[Practical modalities in long-term oxygen therapy and criteria of efficacy].

Different sources of oxygen can be used in patient's homes: gas cylinders, portable liquid oxygen or a concentrator. The choice regarding source is related to the aims (nocturnal oxygenation, oxygen for rehabilitation), the length of daily treatment and the desire for patient autonomy. The selection flow rate during the day, the night and/or during exercise depends essentially on the physiological consequences of oxygen administration, planned in a precise fashion for periods not exceeding 24-48 h. Three types of tests may be retained: 1. A 30 minute day test, 2. A prolonged night study, 3. A polygraphic study. First, the short, resting, day-time, 30 minutes test measuring output from variations of PaO2, PaCO2 and pH before and after 30 minutes of inhalation; simultaneous measurements of PAP (but haemodynamic variations during the test do not carry long term predictive values). Secondly, long term studies at night: these trials may either include simple measurements, such as oxygen saturation with an ear oxymeter or more complex polygraphic measurements. Nowadays for the simple measurements with ear oxymetry, one night on ambient air and one on oxygen seems adequate in providing vital information regarding nocturnal hypoxia and its correction. Thirdly, respiratory polygraphs which provide better information on the mechanism of hypoxia but are much more difficult to use in daily practice. These polygraph studies should be reserved only for high risk sufferers, the obese and snorers. Among the exercise tests necessary to confirm that the benefit of oxygen therapy outweighs the disadvantage of carrying a portable oxygen system, is the Mac Gavin test (distance walked in 12 minutes) completed by doing blood gases to assess the indications and the efficacy of the portable system.