Effect of two different ventilator weaning modes on patients with difficulty weaning

INTERVENTION: Participants are randomly divided using a random number table into the experimental group (PAV+ group) and the control group (PSV group). The participants in the experimental group (PAV+) will be ventilated in PAV+ mode and use PAV+ for a spontaneous breathing test. The participants in the control group (PSV) will be ventilated in PSV mode and use PSV mode for a spontaneous breathing test. The PAV+ group will be set to PAV+ mode and the support level will be adjusted to meet the patients' ventilation needs. Using PAV+ for a spontaneous breathing test, the definition of success is that the subject can tolerate 25% support. If the patient does not tolerate PAV+ mode, they are changed to pressure‐controlled ventilation (PCV) assist‐control (A/C) mode support. The PSV group will be set as PSV mode respiratory support, and the support level will be adjusted to meet patients' ventilation needs. PSV is used for a spontaneous breathing test (PSV 5 cmh2o+peep 5 cmh2o). If the patient does not tolerate PSV mode, they are changed to PCV‐A/C mode support. When the patient reaches the weaning criteria (when the condition is stable), they start weaning for half an hour per day using one of the two weaning modes. Patients are only observed during hospitalization and no follow‐up will be needed. CONDITION: Patients requiring invasive mechanical ventilation ; Respiratory PRIMARY OUTCOME: ; 1. Diaphragm activity and thickening fraction evaluated by phrenic ultrasound every morning when weaning; 2. Ventilator parameters and gas exchange indicators (Peak Inspiratory Pressure [PIP], positive end‐expiratory pressure [PEEP], work of breathing [WOB], FiO2, mechanical energy [MP] , maximal inspiratory pressure [MIP], rapid shallow breathing index [RSBI], pH, PaCO2, ETCO2, PaO2/FiO2, etc) directly observed on the ventilator data acquisition system every day when weaning; 3. First spontaneous breathing test (SBT) time, first SBT success time and extubation success time directly recorded after grouping according to the actual situation of each patient; SECONDARY OUTCOME: ; Obtained from the patient's medical records at discharge:; 1. No ventilator‐free day (VFD) within 28 days; 2. Length of stay in ICU; 3. ICU mortality; 4. Hospitalization mortality; 5. Complications after extubation; 6. Success rate and time of 28‐day machine removal; INCLUSION CRITERIA: 1. Age =18 years old 2. Patients with mechanical ventilation =48 h 3. Patients with mechanical ventilation who meet the first SBT failure (excluding iatrogenic factors) 4. Volunteer to participate in this study and sign the informed consent form. If the subject is unable to read and sign the informed consent form due to incapacity and other reasons, or the subject is a minor, his guardian is required to represent the informed process and sign the informed consent form. If the subject is unable to read the informed consent form (e.g. illiterate subjects), the witness is required to witness the informed process and sign the informed consent form