FIG. 20: It was important that we could show not only that the enrolled patients had persistent hypercapnia, but that they did not have persistent decompensation. So they needed to be assessed at ≥2 weeks after resolution of hypercapnic acidosis, thus demonstrating a persistent hypercapnia with a PaCO2 of >7 kPa and a pH of ≥7.30 for at least 2 weeks preceding the assessment.[1]

The HOT-HMV trial design also stipulated that patients should have chronic hypoxia, using standard criteria that would be accepted for the provision of long-term O2 therapy, ie, a PaO2 <7.3 kPa or <8 kPa with features of secondary organ injury due to hypoxia such as pulmonary hypertension, peripheral edema, or significant nocturnal hypoxia.