Although most EMS jurisdictions hold that oxygen should not be withheld from any patient, there are certain situations in which oxygen therapy can have a negative impact on a patient’s condition.
Oxygen has vasoconstrictive effects on the circulatory system, reducing peripheral circulation and was once thought to potentially increase the effects of stroke. However, when additional oxygen is given to the patient, additional oxygen is dissolved in the plasma according to Henry's Law. This allows a compensating change to occur and the dissolved oxygen in plasma supports embarrassed (oxygen-starved) neurons, reduces inflammation and post-stroke cerebral edema.
Since 1990, hyperbaric oxygen therapy has been used in the treatments of stroke on a worldwide basis. In rare instances, hyperbaric oxygen therapy patients have had seizures. However, because of the aforementioned Henry's Law effect of extra available dissolved oxygen to neurons, there is usually no negative sequel to the event. Such seizures are generally a result of oxygen toxicity, although hypoglycemia may be a contributing factor, but the latter risk can be eradicated or reduced by carefully monitoring the patient's nutritional intake prior to oxygen treatment.
High levels of oxygen given to infants causes blindness by promoting overgrowth of new blood vessels in the eye obstructing sight. This is retinopathy of prematurity (ROP).
Administration of high levels of oxygen in patients with severe emphysema and high blood carbon dioxide reduces respiratory drive, which can precipitate respiratory failure and death.
Care needs to be exercised in patients with chronic obstructive pulmonary disease, especially in those known to retain carbon dioxide (type II respiratory failure) who lose their respiratory drive and accumulate carbon dioxide if administered oxygen in moderate concentration. However the risk of the loss of respiratory drive are far outweighed by the risks of withholding emergency oxygen, and therefore emergency administration of oxygen is never contraindicated.
Oxygen first aid has been used as an emergency treatment for diving injuries for years. The success of recompression therapy as well as a decrease in the number of recompression treatments required has been shown if first aid oxygen is given within four hours after surfacing.
There are suggestions that oxygen administration may not be the most effective measure for the treatment of DCI/DCS and that heliox may be a better alternative. Recompression in a hyperbaric chamber with the patient breathing 100% oxygen is the standard hospital and military medical response to decompression illness and decompression sickness.
Oxygen should never be given to a patient who is suffering from paraquat poisoning unless they are suffering from severe respiratory distress or respiratory arrest, as this can increase the toxicity. (Paraquat poisoning is rare - for example 200 deaths globally from 1958–1978).
Oxygen therapy is not recommended for patients who have suffered pulmonary fibrosis or other lung damage resulting from bleomycin treatment.
Highly concentrated sources of oxygen promote rapid combustion. Fire and explosion hazards exist when concentrated oxidants and fuels are brought into close proximity; however, an ignition event, such as heat or a spark, is needed to trigger combustion. Oxygen itself is not the fuel, but the oxidant.
Combustion hazards also apply to compounds of oxygen with a high oxidative potential, such as peroxides, chlorates, nitrates, perchlorates, and dichromates because they can donate oxygen to a fire.
Concentrated will allow combustion to proceed rapidly and energetically.
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