What rate is best to 'keep vein open' to maintain PIVC patency?

The purpose of slow continuous infusion to keep vein open (KVO) is similar to intermittent flushing. Rinsing the peripheral intravenous catheter (PIVC) (with 0.9% sodium chloride) is thought to maintain catheter patency by preventing internal luminal (inner surface) occlusion. This theoretically reduces the formation of blood clots, bacterial biofilm, drug precipitate (interactions between incompatible fluids/medicines), and reduces the risk of occlusion.1 (Infusion Nurses Society 2016).

The Infusion Nurses' Society (2016)1 indicates that a standard infusion rate, a so-called one size fits all, cannot be determined and needs to consider the age of the patient, fluid and electrolyte balance, and the presence of comorbidities.

If a patient requires only an intermittent infusion of medication (but not hydration), an intravenous solution is infused at a slow rate (5-20 mL/hr depending on the patient) between medication doses to keep both the catheter and vein 'open' and functional.

Preclinical bioengineering studies have demonstrated the importance of flow and pressure (shear force) on the blood components and vein. Researchers have shown that low pressures within the vein (i.e., during low blood flow or stasis) can induce adhesion of white blood cells (WBCs) to the vein endothelium and then platelet activation promoting inflammation, coagulation, and catheter failure.2,3 A KVO Infusion may reduce areas of stasis and risk of coagulation.

Recent preliminary research4 into the optimum KVO infusion rate for PIVCs demonstrated that a low flow rate was associated with areas of blood resistance around the PIVC tip, creating a recirculation zone that may actually promote clots near PIVC tip. An infusion rate nearer that of the blood flow rate in the cannulated vessel was associated with less resistance, reduced stasis, and lower risk of coagulation.

Conversely, other research has demonstrated the impact of excessive forces of the vessel endothelium.5 This suggests that intermediate shear forces (24 dynes/cm2) represent a sweet spot for injection (bolus) and infusion.



Take home message

There is currently no specific guiding principle for choosing between intermittent flush and KVO Infusion. From research to date, it seems that excessively low and high shearing forces contribute to platelet and/or endothelial activation.

It may be that a combination of steady KVO infusion and gentle intermittent flushing is the best way to safely keep PIVCs working.



1. Infusion Nurses Society. Infusion Nursing Standards of Practice. Journal of Infusion Nursing, 2016;39:Suppl.

2. Nifong TP, & McDevitt TJ. The effect of catheter to vein ratio on blood flow rates in a simulated model of peripherally inserted central venous catheters. Chest 2011;140(1):48-53. doi: 10.1378/chest.10-2637.

3. Ploppa A, Schmidt V, Hientz A, Reutershan J, Haeberle HA, & Nohe B. Mechanisms of leukocyte distribution during sepsis: an experimental study on the interdependence of cell activation, shear stress and endothelial injury. Crit Care 2010;14(6):R201. doi: 10.1186/cc9322.

4. Doyle B, Kelsey L, & Shelverton C. 2019. Computational study of 'KVO' in peripheral intravenous cannulas." Vascular Access 2019;5(2): on line. (Abstract)

5. Piper R, Carr PJ, Kelsey LJ, Bulmer AC, Keogh S, & Doyle B. The mechanistic causes of peripheral intravenous catheter failure based on a parametric computational study. Sci Rep 2018;8(1):3441. doi: 10.1038/s41598-018-21617-1.


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