Nitrogen Narcosis

Nitrogen narcosis is a reversible state of impaired judgement and coordination caused by the narcotic effect of nitrogen breathed at raised partial pressure. It resembles alcohol intoxication and increases with depth.

Depth effect. Effects usually begin at around 30 m (4 atmospheres absolute) and are marked at 50 m and over. Judgement, memory and manual dexterity are impaired first, then euphoria or fear, and over 70 to 90 m stupor and loss of consciousness.

Modifiers. Cold, anxiety, fatigue, carbon dioxide retention, alcohol, sedatives and rapid descent worsen it. Experience reduces the effect but not the physiological narcosis.

Importance. Narcosis is a leading contributor to diving errors, such as forgetting gas checks, and to fatal accidents.

Pathophysiology.

Nitrogen is lipid soluble and dissolves in neuronal membranes at high pressure. It alters synaptic transmission through effects on inhibitory and excitatory receptors, depressing cortical and subcortical function.

Onset is within minutes and recovery follows within minutes of ascent, with little or no residual effect.

• Mild: slowed thinking, euphoria, reduced concentration and poor judgement.
• Moderate: impaired coordination, fixation, anxiety, hallucinations, tunnel vision.
• Severe: stupor, loss of memory for the dive, unconsciousness.
• Rapid resolution on ascent to shallower depth.

Red flags.

• Inability to follow signals, unsafe behaviour or loss of consciousness.
• Persisting confusion after surfacing (decompression sickness, carbon dioxide retention, hypoxia).

• Clinical diagnosis from the setting: depth, breathing gas and onset with descent, with prompt recovery on ascent.
• Check blood glucose, oxygen saturation and neurological state after the event.
• Gas analysis for the breathing mix and checks for carbon monoxide when confusion persists.

Differential diagnosis. Hypoxia, carbon dioxide narcosis, carbon monoxide poisoning, oxygen toxicity, decompression sickness, high pressure neurological syndrome, hypoglycaemia, panic, hypothermia.

• Ascend slowly to a shallower depth until symptoms clear. Stop the dive if symptoms persist.
• Buddy support, signalling and controlled ascent; avoid further descent.
• Prevention: limit depth, use helium containing mixes (for example trimix) for dives deeper than about 30 to 40 m, limit exertion and avoid alcohol or sedatives before diving. Keep the equivalent narcotic depth within limits set by the diving supervisor.
• No drug treats the condition. Post-dive review for decompression sickness if confusion persists after surfacing.

Monitoring. Observe for 1 hour after surfacing for any neurological or decompression features.

Referral and escalation. Diving medicine physician for persistent symptoms, unusual susceptibility or accidents; occupational physician for fitness to dive.