A PROPOSED RELATIONSHIP BETWEEN INCREASED INTRAABDOMINAL, INTRATHORACIC, AND INTRACRANIAL-PRESSURE

Objectives: To determine the effect of acutely increased intraabdomina l pressure on pleural pressure, intracranial pressure, and cerebral pe rfusion pressure, and to clarify the relationship between these parame ters. Design: Nonrandomized, controlled study, Setting: Laboratory at a university medical center, Subjects: Yorkshire swine, weighing 15 to 20 kg, interventions: Anesthetized, ventilated swine had a balloon in serted into the peritoneal cavity and catheters placed for measurement of intracranial pressure, pleural pressure, central venous pressure, pulmonary artery occlusion pressure, and mean arterial pressure, Follo wing baseline measurements, intra-abdominal pressure was increased by incrementally inflating the intraperitoneal balloon. All parameters we re remeasured 30 mins after each increase in intra-abdominal pressure, Two groups were studied: a) group 1 (n = 9) animals had intra-abdomin al pressure increased to 25 mm Hg above baseline, then released; b) gr oup 2 (n = 3) animals underwent sternotomy and pleuropericardotomy to prevent an increase in pleural pressure with increasing intra-abdomina l pressure. Measurements and Main Results: Increase of intra-abdominal pressure to 25 mm Hg above baseline caused significant (p<.05) increa ses in intracranial pressure (7.3 +/- 0.6 [SEM] to 16.4 +/- 1.9 mm Hg) , pleural pressure (4.3 +/- 1.3 to 11.8 +/- 1.9 mm Hg), pulmonary arte ry occlusion pressure (9.0 +/- 0.6 to 14.3 +/- 0.8 mm Hg), and central venous pressure (6.6 +/- 0.7 to 10.7 +/- 0.9 mm Hg, The cardiac index (3.4 +/- 0.3 to 1.6 +/- 0.1 L/min/m(2)) and cerebral perfusion pressu re (75.6 +/- 3.6 to 62.0 +/- 6.8 mm Hg) decreased significantly (p<.05 ), whereas mean arterial pressure (82.8 +/- 3.2 to 78.4 +/- 6.6 mm Hg) remained essentially constant, Sternotomy and pleuropericardotomy neg ated all effects of increased intra-abdominal pressure except the decr eased cardiac index (1.6 +/- 0.1 to 2.5 +/- 0.2 L/min/m(2)). Conclusio ns: Acutely increased intra-abdominal pressure causes a significant in crease in intracranial pressure and a decrease in cerebral perfusion p ressure. Increased intra-abdominal pressure appears to produce this ef fect by augmenting pleural and other intrathoracic pressures and causi ng a functional obstruction to cerebral venous outflow via the jugular venous system, it is possible that the same phenomenon may be why per sons with chronically increased intra-abdominal pressure, such as the morbidly obese, suffer from a high frequency rate of idiopathic intrac ranial hypertension.