Effect of Lateral Positioning on Central Venous Pressure

This experimental study was conducted to investigate the effects of lateral positioning on central venous pressure. It was hypothesized that lateral positioning would not significantly change the central venous pressure so long as the subjects were placed on the same horizontal plane for both supine and lateral measurements. It was also hypothesized that the length of time spent in the lateral position would not alter the pressure. It is recognized that several factors do indeed play important roles in the maintenance of central venous pressure. The effect of one particular influencing factor, gravity, was central to this study. The difference in venous pressure due to changes in the length of the effective hydrostatic columns have been well demonstrated in studies in upright and supine subjects. From these studies it was reasoned that theoretically, central venous pressure should not be altered by change in position from supine to lateral so long as the horizontal plane is held constant since in this situation the effective hydrostatic columns do not change. Central venous pressure measurements were done on three horizontal positions and results compared. An experimental research design was used. The experimental variables in the study were the left and right lateral positions. The dependent variable was the central venous pressure. A convenience sampling of ten postoperative patients was included in the study, each patient acting as his own control. The effect of positioning on venous pressure was tested byplacing subjects on the supine and lateral positions, and central venous pressure readings taken at 15-minute intervals over a 45-minute period for each position. The extrathoracic reference point chosen for the supine position was the fifth intercostal space, mid-axillary line, and the level of the fourth intercostal space within the right sternal border for the lateral positions. Horizontal lines extended from these pointes were demonstrated by dissection of cadavers to both go through the right atrium. Results of the study did not support the hypothesis and showed that lateral positioning did indeed effect a change in central venous pressure and this change was found to be statistically significant at the .001 level (F = 473.56). A mean drop of 5.38 cm. ^0 from baseline supine values was observed with left lateral positioning and a drop of 3.65 cm. H2O for the right lateral position. A trend with time was observed on all positions--lowest values were observed at the 30- minute interval. Although the results of the study did not support the hypothesis it was concluded that since the results were very significant, these could be projected to include a larger population. One can take central venous pressure measurements while the patient is on the 90° lateral position and expect that the pressure readings on the lateral positions will be lower than baseline supine readings. For accurate interpretation of venous pressures it will then be necessary to obtain baseline readings for both supine and lateral positions with which to compare subsequent readings