• rss
  • facebook
  • twitter
  • linkedin

Toxic Gases

General Characteristics

  • Toxic gases tend to interfere with one or more of the four phases of oxygen delivery: uptake, diffusion, transport, and utilization
  • Simple asphyxiants displace oxygen from the inspired gas mixture creating diminished uptake
  • Pulmonary irritants cause non-cardiogenic pulmonary edema and impair oxygen diffusion across the alveolar membrane
  • Chemical asphyxiants affect either transport or utilization
  • Agents that disrupt oxygen utilization act at the mitochondrial level

Simple Asphyxiants

  • Simple asphyxiants displace oxygen from air (carbon dioxide, nitrogen, hydrogen, methane, propane)
  • When the concentration of any of gases increase, the fraction of inspired oxygen (FiO2) decreases:
    • At a FiO2 of less than 16% air, hunger, tachypnea, and changes in level of conscious occur
    • At FiO2 less than 10%, loss of consciousness, seizures, or vomiting may occur
  • Treatment is restoration of a higher FiO2 with supplemental oxygen discontinued exposure

Irritant Gases

  • Highly water-soluble agents:
    • Highly water-soluble agents react with water in the upper respiratory tract and produce immediate irritation and discomfort
      • Ammonia, used as an industrial refrigerant, is prototypical
      • Chloramine is created when bleach and ammonia are mixed together
    • Warning symptoms include eye irritation and edema, burning in the throat, and constriction of the upper airway
    • Treatment is aimed supplying supplemental oxygen, discontinued exposure, and monitoring the pulmonary status
  • Intermediate water-soluble agents:
    • The only gas classified as intermediate in solubility is chlorine
    • Chlorine reacts with water in the upper airways to produce hydrochloric and hydrochlorous acids
    • Warning symptoms include burning of the conjunctiva, throat, and the bronchial tree
    • Higher concentrations can produce bronchospasm, lower pulmonary injury, and delayed onset of pulmonary edema
    • Treatment is aimed supplying supplemental oxygen, discontinued exposure, and monitoring the pulmonary status
  • Slightly water-soluble agents:
    • Phosgene is prototypical of the slightly water-soluble gases
    • At concentrations as low as 25 ppm, it can be fatal after even brief exposures
    • It produces minimal warning symptoms consisting of mild irritation of the eyes and upper airways
    • It slowly hydrolyzes to hydrochloric acid in the alveoli to cause delayed onset of pulmonary edema
    • Treatment is supportive, including pulmonary monitoring, and intubation and ventilation as indicated

Chemical Asphyxiants

  • The chemical asphyxiants react in the body to interrupt either the delivery or utilization of oxygen
  • Carbon monoxide binds to hemoglobin creating carboxyhemoglobin and has 250 to 270 times the affinity of oxygen, making it incapable of binding and transporting oxygen
  • Nitrites convert Fe ++ to Fe +++ (methemoglobin), making it incapable of binding and transporting oxygen:
    • Both carboxyhemoglobin and methemoglobin can be measured by co-oximetry on an arterial blood gas analyzer
    • Both are treated with high concentrations of oxygen
    • Hyperbaric oxygen can be used for carbon monoxide exposures with altered level of consciousness and neurologic findings
    • Methemoglobinemia can be treated with methylene blue, which acts as an electron donor, and converts Fe +++ back to Fe ++
    • Patients with methemoglobin levels in excess of 30% should be treated with 1 mg/kg of methylene blue as a 10% solution intravenously
  • Chemical asphyxiants can interfere with the electron transport chain in the mitochondria:
    • These agents include cyanide, hydrogen sulfide, and sodium azide
    • By binding to cytochrome oxidase a3, these agents disrupt aerobic metabolism and create intracellular acidosis
  • Symptoms include headache, alteration of consciousness, seizures, and severe acidosis
  • The cyanide antidote kit contains three components: perles of amyl nitrite, an ampoule of sodium nitrite, and an ampoule of sodium thiosulfate:
    • Either the inhaled amyl nitrite, from a crushed perle, or the intravenous sodium nitrite will induce methemoglobinemia
    • Both cyanide and sulfide will bind with greater affinity to methemoglobinemia than to cytochrome oxidase, forming either cyanomethemoglobin or sulfmethemoglobin
    • The cyanomethemoglobin is detoxified in the liver by the enzyme rhodanase
    • Sodium thiosulfate, the third component of the cyanide antidote kit, will stimulate the conversion of cyanide to sodium thiocyanate, which can be renally excreted
    • The sodium thiosulfate component is indicated only for suspected cyanide exposure, whereas the nitrite components may be used with sulfide, cyanide, or azide exposures
Search ACP Smart Medicine

Search this point-of-care decision support tool today. A free benefit of ACP membership.

Have questions about the new ABIM MOC Program?

Have questions about the new ABIM MOC Program?

ACP explains the ABIM requirements and offers many free solutions to earn MOC points.

One Click to Confidence - Free to members

One Click to Confidence - Free to members ACP Smart Medicine is a new, online clinical decision support tool specifically for internal medicine. Get rapid point-of-care access to evidence-based clinical recommendations and guidelines. Plus, users can easily earn CME credit. Learn more