Parameters:
(1) viscosity of fluid
(2) pressure applied
(3) control devices regulating flow (valves, clamps, etc.)
(4) diameter of infusion needle (assuming rate limiting diameter in system)
(5) number of infusion points
From Poiseuille's law (see 41.26.01) it can be seen that flow can be increased by:
(1) higher pressure
(2) lower viscosity
(3) higher needle diameter
(4) shorter tubing
The viscosity of the fluid can be important when infusing a fluid like blood. The lowest viscosity fluid that can be infused is around that of normal saline, since hypotonic fluids can result in hemolysis.
To infuse fluid rapidly, all flow control devices should be completely open so there is no impediment to flow.
The infusion rate increases proportionate to the amount of pressure applied. Increased pressure can be provided by:
(1) elevating the infusion bag (gravitational)
(2) squeeze the bag
(3) apply a pressure covering
The limits to pressure include:
(1) pressure tolerance of infusion system
(2) lysis or breakdown of cellular elements being infused
(3) ability of blood vessel to tolerate the pressure (large, nondiseased blood vessel better able to tolerate a higher pressure)
Flow rate is affected by the radius of the needle raised to the fourth power. If you need to increase the rate of flow by a factor of X (for example, 2 to double the flow rate):
radius of needle in mm needed to increase flow by a factor of X =
= ((X increase in flow)^0.25) * (radius of current needle in mm)
The more access points the faster fluid can be infused. This tends to be limited by the number of accessible blood vessels that there are. Four infusion points may be the practical limit that can be achieved.
