The oximeter is an instrument for monitoring patients receiving oxygen therapy. It displays pulse oxygen saturation (SpO2), which is a reflection of arterial oxygen saturation (SaO2). An accurate SpO2 value is essential for optimal management of the O2 flow delivered to patients. Several factors can influence this measurement and the choice of ventilatory support: the type of oximeter used, skin pigmentation and the oxygenation goal.

The objective of our study is to evaluate the impact of the oxygenation goal and the oximeter used on oxygen flows in patients with COPD (or with hypercapnia, or at risk of hypercapnia) and in patients without COPD (in particular pneumonia, pulmonary fibrosis and other pathologies) Our hypothesis is that the SpO2 target and oximeter used will have an impact on oxygen flows and that these effects will be synergistic in these different populations.

Inclusion Criteria:

• ≥ 18 years old
• On conventional oxygen therapy with SpO2 between 88 and 100% with the usual oximeter and nasal cannula.
• SpO2 < 92% in ambient air with the usual oximeter

Exclusion Criteria:

• No availability of the SpO2 signal with the usual oximeter
• False nails or nail polish
• Severe anemia documented on the last blood count during the current hospitalization (Hb < 80g/L)