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To evaluate the effect of a stepwise increase in intra-abdominal pressure (IAP) on intracranial pressure (ICP) and to further define the pressure transmission characteristics of different body compartments.A prospective, nonrandomized study.A multidisciplinary intensive care unit at a university medical center.Fifteen patients with moderate-to-severe head injury.All patients were studied after the initial stabilization and resolution of intracranial hypertension. Measurements were carried out before and 20 mins after IAP was increased by positioning a soft, 15-L water bag on the patient’s abdomen.Placing weights upon the abdomen generated a significant increase in IAP, which rose from 4.7 ± 2.9 to 15.5 ± 4.1 mm Hg (p < .001). The rise in IAP caused concomitant and rapid increases in central venous pressure (from 6.2 ± 2.4 to 10.4 ± 2.9 mm Hg;p < .001), internal jugular pressure (from 11.9 ± 3.2 to 14.3 ± 2.4 mm Hg;p < .001), and ICP (from 12.0 ± 4.2 to 15.5 ± 4.4 mm Hg;p < .001). Thoracic transmural pressure, calculated as the difference between central venous pressure and esophageal pressure, remained constant during the protocol. Respiratory system compliance decreased from 58.9 ± 9.8 to 44.9 ± 9.4 mL/cm H2O (p < .001) in all patients because of decreased chest wall compliance. The mean arterial pressure increased from 94 ± 11 to 100 ± 13 mm Hg (p < .01), which allowed the maintenance of a stable cerebral perfusion pressure (82.4 ± 10.3 vs. 84.7 ± 11.5 mm Hg;p = NS) despite the ICP increase.Increased IAP causes a significant rise in ICP in head trauma patients. This effect seems to be the result of an increase in intrathoracic pressure, which causes a functional obstruction to cerebral venous outflow. Routine assessment of IAP may help clinicians to identify remediable causes of increased ICP. Caution should be used when applying laparoscopic techniques in neurotrauma patients.