Basics of Hemodynamic Measurements

A critical step when monitoring cardiopulmonary interactions is ensuring that measured values are accurate and precise. This chapter deals with vascular pressure measurements. These are more prone to measurement errors than respiratory pressure measurements because gas measurements are not influenced by the force of gravity. With current technologies, vascular pressures can be measured with great precision, but the “blind box” of electronic monitors also can result in artifactual values that seemingly look real. Primary goals of vascular pressure measurements are to determine the force distending vessel walls because this gives an indication of the effective volume in the system and, second, the pressure difference between compartments because this determines blood flow. When using standard fluid-filled catheters as part of the measuring system, three factors always must be considered: zeroing, leveling, and calibrating. Changes in the intrathoracic pressure surrounding the heart and blood vessels in the chest add another element that can lead to faulty interpretations of the pressures in this region. The goal of this chapter is to review these principles and to indicate some important common errors in measurement.