Patients with severe pneumonia can develop many complications that can involve the circulatory, digestive or neurological systems. If a patient with severe pneumonia requires a blood transfusion it is mainly because of the serious complication of gastrointestinal bleeding. Severe pneumonia can be associated with acute respiratory distress syndrome and respiratory failure. Severe infection and ischemia and hypoxia can lead to acute gastric mucosal damage, stress ulcers and gastrointestinal bleeding, and excessive bleeding can lead to hemorrhagic shock and severe anemia, both of which require immediate transfusion to correct the anemia. Patients with severe pneumonia may also develop acute respiratory distress syndrome, acute liver and kidney failure, diffuse intravascular coagulation, and other serious life-threatening complications that can be life-threatening if not treated in a timely manner.