Here’s the paraphrased study-note version:

125. Toxicology – Antidote: Hyperbaric Oxygen Therapy (HBOT)

Indications

Hyperbaric oxygen therapy may be considered for selected severe poisonings involving asphyxiant toxins, particularly carbon monoxide poisoning. It has also been discussed as an adjunct in severe hydrogen sulfide or cyanide toxicity, although evidence is much less established for these exposures.

Asphyxiant Toxins

Asphyxiants interfere with normal aerobic metabolism and oxygen utilization.

They can be divided broadly into:

• Simple asphyxiants: Reduce the amount of available oxygen in the surrounding environment.
• Systemic asphyxiants: Interfere with oxygen transport or prevent cells from using oxygen normally.

Examples include:

• Carbon monoxide: Forms carboxyhemoglobin and interferes with oxygen delivery
• Cyanide: Inhibits mitochondrial cytochrome oxidase
• Methemoglobin-forming agents: Oxidize hemoglobin so it cannot effectively carry oxygen
• Hydrogen sulfide: Can inhibit mitochondrial respiration in a manner similar to cyanide

Mechanism of Action

HBOT exposes the patient to 100% oxygen at pressures greater than normal atmospheric pressure, usually in a specialized hyperbaric chamber.

This greatly increases the amount of oxygen dissolved directly in the plasma, allowing oxygen delivery to tissues even when hemoglobin-dependent transport is impaired.

In carbon monoxide poisoning, HBOT also:

• Accelerates removal of carbon monoxide from hemoglobin
• Improves tissue oxygenation
• May reduce ongoing neurologic injury in selected severe cases

Clinical Use

For carbon monoxide poisoning, HBOT may be considered when significant features are present, such as:

• Loss of consciousness
• Persistent neurologic abnormalities
• Myocardial ischemia or serious cardiac involvement
• Severe metabolic acidosis
• Pregnancy with significant exposure
• Other evidence of severe poisoning

Exact indications vary, so consultation with a hyperbaric medicine specialist, poison center, or medical toxicologist is recommended.

Risks and Contraindications

Potential complications include:

• Ear or sinus barotrauma
• Oxygen toxicity
• Pulmonary barotrauma
• Claustrophobia

An untreated pneumothorax is the major absolute contraindication because increased chamber pressure can worsen trapped pleural air.

Key Points

• HBOT increases the amount of dissolved oxygen in plasma.
• Its best-established toxicologic role is in selected cases of severe carbon monoxide poisoning.
• Its role in cyanide and hydrogen sulfide poisoning is much less certain and should not delay established antidotal and supportive treatment.
• Hyperbaric treatment requires specialist consultation and access to an appropriate facility.