The fast flush test - Is the clinical comparison equivalent to its in vitro simulation?

Objective. An in vitro simulation of the fast flush (FL) test has previousl y been used to prove that the FL test measures the dynamic response of enti re the blood pressure monitoring system. This simulation has also been used to confirm that the FL test is equivalent to the "gold standard" test for determining dynamic response, namely the square wave (SW) test. The conditi ons of the iii vitro simulation call be reproduced in vivo during cardiopul monary bypass (CPB) and circulatory arrest. Therefore the present objective was to verify that the previous conclusions about the validity of the FL t est, obtained from an iii vitro model, are equally valid when applied to in vivo clinical conditions. A secondary objective was to determine whether t he patient's arterial tree ha, any affect oil the dynamic characteristics o f fluid-filled manometers. Methods. Fourteen patients were studied during s urgery that required CPB. We measured the dynamic response of the fluid fil led arterial manometer during pulsatile conditions prior to the initiation or CPB, and then repeated the measurements during non-pulsatile CPB. In fou r of the fourteen patients we measured the dynamic response during circulat ory arrest. A manometer, consisting of a fluid-filled tubing component, mea sured the patient's arterial blood pressure as well as the damped sinusoida l wave form created by the fast flush tests. The fluid-filled tubing was co nnected to a transducer (Utah Medical Products, Inc., Midvale, UT). The art erial pressures and the results of flush testing were recorded and displaye d by a monitor (Marquette 7010, Marquette Electronics Inc., Milwaukee, WI). In an additional three patients we measured the dynamic response of thc ma nometer in vitro and then in vivo. Results. The dynamic response of the art erial pressure measuring system was the same during normal pulsatile flow, CPB and circulatory arrest. In addition, the dynamic response of the fluid- filled manometer was the same in vivo as in vitro. Conclusions. The clinica l conditions during CPB and particularly during circulatory arrest duplicat e the in vitro FL test simulation model. These results confirm the validity of the FL test in vivo as well as proving that the dynamic characteristics of a fluid-filled manometer are independent of the patient's vasculature.