A PaO2 of up to 8kPa (60mmHg) was the entry criterion for PaO2 for the MRC study . The main entry criterion for PaO2 for the NOT Trial was a PaO2 below 7.3 kPa (55 mmHg), although patients with a PaO2 of up to 8 kPa (60 mmHg) were included if they also had oedema, secondary polycythaemia, or significant pulmonary hypertension . The mean PaO2 of patients entering both studies was 6.8 kPa (51mmHg). The widely used cut-off PaO2 of 7.3 kPa (55 mmHg) for the prescription of LTOT in guidelines therefore describes the majority of patients entering these two studies in which LTOT improved survival.
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