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- According to Poiseuille's law, the flow rate is proportional to the fourth power of the radius.
- Poiseuille's law describes the flow of fluids through an intravenous fluid catheter. The flow of fluid is associated with the fluid's viscosity, the pressure gradient across the tubing, and the tubing's length and diameter.
- The tubing’s radius is an important relationship. When a catheter's diameter doubles, the flow rate increases by 16 times (r4). The larger the intravenous catheter, the greater the flow. Flow is inversely proportional to fluid viscosity with increasing viscosity decreasing flow through a catheter.
- Blood viscosity increases when hematocrit increases and temperature decreases, hence, warming and diluting blood before administration increases flow rates. Increasing pressure maximizes flow as described by Poiseuille’s equation. This can be achieved by elevating IV bags. Utilizing pressure bags or pressurized infusion devices increases the pressure gradients to optimize flow rates. To maximize flow, rapid infusion is optimized by using the largest diameter and shortest length tubing. Use the lowest possible viscosity of the infused fluid and deliver it under maximum pressure.

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