This is a prospective observational study to observe the diagnostic efficacy of a quantitative ultrasound assessment plan for pathological accumulation in the abdominal cavity space of critically ill patients, and to explore its correlation with patient clinical outcomes.

Intra-abdominal lesions, such as hemorrhage and inflammation/infection, often lead to pathological accumulations, posing serious challenges for critically ill patients. These lesions can rapidly induce intra-abdominal hypertension and organ damage, which may progress to hemorrhagic or septic shock, endangering patients' lives. Intra-abdominal hemorrhage, especially surgery-related hemorrhage, is difficult to detect early, and existing assessment methods like CT scans have limited applicability in critically ill patients. Intra-abdominal infections account for a high proportion of infections in critically ill patients, with concurrent sepsis or shock having high mortality rates. Despite advancements in critical care medicine, the mortality rate from intra-abdominal infections remains stubbornly high. Accurate assessment of the source and extent of infection is crucial for treatment, yet routine physical examinations have low sensitivity in critically ill patients, making imaging examinations the primary method. However, while abdominal CT is considered the gold standard, it is limited by insufficient dynamic monitoring and difficulties in patient transport. Bedside ultrasound plays a significant role in the monitoring of critically ill patients due to its portability, non-invasiveness, and real-time dynamic capabilities. It can assess sources of hemorrhage and infection, quantify the extent of lesions, and monitor hemodynamic changes. Therefore, this study aims to develop a comprehensive ultrasound assessment protocol that covers the peritoneal cavity and posterior peritoneal space. Through a prospective observational study, we aim to validate its sensitivity and specificity in diagnosing pathological accumulations such as intra-abdominal hemorrhage/infection and explore its correlation with patient clinical outcomes.

Inclusion Criteria:

• Age > 18 years old;
• Expected ICU stay ≥ 72 hours;
• Meeting one of the diagnostic criteria for intra-abdominal infection: 1) Single organ infection (such as cholecystitis, appendicitis, diverticulitis, cholangitis, pancreatitis, salpingitis, etc.), which may be accompanied by or without peritonitis, even without perforation; 2) Peritonitis, classified as primary, secondary, or recurrent; 3) Intra-abdominal abscess.

Exclusion Criteria:

• Patients with wounds, redness, swelling, bleeding, or other conditions at the abdominal measurement points that prevent ultrasound assessment;
• Patients with intra-abdominal gas accumulation that affects abdominal ultrasound imaging, making ultrasound quantitative scoring impossible;
• Patients who have not undergone abdominal CT examination within 72 hours of ICU admission;
• Patients who do not consent to participate in this study.

Critically ill patients in the Department of Critical Care Medicine at Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University