The purpose of this study is to investigate in vitro the effects of the flush volumes and concentrations of heparin-saline solutions in maintaining indwelling intermittent (“heparin lock”) injection sites.
Samples from simulated heparin locks to maintain the patency of established intravenous pathways were collected under selected flushing conditions. The Hagen-Poiseuille equation for the flow of a fluid through a tube was used to assess the effects of the concentration of the flush solution, flush speed, tube type and catheter conditions when replacing a pre-existing solution in the tube.
It was found that the observed fluidity of the flush solution in the tube was similar to that predicted by the Hagen-Poiseuille equation, if a small difference between the density of the pre-existing solution and that of the flush solution existed. Comparisons of the results for the replacing ratios of the pre-existing solution by the flush solution revealed the ratio in a coiled tube to be lower than that in a straight tube at the initial phase. Under each of the conditions tested, the flush procedure with the double volumes of a add-on device (two-fold V0) demonstrated a more than 90% replacing ratio. The remaining percentages of heparin concentration in the small diameter and large-diameter catheters were 10.9% and 14.6% after drawing the catheter volume (V0) of the blood backflow into the catheter. However, the percentages were not detectable and 2% after drawing twofold V0, respectively.
Our results indicate that. the Hagen-Poiseuille equation can determine the necessary volume of the heparinized flush solution, based on several factors, including the diameter of the tube or catheter and the V0. To precisely maintain the patency of the heparin locks while minimizing the influx of flush solution to the blood, the use of a small-diameter tube and a large-diameter catheter, and two-fold V0 of 10units JP14 sodium heparin per milliliter of normal saline solution is suggested when there is no flush of the heparin lock with normal saline.
