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Factors affecting the concentration of electrolyte infusions prepared from stock solutions
  1. Thomas M Donaldson1,
  2. Vaithianadan Mani2,
  3. Daniel W Wheeler1,2
  1. 1School of Clinical Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
  2. 2Division of Anaesthesia, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
  1. Correspondence to Dr Daniel W Wheeler, University of Cambridge Division of Anaesthesia, Box 93, Addenbrooke's Hospital, Hills Road, Cambridge CB2 0QQ, UK; dww21{at}


Background Wide variation in the concentrations of electrolyte infusions prepared from stock solutions has previously been reported. Layering of viscous stock electrolyte solutions in their diluent can lead to high concentrations being delivered during the infusion, resulting in potentially very serious medication errors which have caused deaths.

Objective To determine the safest way of preparing homogenous electrolyte solutions for parenteral infusion.

Methods The study examined how the concentration of potassium and magnesium varied during infusions after concentrated stock solutions had been diluted to 400 mmol/l with 0.9% sodium chloride. It also examined the use of syringes compared to polyvinyl chloride (PVC) bags, agitating vigorously with a ‘vortex’ mixer compared to inversion, and the influence of allowing the infusions to stand for 24 h before administration. The study was conducted in November 2009.

Results It was found that, in general, the concentrations of potassium and magnesium solutions are less variable if they are prepared in PVC bags rather than syringes. Vigorous mixing of concentrated stock solutions with diluent and allowing preparations to stand for 24 h also improved the homogeneity of the infusions. However, even with meticulous preparation, some infusions deviated from the expected concentration by more than 10%.

Conclusion It is recommended that electrolyte infusions are prepared and provided by the pharmaceutical industry in prefilled syringes or bags. Given the likely cost of these products, an alternative would be to prepare infusions in pharmacy in advance, using PVC bags rather than syringes, and that they should be agitated vigorously with a ‘vortex’ mixer.

  • Electrolytes
  • administration and dosage
  • infusions
  • intravenous
  • intensive care units
  • statistics and numerical data
  • medication errors
  • prevention and control
  • syringes
  • anaesthetics
  • adult intensive & critical care
  • paediatric intensive & critical care
  • clinical pharmacology
  • quality in health care

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  • Funding This work was funded by the Association of Anaesthetists of Great Britain and Ireland. The work was independent of the funders

  • Competing interests None of the authors has a competing interest to declare. The Postgraduate Medical Centre at Addenbrooke's Hospital, Cambridge, has previously received an unrestricted educational grant from Cardinal Health, manufacturers of infusion devices.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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