[Definition] An asthma attack with severe or progressive dyspnea even after reasonable application of conventional relieving drugs is called asthma critical state (asthma persistent state). Since the bronchial tubes are severely obstructed and life-threatening at this time, treatment should be actively carried out. Pathophysiology】In critical asthma, severe obstruction of airflow in the lower airways increases the closed volume and residual air volume of the lungs, uneven distribution of gas in the lungs, changes in thoracic pressure, increased afterload on the right and left ventricles, and interstitial edema of the lungs, which eventually leads to an imbalance in the ventilation/perfusion ratio, impaired gas exchange, hypoxemia and metabolic acidosis. Severe cases can be combined with respiratory acidosis, respiratory muscle fatigue, and even death. Clinical manifestations] Acute attack of asthma with cough, wheezing, dyspnea, profuse sweating and irritability, or even signs of terminal breathing, incoherent speech, severe cyanosis, impaired consciousness and cardiopulmonary insufficiency. If the respiratory sounds on lung auscultation are distant or no croup can be heard, it indicates severe airway obstruction, which can be life-threatening and should be resuscitated immediately. Blood gas analysis: Early manifestation of critical asthma is hypoxemia and hypocarbia due to compensatory hyperventilation. If the condition deteriorates further, the trend of increased PCO2 indicates severe airway obstruction and the child is in critical condition. Ventilatory function: most children have PEFR