Factors Determining Flow Rates Through Catheters

Several factors determine the rate of flow of fluids through a peripheral or central catheter. These factors can be expressed using the Hagen Poiseuille's Law. It states that the flow (Q) of fluid is related to a number of factors: the viscosity (n) of the fluid, the pressure gradient across the tubing (P), and the length (L) and diameter(r) of the tubing.

Important points:

  • Tubing diameter: An important and frequently cited relationship is that of the tubing's radius. Doubling the diameter of a catheter increases the flow rate by 16 fold (r4). The larger the IV catheter the greater the flow.
  • Tube Length: Flow is inversely proportional to the length of the catheter
  • Fluid Viscosity: Flow is inversely proportional to the viscosity of the fluid.Increasing viscosity decreases flow through a catheter.
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