Incomplete mixing of drugs in intravenous infusions.

Ten nurses and 10 pharmacists or pharmacy technicians added hyperbaric potassium choride (KCl) 20 mEq to four types of iv fluid filled with "one liter" of dextrose, 5 g/dl, in water. Mean potassium concentrations in 240 containers filled under controlled conditions varied more than 12.4% from the mean concentration in 95% of bags and bottles. Mixing was quite incomplete, especially in flexible polyvinylchloride bags. In Viaflex bags that were not purposefully mixed, KCl concentrations during discharge varied from 71 +/- 21 (SEM) mEq/L at the beginning of fluid outflow to 11.8 +/- 3 mEq/L at the end. In a few containers, the maximum KCl concentration was 1000 times greater than the minimum. KCl mixing was improved slightly by storage of the container for 0.5 or 8 h and was greatly improved with vigorous purposeful mixing. There was little inhomogeneity of KCl in glass containers and in semirigid polyolefin containers. When KCl was added to the container during the course of fluid outflow, the maximal KCl concentrations in the discharge fluid were 21 times greater than the expected well-mixed KCl concentrations. Inhomogeneity of mixing of additives to parenteral fluids is another variable in control of drug effects in critical care and this should be minimized by forceful mixing after addition.