Acute indications for therapy include hypoxemia (low blood oxygen levels), carbon monoxide toxicity and cluster headache.

[3][1] Oxygen can be delivered via nasal cannula, face mask, or endotracheal intubation at normal atmospheric pressure, or in a hyperbaric chamber.

[12][13] In context of acute hypoxemia, oxygen therapy should be titrated to a target level based on pulse oximetry (94–96% in most patients, or 88–92% in people with COPD).

[8] Exceptions to these recommendations include carbon monoxide poisoning, cluster headaches, sickle cell crisis, and pneumothorax.

[22][23][24] Careful titration of oxygen therapy should be considered in patients with chronic conditions predisposing them to carbon dioxide retention (e.g., COPD, emphysema).

Transfer from the field to definitive care with titrated oxygen typically occurs long before significant reductions to the respiratory drive are observed.

Some practitioners of alternative medicine have promoted "oxygen therapy" as a cure for many human ailments including AIDS, Alzheimer's disease and cancer.

[citation needed] It has been hypothesized that oxygen therapy may promote accelerated development of atelectasis (partial or complete lung collapse), as well as denitrogenation of gas cavities (e.g., pneumothorax, pneumocephalus).

[35] Mucosal damage is observed to increase with elevated atmospheric pressure and oxygen concentrations, which may result in the development of ARDS and possibly death.

[41][42] Decreased cerebral blood flow and intracranial pressure (ICP) have been reported in hyperoxic conditions, with mixed results regarding impact on cognition.

[47] Among CO2 retainers, excess exposure to oxygen in context of the Haldane effect causes decreased binding of deoxyhemoglobin to CO2 in the blood.

Patients with underlying lung disease such as COPD may not be able to adequately clear the additional CO2 produced by this effect, worsening their condition.

[52]  Rates of oxidative stress appears to be influenced by both oxygen concentration and length of exposure, with general toxicity observed to occur within hours in certain hyperoxic conditions.

[56][57] In the systemic vasculature, oxygen serves as a vasoconstrictor, leading to mildly increased blood pressure and decreased cardiac output and heart rate.

Fire and explosion hazards exist when concentrated oxidants and fuels are brought together in close proximity, although an ignition event (e.g., heat or spark) is needed to trigger combustion.

[65] Highly concentrated oxygen in a high-pressure environment can spontaneously ignite hydrocarbons such as oil and grease, resulting in a fire or explosion.

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.

[citation needed] Patients who are unable to breathe on their own will require positive pressure to move oxygen into their lungs for gaseous exchange to take place.

Many emergency medical service members, first aid personnel, and hospital staff may use a bag-valve-mask (BVM), which is a malleable bag attached to a face mask (or invasive airway such as an endotracheal tube or laryngeal mask airway), usually with a reservoir bag attached, which is manually manipulated by the healthcare professional to push oxygen (or air) into the lungs.

[77]Automated versions of the BVM system, known as a resuscitator or pneupac can also deliver measured and timed doses of oxygen directly to people through a facemask or airway.

Nebulizers use compressed gas to propel liquid medication into therapeutically sized aerosol droplets for deposition to the appropriate portion of the airway.

A typical compressed gas flow rate of 8–10 L/min is used to nebulize medications, saline, sterile water, or a combination these treatments into a therapeutic aerosol for inhalation.

In the clinical setting, room air (ambient mix of several gasses), molecular oxygen, and Heliox[citation needed] are the most common gases used to nebulize a bolus treatment or a continuous volume of therapeutic aerosols.

These masks are normally of a closed design such that leaks are minimized and breathing of room air is controlled through a series of one-way valves.

SARS was identified as being respiratory based, and it was determined that conventional oxygen therapy devices were not designed for the containment of exhaled particles.

[citation needed] Because all exhaled particles are contained within the mask, nebulized medications are also prevented from releasing into the surrounding atmosphere, decreasing the occupational exposure to healthcare staff and other people.

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.

[82] The delivery of supplemental oxygen is most effective if it is made at a point in the breathing cycle when it will be inhaled to the alveoli, where gas transfer occurs.

oxygen delivered later in the cycle will be inhaled into physiological dead space, wher it serves no useful purpose as it cannot diffuse into the blood.

[82] A continuous constant flow rate uses a simple regulator, but is inefficient as a high percentage of the delivered gas does not reach the alveoli, and over half is not inhaled at all.