In vitro model of intravenous fluid administration: analysis of vein resistance to rapid fluid delivery

Rapid fluid administration is the cornerstone of successful trauma resuscitation of patients in a state of shock. Intravenous (IV) fluid delivery is a physical intrusion into a vein which results in a complex interaction between the rigid catheter and the compliant vein. We present an experimental model of IV infusion into a vein-like compliant tube that (a) demonstrated the interdependence between fluid administration and blood flow in a compliant tube and (b) allowed investigation of the contribution of the central venous system (between the infusion site and the heart) to the total resistance to infusion flow rate. The results show that in cases with very high resistance in the central venous system a significant increase of infusion flow rate cannot be achieved just by increasing the infusion pressure. Similarly, in cases of small veins when only small catheters can be used, infusate flow rate may be increased only by using two independent infusion ports. In cases with increased tissue pressure due to edema, gravity-driven infusion may not produce sufficient perfusion of the vascular compartments. It was also shown that the vein valves do not always close, and that peripheral blood flow may continue together with the infusate fluid (e.g., when there is a small downstream resistance and infusion with a small catheter).