Hypoxemia due to respiratory distress in Covid-19 is the deadliest complication in this disease. SARS-CoV-2 lungs infection incites several pathological mechanisms, such as loss of ventilation/perfusion mismatch, no vasoconstriction in response to hypoxia, and an important increment of coagulopathy in the lung alveoli. Therefore, a close relationship occurs of lung injury after virus infection, the resultant hypoxemia which provokes a systemic inflammatory response syndrome, and an acute respiratory distress syndrome (ARDS). The cytokine storm, due to excessive activation of immune cells which generates pro-inflammatory cytokines, is a main factor to explain symptoms worsening in Covid-19 disease, leading to ARDS and death. It is well-known that a close relationship exists among lung damage, hypoxemia and the cytokine storm.