Nitrogen Narcosis - Causes

Causes

The cause of narcosis is related to the increased solubility of gases in body tissues, as a result of the elevated pressures at depth (Henry's law). Modern theories have suggested that inert gases dissolving in the lipid bilayer of cell membranes cause narcosis. More recently, researchers have been looking at neurotransmitter receptor protein mechanisms as a possible cause of the narcosis. The breathing gas mix entering the diver's lungs will have the same pressure as the surrounding water, known as the ambient pressure. For any given depth, the pressure of gases in the blood passing through the brain catches up with ambient pressure within a minute or two and this produces a delay in narcotic effect after coming to a new depth. Rapid compression potentiates narcosis, owing to carbon dioxide retention.

A divers' cognition may be affected on dives as shallow as 10 m (33 ft), but the changes are not usually noticeable. However there is no reliable method to predict the depth at which narcosis becomes noticeable, or the severity of the effect on an individual diver, as the effect may vary from dive to dive (even on the same day).

Significant impairment due to narcosis is an increasing risk below depths of about 30 m (100 ft), corresponding to an ambient pressure of about 4 bar (400 kPa). Most sport scuba training organizations recommend depths of no more than 40 m (130 ft) because of risk of narcosis. When breathing air at depths of 90 m (300 ft)—an ambient pressure of about 10 bar (1,000 kPa)—narcosis in most divers leads to hallucinations, loss of memory, and unconsciousness. A number of divers have died in attempts to set air depth records below 120 m (400 ft). Because of these incidents, the Guinness Book of World Records no longer reports on this figure.

Narcosis has been compared with altitude sickness insofar as its variability (though not its symptoms); its effects depend on many factors, with variations between individuals. Thermal cold, stress, heavy work, fatigue, and carbon dioxide retention all increase the risk and severity of narcosis. Carbon dioxide has a high narcotic potential and also causes increased blood flood to the brain, increasing the effects of other gases. Increased risk of narcosis results from increasing the amount of carbon dioxide retained through heavy exercise, shallow or skip breathing, or because of poor gas exchange in the lungs.

Narcosis is known to be additive to even minimal alcohol intoxication, and also to the effects of other drugs such as marijuana (which is more likely than alcohol to have effects which last into a day of abstinence from use). Other sedative and analgesic drugs, such as opiate narcotics and benzodiazepines, add to narcosis.