Nitrogen narcosis

Background

• Toxic effects of breathing nitrogen-containing gases while at depth
• Called the "rapture of the deep"
• Develops between 3-4ATM (99-132 feet)
  • Rare at depths less than 30 meters (100 ft) unless breathing non-standard air mixtures
  • Similar to alcohol, frequent divers can develop subjective "tolerance" to the effects, but impairment remains
• Can be prevented by using nitrogen-free gas mixture (e.g. heliox), or mixtures with reduced nitrogen content (e.g. helium-nitrogen-oxygen)
• Risk factors = exertion during dive, cold conditions, alcohol intoxication before dive
• Other inert gases cause similar symptoms at depth - severity based on lipid solubility of the gas

Diving Physiology

• Pascals Law applies to the diving body (without air filled areas such as lungs) states that the pressure applied to any part of the enclosed liquid will be transmitted equally in all directions through the liquid.
• Boyles Law applies to the diving body's air filled areas such as lungs, sinuses, middle ear, and states that the volume and pressure of a gas at a given temperature are inversely related.
  • At 2 ATA (10m/33ft) a given gas would be 1/2 it's volume, at 3 ATA (20m/66ft) it would be 1/3 it's volume and so on.

Boyle's Law

Clinical Features

• Insidious onset of symptoms similar to alcohol intoxication (or nitrous oxide inhalation)
  • Early stage: Euphoria, false sense of security, impaired judgement, diminished reaction times
  • Later stage: Impaired concentration and memory, paresthesias, hallucinations
  • Final stage: [Occurs at depths of at least 10-13ATM (333-429 feet)], lethargy and loss of consciousness
• Causes high risk of making bad decisions at depth, i.e. impairs diver's judgment therefore leading to drowning accidents (cause of up to 9% of diving deaths)

Differential Diagnosis

Diving Emergencies

• Barotrauma of descent
  • Otic barotrauma
  • Pulmonary barotrauma
  • Sinus barotrauma
  • Mask squeeze
  • Barodentalgia (trapped dental air causing squeeze)
• Barotrauma of ascent
  • Pulmonary barotrauma (pulmonary overpressurization syndrome)
  • Decompression sickness (DCS)
  • Arterial gas embolism
  • Alternobaric vertigo
  • Facial baroparesis (Bells Palsy)
• At depth injuries
  • Oxygen toxicity
  • Nitrogen narcosis
  • Hypothermia
  • Contaminated gas mixture (e.g. CO toxicity)
  • Caustic cocktail from rebreathing circuit

Evaluation

• Clinical diagnosis

Management

• Ascent - symptoms completely reversed within minutes by ascending to a shallower depth, with no long-term effect
  • Therefore, consider other causes in patients with continued symptoms after ascent

Disposition

• Discharge

See Also

• Scuba diving emergencies