Relationship of residual intraluminal to intrathrombotic pressure in a closed aneurysmal sac

Purpose: This study was undertaken to determine the relationship of residual intraluminal aneurysmal sac pressure (ILASP) to intrathrombic aneurysm sac pressure (ITASP) and to define the relationship between abdominal aorta aneurysm (AAA) size (anteroposterior or transverse diameter), volume of intraluminal thrombus, and residual ITASP. Methods: We measured ILASP and ITASP after proximal aortic neck and distal iliac clamping by placing angiocatheters into the lumen and thrombus of an excluded aneurysm sac in 41 consecutive patients. Simultaneously, mean blood pressure was recorded and aneurysm sac pressure ratio was calculated. Changes in ILASP and ITASP after clamping of the inferior mesenteric artery were recorded. In addition, correlation between AAA size, volume of intraluminal thrombus in AAA, and residual ITASP was determined. Results: Mean ILASP/blood pressure ratio was 0.40 (SD, 0.20). Mean ITASP/blood pressure ratio was 0.37 (SD, 0.23). There was a significant positive correlation of 0.47 between ITASP and ILASP (P =.002). Clamping of the inferior mesenteric artery resulted in markedly decreased ITASP in 2 patients (n = 40) and ILASP in 4 patients (n = 41). Each centimeter increase in AAA size resulted in a 47 mL increase in thrombus volume. Conclusion: Increased ILASP results in corresponding increase in ITASP, and increased AAA size is associated with increased thrombus volume. However, neither thrombus volume nor AAA size has any relationship to ITASP.