EFFECTS OF HYPERVENTILATION AND HYPOVENTILATION ON PACO2 AND INTRACRANIAL-PRESSURE DURING ACUTE ELEVATIONS OF INTRAABDOMINAL PRESSURE WITH CO2 PNEUMOPERITONEUM - LARGE ANIMAL OBSERVATIONS

Background: The side effects of acute elevations in intraabdominal pre ssure (HAP) are related to a multifactorial etiology. Previous studies have reported that acute elevations in LAP produce an immediate incre ase in intracranial pressure (ICP). This study was designed to analyze the reasons for increased ICP during acute elevations of IAP and to d etermine the combined effects of IAP and changes in ventilation indice s on LCP and hemodynamic indices. Study Design: Five pigs were studied . A subarachnoid screw was placed for ICP monitoring. The jugular vein , femoral vein, and femoral artery were cannulated. Mean arterial pres sure (MAP), central venous pressure (CVP), ICP, and arterial pressure of carbon dioxide (PaCO2) were monitored before and after carbon dioxi de pneumoperitoneum was established at 0, 10, and 20 mmHg of IAP. Effe cts of hyperventilation and hypoventilation were recorded and compared with baseline ventilation. Cavography was performed to evaluate the m orphology of the inferior vena cava (IVC) at different levels of LAP. Multiple regression and Student's t-test were used to examine the effe cts of LAP and ventilation on dependent variables. Results: The IVC sh owed a progressive narrowing at the level of the diaphragm as LAP was increased. There was a simultaneous increase in CVP MAP, and ICP. The mean changes in ICP with hypoventilation were significantly larger tha n with hyperventilation. Conclusions: Acutely increased IAP displaces the diaphragm cranially, narrowing the IVC and increasing intrathoraci c pressure. This increases CVP and increases ICP by venous stasis and increased pressure in the sagittal sinus with decreased resorption of cerebrospinal fluid. Hemodynamic changes are directly related to the r ise in ICE Hypoventilation and hypercarbia significantly increase ICP when compared with hyperventilation and hypocarbia. Hyperventilation d oes not significantly decrease ICP during acute elevations of LAP (J A m Cell Surg 1998;187:32-38. (C) 1998 by the American College of Surgeo ns).