Characterization of Flow in Intravenous Infusion Systems

The pressure-flow (P-F) relationship for intravenous infusion systems is found to be nonlinear, and may be expressed by the mathematical model P = RLF + RTF2. The parameters RL and RT both show linear increase with tubing length. Devices have been identified with an isolated effect on RL (5 μfiter) or on RT (check valve). The total RL and RT of an infusion system may be obtained by adding the RL and RT values of component devices. The sources of the turbulence suggested by the nonlinear P-F relationship are discussed. The coefficients RL and RT may relate to actual laminar and turbulent flow conditions. Knowledge of flow characteristics can be used to evaluate and design intravenous tubing systems, particularly for high-flow intravenous fluid resuscitation in surgery or after trauma.