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Understand how POCs work

  1. Apr 15,2018
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Oxygen concentrators are simple devices. POC technology is similar to that of stationary oxygen (floor models) concentrators, which are electric machines that produce a continuous flow of oxygen-enriched air. The oxygen concentrator draws in the ambient air through a series of filters to eliminate dust, bacteria, and other particulates; oxygen-rich gas is then produced in a two-step process.

First, the air is compressed and forced into one of the two sieve beds containing a molecular sieve material made from the mineral zeolite, where nitrogen and water vapour are adsorbed. The remaining ‘product’ gas (concentrated oxygen) exits the sieve bed and is stored in a pressurised reservoir or holding tank. Simultaneously, in the other sieve bed, the pressure is reduced to atmospheric pressure, causing the nitrogen and water vapour to desorb. The desorbed nitrogen and water vapour are then exhausted back into the atmosphere. This method can produce oxygen at a concentration of 90% to 95%, which is an adequate concentration for patients who require additional oxygen to treat respiratory disease. The oxygen is administered by a nasal cannula or mask.

In order to reduce the size and weight of the machine, POCs usually supply a ‘pulse dose’ of oxygen on inhalation only. This reduces the waste of the continuous oxygen supply method used by other oxygen supply systems. POCs have a range of flow settings varying from 1 to 6, with a variable pulse dose per setting of 12 to 36 mL.

Some larger and heavier POCs are also able to produce a continuous flow of oxygen. The limiting factor with producing a smaller continuous flow unit remains the size of the sieve beds and the size of the compressor needed to produce the large volume of oxygen required. So, until the technology changes we will be left with larger and heavier continuous flow units. This is also why portable continuous flow units usually do not put out more than 3 L/min.

A large range of POCs is commercially available. Most models include the following features:

– They can be plugged into standard power supply outlet

– Supplied with or have available an adaptor to power while driving, and have separate rechargeable batteries

Most units also come with a trolley, so they can be wheeled around to help increase your mobility with the unit. The more compact units look more like a camera bag than a medical device.

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