CO + CN + MetHb Toxicity

Cyanide Toxicity
- Etiology
  - Chemical Lab Exposure or exposure to fires that involve plastics, wools, and synthetic materials → uncoupling of the electron transport chain → anaerobic metabolism → lactic acidosis
- Presentation:
  - confusion, tachypnea, hypotension, bradycardia
- Hallmarks: Lactic acidosis + hypotension + initial hypoxia improved by supplemental oxygen even though overall clinical picture doesn’t improve
  - Since tissue is unable to extract oxygen, venous oxygen saturation is higher in cyanide toxicity, sometimes called “arterialization” of the venous blood.
- Tx:
  - The decision to proceed with treatment is made clinically based on marked lactic acidosis and the appropriate clinical scenario, as serum cyanide assays are not readily available
  - Hydroxocobalamin (B12) IV bolus q15min; B12 + CN = B12.
  - Previously: sodium nitrite and sodium thiosulfate → removes cyanide from cytochrome and increases cyanide’s metabolism to a less toxic metabolite → methemoglobinemia or thiocyanate

Carbon Monoxide Toxicity
- Etiology
  - Colorless, odorless, non-irritating gas exposure → has a higher affinity for hemoglobin than oxygen → displaces oxygen from hemoglobin → oxygen-hemoglobin dissociation curve is shifted to the left impairing delivery of oxygen to tissues → tissue hypoxia and neurological damage
- Presentation: Hallmark Cherry Red lips
- Tx:
  - Supplemental oxygen via nonrebreather.
- Hyperbaric oxygen therapies are indicated if coma, syncope, those with neurologic symptoms, hemodynamic compromise, or carboxyhemoglobin levels are greater than 25%. In pregnant patients with carboxyhemoglobin levels are greater than 15%.

Methemoglobinemia
- Etiology
  - Exposure to benzocaine (commonly in teething gels) or exposure to nitrate in water from agricultural runoff → typically in infants especially less than 4 months of age, as they lack a key enzyme that is required for conversion of methemoglobinemia → declining oxygen delivery
  - There should be NO lactic acidosis
- Presentation
  - Hallmarks: Cyanosis + HA + oxygen saturations in the upper 80s even on oxygen
    - Patients look blue because methemoglobin looks blue
  - 20%–30% Methemoglobinemia: Cyanosis. Headache, nausea, and fatigue. Dyspnea, angina, and dysrhythmias can occur, especially in patients with coronary artery disease.
  - 50% Methemoglobinemia: Syncope
  - 70% Methemoglobinemia: Fatal or gravely concerning
- Tx:
  - Supplemental oxygen (will continue to have oxygen saturations in the upper 80s but their pO₂ measured on blood gases will be significantly elevated so they are okay)
    - read low on O2 sat after O2 therapy because external monitors read color wavelengths of methemoglobin
  - Methylene blue for all patients with methemoglobinemia greater than 25% and those with symptoms more than just a headache