Status asthmaticus refers to a severe asthma attack that is ineffective with conventional treatment and generally lasts for more than 12 hours. Status asthmaticus is not an independent type of asthma, but its pathophysiological changes are more serious. If its severity is underestimated or the treatment measures are inappropriate, there is often a risk of death. Autopsy data of patients who died of asthma showed that the most significant abnormality was excessive expansion of the lungs, which was caused by air trapping due to diffuse airway obstruction. There are extensive mucus plugs in the airways, which are composed of mucus, desquamated epithelial cells and inflammatory cells, sometimes forming casts of small bronchi and their branches. The airway walls are thickened, with a large number of eosinophils infiltrating, and smooth muscle and submucosal gland hypertrophy and hyperplasia. The main manifestations of status asthmaticus are shortness of breath, most patients can only speak in a single tone, tachycardia, pulmonary hyperinflation, wheezing, accessory respiratory muscle contraction, pulsus paradoxus and sweating. Diagnosis of status asthmaticus requires exclusion of cardiac asthma, COPD, upper airway obstruction or foreign bodies, and pulmonary embolism. The most objective indicators for determining the degree of airway obstruction are: PEFR and (or) FEV1. Clinical signs indicating critical asthma are: worsening of the condition despite adequate drug treatment; dyspnea affecting sleep and speech; contraction of accessory respiratory muscles; altered mental status; pneumothorax or mediastinal emphysema; pulse rate>120 times/min; respiratory rate>30 times/min; pulsus paradoxus>2.4kPa (18mmHg); FEV1>0.5L; FVC<1L; PEFR<120L/min; PO2<8.66kPa (65mmHg); PCO2 higher than normal.