Endotension in the Closed Aneurysm Sac during Aortic and Iliac Cross Clamping: Implications of Pressure and Flow Measurements

PURPOSE: To relate the mean and pulse pressures in the cross-clamped aortic aneurysm sac to the systemic pressures during open repair (OR) of abdominal aortic aneurysm (AAA). To correlate the intrasac pressures to the number of bleeding lumbar arteries (LA) and the flow pattern of the inferior mesenteric artery (IMA). METHODS: In a prospective study of 55 patients (45 men; median age 69 years, range 47-84) undergoing open repair, the IMA flow and the mean pressure in the aneurysm sac (ASP(mean)) were measured before and after aortic and iliac artery cross clamping. The systemic mean pressure (SP(mean)) was recorded simultaneously. The aneurysm sac (ASP(pulse)) and systemic pulse pressures (SP(pulse)) were calculated, as were the mean pressure ratio (ASP(mean)/SP(mean)) and the pulse pressure ratio (ASP(pulse)/SP(pulse)). Values are given as the median (range). RESULTS: Cross clamping of the proximal aortic neck significantly reduced the mean pressure to 31 mmHg (14-64), with a pressure ratio of 0.39+/-0.14; the pulse pressure decreased to 0 mmHg (0-13) (p<0.001). Additional cross clamping of the iliac arteries did not alter the pressure levels any further. In the patent IMA (n=23), an orthograde median flow of 43 mL/min (2-135) was measured; sequential cross clamping of the aorta and iliac arteries reduced the flow to -6 mL/min (-130 to +21) and -3 mL/min (-120 to +22), respectively. There was no correlation between the pressure ratio and IMA patency, its volume flow, or the number of backbleeding lumbar arteries. CONCLUSIONS: The aneurysm sac is still pressurized with no pulsatility after cross clamping during open AAA repair. The aneurysm mean and pulse pressures did not correlate to the number of backbleeding lumbar arteries. Finally, the pressure ratios did not correlate to the highly variable IMA flow pattern during aortic cross clamping.