Hazardous information from bedside fast-flush device test for fluid-filled pressure monitoring systems.

The fast-flush device test--based on the square-wave principle--has been used in clinical practice to test the accuracy of fluid-filled pressure-monitoring systems. One assumption with the square-wave test is that the system is a second-order approximation. To elucidate the problem, the authors compared, in vitro, a reference test method (frequency response test), valid for second-order systems, with a pure square-wave test and a fast-flush device test. They showed that the two tested systems did not have any relation to the reference system, which suggests that the second-order approximation is not valid. Therefore, the fast-flush device test cannot be used reliably in testing the total chain of catheter, tubing, transducer, and monitor for invasive pressure measurement.