Intra-Abdominal Pressure, Respiratory Mechanics, and Ventilator Liberation After Emergency Major Laparotomy

Background and Rationale Increased intra-abdominal pressure (IAP) may adversely affect respiratory mechanics by displacing the diaphragm cranially, reducing chest wall compliance, and increasing airway pressures. These physiological changes are particularly relevant after emergency major laparotomy, when intra-abdominal sepsis, intestinal edema, fluid resuscitation, and abdominal fascial closure may contribute to elevated IAP. Although previous studies have demonstrated associations between intra-abdominal hypertension and respiratory dysfunction in critically ill patients, prospective evidence examining simultaneous changes in IAP and respiratory system mechanics specifically after emergency major laparotomy remains limited. The relationship between early postoperative IAP trajectories and subsequent ventilator liberation also requires further investigation. Study Design and Measurements This single-center, prospective observational cohort study will investigate longitudinal relationships between IAP, respiratory system mechanics, and ventilator liberation in mechanically ventilated adult patients following emergency major laparotomy. Serial IAP measurements will be obtained using a standardized intravesical technique through an existing urinary catheter. Respiratory mechanics will be assessed at corresponding time points during the first 48 hours after intensive care unit admission. Measurements will be performed under standardized conditions whenever clinically feasible. Static respiratory system compliance will be calculated from tidal volume, plateau pressure, and total positive end-expiratory pressure. Because esophageal pressure will not be measured, lung and chest wall compliance cannot be evaluated separately. Clinical management, including mechanical ventilation, sedation, fluid administration, spontaneous breathing trials, and extubation decisions, will remain entirely under the responsibility of the treating intensive care team. No study-directed therapeutic interventions will be performed. Analytical Approach Repeated measurements will allow the evaluation of both between-patient differences and within-patient changes in IAP and respiratory system mechanics. Linear mixed-effects models will account for the correlation between measurements obtained from the same patient. Early postoperative IAP trajectories will also be characterized using measures of pressure magnitude, cumulative exposure, and temporal change. Their relationship with successful ventilator liberation will be evaluated using competing-risk analysis, with death considered a competing event. The study aims to improve understanding of the physiological interaction between intra-abdominal pressure and respiratory system mechanics and to provide evidence supporting the identification of patients at risk of prolonged invasive mechanical ventilation after emergency major laparotomy.