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

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.

Audit carried out over 3 weeks in May 2006 and completed in May 2007.

The adult neurosciences critical care unit of a UK university teaching hospital.

Daily collections of discarded syringes containing midazolam, insulin, norepinephrine, dopamine, potassium or magnesium.

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 Mg(2+), 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.

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.