Can you do this drug calculation? With added answer, and explanation

Yesterday we invited readers to see if they could do the sort of drug calculation that nurses regularly do when giving medicine to patients through drug infusion pumps (see original post, also copied below). Congratulations to @tomhoward87, @geeoharee and @JonMendel who gave the correct answer, which is 1.2mL per hour – a figure that is actually written on the original pharmacy label (see Figure 1 at the end of this post).

Unfortunately this example is from a real-world situation, in which this correct rate was not used. The patient received the drug at a rate of 28.8mL per hour instead of 1.2mL per hour resulting in an overdose of fluoracil which contributed to their death. The patient had received, in four hours, a dose of drug that was intended to be administered over a period of four days.

The Institute for Safe Medication Practices Canada published its report “Fluorouracil Incident Root Cause Analysis” (PDF) in 2007 and found that there were a number of factors that led to the patient’s death, and the confusing label was just one aspect of this.

“The patient received fluorouracil at a rate 24 times greater than the intended rate of infusion. This resulted in an overdose of fluorouracil, i.e., the full 4 days of a high-dose protocol (5250mg) was administered over a period of 4 hours.

Seven causal chains led to an infusion rate entered as 28.8 mL/h instead of 1.2 mL/h: miscalculation; opportunity for false confirmation on label; information required to program pump not part of medication administration record; double check process failed; complex workload and multitasking; no feedback from pump; and low knowledge of hazard.”
[emphasis added]

The label included more information than was needed by the nurse to perform, or check, the calculation. Although the correct information (1.2mL/h) is visible it is competing with other bits of information that are equally prominent. If the calculation is performed, and an error is made, there is misinformation on the label (28.8mL/h) that could be used in confirming (wrongly) that the ‘right’ answer has been calculated. (The information in the  label below is taken from an example of the original label, on page 59 of this report into the patient’s death.)

In an example test, as part of the investigation, five nurses were asked to programme an infusion pump using the information in this label – three of them programmed the pump incorrectly and one entered 28.8mL/h before correcting themselves.

In ‘Designing IT to reduce drug dose error‘ Prof Harold Thimbleby (Swansea University) suggests making the important information more obvious, as in the example below.

Fluorouracil improved label

“Mock up of an improved drug bag label. As well as highlighting the required dose, we have made the expiry, the times etc. easier to read; we have also removed the 28.8 mL per day dose as we know the infusion pump on the ward has to be programmed in mL per hour. Depending on the therapy, one might choose to make different information more prominent; here, we have made the dose rate in mL per hour prominent, as the incorrect calculation of this rate was a factor in a fluorouracil overdose fatality.”

CHI+MED is a research project that is looking at ways of making the use of interactive medical devices (such as drug infusion pumps used in chemotherapy) safer. Changes to the design of the pump’s number entry interface (the bit where you type in numbers) can make it more or less likely that an error will be made. Bugs in the software can make it more likely that a correctly typed number might be misinterpreted or ignored by the machine.

Pumps aren’t used in isolation of course, they’re programmed by busy people in a high-pressure environment so it’s helpful to see medical devices in a wider context, and think about other ways in which people can be supported to use them safely. You can find out more about CHI+MED and download our (freely available) research publications, which cover many different aspects of interaction design, patient safety and ergonomics.

Original post

Here is the sort of calculation that some nurses do everyday.

In this example a patient needing chemotherapy medication is to be given the drug fluorouracil over a period of several days via an infusion pump. The pump will gradually deliver the medicine at a steady rate, and this rate needs to be entered into the pump by the nurse. What rate should the nurse use?

“A patient is to be given 5,250 mg fluorouracil at a concentration of 45.57 mg per mL over 4 days. What is the rate in mL per hour needed to program the patient’s infusion pump?

In a typical hospital environment these numbers have to be picked out from a complex background of pharmaceutical data printed 
on a drug label (see Figure 1). Poor information design makes the nurses’ task harder.”

Figure 1




This entry was posted in case studies, CHI+MED, CHI+MED people, CHI+MED research, health / medical, interaction design, medical devices, patient safety and tagged , , , . Bookmark the permalink.

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