Effects of increased intra-abdominal pressure upon intracranial and cerebral perfusion pressure before and after volume expansion.

OBJECTIVE: To study the effects of elevated intra-abdominal pressure (IAP) upon intracranial (ICP) and cerebral perfusion pressure (CPP) before and after intravascular volume resuscitation.
MATERIALS AND METHODS: Intra-abdominal pressure was increased in five anesthetized swine by inflating an intraperitoneal balloon until the IAP was 25 mm Hg above baseline. Intravascular volume was then expanded and finally abdominal decompression was performed. Changes in ICP and systemic and pulmonary hemodynamic parameters secondary to increasing IAP were measured. The effect upon CPP was derived from these measurements. PaO2 and PaCO2 were maintained relatively constant by increasing ventilatory rate.
MEASUREMENTS AND MAIN RESULTS: Elevated IAP significantly increased ICP (7.6 +/- 1.2 vs. 21.4 +/- 1.0), pleural pressure and central venous pressure; whereas cardiac index and CPP (82.2 +/- 6.3 vs. 62.0 +/- 10.0) decreased significantly. Intravascular volume expansion further significantly increased ICP (27.8 +/- 1.0), and significantly increased both mean arterial pressure (83.4 +/- 14.0 versus 103.4 +/- 8.9) and CPP (75.6 +/- 9.0). Abdominal decompression returned ICP (11.2 +/- 1.8) toward baseline and further increased CPP (79.8 +/- 9.7).
CONCLUSIONS: Elevated IAP increases ICP and decreases CPP and cardiac index. Volume expansion further increases ICP yet improves CPP via its greater positive effect upon mean arterial pressure (*p < 0.05, analysis of variance. All measurements are mean +/- SEM in mm Hg).