The British Medical Research Council (MRC) study  and the American Nocturnal Oxygen Therapy Trial (NOTT or NOT Trial) , published in the early 1980s, demonstrated that oxygen for more than 15h per day improved survival in hypoxaemic patients with severe COPD. This led to the original definition of LTOT as 'the provision of oxygen for 15 h or more a day for a prolonged period'. Most patients using LTOT do not need to be on continuous oxygen with the associated implications of restricted mobility, although survival with LTOT improves as the hours of daily use are increased from 15 h to 20h [1,2]. However, there is a small group of patients with COPD who have very severe chronic hypoxaemia, and in these patients oxygen, provided by a concentrator (and cylinders), is used continuously in an attempt to correct life-threatening hypoxaemia as well as to prevent the complications of chronic hypoxaemia.
The recommended  indications for LTOT in COPD are that:
2 PaO2is between 7.3kPa and 8kPa (55mmHg and 60mmHg), with:
(a) Secondary polycythaemia
(b) Peripheral oedema
(c) Pulmonary hypertension
(d) Nocturnal hypoxaemia.
The patient should be assessed when breathing air and clinically stable for the previous 4 weeks. These recommendations are mainly derived from the MRC study of 87 patients and the NOT Trial involving 203 patients [1,2]. These landmark studies used different designs, but in neither was the patient blinded to the treatment. This would have required a comparison with 'sham' oxygen, i.e. air, delivered to the patient, in comparison with oxygen. In the MRC study , oxygen prescribed for at least 15 h per day was compared with a control group who did not have oxygen. Mortality over 5 years was reduced from 67% in the control group to 45% in the group treated with oxygen. While the treated group was prescribed at least 15 h of oxygen, actual use was not measured. In the NOT Trial , nocturnal oxygen therapy was compared with continuous oxygen therapy. Mortality was halved at 2years, from 44% in the group receiving oxygen overnight to 22% in the group receiving continuous oxygen therapy. Mean oxygen use in the NOT Trial was 12h in the nocturnal oxygen therapy group and 18h in the continuous oxygen use group over an average period of 19months.
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