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Gas intoxication: causes, symptoms, diagnosis, treatment
Last reviewed: 07.07.2025
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O2 intoxication
O2 intoxication usually occurs when breathing air with a partial pressure of O2 of 1.6 atm, equivalent to a depth of approximately 200 feet. Symptoms include paresthesia, localized seizures, dizziness, nausea, vomiting, and visual field constriction. About 10% of patients develop generalized seizures or syncope, usually resulting in drowning.
Nitrogen narcosis
When breathing compressed air at depths greater than 30 m (>100 ft), the elevated partial pressure of N causes effects similar to nitrous oxide (laughing gas). Nitrogen narcosis (nitrogen intoxication) causes symptoms and signs similar to those of alcohol (e.g., intellectual and neuromuscular impairment, behavioral and personality changes). Impaired critical judgment may lead to drowning. Hallucinations and loss of consciousness may occur at depths greater than 91 m (>300 ft).
Since most divers improve rapidly upon surfacing, diagnosis is clinical. Treatment involves immediate but controlled ascent. Nitrogen narcosis can be prevented by using helium to dilute O2 in deep diving, since helium does not have the anesthetic properties of N. However, the use of pure helium-oxygen mixtures increases the risk of developing neurological damage due to high pressure.
CO2 poisoning
Hypoventilation may be caused by inadequate breathing, a tight diving suit, physical exertion, regulator dysfunction, deep diving, or contamination of the air supply with exhaled gas. Hypoventilation may increase blood CO2, causing shortness of breath and sedation. In severe cases, nausea, vomiting, dizziness, headache, rapid breathing, seizures, confusion, and loss of consciousness may occur.
Moderate poisoning is suspected if the diver frequently develops dive-related headaches or decreases in air volume. Hypoventilation usually resolves during ascent. Therefore, post-dive blood gas analysis usually does not reveal an increase in CO2. Treatment is gradual ascent and cessation of diving or elimination of the cause.
Carbon monoxide poisoning
Carbon monoxide can enter a diver's breathing mixture if the air compressor intake valve is located too close to the engine exhaust pipe, or if the lubricating oil in a faulty compressor overheats and partially ignites ("flashes"), releasing carbon monoxide.
Symptoms include nausea, headache, general weakness, clumsiness, and mental changes. In severe cases, seizures, fainting, or coma may occur. Diagnosis is by elevated blood CO (COHb); pulse oximetry is useless because it usually shows normal levels because it cannot distinguish oxyhemoglobin from carboxyhemoglobin. The air supplied to the diver can be tested for CO.
Treatment - inhalation of 100% O with a large flow, best through a non-reversible mask, which reduces the half-life of COHb from 4-8 hours in room air to 40-80 minutes. In severe cases, treatment with hyperbaric O2 is indicated, which improves tissue oxygenation and further reduces the half-life of COHb to 15-30 minutes.
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Neurological high blood pressure syndrome
A poorly understood syndrome of neuromuscular and brain disorders may develop at depths of 180 m (600 ft), particularly when the diver is rapidly compressed while breathing helium/oxygen. Symptoms include nausea, vomiting, fine tremors, incoordination, dizziness, fatigue, drowsiness, myoclonic jerks, gastric spasms, and intellectual and psychomotor impairment. Diagnosis is clinical.