Insufficient oxygen concentration obtained at domiciliary controls of eighteen concentrators.

The oxygen concentration (O2%) produced by 12 type A concentrators, with a working time of 28-18,099 h, and 6 type B concentrators, with a working time of 0-3,033 h, was measured over a 12 month period in the user's home, at a flow rate of 2 l.min-1. One hundred and two measurements of O2% (mean 82.9), made at least once monthly by a visiting nurse, showed that type A concentrators were usually delivering less than 92% expected O2. Four concentrators were delivering less than 40% O2 after a working time of only 4,000 h. Sixty two measurements made by the manufacturer confirmed these findings (mean 86.8). The 18 measurements performed by the nurse on the type B concentrators showed expected O2% values (mean 93.1). Our study demonstrates the necessity of regular clinical and technical surveillance, at the user's home, during long-term domiciliary oxygen therapy and the need for the manufacturer to incorporate an alarm system monitoring the O2% into oxygen concentrators.