Interaction of normal saline solution with ultrasound contrast medium: significant implication for sonographic diagnosis of vesicoureteral reflux

Abstract.

The sonographic diagnosis of vesicoureteral reflux with intravesical administration of ultrasound contrast media is on the rise. In few cases did we encounter rapid dissolution of microbubbles in the bladder filled with normal saline. The aim of this study was to find out whether there is any interaction between normal saline and ultrasound contrast media and, if so, to elucidate the cause for the interaction. In an in vitro experimental setup the mixtures of various normal saline solutions and a galactose-based ultrasound contrast medium (Levovist) were scanned under pre-defined parameters. The duration of contrast was determined. Oxygen concentration of the solutions was measured (pO₂ and O₂ mg/l). The US contrast medium had significantly longer contrast duration when mixed with normal saline from plastic containers rather than glass containers. The contrast duration difference was even more between normal saline from containers sealed under vacuum and those not sealed under vacuum: 0.7 and 12 min, respectively. The oxygen concentration in normal saline from vacuum-sealed containers is one-third or less that from non-vacuum-sealed containers. The high concentration of dissolved oxygen in the normal saline seems to prevent the diffusion of air from the microbubbles into the solution and thus their collapse. Desaturated normal saline has detrimental effect on microbubbles of the galactose-based US contrast medium. For the purpose of filling the bladder during contrast-enhanced voiding urosonography only normal saline solution from non-vacuum-sealed containers should be used. For practical purposes, normal saline from plastic containers is safest.