Nitrogen Narcosis

What is it?

Nitrogen narcosis is an effect on the brain of gaseous nitrogen that occurs to divers who go below 100 FSW, due to the laws of partial pressures. Nitrogen is an inert gas existing in largest quantity in the atmosphere, 79% in air. It is inert, meaning that it does not take part in energy transformations. It is the gas that causes nitrogen narcosis through the effect of Dalton’s and Henry’s laws and it is the gas that causes decompression sickness on ascent from depth with reduction of pressure, (Boyle’s Law). Nitrogen is the gas that determines decompression schedules.

What are some of the effects?

Complex reasoning decreases 33% and manual dexterity decreases 7.3%. The condition causes loss of motor function and decision making ability and can be more clearly defined as causing one to become “drunk”, as with alcoholic beverages. The comparison to having had “three Martinis” is apt, and it has been stated that one should consider the narcotic effect of one Martini for every 50 feet of sea water.

What are Dalton’s and Henry’s Laws?

Dalton’s Law states that the total pressure exerted by a mixture of gases is equal to the sum of the pressure of each of the different gases making up the mixture – each gas acting as if it alone was present and occupying the total volume. This same law causes oxygen toxicity and enhances the role of contaminant gases such as carbon monoxide and hydrocarbons.
The law is stated as:

p ATA=pO2 + pN2 + p other gases
thus: pN2= fN2 x ATA

Henry’s law states that, in a fluid the volume of a gas is directly proportional to the pressure above the fluid, or the partial pressure of the gas to which the fluid is exposed.

How does nitrogen affect the nervous system?

There is a critical volume hypothesis that states there to be an increased volume of nitrogen in the membranes and this relates to solubility. This explains the pressure reversal of anesthetics. Nitrogen narcosis is potentiated by increased CO2 levels.

How can it be prevented?

Avoid deep diving below 100 feet sea water. Certain factors increase the possibility of nitrogen narcosis:

Heavy work and fatigue
CO2 retention

How is nitrogen narcosis treated?

Treatment of nitrogen narcosis is immediate controlled ascent to the surface, with the buddy or divemaster observing the diver for unusual behavior, administration of O2 and temporary cessation of diving. Prevention should be the best treatment, with no further diving below 100 feet.

Risk Assessment for Divers

Severity of Harm possible – Drowning would be the worst case scenario.
Likelihood of Harmful Outcome. The likelihood of a serious outcome is dependent upon numerous factors we are unable to predict. Given the usual controlled recreational diving situation a harmful outcome is very unlikely.
Risk factors, Avoidable? Yes [see modifiers above]


Ernest S. Campbell, M.D., FACS

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