Oxygen Flow Rates and Prescriptions: What Families Should Know

What oxygen therapy is for

Oxygen therapy treats low oxygen in the blood (hypoxaemia). In long-term lung disease such as COPD or pulmonary fibrosis, heart failure, and after severe pneumonia, a person's blood oxygen can stay low. Oxygen supplements the air they breathe, easing breathlessness for some people, protecting the heart and organs, and, in selected cases of chronic low oxygen, improving survival when used for enough hours per day. It is not a general treatment for breathlessness caused by anxiety or other reasons and does not suit everyone with a low reading. A doctor, usually a chest physician, assesses this using tests, not the home oximeter alone. See pulse oximeter accuracy for why a fingertip reading can mislead.

What a prescription usually contains

A good home oxygen prescription states:

• The flow rate in litres per minute (L/min), for example 2 L/min.
• The device and delivery method: nasal cannula or mask, and sometimes the type of mask.
• The hours per day: for example, at least 15 hours a day, including night, for long-term oxygen therapy, or only at night, or only on exertion.
• When it should be used: at rest, with activity, during sleep, or all three, and whether the flow differs for each. For example, 2 L/min at rest and 3 L/min on exertion.
• The target oxygen saturation range, such as 88 to 92 per cent for people at risk of carbon dioxide retention, or 94 to 98 per cent for others.
• The source: concentrator, cylinder, portable or a mix.
• Review date.

Ask the doctor to write it all down, and keep a copy with the machine and in the health record.

How doctors decide the flow

Doctors look at oxygen levels measured at rest while the person is stable, often using arterial blood gas tests or careful oximetry on two occasions weeks apart, and at symptoms, the heart, and sometimes tests of walking and of oxygen during sleep. They adjust the flow to bring oxygen into the target range without raising carbon dioxide too far. For some people they check blood gases after starting oxygen. This is why a flow set by a relative or a shopkeeper, or copied from a neighbour, is not a safe guide.

In India, many people receive oxygen during a hospital stay and are discharged with a number that was set during the acute illness. As the person recovers, the need may fall. Ask for a review a few weeks after discharge. Do not continue indefinitely just because oxygen was needed once. See home oxygen during recovery from pneumonia or severe infection.

Reading the flow meter

Concentrators and cylinders have a flow meter. On many, a small ball or float rises in a tube beside a printed scale in litres per minute. Others have a dial. To read it:

1. Look at the meter at eye level. 2. For a ball float, read at the centre of the ball, or at the top, as the manual specifies. 3. Compare with the number prescribed and set the knob so the float sits at the line. 4. Do not leave the float between lines or guess.

Dial regulators on cylinders have click positions; set to the correct number. Check regularly that the setting has not been moved by children, pets or cleaners. Tape a note beside the dial saying "Prescribed flow: __ L/min. Do not change." Do not rely on the tape to cover the knob in a way that makes it hard to turn off in an emergency.

Continuous flow and pulse dose

Most home concentrators and cylinders give a continuous flow: oxygen flows all the time at the set rate. Many portable concentrators give a pulse dose: a puff of oxygen each time the person breathes in. The numbers on pulse devices (1 to 5, for example) are settings, not litres per minute, and a given setting on one model does not equal the same continuous flow on another. If your parent switches between machines, ask the doctor or supplier to confirm the equivalent setting on the portable model, and check oxygen levels at rest and on exertion. See portable oxygen concentrators: travel and daily use.

Resting, exertion and night flows

Some people need more oxygen when walking, bathing or climbing steps than when sitting. Others need extra at night, when breathing slows and oxygen can fall. The prescription may therefore include different flows for different situations. Do not make this up yourself. Ask:

• Do we change the flow when walking, and by how much?
• Do we use oxygen during bathing and meals?
• What should we do if the number drops during activity?
• Does the night flow differ?

A written plan reduces arguments and risk.

What the target saturation means

Doctors give a target range for the oxygen saturation (SpO2) on the oximeter. For people with long-term lung disease who retain carbon dioxide, this is often 88 to 92 per cent, which is lower than the usual 94 to 98 per cent. The aim is enough oxygen to protect organs without suppressing the drive to breathe. A reading above target is not necessarily "better" and, in such patients, may be harmful.

• Do not chase 98 or 100 per cent by raising the flow.
• Do not panic at a number in the target range that looks low to you.
• Do call the doctor if readings are persistently below the target range at the prescribed flow, or above it, or if there are symptoms such as drowsiness, confusion or morning headaches.

Readings can be wrong; check technique and the finger first; see pulse oximeters: how they work and how to use one and when oxygen saturation is low: what to do.

Why families must not change the flow

• Too much oxygen can cause carbon dioxide retention in some lung conditions, leading to headache, drowsiness, confusion and, in severe cases, loss of consciousness.
• Too little oxygen leaves organs short of oxygen and strains the heart.
• Breathlessness is not always low oxygen. It can come from anxiety, fluid, infection, anaemia or a blocked airway; oxygen may not help and can delay proper treatment.
• A change in need is a medical signal. If your parent needs more oxygen than before, something has changed and a doctor should look for the cause.

So the rule is: never change the prescribed flow or hours yourself. If your parent seems worse, check the equipment, sit them upright, follow the action plan, call the doctor, and call 112 if severe. Do not "try a bit more" and wait.

Common flow-related mistakes

• Turning up the dial because the person looks breathless.
• Turning it down to save oxygen from a cylinder.
• Using a mask at the wrong flow; many masks require a minimum flow to avoid re-breathing exhaled air. Follow the doctor's advice; see nasal cannulas and oxygen masks: choosing and caring for them.
• Leaving the flow on when the cannula is not in use, wasting oxygen and creating a fire risk.
• Forgetting to switch the flow meter back after cleaning.
• Copying a flow from a different patient or hospital document.
• Using extra-long tubing that reduces the real flow.

Fire and safety reminder

Whatever the flow, oxygen creates fire risk. No smoking, no flames, no oil or grease on the face and connections, and keep heat sources away. See using an oxygen concentrator safely at home, oxygen cylinder safety at home and safe use of oxygen and electrical equipment.

Reviews and weaning

Oxygen needs change. After a pneumonia or flare-up, a person may recover and no longer need it. Others need it for life. Doctors usually reassess after about three months of stability and then at intervals. Do not stop oxygen on your own because your parent feels better, or because the oximeter looks good; ask the doctor to test. If the doctor reduces or stops oxygen, ask for written instructions.

Keeping a record

Keep a log with: date and time, flow used, device, oxygen reading, symptoms, activity, and any problems. Bring it to appointments. This helps the doctor fine-tune the prescription. See keeping a health record at home.

When to ask a professional

Ask the doctor for the flow, hours, target range, exertion and night rules, in writing, and for a review date. Ask what to do in a flare-up and when to go to hospital; see building a COPD action plan with your doctor. Ask the supplier how to read your meter. Call the doctor the same day if breathlessness increases, if readings fall below the target at the prescribed flow, or if your parent is drowsy, confused or has morning headaches. Call 112 for severe breathlessness, blue lips, chest pain, collapse or confusion.