Blood inflow into vascular catheters following injection of saline solution and contrast medium. Model experiments

Variability in infusion pressure and continuous flow rate delivered from pressurized bag pump flush systems

Using 10 different infusion bag pressure pumps, indicated manometer pressures were compared with measured infusion pressures proximal to the flow-regulating device in an in vitro experiment. Flow rates delivered through the flow-regulating device were gravimetrically measured at different monitored pressure levels. Significant differences were found between manometer and measured infusion pressures among the tested pressure bagpumps (e.g. 500 ml bag volumepressurized to 300 mmHg manometerpressure: 219.6 +/- 7.8 to 407.2 +/- 2.7 mmHg). The infusion pressures were additionally affected by the vertical level of the infusion bag pump and by the volume of the infusion bag. Flow rates delivered through the flow-regulating device were directly correlated to the measured infusion pressure (r2= 0.9926). Differences inflow rates can have a considerable impact on maintaining catheter patency and avoidance of fluid overload and retrograde flushing into the central arterial circulation in neonates and small children. A simple manoeuvre using the invasive pressure transducer allows monitoring and adjustment of the infusion pressure in the clinical setting.

Always flush the sampling port before flushing the arterial cannula in pediatric patients

BACKGROUND

Blood sampling from arterial lines is a frequent event in anesthesia and critical care. To avoid clot formation, both the stopcock outlet and the cannula must be flushed after sampling. We investigated in a bench experiment whether fluid flow through the cannula is affected by the sequence of flushing procedures.

METHODS

Continuity of fluid delivery from a vascular cannula was gravimetrically determined using two different flushing techniques with either a syringe pump flush system or a bag flush system. The procedures comprised first flushing the stopcock towards the cannula and then towards the stopcock sampling outlet or the reverse order. Experiments were repeated in triplicate and two sets for each flushing system at hydrostatic pressures of 37 mm Hg and 74 mm Hg.

RESULTS

The main finding of the study was that flushing the stopcock towards the outlet after flushing the cannula resulted in considerable retrograde aspiration volumes and zero flow times, in particular in combination with syringe pump flush systems. At a hydrostatic pressure of 74 mm Hg, the observed zero flow time at the cannula tip amounted to (mean+/-SD) 0.1+/-0.01 min with the bag flush system and 7.7+/-0.5 min with the syringe pump flush system. The related retrograde aspiration volumes were 2.2+/-0.7 microl with the bag system and 30.0+/-2.0 microl with the syringe pump system. No backflow was recorded when the stopcock was first flushed to ambient pressure and then afterwards towards the cannula.

CONCLUSION

Opening a flush system to ambient pressure affects the continuity of fluid delivery, particularly when using syringe pump flush systems. After blood sampling, the stopcock outlet should be flushed first followed by cannula flushing.

Blood back flow into angiographic catheters

PURPOSE

Because of a potential impact on thrombus formation, this study determines the degree of blood back flow into catheters filled with different fluids.

MATERIALS AND METHODS

Catheters filled with saline or non-ionic or ionic contrast medium were placed in pulsatile circulating human blood in vitro. Catheter orientation was varied, and blood back flow was recorded.

RESULTS

When the leading end of the catheter was angled downward, blood back flow into a contrast material-filled catheter was far greater than that into a saline-filled catheter (7.0 vs 0.5 cm). Conversely, when the leading end of the catheter was horizontal, blood back flow was much greater when the catheter contained saline versus contrast media (3.6 vs 0.4 cm). Ionicity of contrast material did not affect back flow.

CONCLUSION

Back flow of blood into a catheter can be considerable and is dependent on the type of fluid within the catheter and orientation of the leading end of the catheter. Angiographic techniques adjusted to these findings are important to maintain patient safety.

Effect of catheter flush fluids on blood coagulation and aggregation of platelets

The effect upon blood coagulation and aggregation of platelets of a polysaccharide catheter flush fluid (flush fluid E) was investigated and compared with isotonic saline and Isopaque Cerebral. The result indicates that flush fluid E does not activate the coagulation system.

Blood inflow and coagulation in vascular catheters. Comparison of the effect of polysaccharide solutions, saline and contrast medium

Inflow of blood into intraarterial catheters in dogs following single and continuous injections of saline, contrast medium and polysaccharide fluids were analysed with special reference to the influence of their density and viscosity. Clot formation was also analysed and the favourable properties of one variant of the polysaccharide fluids were demonstrated.

Blood flow into vascular catheters of different size and number of sideholes. Model experiments with flush fluid injections

Using an experimental model of the arterial circulation system, inflow of blood into polyethylene catheters following injection of contrast medium and isotonic saline solution was evaluated. The experiments included an analysis of the influence of density and viscosity of the flush solutions as well as the effect of catheters of different sizes with and without sideholes.