What is the name of the effect characterized by central nervous system (CNS) symptoms that occur after exposure to oxygen at high partial pressures > 3 atmospheres absolute (ATM)?

Central Nervous System Oxygen Toxicity: The Paul Bert Effect

The CNS symptoms that occur after being exposed to oxygen at high partial pressures > 3ATM is called the Paul Bert effect.

Pathophysiology of the Paul Bert Effect

• The Paul Bert effect refers specifically to central nervous system oxygen toxicity that occurs when breathing oxygen at high partial pressures exceeding 3 atmospheres absolute (ATM) 1
• This effect is characterized by neurological symptoms that can progress to convulsions resembling grand-mal epileptic seizures, which may lead to drowning and death in diving scenarios 2, 3
• Exposure to oxygen at partial pressures above 1.4 ATA can trigger CNS toxicity, with risk increasing significantly at pressures above 3 ATM 4

Clinical Manifestations

• Early warning signs and symptoms before severe manifestations include:

  • Limb convulsions and muscle twitching 3
  • Hyperventilation and difficulty maintaining steady depth during diving 3
  • Headache and visual disturbances 3
  • Facial muscle twitching 2, 3
  • Nausea 2

• Advanced symptoms that may occur after detachment from oxygen source:

  • Loss of consciousness 3
  • Confusion and disorientation 3
  • Weakness and dizziness 3
  • Generalized seizures 4

Risk Factors

• Elevated carbon dioxide levels (hypercapnia) significantly increase the risk of developing CNS oxygen toxicity 2
  • CO₂ levels above 3 kPa inspired CO₂ have been associated with CNS oxygen toxicity symptoms even under normobaric conditions when breathing 100% oxygen 2
• Exercise during exposure to high oxygen partial pressures increases risk 5
• Immersion in water may alter physiological responses and increase susceptibility 5
• Duration of exposure - longer exposure time at high PO₂ leads to faster development of more serious pathology 4

Physiological Monitoring and Prediction

• Recent research has identified potential early warning indicators:
  • Electrodermal activity (EDA) shows significant elevation approximately 57 ± 79 seconds (median 10 seconds) before the onset of definite CNS oxygen toxicity symptoms 5
  • Time-varying spectral indices of EDA may have predictive value for CNS oxygen toxicity with high sensitivity 5

Recovery and Safety Considerations

• Recovery from CNS oxygen toxicity in rats has been demonstrated to occur at oxygen partial pressures below 304 kPa (approximately 3 ATM) 1
• No symptoms related to CNS oxygen toxicity have been reported when diving with oxygen rebreathers at depths shallower than 3 meters of seawater 1
• For Special Operations Forces divers using closed-circuit rebreathers with 100% oxygen, careful monitoring and strict adherence to depth limitations are essential to prevent the Paul Bert effect 4

Clinical Implications

• In diving medicine, awareness of any unusual sensation during high-pressure oxygen exposure should prompt immediate action to prevent potentially dangerous situations 3
• On average, divers experiencing oxygen toxicity reported at least two symptoms (mean 3.4) a minimum of 5 minutes before termination of dives 3
• The Paul Bert effect represents a significant risk in military diving operations, technical diving, and hyperbaric oxygen therapy when pressures exceed 3 ATM 4