Mixed venous oxygen saturation (SvO2) refers to the oxygen saturation in pulmonary arterial blood, which reflects the degree of tissue oxygenation and is influenced by both oxygen supply and oxygen consumption. Both a decrease in oxygen supply and an increase in oxygen consumption can lead to a decrease in SvO2. The cardiac index is calculated from the volume per beat and body surface area, and is an important indicator of circulatory efficiency, cardiac contractile performance, and assessment of cardiac pump function, which can objectively and specifically reflect cardiac hemodynamic changes. SvO2 has been clinically reported to be highly correlated with cardiac output (CO) and cardiac index (CI), and the decrease in SvO2 is caused by cardiovascular abnormalities limiting cardiac output and insufficient blood oxygen band capacity. It has been found that there is a strong clinical correlation between correlated changes in SvO2 and CI and patient survival, and that failure to increase cardiac output in the presence of significant venous hypoxemia can reduce survival. The remission phase may be without abnormal signs. The thorax is bulging during attacks, with hyperclear sounds on percussion, mostly with extensive expiratory phase predominant croup and prolonged expiration. Signs such as labored breathing, profuse sweating, cyanosis, paradoxical chest and abdominal movements, increased heart rate, and odd pulse are often present during severe asthma attacks. Routine blood tests: there may be increased eosinophils during an attack, but most of them are not obvious. If the infection is complicated, there may be increased white blood cell count and increased percentage of classified neutrophils. Sputum examination: smear is visible under the microscope with more eosinophils, acantholytic crystals formed by degeneration of eosinophils, mucus plug and clear asthma beads (Laennec beads). In case of combined respiratory bacterial infections, sputum smear Gram stain, cell culture and drug sensitivity test help to diagnose the pathogenic bacteria and guide the treatment.