This study will provide individualized objective indicators for patients undergoing invasive mechanical ventilation. It will set specific assessment parameters for weaning and extubation for different patients, increase the success rate of weaning, avoid the damage and medical risks of re-intubation, and shorten the hospital stay. The main observation targets of this study are: whether weaning is successful; the secondary targets are: specific numerical values of diaphragmatic mobility along the midclavicular line and midaxillary line, oxygenation index, and whether re-intubation occurs within 48 hours. This study is an observational study. The expected study duration is 18 months, and there is no risk of study interruption.