- 1 Other Names
- 2 Background
- 3 Pathophysiology
- 4 Risk Factors
- 5 Differential Diagnosis
- 6 Clinical Features
- 7 Evaluation
- 8 Classification
- 9 Management
- 10 Rehab and Return to Play
- 11 Complications and Prognosis
- 12 See Also
- 13 References
- Oxygen Toxicity
- Paul Bert effect
- Pulmonary oxygen toxicity
- This page refers to oxygen toxicity associated with breathing oxygen at higher partial pressures than normal
- Primarily referencing diving and other sports and recreational activities
- Named after Paul Bert, the French physiologist who first described it in 1878
- Incidence in closed circuit oxygen rebreather
- Characterized by breathing oxygen at higher partial pressures than normal
- Heavily correlates with dive depth, exposure time
- Patients tend to have traciobronchial symptoms initially, CNS symptoms in more severe cases
- Oxygen partial pressure ranges
- "Green Light" region is 1.4 ATA or less (about 82 feet/ 25 m on 40% oxygen mix)
- For open circuit scuba, CNS toxicity is unlikely
- "Yellow Light" is between 1.4 and 1.6 ATA (about 99 feet/ 30 m on 40% oxygen mix)
- Risk is low, but slim margin of error for developing oxygen toxicity
- Increasing depth, strenuous exercise or other emergencies increase the risk
- "Red Light" is above 1.6 ATA
- Recreational divers should not exceed this level
- Even mild exercise breathing high-density nitrox increases risk
- "Green Light" region is 1.4 ATA or less (about 82 feet/ 25 m on 40% oxygen mix)
- Exact mechanism of toxicity is not fully understood
- Directly related to duration of exposure, partial pressure of oxygen
- Depth/ ATM
- Partial pressure of O2 at sea level is 0.21 ATM
- FiO2 of 40% or less, equivalent to 0.40 ATM, can be tolerated indefinitely
- Occurs faster, at lower partial pressure than CNS toxicity
- No predictable pattern or sequence of symptoms
- Hyperoxia: an excess of oxygen in body tissues
- Physical effects
- Drying of the respiratory mucosa
- Adverse affects on the respiratory mucous blanket and the activity of cilia may result
- For these reasons, oxygen is typically humidified
- Physiological effects
- Vasodilatation of the pulmonary vasculature and vasoconstriction of the systemic circulation.
- High oxygen concentrations may indirectly ameliorate the inflammatory response by reducing tissue hypoxia
- This occurs as a consequence the levels of hypoxic inducible factor-1a (HIF-1a), a key regulatory molecule of both hypoxia and the inflammatory response
- In patients with COPD, they may develop hypercapnic respiratory failure
- Reactive Oxygen Species (ROS)
- Most probably mechanism related to an overflow of reactive oxygen species (ROS) in the brain after an increase of cerebral blood flow
Consequences of Hyperoxia
- Latent period is inversely proportional to the level and duration of inspired oxygen
- First manifestation of pulmonary toxicity is tracheobronchial irritation (substernal chest pain, pleuritic pain, cough, progressive dyspnea)
- May occur as fast as 14 hours at 100% oxygen
- Decrease in forced vital capacity is the most widely applied index of oxygen toxicity
- This has been shown to occur as early as 24 hours after continuous exposure to 100% oxygen
- Late findings include pulmonary edema, ARDS
- Start with visual changes such as tunnel vision, tinnitus, nausea, facial twitching, dizziness and confusion.
- Followed by tonic clonic seizures and subsequent unconsciousness.
- There appears to be no consistent pattern in the appearance of minor signs before the development of seizures.
- Prolonged exposure to high, inspired fractions of oxygen damages the retina
- In infants, risk factor for retinopathy of prematurity
- Hyperoxic myopia tends to be seen in adults
- Other organs have been implicated
- Oxygen Concentration
- Duration of exposure
Differential Diagnosis Dive Medicine
- Barotrauma of descent
- At depth injuries
- Oxygen Toxicity: harmful effects of breathing oxygen at higher partial pressures than normal
- Nitrogen Narcosis: toxic effects of breathing nitrogen-containing gases while at depth
- Hypothermia: decrease core temperature with prolonged exposure to cold water
- Carbon Monoxide Toxicity: CO toxicity typically results from a faulty air compressor
- Caustic Cocktail: Inhalation of absorbent material used to scrub CO2 mixes with water
- Barotrauma of ascent
- Initial symptoms are typically trachobronchial including pleuritic chest pain, dypsnea, coughing
- CNS symptoms include tunnel vision, tinnitis, nausea, twitiching, irritability, seizure
- Patients may complain of flashing lights, tunnel vision
- Tinnitus (loud ringing or roaring in ears)
- Change in mental status including confusion, lethargy
- Nausea, vertigo
- Numbness or tingling
- Muscular twitching, especially at the lips
- Grand mall convulsion
- Visual disturbances generally precede convulsions
- Physical Exam
- Important to perform a thorough neurological exam
- CNS symptoms may include irritability, cold shivering, twitching, tonic-clonic activity
- Lung exam may reveal rales, uncontrollable coughing, hiccups
- ENT exam can reveal hyperemia of nasal mucosa
- Diagnosis is primarily clinical
- Standard Chest Radiograph
- Should be obtained if diagnosis unclear or patient is ill appearing
Pulmonary Function Testing
- Strongly consider to assess status or establish baseline
- Trending helps guide clinical picture
- Not applicable
- Reduce exposure to increased oxygen levels
- Reduce partial pressure of inhaled oxygen
- As low as tolerated while still maintaining tissue perfusion
- For patients who require Hyperbaric Oxygen Therapy
- Consider anti-epileptic medications, prolonged air breaks, limited treatment pressure
- "Air breaks": allow intermittent air-breathing while in the hyperbaric environment, may decrease oxygen toxicity by a factor of 10
- Deep diving
- May require breathing mixtures that contain less than 21% oxygen to reduce toxicity risk
- Patients typically require admission to the hospital
- See: Dive Medicine Prevention
- Oxygen Toxicity
- Pay close attention to partial pressure, exposure time
- The U.S. Navy uses 1.3 ATA as the maximum limit in its closed-circuit rebreathers
- National Oceanic and Atmospheric Administration (NOAA) recommends a more conservative 180 minutes at 1.3 ATA for normal exposures and 240 minutes only for exceptional exposures
- Professional Association of Diving Instructors (PADI) has proposed a limit of 1.4 ATA for open-circuit nitrox scuba diving
- Shallow exposure times in the 1.3 to 1.4 ATA range are mainly to avoid lung oxygen toxicity
- The NOAA limit for nitrox diving at 1.6 ATA is 45 minutes for normal diving and 120 minutes for exceptional exposure diving
- Breathing 100 percent oxygen during a decompression stop at 20 feet (6.1 meters) is a common practice
Rehab and Return to Play
- No clear rehab guidelines
Return to Play/ Work
- Needs to be updated
Complications and Prognosis
- CNS Toxicity
- With removal of the inciting agent; no long term neurological damage typically occurs
- Pulmonary Toxicity
- Damage due to oxygen-induced pulmonary toxicity is reversible in most adults.
- Pulmonary Edema
- Acute Respiratory Distress Syndrome (ARDS)
- Retinopathy of prematurity can be seen in infants
- Hyperoxic myopia
- Delayed cataract formation
- Tonic-clonic activity
- Bert P. (1878). La Pression Barométrique: Recherches de Physiologie Expérimentale. Paris: Masson.
- Harabin A. L., Survanshi S. S., Homer L. D. (1995). A model for predicting central nervous system oxygen toxicity from hyperbaric oxygen exposures in humans. Toxicol. Appl. Pharmacol. 132, 19–26. 10.1006/taap.1995.1082
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- Domachevsky L, Rachmany L, Barak Y, Rubovitch V, Abramovich A, Pick CG. Hyperbaric oxygen-induced seizures cause a transient decrement in cognitive function. Neuroscience. 2013 Sep 05;247:328-34.
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- Xiao Y, Xiong T, Meng X, Yu D, Xiao Z, Song L. Different influences on mitochondrial function, oxidative stress and cytotoxicity of antibiotics on primary human neuron and cell lines. J Biochem Mol Toxicol. 2019 Apr;33(4):e22277.