A portable oxygen concentrator is a device used to provide oxygen therapy to people that require greater oxygen concentrations than the levels of ambient air. It is similar to a home oxygen concentrator, but is smaller in size and more mobile. They are small enough to carry and many are now FAA-approved for use on airplanes.
Development
Medical oxygen concentrators were developed in the late 1970s. Early manufacturers included Union Carbide and Bendix Corporation. They were initially conceived of as a method of providing a continuous source of home oxygen without the use of heavy tanks and frequent deliveries. Beginning in the 2000s, manufacturers developed portable versions. Since their initial development, reliability has been improved, and POCs now produce between one and six liters per minute of oxygen depending the breathing rate of the patient. The latest models of intermittent flow only products weighed in the range of from 2.8 to 9.9 pounds and continuous flow units were between 10 and 20 pounds.
Operation
POCs operate on the same principle as a home concentrator, pressure swing adsorption. The basic set up of a POC is a miniaturized air compressor, a cylinder filled containing the sieve, a pressure equalizing reservoir and valves and tubes. During the first half of the first cycle the internal compressor forces this air through a system of chemical filters known as a molecular sieve. This filter is made up of silicate granules called zeolite which attract nitrogen molecules onto their surfaces more strongly than they attract oxygen molecules – this takes the nitrogen out of the air and concentrates the oxygen. When the desired purity is reached and the first cylinder reaches roughly 20 psi the oxygen and small amounts of other gases are released into the pressure equalizing reservoir. As the pressure in the first cylinder drops the nitrogen is desorbed, the valve is closed, and the gas is vented into the ambient air. Most of the oxygen produced is delivered to the patient; part is fed back into the sieves to flush away left over nitrogen, and prepare the zeolite for the next cycle. The atmosphere contains around 21% oxygen and 78% nitrogen; the 1% remainder is a mixture of other gases which pass through this process. A POC system is functionally a nitrogen scrubber capable of consistently producing medical-grade oxygen of up to 90%. The most important consideration for a POC is its ability to supply adequate supplementary oxygen to relieve hypoxia during normal activities and based on the patients breathing cycles. Other variables include maximum oxygen purity, the number and increment of settings for adjusting oxygen flow, and battery capacity and power cord options for recharging.
Pulse dose
Pulse dose POCs are the smallest units, often weighing as little as 5 pounds. Their small size enables the patient to not waste energy gained from the treatment on carrying them. Here the unit intermittently administers a volume of oxygen in milliliters per breath. Their ability to conserve oxygen is key to keeping the units so compact without sacrificing the duration of oxygen supply. Most of the current POC systems provide oxygen on a pulse delivery and are used with a nasal cannula to deliver the oxygen to the patient.
Continuous flow
With continuous flow units, oxygen delivery is measured in LPM. Providing continuous flow requires a larger molecular sieve and pump/motor assembly, and additional electronics. This increases the device’s size and weight. There are some units available that are capable of functioning in either mode. With on-demand or pulse flow, delivery is measured by the size of the "bolus" of oxygen per breath.
On 13 May 2009, the United States Department of Transportation ruled that air carriers conducting passenger flights of greater capacity than 19 seats, must allow travelers with a disability to use an FAA-approved POC. The DOT rules have been adopted by many international airlines. A list of POCs approved for air travel is on the FAA website.
Nighttime use
On-demand units are not advised for patients that experience oxygen desaturation due to sleep apnea, and a CPAP mask is generally advised for them. For patients whose desaturation is due to shallow breathing, the nighttime use of POCs is a useful therapy. Especially with the advent of alarms and technology that detects a patient's slower breathing during sleep and adjusts the flow or bolus size accordingly.
