330 Guide Wire Sheath: A Novel Approach to Central Venous Manometry

Abstract

Combined use of manometry and ultrasound significantly reduces the risk of arterial cannulation during central line placement. We report a novel approach to manometry that eliminates the need for extra personnel and equipment by utilizing the plastic guide wire sheath from the central line kit as a manometer. We performed a bench study utilizing a traditional mercury gauged sphygmomanometer to create a series of increased pressure levels within a 1L bag of saline as the reference standard. The saline bag was cannulated with a typical central line catheter. The guide wire sheath was then straightened, marked in 0.5 cm increments and placed into a stopcock in a vertical orientation. The sphygmomanometer pressures were increased in increments of 2 mm Hg and the corresponding rise in the saline column within the guide wire sheath was recorded. The guide wire sheath can theoretically measure pressures up to 40 mm/hg provided that it is positioned vertically. If a patient’s blood were to flow over the top of the guide wire sheath, then it would be reasonable to conclude that the catheter is located in an artery and should not be cannulated in an actual clinical scenario. A correlation coefficient was calculated to assess the relationship between the device measurements and the reference standard. We obtained a total of 20 measurements. The initial measurement of 4 mmHg was then increased in increments of 2 mmHg for each subsequent reading. 19 out of the 20 measurements were included in the analysis as the novel device overflowed at 40 mmHg. The mean difference in measurement between the reference standard and the novel devices was 2.89 sd 1. 38 (95% CI 2. 23-3. 56). With respect to the 19 measurements included in the analysis, 11 (58%) had differences lower than the mean difference of 2.89. Of the 9 measurements that were greater than the mean the greatest difference was only 1.61 above the mean difference of 2.89 mmHg, with the average amount above the mean difference being only 1.22 mmH above the reference standard, sd 0.42 (95% CI 90-1. 54). We observed a strong positive correlation between the reference standard and novel device measurements (r=0. 99, p<0. 001). Table 1 shows the raw measurement data. This simple, novel method of vascular pressure measurement had strong positive correlation with reference standard values. Further studies are warranted to assess the feasibility of this tool in a variety of clinical settings.