Prone Positioning Short-term Effects on Tissue Oxygen Saturation in Critical COVID-19 Patients

After obtaining consent to participate in the study, the subjects included in the study will undergo a baseline 15-minute measurement of tissue oxygen saturation (StO2) measured non-invasively on the forearm by means of near-infrared spectroscopy (NIRS). Once a baseline stable StO2 value is obtained, a provocative test, consisting of a transient vascular occlusion, will be performed. The test will allow the obtention of a local metabolic rate, and a StO2 recovery rate after the ischemic stimulus. Tissue oxygenation measurements will be performed in supine position, immediately before changing to prone positioning, and repeated after 20 minutes of stabilization, once in prone position.