider secondary respiratory disorder.
Metabolic Alkalosis Loss of H+ leads to an increase in HCO俗 , when renal excretion of HCO俗 is not equal Urine Chloride <20 mEq/L Chloride Responsive Gastrointestinal Loss Renal Loss Alkali Administration Contraction Alkalosis >20 mEq/L Chloride Resistant Hyperaldosteronism Zebras Call Nephrology to its production a metabolic alkalosis manifest.
Chloride Responsive Metabolic Alkalosis Delivery of NaCl to the distal tubule in the presence of Aldosterone results in H+ and K+ loss which maintains alkalosis. GI Loss Vomiting, NG Tube Renal Loss Diuretics Alkali Administration Contraction Alkalosis Volume Loss leads to RAAS activation which causes a metabolic alkalosis.
Mixed Disorders Expected Respiratory Compensation for Metabolic Alkalosis For every 1mEq/L increase in [HCO俗 ], PCO2 should increase 0.7 mm Hg If PCO2 is not equal to expected compensatory value consider secondary respiratory disorder.
Respiratory Acidosis Hypoventilation CNS Depression Respiratory Muscle Weakness Airway Obstruction V/Q Mismatch
Causes of Respiratory Acidosis CNS Depression Stroke Opiates Respiratory Muscle Weakness Myasthenia Gravis Chest Wall Deformity Airway Obstruction COPD V/Q Mismatch Pulmonary Embolism
Mixed Disorders It is physically impossible to have a Respiratory Acidosis and Respiratory Alkalosis at the same time! Expected Renal Compensation for Respiratory Acidosis Acute 1 mEq/L increase in [HCO俗 ] for each 10 mm Hg increase in PCO2 Chronic 3.5 mEq/L increase in [HCO俗 ] for each 10 mm Hg increase in PCO2 If [HCO俗 ] is not equal to expected compensatory value consider secondary metabolic disorder.
Respiratory Alkalosis Respiratory Alkalosis Pulmonary Vasculature Disease Pulmonary Parenchymal Disease Hyperventilation
Respiratory Alkalosis Chronic Respiratory Alkalosis typically has comorbid hyperchloremia Due to retention of Cl- as HCO俗 is excreted in the kidneys. Causes Pulmonary Vasculature Disease Pulmonary HTN Pulmonary Parenchymal Disease Pulmonary Fibrosis Pneumonia Hyperventilation Anxiety Asprin Toxicity Pregnancy
Mixed Disorders It is physically impossible to have a Respiratory Acidosis and Respiratory Alkalosis at the same time! Expected Renal Compensation for Respiratory Alkalosis Acute 2 mEq/L decrease in [HCO俗 ] for each 10 mm Hg decrease in PCO2 Chronic 4-5 mEq/L decrease in [HCO俗 ] for each 10 mm Hg decrease in PCO2 If [HCO3-] is not equal to expected compensatory value consider secondary metabolic disorder.
References Internal Medicine ESSENTIALS for Students: A Companion to MKSAP速 for Students 5 (2011)- American College of Physicians Step-Up to Medicine Second Edition (2008)- S. Agabegi & E. Agabegi Up to Date: Approach to the adult with metabolic acidosis; Methanol and ethylene glycol poisoning; Serum osmolal gap; Urine anion and osmolal gaps in metabolic acidosis; Pathogenesis of metabolic alkalosis

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Metabolic disorders

  • 2. Arterial Blood Gas pH/PaCo2/PaO2/ HCO俗 /O2 Sat 7.4/40/95/24/98 First determine if the patient is Oxygenating by determining the Pa02/FiO2 PaFi >300 is normal
  • 3. Primary Disorder Start at HCO俗 HCO俗 Normal HCO俗 21-27mEq/L Normal pH 7.35-7.45 Decreased pH Low Metabolic Acidosis High Respiratory Alkalosis Elevated pH Low Respiratory Acidosis High Metabolic Alkalosis
  • 4. Metabolic Acidosis Always Calculate Anion Gap Normal AG 12 賊2 Normal Osmolal Gap <10 Normal Urine AG 30-50 Anion Gap Elevated Osmolal gap Elevated Consider Ethylene Glycol or Methanol Normal Consider Ketoacidosis, Lactic Acidosis, Renal Failure, ASA Toxicity Normal Urine Anion Gap Negative Extra Renal Cause Positive Renal Cause
  • 5. Anion Gap Anion Gap= [Na+] [Cl- + HCO俗 ] Cations Na+ Anions Unmeasured Anions HCO俗 Cl-
  • 6. Low Anion Gap Most unmeasured anions consist of albumin Hypoalbuminemia may cause a low AG Serum AG falling by 2.5meq/L for every 1 g/dL (10 g/L) reduction in the serum albumin concentration Increased Light Chains (Multiple Myeloma)is an unmeasured cation This results in a Low Anion Gap
  • 7. Methanol MUDPILES Uremia Diabetic Ketoacidosis Paraldehyde Isoniazid or Iron tablets Lactic Acidosis Ethylene Glycol Salicylate Toxicity
  • 8. Osmolal Gap Osmolal Gap = [Measured Osmolality] [Calculated Osmolality] Normal Osmolality: 280 mosmol/kg Calculated Osmolality = 2 + 18 + ( 牛 2.8) Reasons for Increased Osmolal Gap: The presence of an additional solute or solutes ( i.e. Ethanol, Methanol, or Ethylene Glycol The measured sodium concentration may be spuriously reduced (called pseudohyponatremia) with marked hyperlipidemia or hyperproteinemia.
  • 9. Urine Anion Gap Urine AG= ([UNa+] + [UK+]) [UCl-] Normal Urine AG: 30-50mEq/L Indirect estimate of urinary ammonium (NH4+) excretion, which is not measured directly in clinical practice. Extrarenal causes have an increase in NH4+ excretion because they kidneys are responding appropriately to the acidosis and attempting to rid the body of H+. NH4+ is excreted in the form of NH4Cl thereby making the UAG negative. Urine Renal Cell Blood NH4+ NH4+ Cl- NH4Cl NH3 H+
  • 10. Positive Urine Anion Gap Renal Causes Renal Tubular Acidosis Urine Renal Cell Blood NH4+ NH4+ Cl- NH4Cl NH3 H+
  • 11. RTA Type 2 (proximal) RTA Type 1 (distal) RTA Type 4 H+
  • 12. Mixed Disorders Is there a compounding metabolic or respiratory disorder? Determine what the HCO俗 would be if there were no Anion Gap by calculating the Corrected [HCO俗 ]. Determine if the change is PCO2 is appropriate compensation for the primary metabolic acidosis. Corrected [HCO俗 ] = measured [HCO俗 ] + [AG 12] Expected Respiratory Compensation Acute = . HCO俗 + Chronic 躯2 = HCO俗 + 15 Quick Check PCO2 value should approximate last 2 digits of pH If PCO2 is not equal to expected compensatory value consider secondary respiratory disorder.
  • 13. Metabolic Alkalosis Loss of H+ leads to an increase in HCO俗 , when renal excretion of HCO俗 is not equal Urine Chloride <20 mEq/L Chloride Responsive Gastrointestinal Loss Renal Loss Alkali Administration Contraction Alkalosis >20 mEq/L Chloride Resistant Hyperaldosteronism Zebras Call Nephrology to its production a metabolic alkalosis manifest.
  • 14. Chloride Responsive Metabolic Alkalosis Delivery of NaCl to the distal tubule in the presence of Aldosterone results in H+ and K+ loss which maintains alkalosis. GI Loss Vomiting, NG Tube Renal Loss Diuretics Alkali Administration Contraction Alkalosis Volume Loss leads to RAAS activation which causes a metabolic alkalosis.
  • 15. Mixed Disorders Expected Respiratory Compensation for Metabolic Alkalosis For every 1mEq/L increase in [HCO俗 ], PCO2 should increase 0.7 mm Hg If PCO2 is not equal to expected compensatory value consider secondary respiratory disorder.
  • 16. Respiratory Acidosis Hypoventilation CNS Depression Respiratory Muscle Weakness Airway Obstruction V/Q Mismatch
  • 17. Causes of Respiratory Acidosis CNS Depression Stroke Opiates Respiratory Muscle Weakness Myasthenia Gravis Chest Wall Deformity Airway Obstruction COPD V/Q Mismatch Pulmonary Embolism
  • 18. Mixed Disorders It is physically impossible to have a Respiratory Acidosis and Respiratory Alkalosis at the same time! Expected Renal Compensation for Respiratory Acidosis Acute 1 mEq/L increase in [HCO俗 ] for each 10 mm Hg increase in PCO2 Chronic 3.5 mEq/L increase in [HCO俗 ] for each 10 mm Hg increase in PCO2 If [HCO俗 ] is not equal to expected compensatory value consider secondary metabolic disorder.
  • 19. Respiratory Alkalosis Respiratory Alkalosis Pulmonary Vasculature Disease Pulmonary Parenchymal Disease Hyperventilation
  • 20. Respiratory Alkalosis Chronic Respiratory Alkalosis typically has comorbid hyperchloremia Due to retention of Cl- as HCO俗 is excreted in the kidneys. Causes Pulmonary Vasculature Disease Pulmonary HTN Pulmonary Parenchymal Disease Pulmonary Fibrosis Pneumonia Hyperventilation Anxiety Asprin Toxicity Pregnancy
  • 21. Mixed Disorders It is physically impossible to have a Respiratory Acidosis and Respiratory Alkalosis at the same time! Expected Renal Compensation for Respiratory Alkalosis Acute 2 mEq/L decrease in [HCO俗 ] for each 10 mm Hg decrease in PCO2 Chronic 4-5 mEq/L decrease in [HCO俗 ] for each 10 mm Hg decrease in PCO2 If [HCO3-] is not equal to expected compensatory value consider secondary metabolic disorder.
  • 22. References Internal Medicine ESSENTIALS for Students: A Companion to MKSAP速 for Students 5 (2011)- American College of Physicians Step-Up to Medicine Second Edition (2008)- S. Agabegi & E. Agabegi Up to Date: Approach to the adult with metabolic acidosis; Methanol and ethylene glycol poisoning; Serum osmolal gap; Urine anion and osmolal gaps in metabolic acidosis; Pathogenesis of metabolic alkalosis

Editor's Notes

  • #8: Paraldehyde: Anticonvulsant,Anxiolytics, Sedatives, and Hypnotics
  • #10: Extrarenal causes have an increase in NH4+ excretion because they kidneys are responding appropriately to the acidosis and attempting to rid the body of H+. NH4+ is excreted in the form of NH4Cl thereby making the UAG negative.