Beware of double key-bounce errors

April 17, 2006

The Institute for Safe Medication Practices and ECRI, a medical device safety research company, are investigating a potentially dangerous problem with smart infusion pumps programming pads.

"We have received reports of unintended repeats of the same number," said Allen J. Vaida, Pharm.D., ISMP executive director. ISMP calls these double key bounces and differentiates the problem from entry errors occurring when a key is accidentally pressed twice-a problem termed double-keying errors. "This is a separate issue, which may involve a flaw in the data entry pads on smart pumps," said Vaida.

It is important that health-system pharmacists be aware of this potential problem, Vaida noted. "They have responsibility for setting up the drug-information library used to program these pumps and need to know the potential danger of incorrect programming at administration." According to a recent survey by ASHP, 32% of the nation's hospitals use smart infusion pumps. Of facilities using the smart infusion pumps, 84% reported using them through-out the hospital, and 77% reported using pharmacist-programmed drug libraries.

One report involved the Alaris SE Pump. A nurse noted an infusion pump delivering the sedative propofol at 225 ml per hour instead of 25 ml per hour. "She thought she had pressed the No. 2 key too long, causing a double-keying error," Vaida said, "but when she tested the pump, she could not recreate the error."

According to ISMP, hospitals have found that double key bounces appear to be related to pressure used to activate a pump's key, as well as to the length of time the key is held down. "They were able to duplicate the double key-bounce error only by pressing softly, or partially, on the key for a time, as one might do if programming the pump from an odd angle rather than standing directly in front of it," explained Vaida. "They found that firmly pressing a fully engaged key for several seconds, as the nurse in the other hospital had done to try to duplicate the error, did not cause a double key bounce." One hospital reported it was able to replicate double key bounce errors on both the Sigma 8000 and 6000+ infusion pumps, manufactured by Sigma International, as much as 20% of the time by partially depressing number keys to a shallow depth, according to ISMP.

ISMP is concerned that double key bounces and double-keying errors may not be detected if high levels of background noise occur while pumps are programmed and if what the agency calls confirmation bias occurs when nurses view pump screens. Pumps are generally programmed to provide an audible beep for each digit registered, so they should beep twice if either type of error occurs. In addition, a display of entered values should appear on infusion-pump screens. "Sometimes staff reported overlooking the extra digit on the screen because they saw only what they expected to see," said Vaida.

"We report on what our readers report to us," Vaida continued, adding that the agency has contacted both Cardinal Health, manufacturer of the Alaris pump, and Sigma International. "The companies have for the most part been cooperative," he said.

"Cardinal Health deals with all sources of customer complaints with an appropriate sense of urgency, performing detailed failure investigations and taking corrective actions as necessary," said Bill Murphy, senior VP for quality affairs in the clinical technologies and services division of Cardinal Health. ECRI is also investigating double key-bounce errors and has begun testing brands of infusion pumps to better understand the problem.

"We've been investigating for about six months and so far haven't determined if the problem is widespread or is more common to one pump than others," said Mark Burley, ECRI VP for forensic investigation. "Our investigation is ongoing."