Miscalculated drug dosages because of confusion when patients' weights are converted from pounds to kilograms are common and can result in patients' receiving potentially fatal overdoses. These errors persist despite years of adverse incidents, warnings and recommended fixes, patient-safety experts say.
And the implementation of electronic health records is exacerbating the problem. EHR systems may contain default values or rely on use of both the metric system and English units of measurements, making it easier for mistakes to occur.
“It's crazy that we still use pounds in healthcare; it's like the Stone Age,” lamented Sheila Rossi, a patient-safety analyst for the ECRI Institute, a not-for-profit based in Plymouth Meeting, Pa., that evaluates medical devices, procedures, drugs and processes. In April, ECRI listed medication errors related to confusion between the English and metric systems on its Top 10 list of patient-safety concerns for healthcare organizations. The group recommended a kilogram-only approach. “In theory, it's an easy fix,” Rossi said. "But there are hurdles.”
Errors related to measurement conversions arise from a variety of factors, including human calculation errors; EHR settings that can erroneously convert a number meant to be in kilograms into pounds, or vice versa; lack of consistent use of one measurement system; and poor communication because of overreliance on technology.
For years, the American Academy of Pediatrics, the Institute for Safe Medication Practices and the Centers for Disease Control and Prevention have promoted the sole use of the metric system, particularly for pediatric dosing and weight measurements. But not all facilities have made the switch. That is attributed to the cost of purchasing new weight scales, lack of tracking to know how often errors occur, and cultural resistance in the U.S. to switching to the metric system.
It's not uncommon for U.S. healthcare facilities to use both the traditional English system, based on units of 12, and the metric system, based on units of 10. That's a major safety problem, because weights calculated in pounds need to be converted into kilograms, and clinical staff may be asked to select either pounds or kilograms on paper forms or drop-down menus on EHRs.
Researchers in the field of how human factors affect industrial performance “will tell you that now you've shifted something to a person to figure out in a system where there is a lot of chaos and interruptions,” said Dr. Hardeep Singh, a quality and safety researcher at the Michael E. DeBakey VA Medical Center in Houston. Ideally, the system should be standardized so only one type of measure is used.
“Humans make mistakes. That's why we need additional safeguards,” he said.
It's hard to know the frequency of medication errors related to measurement system conversions because not all healthcare facilities track the problem. The Pennsylvania Patient Safety Authority, which requires mandatory reporting, issued an advisory in 2009 noting that 480 adverse-event reports cited medication errors resulting from breakdowns during obtaining, documenting or communicating patient weights. Forty-three percent of these errors led to excessive medication dosages, while 21% led to too-low dosages.
The issue is more likely to be tracked in outpatient pediatric settings, where dosing measures and instructions on packaging can lead to errors by parents and child caregivers. Every eight minutes, one child experiences an out-of-hospital medication error, according to a study published last October in the journal Pediatrics.
That study estimated that an average of 63,358 such errors occurred each year between 2002 and 2012. Nearly a fifth of the errors resulted from incorrect dosage, a problem that had increased in frequency by 67% since 2002. Another 8.2% of the errors resulted from “confused units of measure,” an 84% increase during the time period studied.
In his new book, “The Digital Doctor,” Dr. Bob Wachter, a patient-safety expert at University of California, San Francisco, described a case of this type of error at his own hospital. In 2013, a 16-year-old high school student went into code blue after being given a massive overdose of antibiotics because of a mistake associated with a weight measurement mix-up. Fortunately, the boy recovered.
ECRI's Rossi described a near-miss she had with her own toddler in 2014. He had been weighed in pounds at a Pennsylvania hospital, but his weight was entered into the EHR in kilograms, which more than doubled his actual weight. He received a dose of an antihistamine based on the erroneously high weight. Because of Rossi's familiarity with weight-based dosing errors, she and her husband ignored the doctor's dosage recommendation. “We only gave him half,” she said. “Luckily we did, because the next day the physician called and said there had been a mix-up.”
Modern Healthcare recently reported a 2013 case in Maryland in which a couple found their 2-year-old boy unresponsive and turning blue hours after the toddler was sent home from Sinai Hospital of Baltimore's emergency department for treatment of a fractured thigh bone.
His actual weight of 35 pounds—about 16 kilograms—had erroneously been entered into the EHR as 35 kilograms during the pre-surgical admission process. The nurse hand wrote “35” onto a form without noting whether it was in pounds or kilograms. When the information was copied into the child's electronic health record, the software automatically interpreted the weight in kilograms—its default setting—or 77 pounds. The boy was prescribed more than twice the normal dose of a drug at discharge.
Emergency medical technicians raced the child back to the hospital, where he was revived and readmitted, according to a report filed with the CMS.
This is not just a problem among children. Dosages of certain emergency medications and heart drugs also may be weight-based. For example, two drugs included on a list of the top 10 medications involved in wrong-weight errors compiled by the Pennsylvania Patient Safety Authority were nesiritide, which is used in patients with acute decompensated heart failure, and propofol, a sedative commonly used before surgery.
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Safety experts say that the Sinai Hospital of Baltimore pediatric incident revealed a combination of human error, failure to use consistent systems and poor handoff communications, and that it presents a learning opportunity for other hospitals. “It's the perfect intersection of humans and technology and the things that can go wrong,” Singh said. In a system standardized to use only kilograms or pounds, the potentially fatal problem could have been prevented, he added.
Bill Marella, ECRI's executive director of operations and analytics, said in the Baltimore case, the EHR was at fault—not for causing the original error, “but rather for not helping to correct it.” A weight of 77 pounds for a 2-year-old would be considered “off the charts high,” and that's something a well-designed EHR system should have flagged.
Barbara Epke, vice president for quality at LifeBridge Health, the system that owns Sinai Hospital, said that at the time of the incident, the facility already required patient weights be recorded and put into the EHR exclusively in kilograms.
The facility “took swift and decisive action” to prevent future human error, she added. The hand-written, pre-operative form was revised to use only kilograms. Scales in the hospital were set to kilogram-only, and scales that could not be set were removed from service. Preventive maintenance now includes mandatory checks to ensure scales remain locked into kilograms. Finally, the hospital said it is investigating kilogram-only scales for future use.
Those are important steps, said Michelle Mandrack, director of consulting services for the Institute for Safe Medication Practices. She and others also discourage clinicians from relying on someone else's word without weighing the patient themselves.
Marella said problems due to inaccurate measurement conversions likely happen in U.S. hospitals every day. He encourages facilities to begin tracking these incidents. But in the meantime, he recommends implementing best practices for standardization. “You don't need to capture every instance of every type of event in order to make improvements,” he said.
—with Darius Tahir