Hemodynamic changes during acute elevation of intra-abdominal pressure in rabbits

BACKGROUND: The intra-abdominal pressure (IAP) may be increased during pneumoperitoneum for minimally invasive surgery, after high tension repairs of congenital abdominal wall defects, major abdominal surgery, liver transplantation, abdominal trauma, peritonitis or ileus. The aim of this study was to investigate hemodynamic changes during elevation of IAP using an experimental setting, which mirrors anatomical and physiological conditions of neonates and small infants as closely as possible. METHODS: In five fasted, anesthetized, mechanically ventilated and multicatheterized New Zealand rabbits, the IAP was gradually increased by intra-abdominal infusion of normal saline (total volume 1000 ml). At baseline and after each infusion of 100 ml normal saline cardiac output (CO, transcardiopulmonary thermodilution), pressure in the superior (SVCP) and inferior vena cava (IVCP), mean arterial pressure (MAP), peak airway pressure (PAP) and IAP was recorded. RESULTS: During the study, IAP, SVCP and IVCP increased significantly. IVCP was significantly higher than SVCP from timepoint 200 ml to study end. After abdominal decompression IAP, SVCP and IVCP decreased to baseline levels. Changes in MAP were not significant. CO increased significantly from baseline to timepoint 200 ml (peak value), remained nearly constant until timepoint 800 ml and decreased thereafter until the abdominal infusion ceased. After abdominal decompression CO returned to baseline level. SVCP, IVCP and PAP correlated significantly with IAP (SVCP, r = 0.73; IVCP, r = 0.97; PAP, r = 0.94; P < 0.0001). CONCLUSIONS: The hemodynamic changes caused by increased IAP cannot be recognized by routine monitoring of arterial blood pressure and transcutaneous oxygen saturation. The increase in central venous pressure may be misinterpreted as an elevation of cardiac preload. One major effect of a prolonged increase in IAP is a decreased CO.