About 100 people in France suffer from chronic respiratory failure which requires home oxygen therapy, most often long term. The constraints of this therapy are notably linked to the source of oxygen used: oxygen concentrators (or extractors) supply oxygen from an inexhaustible source: the ambient air.

Air is made up of 78% nitrogen and only 21% oxygen. The oxygen concentrator or extractor filters the ambient air by passing it through the pores of a molecular sieve which retains the nitrogen molecules and allows those of oxygen to pass. The air thus filtered contains 90% pure oxygen for a flow rate of 2,5 liters per minute.

Structure of oxygen concentrators

Oxygen concentrators deliver an oxygen flow that can range, depending on the model, from 2 to 10 liters per minute. The air sucked in is first of all filtered to rid it of impurities (dust, etc.), then it passes under high pressure in a cylinder filled with zeolite which fixes nitrogen and allows oxygen to pass.

Two cylinders operate cyclically: one works while the other is cleaned. The oxygen enriched air can then be humidified by passing through a container of sterile water before being inhaled by the user through goggles or an oxygen mask.

The classic models used at home are small “furniture” on casters weighing 14 to 25 kilograms that work on the mains (220V).

Lighter, battery-operated models allow autonomous trips of a few hours outside the home. Transportable models (on cart) weigh 8 to 10 kilos, and portable models (in shoulder bag) weigh 2 to 4 kilos. Their weight is often linked to their number of batteries, and therefore to their autonomy capacity.

Long-term oxygen therapy can be prescribed in the context of chronic respiratory pathologies:

• Chronic obstructive pulmonary disease (COPD);
• cystic fibrosis;
• pulmonary arterial hypertension;
• Sleep Apnea ;
• or short term (less than 3 months) for the treatment of respiratory or ENT diseases;
• it can also be prescribed in case of dyspnea in palliative care or at the end of life.

The flow of oxygen

The oxygen flow is adjusted according to the patient’s clinical parameters and lifestyle. We determine two values:

• the flow of oxygen during exercise (determined by a 6-minute walk or by a stress test);
• the flow at rest.

The oxygen flow is delivered either continuously or by pulse. In the latter case, there is no “waste” of oxygen, which further reduces the size of the concentrator. The other advantage is that the patient must make the effort to inhale instead of remaining passive. In the case of sleep apnea, the flow is continuous, because breathing during sleep is shallower, so the oxygen supply is less.

Indications

Long-term oxygen therapy is prescribed:

• in the case of other chronic respiratory insufficiencies (cystic fibrosis, pulmonary arterial hypertension, pneumopathy, etc.) when PaO2 <60 mmHg.

Exclusive ambulation oxygen therapy is prescribed:

• in people with exertional oxygen desaturation defined by PaO2 <60 mmHg or by a decrease in SpO2 oxygen saturation of at least 5%. The use of a concentrator is therefore only necessary during efforts.

The stages of operation

• Plug in the concentrator and turn it on: an audible alert sounds for a few seconds;
• Wait 5 to 10 minutes for the oxygen level to reach 100%;
• Adjust the flowmeter until the ball is stabilized at the prescribed level;
• If necessary, connect the oxygen outlet to the humidifier;
• Then connect the tubing to the concentrator on one side, and to the glasses or mask on the other;
• Check that oxygen is coming out of the tubing;
• Put on the glasses or mask, and breathe;
• At the end of the session, turn off the device.

Security

• The quantity of oxygen delivered to the patient is constantly monitored;
• In the event of a power failure, an alarm is triggered and a battery takes over;
• In the event of an overcurrent, the circuit is automatically cut off.

The interview

• At least once a week, dust the concentrator, including the inlet ports;
• Change the water in the humidifier every day, clean it with soapy water, and descale it with white vinegar regularly;
• Change glasses or oxygen mask every two weeks;
• Clean the dust filter after every 100 hours of use and change it when it starts to wear out.

Precautions to take

• Make sure that there is a clear space all around the appliance for its correct operation; do not cover it; do not put it on a carpet that is too soft (some devices have their ventilation system located below);
• Oxygen is a flammable gas so make sure to keep the concentrator away from all fuels (oil, grease, cigarettes, etc.) and ventilate the room well;
• When transporting, do not put it to bed.

The different models

A good oxygen extractor should be very reliable, robust, quiet, have a good cooling system, and be easy to use. The different parameters to be taken into account are:

• oxygen flow;
• battery life for outdoor use;
• the flow: continuous or by impulse;
• use: “sedentary” indoors or “mobile” outdoors;
• the price: some models are available for rental.

The medical prescription must specify:

• the flow of O2 in liters per minute at rest;
• the mode of administration: pulsed or continuous;
• the duration of administration per day and / or the number of daily sessions.

Alternatives to the oxygen concentrator

There are other types of oxygen sources for home oxygen therapy. Other than that they do not use air to produce oxygen, they are of the same clinical value. These are :

• gaseous compressed oxygen cylinders: they are generally used in addition to concentrators, in the event of a breakdown or for walking;
• liquid oxygen tanks which allow a very large quantity of oxygen to be stored in a very small volume (1 liter of liquid oxygen can provide 860 liters of gaseous oxygen).

These two models have the major drawback of having to be recharged regularly, unlike the extractor. The fear of leakage and the fear of running out of fuel are all sources of stress for the user.

Originally

The principle of the molecular sieve was developed by JW Mc Bain in 1756. It was then a solid and porous filter which blocked certain molecules at the level of its pores and allowed others to pass.