Nitrogen narcosis

Nitrogen narcosis

• Nitrogen narcosis is an altered state of consciousness associated with breathing air at high barometric pressures (greater than 4 atm) during underwater diving or in a hyperbaric chamber
• Manifests as temporary impairment of cognitive and neuromuscular performance and personality and behavior changes, similar to those of alcohol intoxication
• Symptoms are typically associated with deeper dives (below 30 m) and increase in severity with increasing depth; however, there is individual variation in susceptibility and some individuals may develop symptoms at shallower depths
• Diagnosed on the basis of characteristic symptoms and signs of intoxication that occur in a hyperbaric environment (eg, underwater diving) or in a hyperbaric chamber and resolve with return to environment with lower or normal pressure
• Management consists of controlled ascent/decompression while protecting diver or hyperbaric chamber occupant from injury, drowning, or inappropriate behavior

Pitfalls

• Ascending too rapidly when nitrogen narcosis is recognize

Nitrogen narcosis is an altered state of consciousness associated with breathing air at high barometric pressures (greater than 4 atm), which may occur during underwater diving or in a hyperbaric chamber

High partial pressure of nitrogen results in a temporary impairment of cognitive and neuromuscular performance as well as personality and behavior changes, similar to those of alcohol intoxication 

Resulting impairment in judgment and reactions may precipitate diving accidents and drowning

Also called inert gas narcosis, compressed air intoxication, and rapture of the deep

Clinical Presentation

History

• Onset of symptoms is insidious and resembles those of intoxication with alcohol or benzodiazepines; may be noticed by other divers while underwater 
• Symptoms are typically associated with deeper dives (greater than 30 m); however, individuals vary in susceptibility and some may develop symptoms at shallower depths 
• At depths less than 30 m, most symptoms are benign and difficult to recognize; may include mild impairment in novel tasks or impaired reasoning 
• At depths of 30 to 50 m (4-6 atm), manifestations include: 
  • Mild amnesia
  • Delayed response to visual or auditory stimuli
  • Overconfidence, sense of well-being
  • Calculation errors, poor choices
  • Laughter (in hyperbaric chamber) or anxiety (in cold water)
• At depths of 50 to 70 m (6-8 atm), manifestations include: 
  • Confusion, impaired judgment
  • Hallucinations
  • Delayed responses to signals or instructions
  • Uncontrolled laughter, hysteria (in hyperbaric chamber)
  • Feelings of terror (in some)
• At 70 to 90 m (8-10 atm), manifestations include: 
  • Confusion
  • Memory loss
  • Stupefaction
• At depths exceeding 90 m (more than 10 atm), manifestations include: 
  • Incapacitation
  • Hallucinations and increased intensity of vision and hearing
  • Unconsciousness
  • Death
• Ascent results in complete resolution of symptoms and signs 

Physical examination

• Ascent results in rapid resolution of symptoms and signs with no residual effects and no abnormal physical examination findings 
• While still underwater, other divers may notice signs such as confusion, delayed responses, and memory loss 

Causes

• High partial pressure of nitrogen as a result of breathing air at high barometric pressures (greater than 4 atm) during underwater diving or in a hyperbaric chamber

Risk factors and/or associations

Other risk factors/associations

• Individuals vary considerably in susceptibility 
• Factors that may affect susceptibility while diving include: 
  • Increased depth
  • Hypercapnia
  • Fatigue and exertion
  • Hypothermia
  • Anxiety
  • Alcohol intoxication
• Researchers or health care providers attending to patients receiving hyperbaric oxygen therapy in multiplace hyperbaric chambers are at risk of nitrogen narcosis, as they breathe nitrogen at high partial pressure in the atmosphere (unlike the patients who are breathing 100% oxygen in a hood)
  • Can occur in patients receiving hyperbaric oxygen therapy during an air break (period when patient is switched from 100% oxygen to air to reduce the risk of oxygen toxicity)

Diagnostic Procedures

Primary diagnostic tools

• Diagnose on basis of characteristic symptoms and signs of intoxication that occur in a hyperbaric environment (eg, underwater diving) or in a hyperbaric chamber and resolve with return to lower or normal-pressure environment 

Procedures

Complications

Differential Diagnosis

Most common

• Oxygen toxicity
• Hypoglycemia
• Hypothermia
• High-pressure neurologic syndrome 
• Carbon dioxide toxicity

Treatment Goals

• Relieve symptoms of intoxication by return to lower pressure environment 
• Prevent injury or drowning as result of impairment

Treatment Options

Initiate controlled ascent or return to normal-pressure environment 

• Return to lower pressure environment underwater or in a hyperbaric chamber should be gradual in accordance with decompression parameters (indicated on dive computer or dive table) to prevent decompression sickness and arterial gas embolism
• Halting descent during dive can be helpful when ascent is not immediately possible (owing to a need for a decompression stop during a dive)

Protect diver or hyperbaric chamber occupant from injury, drowning, or inappropriate behavior while underwater or inside hyperbaric chamber

Nondrug and supportive care

Procedures

Complications

Complications 

• Drowning
• Rapid ascent, due to loss of judgment or disorientation, can lead to any of the following diving accidents:
  • Decompression sickness
  • Pneumothorax
  • Pneumomediastinum
  • Arterial gas embolism

Prognosis

• No long-term sequelae result from nitrogen narcosis itself; symptoms clear rapidly as the partial pressure of nitrogen is reduced with return to normal barometric pressure 
• Estimated to contribute to 3.6% to 9% of diving fatalities owing to effects on judgment and performance 

Prevention

• Counsel patients to avoid diving to depths of greater than 30 m 
• For deeper dives, some or all nitrogen in breathing gas is replaced with helium, which has no narcotic effect 
• Divers should always go with a buddy

Sources

Bove AA: Diving medicine. Am J Respir Crit Care Med. 189(12):1479-86, 2014 Reference