Variability in the concentrations of intravenous drug infusions prepared in a critical care unit

Objective: To quantify the variability in the concentration of drug infusions prepared on an intensive care unit and establish whether there was a relationship between the quality of syringe labeling and drug preparation. Design: Audit carried out over 3 weeks in May 2006 and completed in May 2007. Setting: The adult neurosciences critical care unit of a UK university teaching hospital. Interventions: Daily collections of discarded syringes containing midazolam, insulin, norepinephrine, dopamine, potassium or magnesium. Measurements and results: Residual solutions in the syringes were sampled and the concentrations measured. Syringe labels were inspected and awarded a score for labeling quality based on an 11-point scale. A total of 149 syringes were analyzed. Six of the magnesium syringes contained 4 - 5 times too much Mg2+, presumably because of confusion about converting millimoles to grams. The majority of the other infusions differed from the expected concentration by more than 10%. Magnesium infusions were least likely to be properly labeled (p = 0.012), and there was a positive correlation between quality of syringe labeling and drug preparation (p = 0.002). After the introduction of a new electrolyte prescription chart, magnesium and potassium preparation significantly improved but there was still substantial variability. Conclusions: These findings present a strong argument for the use of pre-prepared syringes or standardized drug preparation and labeling systems. They also highlight once again the difficulties healthcare professionals encounter when dealing with different ways of expressing drug concentrations.