Oxygen Therapy

Oxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care. Oxygen is essential for cell metabolism, and in turn, tissue oxygenation is essential for all normal physiological functions.[1]

High blood and tissue levels of oxygen can be helpful or damaging, depending on circumstances and oxygen therapy should be used to benefit the patient by increasing the supply of oxygen to the lungs and thereby increasing the availability of oxygen to the body tissues, especially when the patient is suffering fromhypoxia and/or hypoxaemia.

Indications for use

Oxygen is used as a medical treatment in both chronic and acute cases, and can be used in hospital, pre-hospital or entirely out of hospital, dependant on the needs of the patient and their medical professionals’ opinions.

A common use of supplementary oxygen is in patients with chronic obstructive pulmonary disease (COPD),the occurrence of chronic bronchitis or emphysema, a common long term effect of smoking, who may require additional oxygen to breathe either during a temporary worsening of their condition, or throughout the day and night. It is indicated in COPD patients with PaO
2 ≤ 55mmHg or SaO
2 ≤ 88% and has been shown to increase lifespan.[2]

Oxygen is often prescribed for people with breathlessness, in the setting of end-stage cardiac or respiratory failure, advanced cancer or neurodegenerative disease, despite having relatively normal blood oxygen levels. A 2010 trial of 239 subjects found no significant difference in reducing breathlessness between oxygen and air delivered in the same way.[3]

Use in acute conditions

Oxygen is widely used in emergency medicine, both in hospital and by emergency medical services or advanced first aiders.

In the pre-hospital environment, high flow oxygen is definitively indicated for use in resuscitation, major trauma, anaphylaxis, major haemorrhage, shock, activeconvulsions and hypothermia.[1][4]

It may also be indicated for any other patient where their injury or illness has caused hypoxaemia, although in this case oxygen flow should be moderated to achieve target oxygen saturation levels, based on pulse oximetry (with a target level of 94–98% in most patients, or 88–92% in COPD patients).[1]

For personal use, high concentration oxygen is used as home therapy to abort cluster headache attacks, due to its vaso-constrictive effects.[5]

Delivery

Various devices are used for administration of oxygen. In most cases, the oxygen will first pass through a pressure regulator, used to control the high pressure of oxygen delivered from a cylinder (or other source) to a lower pressure. This lower pressure is then controlled by a flowmeter, which may be preset or selectable, and this controls the flow in a measure such as litres per minute (lpm). The typical flowmeter range for medical oxygen is between 0 and 15 lpm with some units able to obtain up to 25 liters per minute. Many wall flowmeters using a Thorpe tube design are able to be dialed to “flush” which is beneficial in emergency situations.

Supplemental oxygen

Many patients require only a supplementary level of oxygen in the room air they are breathing, rather than pure or near pure oxygen,[9] and this can be delivered through a number of devices dependant on the situation, flow required and in some instances patient preference.

A nasal cannula (NC) is a thin tube with two small nozzles that protrude into the patient’s nostrils. It can only comfortably provide oxygen at low flow rates, 2–6 litres per minute (LPM), delivering a concentration of 24–40%.

There are also a number of face mask options, such as the simple face mask, often used at between 6 and 12 LPM, with a concentration of oxygen to the patient of between 28% and 50%. This is closely related to the more controlled air-entrainment masks, also known as Venturi masks, which can accurately deliver a predetermined oxygen concentration to the trachea up to 40%.

In some instances, a partial rebreathing mask can be used, which is based on a simple mask, but featuring a reservoir bag, which increases the provided oxygen rate to 40–70% oxygen at 5 to 15 LPM.

Non-rebreather masks draw oxygen from an attached reservoir bags, with one-way valves that direct exhaled air out of the mask. When properly fitted and used at flow rates of 10-15 LPM or higher, they deliver close to 100% oxygen. This type of mask is indicated for acute medical emergencies.

Demand valves or oxygen resuscitators deliver oxygen only when the patient inhales, or, in the case of an apnic (non-breathing) victim, the caregiver presses a button on the mask. These systems greatly conserve oxygen compared to steady-flow masks, which is useful in emergency situations when a limited supply of oxygen is available and there is a delay in transporting the patient to higher care. They are very useful in performing CPR, as the caregiver can deliver rescue breaths composed of 100% oxygen with the press of a button. Care must be taken not to over-inflate the patient’s lungs, and some systems employ safety valves to help prevent this. These systems may not be appropriate for unconscious patients or those in respiratory distress, because of the effort required to breathe from them.

Negative effects

Many EMS protocols indicate that oxygen should not be withheld from any patient, while other protocols are more specific or circumspect. However, there are certain situations in which oxygen therapy is known to have a negative impact on a patient’s condition.[19]

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 to 1978).[20] Oxygen therapy is not recommended for patients who have suffered pulmonary fibrosis or other lung damage resulting from bleomycin treatment.[21]

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).

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,[22][23] 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.

Oxygen first aid has been used as an emergency treatment for diving injuries for years.[24] Recompression in a hyperbaric chamber with the patient breathing 100% oxygen is the standard hospital and military medical response to decompression illness.[24][25][26] 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.[27] There are suggestions that oxygen administration may not be the most effective measure for the treatment of decompression illness and that heliox may be a better alternative.[28]

Chronic obstructive pulmonary disease

Care needs to be exercised in patients with chronic obstructive pulmonary disease, such as emphysema, especially in those known to retain carbon dioxide (type II respiratory failure). Such patients may further accumulate carbon dioxide and decreased pH (hypercapnation) if administered supplemental oxygen, possibly endangering their lives.[29] This is primarily as a result of ventilation–perfusion imbalance (see Effect of oxygen on chronic obstructive pulmonary disease).[30] In the worst case, administration of high levels of oxygen in patients with severe emphysema and high blood carbon dioxide may reduce respiratory drive to the point of precipitating respiratory failure, with an observed increase in mortality compared with those receiving titrated oxygen treatment.[29] 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. Transfer from field care to definitive care, where oxygen use can be carefully calibrated, typically occurs long before significant reductions to the respiratory drive.

A 2010 study has shown that titrated oxygen therapy (controlled administration of oxygen) is less of a danger to COPD patients and that other, non-COPD patients, may also, in some cases, benefit more from titrated therapy.[29]

Fire risk

Highly concentrated sources of oxygen promote rapid combustion. Oxygen itself is not flammable, but the addition of concentrated oxygen to a fire greatly increases its intensity, and can aid the combustion of materials (such as metals) which are relatively inert under normal conditions. 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.[31] A well-known example of an accidental fire accelerated by pure oxygen under pressure occurred in the Apollo 1 spacecraft in January 1967 during a ground test; it killed all three astronauts. A similar accident killed Soviet cosmonaut Valentin Bondarenko in 1961.

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 O
2 will allow combustion to proceed rapidly and energetically.[31] Steel pipes and storage vessels used to store and transmit both gaseous and liquid oxygen will act as a fuel; and therefore the design and manufacture of O
2 systems requires special training to ensure that ignition sources are minimized.[31] Highly concentrated oxygen in a high-pressure environment can spontaneously ignite hydrocarbons such as oil and grease, resulting in fire or explosion. The heat caused by rapid pressurization serves as the ignition source. For this reason, storage vessels, regulators, piping and any other equipment used with highly concentrated oxygen must be “oxygen-clean” prior to use, to ensure the absence of potential fuels. This does not apply only to pure oxygen; any concentration significantly higher than atmospheric (approximately 21%) carries a potential risk.

Hospitals in some jurisdictions, such as the UK, now operate “no-smoking” policies, which although introduced for other reasons, supports the aim of keeping ignition sources away from medical piped oxygen. Other recorded sources of ignition of medically prescribed oxygen include candles, aromatherapy, medical equipment, cooking, and unfortunately, deliberate vandalism. Smoking pipes, cigars and cigarettes are of special concern. This does not entirely eliminate the risk of injury with portable oxygen systems, especially if compliance is poor.[32]

Oxygen therapy while on aircraft

In the United States, most airlines restrict the devices allowed on board aircraft. As a result passengers are restricted in what devices they can use. Some airlines will provide cylinders for passengers with an associated fee. Other airlines allow passengers to carry on approved portable concentrators. However the lists of approved devices varies by airline so passengers need to check with any airline they are planning to fly on. Passengers are generally not allowed to carry on their own cylinders. In all cases, passengers need to notify the airline in advance of their equipment.

Effective May 13, 2009, the Department of Transportation and FAA ruled that a select number of portable oxygen concentrators are approved for use on all commercial flights.[33] The list of approved portable oxygen concentrators includes the Respironics EverGo, the Invacare XPO2, the Invacare Solo 2 and others.[34]

FAA regulations require larger airplanes to carry D-cylinders of oxygen for use in an emergency.