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

This prospective observational cohort study aims to investigate the relationship between intra-abdominal pressure (IAP), respiratory system mechanics, and successful liberation from invasive mechanical ventilation in adult patients admitted to the intensive care unit (ICU) following emergency major laparotomy. Increased intra-abdominal pressure may impair respiratory mechanics by reducing chest wall compliance, increasing airway pressures, and limiting diaphragmatic movement. These physiological changes may contribute to prolonged mechanical ventilation and difficulties in ventilator liberation. The study will enroll 100 adult patients who undergo non-traumatic emergency major laparotomy with primary fascial closure and require invasive mechanical ventilation upon postoperative ICU admission. Intra-abdominal pressure will be measured using a standardized intravesical technique through an existing urinary catheter. Serial measurements will be performed during the first 48 hours after ICU admission, alongside simultaneous assessments of respiratory system mechanics, including static respiratory system compliance and driving pressure. The primary objectives are to evaluate the longitudinal association between IAP and static respiratory system compliance and to investigate whether early IAP trajectories are associated with time to successful liberation from invasive mechanical ventilation within 28 days. Secondary outcomes include driving pressure, mechanical ventilation status on day 7, extubation failure, ventilator-free days through day 28, and mortality. All clinical management decisions, including ventilator settings, sedation, spontaneous breathing trials, extubation, and tracheostomy, will remain under the responsibility of the treating ICU team. No study-directed therapeutic interventions will be performed.

Inclusion Criteria: * Age 18 years or older. * Undergoing non-traumatic emergency major abdominal surgery performed through an open laparotomy. * Direct admission to the intensive care unit following surgery. * Receiving invasive mechanical ventilation through an endotracheal tube or tracheostomy at the time of postoperative ICU admission. * Primary abdominal fascial closure performed at the end of surgery. * Presence of an indwelling urinary catheter allowing intra-abdominal pressure measurement using the intravesical technique. * Availability of simultaneous intra-abdominal pressure and respiratory mechanics measurements at the initial assessment after ICU admission. * Written informed consent obtained from the patient or, when the patient lacks decision-making capacity, from a legally authorized representative or an eligible relative in accordance with applicable regulations and ethics committee requirements. * Additional written consent obtained from the patient for continued participation if decision-making capacity is regained during the study. Exclusion Criteria * Age younger than 18 years. * Elective abdominal surgery. * Abdominal surgery completed laparoscopically without an open laparotomy. * Laparotomy performed for traumatic injury. * Open abdomen or temporary abdominal closure at the end of surgery. * Planned second-look laparotomy or planned surgical reintervention within the first 48 hours. * Absence of invasive mechanical ventilation at postoperative ICU admission. * Bladder injury, previous bladder surgery, neurogenic bladder, or other urinary tract conditions that may compromise the reliability of intravesical pressure measurements. * Contraindication to urinary catheterization or inability to obtain reliable intra-abdominal pressure measurements through the urinary catheter. * Bronchopleural fistula, significant endotracheal tube or ventilator circuit leakage, or other mechanical problems preventing reliable measurement of plateau pressure and static respiratory system compliance. * Extracorporeal membrane oxygenation (ECMO) support. * Pre-existing dependence on chronic invasive mechanical ventilation. * Advanced neuromuscular disease, high-level spinal cord injury, or known diaphragmatic paralysis directly affecting ventilator liberation. * Pregnancy. * A decision for exclusively palliative care or limitation of life-sustaining treatment at ICU admission. * Refusal to participate by the patient or legally authorized representative, or inability to obtain written informed consent. * Inability to obtain simultaneous baseline intra-abdominal pressure and respiratory mechanics measurements at ICU admission.