supplemental oxygen
Supplemental oxygen is the everyday business end of oxygen therapy: the extra oxygen actually flowing into a patient through nasal prongs or a mask. Where oxygen therapy is the overall treatment and its prescription, supplemental oxygen is the practical act of giving oxygen on top of the air the person is already breathing, to push their blood oxygen back up into a safe range.
The amount delivered depends on both the device and the flow. Thin nasal prongs at one to a few litres a minute add a modest amount, suitable for mild hypoxemia and comfortable for eating and talking. Simple face masks and reservoir (non-rebreather) masks supply progressively higher concentrations for moderate to severe needs. The right choice matches the device to how much oxygen the patient needs and how the device fits their breathing pattern.
Supplemental oxygen is appropriate whenever blood oxygen is low — in acute illness, after surgery, during transport, or long-term at home for chronic lung disease. An honest caveat: it is for hypoxemia, not for breathlessness alone, and in a person who feels short of breath but has normal oxygen levels it offers no benefit. As with all oxygen, the dose is guided by a target saturation, and care is needed in those prone to carbon dioxide retention.
A post-operative patient whose saturation dips to 90 percent is given two litres of supplemental oxygen by nasal prongs, which brings it comfortably back to 96 percent.
Extra oxygen by prongs or mask raises a low blood oxygen back into the safe range.
Nasal prongs deliver a variable concentration that depends on the patient's own breathing; masks designed to fix the oxygen fraction give a more predictable amount.