Continuous flow machines supply the patient with a continuous supply of oxygen, preferred by some patients who have very poor respiratory effort and a low oxygen level although some oxygen is wasted while the patient is exhaling and the supply can be used up quickly but do offer the patient mobility and freedom.
On-demand (also called intermittent-flow or pulse-dose) portable oxygen concentrators (POCs) are the smallest, often the size of a briefcase or picnic cooler and weigh about 2kg. They can deliver oxygen only when patients inhale which avoids any waste of oxygen when the patient exhales. Their ability to conserve oxygen and not waste it is key to keeping the units so compact as the oxygen supply will last longer. Their size allows them to be sleek and come with easy to carry bags allowing the flexibility to take these units almost anywhere, even to high altitudes, as long as there’s sufficient battery run time until the next opportunity to recharge it.
Another type of POC combines pulse and continuous-flow to meet a wider range of patient needs. These dual-supply concentrators can provide a larger volume of oxygen than smaller pulse units, however they need bigger, heavier battery supplies (otherwise the battery run time is reduced) and they are heavier, between 5 and 10kg. These dual-system converters often come with built-in wheels or a cart to make them easier to carry and move around without compromising the patient’s mobility.
There are different brands with slightly different characteristics, but the most important thing for the patient to consider when choosing which type of POC to have is their medical needs around the supply of oxygen they need.
With continuous-flow, oxygen delivery is measured in LPM (litres per minute). With pulse-flow delivery is measured by the size (in millilitres) of the ‘bolus’ of oxygen per breath, referring to the burst of oxygen released when you inhale. Other important considerations include the maximum oxygen percentage it can achieve, the number and increment of settings for adjusting oxygen flow, battery capacity and power cord options for recharging.
Your oxygen requirements during sleep is another variable. Usually pulse-flow oxygen concentrators are not used by patients while they sleep, as sometimes the machine is not able to detect when the patient is inhaling, as night-time breathing is low and shallow. Sleep apnoea patients are specifically not advised to use Pulse-flow units as they usually require a CPAP (Continuous Positive Airway Pressure) mask. For patients without apnoea, the use of portable concentrators during sleep is increasing as their preferred choice, especially with the addition of alarms and technology that detects a patient’s slower breathing during sleep and the machine will then adjusts the flow or bolus size accordingly. Continuous-flow mode is considered safer for night use when used with a CPAP machine. Some larger portable oxygen concentrators are designed to operate in both continuous-flow mode and pulse-flow mode.