An In Vitro Analysis of Central Venous Drug Delivery by Continuous Infusion: The Effect of Manifold Design and Port Selection

BACKGROUND: Central venous catheters are used extensively in anesthesia and critical care. Multiport manifolds allow for simultaneous administration of multiple medication infusions into a common central venous catheter lumen. The structures of such manifolds vary considerably. In this study, we quantitatively compared, in a laboratory model of continuous drug infusion, the drug delivery dynamics of a traditional stopcock manifold and a microinfusion manifold constructed to minimize dead volume. METHODS: A syringe pump infused a saline carrier solution at a low flow rate frequently used in an intensive care unit (10 mL/h) through a multiport manifold connected to the 16-gauge lumen of a standard 16-cm triple-lumen catheter. The model drug methylene blue (3 mL/h) joined the carrier flow at the first, second, or fourth stopcock of a traditional manifold or 1 of 2 positions in a microinfusion manifold, a new device designed to minimize dead volume. Effluent samples were collected every minute for quantitative spectrophotometric analysis of delivery onset and offset. RESULTS: Onset and offset times differed significantly among individual ports of the traditional 4-stopcock manifold. There was also a significant difference between the 2 ports of the microinfusion manifold, but this was less pronounced. Both ports of the microinfusion manifold yielded delivery dynamics that were similar to the most downstream port of the 4-stopcock manifold. There was good correlation between dynamic data and dead volume for each of the manifolds. CONCLUSIONS: Using a traditional stopcock manifold, port selection significantly affects drug delivery dynamics for continuous infusions. The findings provide quantitative support for the concept that the most critical infusion should join the system at the manifold port closest to the patient. Port selection was less important for the microinfusion manifold and dynamics were faster compared with the second and fourth ports of the stopcock manifold. The smaller dead volumes of the microinfusion manifold minimize unwanted delays in drug delivery onset and offset allowing more precise control over drug delivery by continuous infusion.