Nitrogen narcosis

Causes and mechanism

Under pressure more nitrogen dissolves into body tissues and the central nervous system. The precise neurochemical mechanism is complex and not fully resolved, but the narcotic effect correlates with gas solubility in lipids and interference with neuronal function. In practice, symptoms are tied to the partial pressure of nitrogen rather than the absolute amount breathed.

Symptoms and signs

Effects resemble alcohol intoxication and vary between individuals and dives. Common signs include impaired judgment, slowed reaction time, euphoria or anxiety, tunnel vision, difficulty concentrating, and reduced motor coordination. Because judgment and decision-making are affected, narcosis is a safety concern for deep dives.

• Impaired decision-making and attention
• Reduced manual dexterity and slowed responses
• Perceptual changes such as tunnel vision or illusion

Prevention and management

The principal remedy during a dive is a controlled ascent to reduce nitrogen partial pressure; symptoms typically resolve quickly with shallower depth. Preventive strategies include limiting dive depth, gradual acclimatization, conservative dive planning and using gas mixes that replace part of the nitrogen with helium (for example, heliox or trimix) for deep technical or commercial diving.

History and distinctions

The phenomenon has long been recognized by divers and historically called the "rapture of the deep." It is distinct from decompression sickness and oxygen toxicity: nitrogen narcosis appears while at depth and reverses on ascent, whereas decompression sickness results from bubble formation during ascent and oxygen toxicity stems from high partial pressures of oxygen. For more technical guidance see diving medicine resources.