Chronic low blood oxygen (hypoxaemia): causes, effects and long-term oxygen

Hypoxaemia is the medical word for a lower than normal level of oxygen in the blood. When it is a temporary problem, such as during a chest infection, it settles as the illness is treated. Chronic hypoxaemia is when it persists, usually for months or years, because the lungs can no longer pass enough oxygen into the bloodstream.

Royal Papworth Hospital describes the wider picture as chronic respiratory failure, which develops slowly, so that the body may be able to adapt to slightly lower levels of oxygen and higher levels of carbon dioxide. The adaptation is not free. It places continuing strain on other organs, which is why long-term low oxygen is treated seriously even when someone seems to be coping.

In older adults the cause is almost always a long-term lung condition. The NHS describes COPD as a group of lung conditions, including emphysema and chronic bronchitis, which mainly affects middle-aged or older adults who smoke and in which damage to the lungs is permanent. Royal Papworth names COPD and bronchiectasis as examples of long-term conditions that can lead to a lack of oxygen alone.

The lungs are not the only route. Royal Papworth lists chest wall disorders, neuromuscular disorders and neurological disorders among the conditions that may benefit from home ventilation, because in those conditions the failure is of the pump rather than the lung itself.

A lack of oxygen causes restlessness, confusion, agitation and breathlessness, according to Royal Papworth. In chronic cases the day-to-day picture is usually quieter: breathlessness on effort, tiredness, poorer concentration and reduced stamina. Many people simply adjust their lives downward without noticing how much they have given up.

The risk to the heart is the key long-term concern. Royal Papworth says a persistently reduced level of oxygen can damage the heart, resulting in fluid retention. If carbon dioxide is also retained, the symptoms can include morning headaches, drowsiness and confusion, a pattern that suggests the problem needs specialist assessment.

The NHS lists a blood oxygen test, in which a peg-like device is attached to a finger to measure the level of oxygen in the blood, among the further tests for COPD. Royal Papworth says respiratory failure can usually be confirmed by an arterial blood gas sample taken from an artery, usually at the wrist, which gives accurate information about both oxygen and carbon dioxide.

Related tests help to explain the cause. For COPD the NHS describes spirometry, a breathing test showing how well the lungs work, a chest X-ray, blood tests and sometimes an ECG, echocardiogram or CT scan. If a more comprehensive assessment is needed Royal Papworth mentions an overnight sleep study and lung function studies.

The NHS explains that oxygen at home is delivered through nasal tubes or a mask, that the tubes are long enough to move around the home while connected, and that portable tanks are available for use away from home. Long-term oxygen treatment should be used for at least 15 hours a day. Ambulatory oxygen, used when walking or being active, may be offered instead if blood oxygen is normal at rest but falls on exercise.

Oxygen is a medicine with rules. The NHS says not to smoke when using oxygen, and Royal Papworth explains that for type 1 failure oxygen alone may be enough, while for type 2 failure, with high carbon dioxide, non-invasive ventilation is needed and is usually only required during sleep. The aims are to reduce symptoms and improve quality of life, and to slow or prevent further deterioration.

The NHS says that if COPD causes a low level of oxygen in your blood you may be advised to have oxygen at home, so the decision follows measurement of your blood oxygen and discussion with your doctor. Home oxygen is arranged through the NHS pathway in the UK; private consultations can repeat the assessment tests.

The NHS says that stopping smoking is the most effective way of preventing COPD from getting worse and that it is never too late to stop. Pulmonary rehabilitation, with at least 6 weeks of group exercise and education, improves how much you can do before getting out of breath, and your self-confidence and emotional wellbeing.

Vaccination protects against infections that can tip someone from stable to acutely unwell. The NHS recommends the pneumococcal vaccine for adults over 65, the flu vaccine for people with certain long-term conditions, and the RSV vaccine for adults aged 75 and over. Supportive care also includes social care and support assessments, which the NHS signposts.

Contact the GP or specialist team if breathlessness, swelling or sleepiness is increasing, or if you have signs of a chest infection such as more coughing or a change in phlegm colour. Call 999 or go to A&E if you are struggling to breathe, have pale, blue or blotchy lips, skin or tongue, or suddenly feel confused, as the NHS advises for lung infections.