The theory and practice of retrograde infusion: influence of tube diameter on drug delivery

This work identifies a model for the flow dynamics of retrograde drug infusion, thereby helping to clarify the influence of variables on drug dilution in the apparatus and hence drug infusion rate. The study is a 2(3) factorial design that focuses on the influence of tube diameter (0.065 vs. 0.120 inches) in conjunction with changes in injected drug volume (2.0 vs. 5.0 ml) and iv flow rate (2.0 vs. 10.0 ml h-1). Each of the three variables was shown to exert a statistically significant (p = 0.01) effect on the total volume of fluid necessary to clear a dose from the retrograde apparatus. In all cases studied, smaller diameter tubes, larger injected drug volumes, and slower iv flow rates decreased the total volume fraction (F0.95). Within the confines of the study, practitioners may use an F0.95 value of 1.5 to predict the time at which a patient's retrograde drug infusion is likely to be complete. This, in turn, may be used to facilitate proper timing of blood sampling for therapeutic drug monitoring as well as other pharmacokinetic manipulations.