Potassium maldistribution revisited

Abstract

Background: This study investigated maldistribution of concentrated 15% potassium chloride after injection into one-liter, flexible, Ringer’s lactate bags.
Methods: Twenty milliliters of concentrated 15% potassium chloride was injected into suspended, flexible, liter bags of Ringer’s lactate. The potassium was injected by hand, over either four (“fast”) or twenty (“slow”) second periods. The effect of two successive bag inversions on maldistribution was also investigated. A simulated infusion at 600 ml per hour was controlled using a volumetric pump. Sampling occurred at 5-minute intervals for the first 20 minutes and at 10-minute intervals thereafter until 90 minutes. Potassium concentrations were measured using an accurate, calibrated wide range analyzer not requiring specimen dilution. This experiment was repeated once. A duplicate set of experiments was performed with Bonney’s blue dye added to the potassium concentrate. Bonney’s blue distribution was evaluated visually.
Results: Significant maldistribution occurred. Maldistribution was not dependent on the injection rate. After 20 to 30 minutes of commencing the infusion, maldistribution resulted in delivery of up to 64 to 85% respectively of the available potassium. Two bag inversions effectively homogenised the solution. The distribution of Bonney’s blue stained concentrated potassium was inconsistent with measured potassium concentrations.
Conclusions: In cardiac and other surgery, point of care potassium supplementation is frequently required. Anaesthetists should be cognisant of eliminating not only errors of substitution, but also maldistribution of concentrated potassium. Potassium infusion rates should be controlled, preferably using an electronic infusion controller.

Keywords: potassium, hyperkalemia, anaesthesia related death, drug error, maldistribution, layering, complication, preventable, mixing, homogenization, mortality, magnesium, dye, indicator, mistake