The image below is an example of a rapid volume infusion device.

(a)        What are the major determinants of fluid flow through this device?

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College Answer

Pressure gradient, radius of the catheter raised to the power of 4 (r4) and length of the catheter. As described by the simplified Poiseuilles formula for laminar flow through tube

Flow α ∆ρ.r4/l


Even more simplified, Poiseuilles formula is:

Flow = (π × pressure gradient × radius4) / ( 8 × viscosity × length of tubing)

Thus, for every doubling of the radius, the flow rate increases by the fourth power, or by sixteen times. Length of tubing and viscosity matter, but are not as important.

The Rapid Infusion Catheter (RIC) is discussed in some brief detail in one of the Equipment and Procedures "required reading" chapters. It is unlikely to come up again as an examinable topic.


Sutera, Salvatore P., and Richard Skalak. "The history of Poiseuille's law."Annual Review of Fluid Mechanics 25.1 (1993): 1-20.

REETER, ALAN K., and KENNETH V. ISERSON. "A New Device For Rapid Fluid Replacement." Journal of Clinical Engineering 9.1 (1984): 37-42.