Long-term oxygen therapy (LTOT) revisited: in defense of traditional LTOT systems.

In the last two decennia the stationary oxygen concentrator has been the most cost effective oxygen source for most patients using long-term oxygen therapy (LTOT). In most countries the oxygen concentrator has, therefore, largely replaced stationary oxygen cylinders with a volume of 10 litres or more. The oxygen concentrator is very convenient and safe for home use. However, for patients needing an oxygen flow rate of > 3 L/min the oxygen concentration delivered may be insufficient to meet the patient’s oxygenation needs. At present, stationary oxygen cylinders are only being used as a back up for the oxygen concentrator in case of power failure or in the rare circumstance that there is no electrical power. Small oxygen cylinders for ambulatory use are, however, still being used to a great extent. They are made of aluminium, composite or steel. Their capacity is determined by their volume and pressurization, which may go up to 200 bars in steel cylinders. Their capacity remains, nonetheless, small and decreases even further with less weight. To increase their capacity they may be supplied with a demand oxygen delivery system (DODS), but the clinical performance of these devices is highly variable and may contribute to limitations in exercise tolerance. For patients who are still active the liquid oxygen system may be a better alternative. This system is not only reliable and very convenient for both home and ambulatory use but it also provides high oxygen purity, irrespective of the oxygen flow rate used. With a continuous flow rate of 1 L/min patients may stay away from home for a whole day. Even patients with a continuous flow rate of 3 L/min may stay away from the stationary canister for as long as 10 h if they use two portable canisters. If combined with an oxygen conserving device, such as a transtracheal catheter or a DODS, this may even double. In order to reduce the full weight of