Hematology and Oncology Book

http://www.fpnotebook.com/

Methemoglobinemia

Advertisement

  1. Pathophysiology
    1. Hereditary Methemoglobinemia
    2. Acquired Methemoglobinemia
      1. Exposure to drugs with amino or nitro group
      2. Chemical exposure results in changed Hemoglobin iron
        1. Oxidizes ferric Hemoglobin (Fe3+)
        2. Results in ferrous Hemoglobin (Fe2+)
    3. Oxyhemoglobin becomes non-Oxygen carrying Methemoglobin
      1. Left Shifts oxyhemoglobin dissociation curve
      2. Impairs oxygen unloading to tissues
  2. Hereditary Methemoglobinemia Types
    1. Cytochrome b5 Reductase Deficiency
      1. Autosomal recessive inheritance
      2. Two types
        1. Type I: Lifelong asymptomatic cyanosis
        2. Type II: Cyanosis with mental retardation
      3. Associated conditions in some cases
        1. Mild Polycythemia
    2. M Hemoglobins (5 Hemoglobin variants)
      1. General
        1. Autosomal dominant inheritance
        2. M Hemoglobins are asymptomatic except for cyanosis
      2. Alpha chain variants (cyanosis at birth)
        1. Hemoglobin M Boston
        2. Hemoglobin M Iwate
      3. Beta chain variants (cyanosis at 4-6 months)
        1. Hemoglobin M Saskatoon
        2. Hemoglobin M Hyde Park
        3. Hemoglobin M Milwaukee
  3. Acquired Methemoglobinemia Causes (Oxidizing agents)
    1. Nitrites
    2. Nitroglycerin
    3. Nitroprusside
    4. Nitrates
    5. Aniline
    6. Paints
    7. Varnishes
    8. Inks
    9. Phenacetin
    10. Sulfonamides
    11. Pyridium
    12. Dapsone
    13. Primaquine
    14. Lidocaine
    15. Procaine
    16. Benzocaine
    17. Nitrophenol
    18. Toluidine
    19. Nitrobenzene
    20. Isobutyl nitrate
  4. Signs and symptoms
    1. Methemoglobin >15%
      1. Cyanosis
      2. Asymptomatic
    2. Methemoglobin >30%
      1. Fatigue
      2. Headache
      3. Dizziness
      4. Tachycardia
      5. Weakness
    3. Methemoglobin >55%
      1. Dyspnea
      2. Bradycardia
      3. Hypoxia
      4. Acidosis
      5. Seizures
      6. Coma
      7. Arrhythmia
    4. Methemoglobin >70%
      1. Death
  5. Complications
    1. Hyperkalemia
    2. Renal Failure
      1. Occurs 1-3 days after exposure
  6. Labs
    1. Arterial Blood Gas (ABG)
      1. Normal arterial pO2
    2. Oxygen Saturation decreased
    3. Venipuncture
      1. "Chocolate brown" appearance to blood
      2. No change with exposure to oxygen
      3. Color fades with exposure to potassium Cyanide 10%
  7. Management: Severe acquired methemoglobinemia
    1. ABC Management
    2. Oxygen 100%
    3. See Toxin Ingestion Management
    4. Methylene Blue
      1. Dose: 1-2 mg/kg (1% solution) over 5 min
      2. Reduces Methemoglobin by 50% within 1 hour
      3. Indications
        1. Methemoglobin > 30 g/L
        2. Methemoglobinemia with Hypoxia
      4. Contraindications
        1. G6PD Deficiency
        2. M Hemoglobin (not effective)
    5. Transfuse packed Red Blood Cells
      1. Goal Hemoglobin: 15 g/dl
    6. Exchange Transfusion
  8. References
    1. Wilson (1991) Harrison's Medicine, p. 1549

Navigation Tree