This study aims to adopt a randomized crossover design to compare the effects of end-expiratory transpulmonary pressure-guided PEEP titration and EIT-guided PEEP titration on local lung ventilation, shunt, dead space, and ventilation-perfusion (V/Q) ratio as monitored by EIT. Additionally, it will evaluate their impact on respiratory mechanics, chest wall mechanics, mechanical power, hemodynamics, gas exchange, intra-abdominal pressure, abdominal perfusion pressure, and renal perfusion. By identifying an optimal PEEP titration strategy for patients with intra-abdominal hypertension (IAH) and acute respiratory distress syndrome (ARDS), this study aims to develop a mechanical ventilation approach that maintains lung recruitment and minimizes lung injury while avoiding adverse effects on other organs. The findings could facilitate the clinical application of this strategy and benefit a broader population of patients with IAH and ARDS.

Inclusion Criteria:

1. age: 18-80 years;
2. meets IAH ≥12 mmHg;
3. meets the diagnostic criteria of the Berlin definition of ARDS;
4. PaO2/FiO2 ≤ 200;
5. within 36 hours of invasive mechanical ventilation;
6. patients or their family members were consulted, agreed to participate in the trial, and signed an informed consent form.

Exclusion Criteria:

1. Age <18 years or age >80 years;
2. uncorrected shock of any type;
3. chronic obstructive pulmonary disease, interstitial lung disease, pulmonary embolism, right heart failure, pulmonary hypertension, or severe cardiac arrhythmia;
4. pneumothorax or bronchopleural fistula or lobectomy or other surgery of the lungs within 2 weeks of surgery;
5. non-invasive ventilation or transnasal high-flow oxygen;
6. with relevant contraindications to the application of EIT (large chest skin injuries, infections, pacemaker implanters, in vivo automatic defibrillator implantation, etc.) pneumothorax, mediastinal emphysema, massive pleural effusion;
7. oesophageal obstruction, oesophageal perforation, severe oesophageal variceal bleeding, upper gastrointestinal surgery, and other factors that make it impossible to place an oesophageal pressure catheter;
8. diaphragmatic hernia, thoracic deformity; patients with obvious pulmonary hernias;
9. prolongation of prothrombin time (PT), activated partial thromboplastin time (APTT) to two times the high limit of normal values or with active bleeding in the nasopharynx;
10. severe neurological disease: intracranial hypertension or neuromuscular disease, etc;
11. pregnant and lactating women;
12. patients to be treated with ECMO;
13. re-admission to the ICU of patients who have already been included in this study, or who are participating in other clinical studies;