Comparing Innovative and Traditional Ventilation Strategies on Atelectasis and Prognosis in Elderly Patients

This study was divided into two parts, taking elderly patients undergoing general anesthesia surgery as the research subjects, through factorial design: 1. It was verified that in elderly patients undergoing general anesthesia surgery, innovative lung-protective ventilation strategies can reduce the occurrence of atelectasis and reduce the incidence of ventilator-related lung injury and postoperative pulmonary complications more than traditional lung-protective ventilation strategies; 2. On the basis of part one study proving that innovative lung-protective ventilation strategies can reduce the incidence of postoperative atelectasis and other complications in elderly patients undergoing general anesthesia surgery compared with traditional lung-protective ventilation strategies, further comparisons were made between the two factors of "positive pressure extubation" and "improved early postoperative respiratory training" in the innovative lung protective ventilation strategy, and whether there was an interaction between the two.

More and more people need to undergo general anesthesia surgery at least once in the lifetime, and patients who undergo general anesthesia surgery often have postoperative pulmonary complications, and the occurrence of postoperative pulmonary complications is related to the prolongation of the patient's hospital stay and postoperative mortality. This is contrary to the current goal of rapid postoperative recovery.

The International Expert Consensus on Strategies for Pulmonary Protective Ventilation states that age \> 50 years is one of the greatest risk factors for postoperative pulmonary complications. This means that even older patients with largely unimpaired preoperative lung function are more likely to develop postoperative pulmonary complications than younger patients. Therefore, the investigators set the study to elderly patients undergoing general anesthesia surgery.

The traditional lung-protective ventilation strategies commonly used to reduce atelectasis and ventilator-related lung injury during general anesthesia surgery is controversial and mixed. Based on literature review and preliminary experiments, this study focuses on extubation and post-extubation, which is a critical period of atelectasis development, combines positive pressure extubation technology with improved postoperative early breathing training, replaces the controversial continuous positive airway pressure（CPAP）support and alveolar recruitment manoeuvres in traditional lung protective ventilation strategies, and explores a new respiratory management strategy with more operability and clinical effect to reduce complications such as postoperative atelectasis in elderly patients.

This study was originally a single-center clinical study and has been registered in the Chinese Clinical Trial Registry（Registration number：ChiCTR2300071364）. It was later changed to a multi-center clinical study, so it was re-registered.

Eligibility Criteria:
Inclusion Criteria:

1. Elderly patients aged ≥ 60 years old who undergo laparoscopic abdominal surgery；
2. Body mass index（BMI） \<30；
3. American society of anesthesiologists physical status classification system（ASA）:I-III；
4. When the patient inhales air before surgery, SPO2≥94%；
5. The duration of the operation is 2-7 hours, and the pneumoperitoneal pressure is 10-14mmHg.

Exclusion Criteria:

1. Patients with acute respiratory distress syndrome or pulmonary hypertension (pulmonary systolic blood pressure ≥ 40mmHg) or bronchiectasis or lung malignant tumors
2. Patients with acute respiratory infections within one month before surgery
3. Patients who have undergone cardiopulmonary surgery
4. Receiving invasive mechanical ventilation for more than 30min within 30 days before surgery
5. Patients with peak airway pressure \> 35 cm H2O during intraoperative mechanical ventilation
6. Patients with severe organic lesions of the heart such as obvious heart failure and coronary heart disease
7. Patients with preoperative anemia (Hb\<10g/L)
8. Patients with hypoproteinemia before surgery (albumin \< 35 g/L)
9. Patients with tracheostomy and severe difficult airway
10. Patients with sleep apnea syndrome
11. Patients with intraoperative heavy bleeding (50% of the circulating blood volume is lost ≥ 3 hours)
12. Patients with mental illness, impaired consciousness and communication disorders
13. Patients who refuse to participate in this trial