EFFECTS OF INJECTION SITE AND FLOW-RATE ON THE DISTRIBUTION OF INJECTED SOLUTIONS IN AN EXTRACORPOREAL MEMBRANE-OXYGENATION CIRCUIT

The effects of injection site and flow rates on drug distribution with in an extracorporeal membrane oxygenation (ECMO) circuit were studied. Two commercially available reservoirs (30 mL and 50 mL) were connecte d to a closed ECMO circuit that did not include the membrane oxygenato r and heater. The circuit was filled with 150-170 mL of a 9.5% dextran solution in deionized, distilled water with a viscosity approximating that of blood. Flow rates of the circulating solution were set at 75 mL/min and 375 mL/min. Bordeaux red dye was injected into an ECMO circ uit at prereservoir, postreservoir, and intrareservoir sites, and samp les were obtained from these sites for analysis. Gentamicin was also i njected at the prereservoir site, with samples obtained from the reser voir, reservoir tubing, and the prereservoir and postreservoir sites. Postreservoir dye injections resulted in complete mixing at any flow r ate. Prereservoir injections at flow rates less than 250 mL/min result ed in incomplete mixing of dye, whereas intrareservoir injections resu lted in incomplete mixing at any flow rate. Gentamicin injection was a lso affected by flow rate, resulting in higher concentrations within t he reservoir and reservoir tubing. In patients on ECMO, drug distribut ion may be substantially altered if drugs are given as a bolus at prer eservoir or intrareservoir sites. Efforts should be made to select inj ection sites that will provide safe and therapeutic drug delivery whil e minimizing the effects of the ECMO circuit on drug distribution.