A Method for Determining the Location of the Central Venous Reference Point in Subjects with Hyperinflation Lung Disease

This descriptive exploratory study was designed to identify a method for determining the most consistent extrathoracic landmark for measuring the zero reference point of central venous pressure in subjects with hyperinflation lung disease. The primary purpose of this study was to find a method to determine if the external reference point that is currently being used on patients with hyperinflation lung disease represents the true zero point of central venous pressure. The first method explored the use of cadaver subjects during post-mortem examination to determine the location of the hydrostatic zero point. This method was eliminated because a question arose concerning the possibility of organ shift after death. A second method examined subjects undergoing cardiac catheterization. Because these subjects were candidates for coronary bypass surgery none had hyperinflation lung disease. A second, and extremely limited group undergoing cardiac catheterization were those with mild to moderate hyperinflation lung disease. These subjects were being considered as candidates for the pulmonary rehabilitation program. The method tested in this study used hospitalized subjects who met the criteria for hyperinflation lung disease and who had central venous catheters. Various measurements were taken with a caliper and tape measure. Anteroposterior and lateral supine chest films were taken and the catheter tip was identified according to its anatomical position within the thoracic cavity. Computations were made to correct for the radiological magnification error. Four subjects were tested in this manner. In one subject the catheter position was aberrant. A standard extrathoracic reference point of the fourth intercostal space at the sternal margin, five centimeters below the sternum was used. The catheter tips varied from 0.5 centimeters above to 2.5 centimeters below the standard reference point. The research design used provided the desired information for this study. It is recommended that this method be used on a larger sample group to evaluate the significance of the deviations found