The purpose of this study is to characterize microvascular reactivity on the forearm muscle using non-invasive near-infrared spectroscopy in critically ill COVID-19 patients, and to correlate its alterations with 28-day mortality in ICU COVID-19 patients.

After giving consent to participate in the study, the subjects included in the study will undergo a 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. This StO2 recovery rate will be considered as a reflection of the endothelial health of the patient.

Patients will be studied as soon as possible after admission to the ICU, and followed-up until ICU discharge or death.

Inclusion Criteria:

• Recent diagnosis of SARS-CoV2 infection
• Arterial hypoxemia and bilateral alveolar infiltrates, not explained by cardiac dysfunction or fluid overload.

Exclusion Criteria:

• Severe peripheral vasculopathy
• Raynaud's syndrome
• Skin lesions or trauma in upper limbs interfering the placement of NIRS probe and/or the occlusion tourniquet
• Deep venous thrombosis in the upper limbs

Critical COVID-19 patients with respiratory impairment admitted to the Intensive Care Unit