The practice of determining the amount of flush needed for the delivery of intravenous (IV) medications via a soluset has relied heavily upon tradition rather than evidence-based practice. Administering IV medications to pediatric patients usually requires the use of a soluset and IV tubing to decrease the risk of fluid overload. A nurse injects the medication into a soluset, runs it through the tubing in a timed way until the soluset is empty, and then adds a flush solution to the soluset to accommodate for the dead space of the IV tubing and complete the delivery of the medication to the patient.
Intraluminal tubing diameter and tubing length determine the dead space of the IV tubing.Standard practice at The Children’s Hospital of Philadelphia (CHOP) was to dilute the medication in the soluset with a volume of 15 to 20 mL and then flush with the same volume. As pump manufacturers changed and, therefore, pump tubing, nurses continued to use these same volumes for flushing. Nurses also used similar volumes for the gravity soluset.
If extension tubing was added to the soluset, nursing staff still infused the 15-20 mL of flush. With this practice, some of the diluted medication may be delivered to the child, but some is most likely remaining within the tubing. A laboratory study was designed to identify the amount of fluid required to flush dye through different types of IV tubing. A clinical study, which tested the results of the laboratory study, measured the concentration of drug remaining in IV tubing after delivering drug and flush.
This article describes these studies for determining the appropriate amount of flush needed to deliver ; 95% of the medication supplied by the pharmacy.Review of LiteratureThe amount of IV flush solution needed to deliver medication through soluset tubing has received little attention in the nursing literature. Most institutions that use solusets for delivering IV medications generally add an additional 20 to 30 mL flush to ensure that all of the medication clears the tubing and is infused into the child (Axton ; Hall, 1994). Since the dead space of the soluset tubing generally held between 20 to 30 mL of fluid, the practice was to flush with one time the volume of the dead space of the tubing to clear the medication through the tubing.
In the search for another method for IV administration, Axton and Hall (1994) investigated the use of the syringe pump method. In guidelines on the administration of IV medications by syringe pump, a 5 mL flush was selected to ensure that the total dose of medication was infused although the tubing chosen only held 3.8 mL. Since there was no explanation for why a 5 mL flush volume was chosen, it seems that flushing the tubing with as least one time the volume was accepted practice for assuring delivery of medication.
Reid and Frey (1992) reported a study in which two IV administration set-ups for the delivery of medications and parenteral nutrition via central lines were compared. Although the amount of flush solution utilized per day for the two techniques was studied, there was no description concerning how the decision was made on the volume of flush to recommend. Recommendations were to use consistent flush amounts and to identify volumes of tubing and add-on devices so accurate flush amounts could be utilized.An understanding of how fluids flow through tubing helps one grasp why more than the volume of the tubing is needed to flush the medication through the tubing.
Fluid flow dynamics can be characterized as either turbulent or laminar. With turbulent flow, fluid travels straight down the tubing and mixing is uniform. If tubing held 0.6 mL of fluid (dead space), and a medication was pushed forcefully through the tubing, it would take only 0. 6 mL of fluid to push the medication through the tubing. The only time turbulent flow occurs in the clinical setting is during rapid IV push of fluid (Jew, Gordin, ; Lengetti, 1997).Since the flow rate of most IV medications delivered to children is not rapid, laminar fluid flow is the prevalent pattern in the clinical setting. During laminar flow, the medication in the center of the tubing travels more quickly, while the medication along the sides slows down.
The drug spreads out as it travels through the IV tubing (Leff ; Roberts, 1992) (see Figure 1). Because of this dispersion of drug, the amount of flush recommended to move the drug through the tubing increases. A recommendation of at least 1.5 times the priming volume of the tubing system was suggested to ensure that at least 95% of a dose of medication is delivered to the patient (Jew et al. , 1997).
Because of the lack of data confirming volume of flush solution and armed with the information about the laminar flow pattern of fluids through tubing, studies were undertaken to discover how much flush volume was needed to deliver ; 95% of 1V medications.The first study was conducted in the chemistry laboratory to determine the volume of solution required to flush a colored-containing theraputic agent through the tubing. The design of the experiment was to use standard elements of intravenous drug administration (large volume pump, syringe pump, or gravity set) and to couple those elements in series with a recording spectrophotometer (Hewlett Packard 8452A Diode Array Spectrophotometer).
The spectrophotometer is a device used in clincal chemistry to meaure the concentration of substances in a solution. The spectrophotometric readings are independent of the intravenous drug administration method used. The output of the intravenous set was connected to a spectrophotometric microflow cell with a 1 mm Teflon tube that represented the venous access to the patient in the model. The outflow of the flow cell was to waste.
This study did not control for different geometry or configurations for arranging the connecting tubing.The length and diameter of the connecting tubing in each set determined the dead space (volume) of the infusion setup. A bolus of methylene blue dye was injected into the soluset and the resulting solution was flowed at rates of 24 to 240 mL/hr through the microflow cell in the spectrophotometer. The wavelength maximum of methylene blue (650 nm) was chosen for monitoring the profile of the flowing mixture.
The concentration was selected to fall within the photometric range. Once the initial mixture had emptied from the soluset, a fixed (dead) volume of flush solution was added to the device with uninterrupted flow. The second, third, and following fixed volumes were added to flush out the dye completely.The absorbency of the flowing solution was recorded at intervals of 15 seconds for a total time up to 900 seconds.
There are several general features seen in the resulting curve that is created by the diffusion of the dye in the flowing solution between the soluset and spectrophotometer. The initial region from the start of flow to the rise of the absorbency is a “lag,” and this lag corresponds to the dead volume of the tubing connecting the soluset to the spectrophotometer. If no diffusion occurred in the flowing solution, an immediate rise in the absorbency would occur when the dye solution reached the spectrophotometer and remain constant until the volume of the dye solution had passed through the flow cell, at which time the absorbency would return to baseline instantaneously.
The configuration to generate a rectangular shaped curve would require the soluset be connected directly to the spectrophotometer, as when a nurse gives an IV push medication directly into the catheter. However, inspection of the experimental curve shows a gradual rise of the absorbency to a high point at which time the absorbency begins to fall as the dye is flushed out of the connecting tubing. The gradual rise and slow fall is due to the diffusion of the dye in the flowing solution, as seen when a nurse gives the IV medication via soluset. The high point of the curve is approaching the maximum value for the dye solution (not determined experimentally). If “steady state” had been achieved, a flat or constant region would have been noted.
