The microcirculatory alterations is common in circulatory failure, especially during sepsis. The severity of these changes and their sustainability are responsible of multi organ failure and ultimately death. The optimization of microcirculatory flow could be a central objective of the management of patients hospitalized in intensive care.

Microcirculation includes all blood vessels of a diameter smaller than 100 micrometer. It represents the largest heat exchange surface of the body and is involved in tissue oxygenation. Microcirculatory flow is conditioned by the macrocirculation (heart rate and blood pressure) and the state of the microcirculation (thrombosis, vasoconstriction ...). The role of the CO2 in regulating microcirculatory flow is little studied. A recent work of our team and the oldest work in the literature lead to believe that CO2 has a specific role in modulating microcirculatory flow. No study to date precisely studied the impact of changes in the microcirculatory flow carbonemia .

The hypocapnia test is carried out in a standardized manner by inhalation of a mixture enriched in CO2 7% allows a significant increase in carbonemia. Hypocapnia will in turn obtained by a calibrated voluntary hyperventilation test.

Direct visualization of microcirculation by confocal microscopy is now considered the gold standard for exploring the microcirculation.

Inclusion Criteria:

• patients from achieving hypercapnia test the CHU of Saint-Etienne
• non smoking
• non diabetic
• affiliated with or entitled to a social security system
• Written consent

Exclusion Criteria:

• subjects not performing the test hypercapnia in full
• patients with dermatological pathology at the study area
• patient with Raynaud's syndrome
• Patients with known bleeding disorders
• refusal to consent