Dosage Calculations| Dosages May Be Accurate, but the Ways to Figure Them Aren’t

Dosage Calculations| Within the next several weeks, the hospital’s Emergency Department should receive a new scale. It’s not just any scale; it will be used to weigh stroke and other patients who need potentially lifesaving but also risky blood-thinning medications.

It’s a much-needed solution. A patient’s weight, after all, determines the precise dose a stroke or heart patient needs for life-saving clot-buster drugs. But, pressed to shave seconds off their responses to these patients, emergency room clinicians everywhere have long estimated the patient’s weight, and based their dosage calculations and orders on it.

A small UCH study, however, found 77 percent of the estimates are incorrect, so the wisdom of purchasing a scale to ensure a true reading seems indisputable.

Yet adopting a simple scale is a perfect symbol of the delicacy of decision making at a hospital like UCH, which practices evidence-based medicine. The concern over taking the time to weigh a patient in an emergency continues.

It’s undeniably important to obtain a weight that is as accurate as possible before administering so-called “clot-busting” medications like heparin or tissue plasminogen activator (tPA), which is frequently used to treat stroke victims. Too little medication and the clot might not dissolve; too much and the patient could hemorrhage.

Estimating a patient’s weight has left no evidence to conclude with certainty that the practice has led to poor patient outcomes. As a result, physicians, nurses, radiologists, pharmacists and others who deliver critical care still must balance the benefits of obtaining a precise weight against the need to deliver care as quickly as possible to a stroke victim losing brain cells with each tick of the clock.

UCH’s Emergency Department decided to purchase the scale, which will be placed in the ambulance bay just outside the entrance (see sidebar) only after a multidisciplinary team conducted a retrospective study of stroke patients who received tPA at UCH. The team ultimately produced a poster presentation of its work, and have submitted a manuscript of their study to the Journal of Emergency Nursing.

The study showed the weight estimations for roughly three-quarters of the patients were incorrect, although the dosing errors that resulted from the differences between the estimated and actual weights were not statistically significant.

Further clouding the question is the fact that no one has established an acceptable range of error in dosing tPA, said the hospital’s Clinical Director of Stroke Services Alex Graves, MS, ANP, a member of the team that conducted the study.

“It’s hard to make a [policy] decision without a reference range,” she said.

Graves said she’s all for using the scale to weigh patients if it leads to better outcomes. But she is concerned that getting a stroke patient on the scale and calculating his or her weight could delay treatment.

The hospital aims to administer tPA to stroke patients who need it no longer than 60 minutes after they arrive at the door of the ED. That hour already is crammed with blood draws, labs, a trip to CT imaging and a host of other diagnostic tasks.

“I’m excited to have the scale, but I worry about adding steps,” she said. “Having one more thing on the to-do list is concerning. We don’t want to add much time.”

In fact, hospitals are not required to weigh patients before they administer weight-based medications. The discussion arose at UCH nearly two years ago, Graves said, after the Joint Commission completed the biannual on-site visit required for the hospital to maintain designation as a Primary Stroke Center (PSC).
The hospital earned PSC redesignation, but a Joint Commission surveyor asked if providers obtain actual or estimated weights from stroke patients.

“The surveyor said we couldn’t be cited [for estimating weight], but there was a strong recommendation that we get the actual weight,” Graves said.

Meanwhile, two nurses in the Neuro ICU with certifications in critical care, Anna Verhage and Brian Richlik, noticed their unit was admitting more stroke patients.

Because the Neuro ICU weighs all its patients on admission, they were able to compare stroke patients’ estimated and actual weights.

“We noticed big fluctuations in tPA dosing,” Ver Hage said. She and Richlik couldn’t determine if under- or overdosing the patients had an effect on patients’ outcomes, but they believed the estimated-vs.-actual weight question was well worth pursuing. Both became part of the team that eventually conducted the stroke patient study.

“These are touchy medications,” Richlik said. “We want to be really accurate on weight with the patients [who receive them].”

Rather than simply purchase a scale on the Joint Commission’s recommendation, Graves, Ver Hage and Richlik decided to quantify the discrepancy between the estimated weight of stroke patients obtained in the ED and the actual weight recorded in the ICU.

“To support the need for a scale, we wanted to do a study to prove or disprove the accuracy of the weights we got in the ED,” Graves said.

Research Nurse Scientist Mary Beth Flynn Makic, RN, PhD, also part of the study team, said the debate about tPA and other weight-based drug dosing raised a “burning clinical question. If we’re not getting the actual weight until the patient gets to the ICU,” she asked, “how accurately are we dosing?”

Makic helped walk the team through obtaining COMIRB (Colorado Multiple Institutional Review Board) approval to conduct a study. She also played a key role in collecting the data and analyzing and interpreting the results from their review of the medical records of 26 stroke patients admitted to the hospital between June 2009 and June 2010.

Seventy-seven percent of the estimated weights for these patients were either over or under the true weight, Makic said. All the other patients weighed 100 kilograms (220 pounds) or more, and received the same dose of tPA, she added.

“Nobody was on the money,” Makic said. “We don’t have the data to say if that resulted in complications, but it does tell us we’re not great at estimating weight. We should get it right.”

The soon-to-arrive scale will be used not only for patients who need tPA, but also those who receive intravenous heparin, another medication that requires weight-based dosing, said ED Nurse Manager April Koehler, RN.

In one recent case, Koehler said, a patient who needed heparin couldn’t stand, so staff made a weight estimate that was off by nearly 20 pounds. That resulted in a significant medication under-dose, she said.
“The patient was okay, but it was a real eye-opener,” Koehler said

Graves said she’s heard plenty of interest in the weight-based dosing question from her stroke coordinator colleagues around the state, some of whom have purchased equipment with scales. She’s optimistic that the ED’s new equipment will improve the quality of care, but she’s reserving judgment until it’s been tested.
“As with any new device,” she concluded, “we’re leery until we see how it works.