Aneurysm sac pressure monitoring: effect of technique on interpretation of measurements.

OBJECTIVES The purpose of this study is to determine the accuracy of measuring pressure with a fluid filled pressure device (needle) and a non-fluid filled pressure device (catheter) inside a thrombosed aneurysmal sac after exclusion from circulation by endovascular grafting. METHODS In a static environment, consisting of a syringe to which a pressure monitoring kit was connected, experiments were performed to study the influence of the type of device (either needle or catheter) and the effect of the characteristics of the medium on the accuracy and reproducibility of pressure measurements. The pressures obtained with the needle in the different kinds of media were compared with those obtained in blood. Similar experiments were performed using a pressure catheter. Subsequently, pressure measurements were performed in a dynamic and physiological environment. This environment consisted of an artificial circulation in which an aneurysm, constructed of porcine aorta and filled with human aortic thrombus, was mounted. The pressures were compared and analyzed by Bland-Altman plots. RESULTS Under static conditions, the pressure levels obtained by a needle in blood, starch solution and thrombus were similar. Under identical conditions, pressures obtained by a catheter in starch solution were significant lower than the pressures measured in blood (P<0.05). Under dynamic pressure conditions the reproducibility of pressures obtained with the needle inserted in the human thrombus was very poor. CONCLUSION A needle pressure measuring device, inserted into media like human fibrin thrombus, does not yield accurate and reproducible results. A catheter with a tip-sensor rather than a needle is superior to study the pressure in the aneurysm sac after EVAR.