Multi-infusion setups for medication administration in Intensive Care Units seem uncontrolled due to flow and pressure differences between syringe pumps. To investigate the dynamics and interaction of multi-infusion, a dedicated set-up was developed to measure the concentrations of fluids dynamically in multiple lines using absorption spectral-photometry. For feasibility testing and calibration, various dyes and concentrations were investigated to find the optimal settings. The developed method was validated and showed satisfactory results for determining mixtures of up to three different dyes in different ratios, with average recoveries of 105.0% (±11.01) for two dyes and 99.6% (±6.26) for three dyes. The method was applied in initial simulation experiments for measuring effects of manipulations in a multi-infusion set-up simulating a clinical situation. Results showed evidence for mutual influencing of separate infusion lines. The method developed for measuring the fluid dynamics of multi-infusion will contribute to a better insight and controlled administration of medications.