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Journal of Neuroscience Nursing:
doi: 10.1097/JNN.0b013e318298641b
Article

Estimated Versus Actual Weight When Dosing rt-PA in Acute Ischemic Stroke: Is There a Difference?

Graves, Alexandra; VerHage, Anna; Richlik, Brian; Makic, Mary Beth Flynn

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Author Information

Questions or comments about this article may be directed to Alexandra Graves, RN MS ANP-BC, at Alexandra.graves@ucdenver.edu. She is the Clinical Director of Stroke Services at the University of Colorado Hospital, Aurora, CO.

Anna VerHage, RN BSN CCRN CNRN, works in the Neurosurgical ICU at the University of Colorado Hospital, Aurora, CO.

Brian Richlik, RN BSN CCRN CNRN, is a Level IV Clinical Nurse in the Neurosurgical ICU and is a Member of the Stroke Council at the University of Colorado Hospital, Aurora, CO.

Mary Beth Flynn Makic, PhD RN CNS CCNS, is a Research Nurse Scientist, University of Colorado Hospital, and an Associate Professor (Adjoint) at the College of Nursing, University of Colorado, Aurora, CO.

The authors declare no conflicts of interest and have no disclosures.

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Abstract

Introduction: Intravenous (IV) recombinant tissue plasminogen activator (rt-PA) is the standard of care for patients exhibiting signs of acute ischemic stroke. IV rt-PA uses weight-based dosing, and often an estimated weight is used. The clinical effects of using estimated weight in dosing IV rt-PA remain unclear. The goal of this descriptive study was to determine if there was a significant difference in estimated versus actual weight dosing of rt-PA.

Methods: A retrospective chart review was performed to compare estimated versus actual patient weight. The sample consisted of patients from the hospital database who received IV rt-PA during June 2009–June 2010. Patients were included if they presented to the emergency department with stroke symptoms, received IV rt-PA, and had documented estimated and actual weights. Recorded (prescribed) dosing of IV rt-PA was compared with the suggested dosing using the admission weight. The differences between the weights and doses were calculated, analyzed, and categorized as being underdosed or overdosed.

Results: Twenty-six charts met the inclusion criteria. Using descriptive statistics and tests of difference, the mean estimated weight was 79.9 kg (±3.92 kg) and the mean actual weight was 78.5 kg (±3.86 kg); four patients had an estimated weight discrepancy of ≥5 kg. Six had correct estimated dosing; however, all of these patients were greater than 100 kg and received the maximum dose of 90 mg. Eleven patients’ estimated weights were underestimated, resulting in underdosing of IV rt-PA. Nine estimated weights were overestimated, leading to overdosing of the medication, but none of the dosing overages exceeded 10%. No statistical significance was found between the two groups’ estimated weights or dosing errors, t(26) = 0.69, p = .79.

Discussion: Results from this study found documented estimated weights were not significantly different from actual weights and the precision of estimated weight were similar to weights obtained using a scale. Despite these results, methods for obtaining actual weights in the emergency department for high-risk patients should be explored.

Stroke is the fourth leading cause of death and the leading cause of serious long-term disability in the United States (Minino, Murphy, Xu, & Kochanek, 2011). An estimated 795,000 people experience a new or recurrent stroke each year, and 1 of 18 deaths are because of stroke in the United States (Rogers et al., 2011). Significant interventions to reduce morbidity and mortality associated with ischemic stroke have been implemented focusing on the early recognition of stroke symptoms and treatment with clot dissolving agents, specifically, recombinant tissue plasminogen activator (rt-PA). Studies have shown that, when rt-PA is administered within 4.5 hours after the initial onset of stroke symptoms, the morbidity and mortality of the individual is reduced (Hacke et al., 2008; National Institute of Neurological Disorders and Stroke [NINDS] rt-PA Study Group, 1995). Intravenous (IV) rt-PA uses weight-based dosing, and in the absence of a scale, an estimated weight may be obtained from the patient, family member, patient’s nurse, or physician. A study by Hall, Larkin, Trujillo, Hinds, and Delaney (2004) found that patients were nine times more likely to accurately estimate their own weight compared with providers, yet patients were often unable to estimate their weight within 5 kg. An inaccurate weight may contribute to a negative outcome for the patient, in both overestimations and underestimations of rt-PA dosing. Few studies have been conducted exploring the impact of inaccurate weight estimation and rt-PA dosage calculations for drug administration for the treatment of stroke (Breuer et al., 2010; Messe et al., 2004, 2011).

Current evidence suggests that the optimal weight-based dose of rt-PA is 0.9 mg/kg for patients weighing less than 100 kg (220 lbs) and a maximum dose of 90 mg is used for patients who exceed 100 kg (American Heart Association, 2012; Summers et al., 2009). For maximal clinical effectiveness, IV rt-PA must be given quickly in the management of a patient with an acute ischemic stroke (Zoppo, Saver, Jauch, & Adams, 2009). “Target: Stroke,” a national quality improvement initiative of the American Heart/American Stroke Association, includes treating eligible patients within 60 minutes or less from the time they arrive in an emergency department (American Heart Association, 2012; Summers et al., 2009). Although emergency departments are designed for the rapid evaluation and treatment of patients with stroke, several barriers may exist in meeting the door-to-drug 60-minute goal. One of the ten “Target: Stroke Best Practice Strategies” involves mixing rt-PA and setting up the bolus and 1-hour infusion pump as soon as the patient is recognized as a potential treatment candidate. This allows for the administration to occur as soon as the medical decision to treat is made; however, dosing the drug is dependent on the knowledge of the patient weight. Many emergency departments are not equipped to obtain an exact weight, and an estimated weight given by the patient, family, nurse, or the treating provider is used to determine the dosing of rt-PA to treat stroke symptoms (Messe et al., 2011).

The clinical effects of using estimated versus actual weight in dosing IV rt-PA remain unclear. It is important to consider that overdosing may lead to an increase in complications such as intracerebral hemorrhage (ICH) and excessive bleeding and underdosing may potentially lead to decease in drug effectiveness resulting in lack of stroke symptom improvement. In a secondary analysis of the data from the NINDS rt-PA Stroke Study, Messe and colleagues found that estimated weights versus actual weights were the primary source of variability in the actual dose of administered rt-PA (Messe et al., 2011). The researchers did not find a correlation between decreased effectiveness of therapy because of an underestimating of weight, and the risk of ICH was not significantly different in patients who received an overdose of >10% of the rt-PA compared with patients who received a more accurate weight-based dose. However, higher rates of ICH have been documented in patients who receive doses of >0.95 mg/kg (Acheampong & Forg, 2012). Patients’ accurate weight dictates the accuracy of their rt-PA dose, thereby impacting drug safety and efficacy. Thus, to dose correctly and effectively treat patients, an accurate weight to determine rt-PA dosing is needed. Therefore, the purpose of this descriptive study was to examine the difference in estimated versus actual weight dosing of rt-PA administered to patients with acute ischemic stroke who presented to the emergency department.

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Methods

The study was conducted in a 450-bed academic medical center that is also designated as a Joint Commission Primary Stroke Center. Institutional review board permission was obtained to conduct the study. A retrospective chart review was performed to compare estimated versus actual patient weight when dosing IV rt-PA in the acute ischemic stroke population. The sample consisted of patients from the hospital stroke database who were admitted to the emergency department and received IV rt-PA during June 2009–June 2010. Patients were included if they presented to the emergency department with signs or symptoms of stroke, received IV rt-PA while in the emergency department, and had a weight documented in the medical record.

Data from electronic and paper charts were reviewed using a standardized data collection tool. Chart review process occurred as a team of five, including two neuroscience ICU nurses, stroke coordinator and former emergency department nurse, research nurse scientist, and stroke database analyst. The multidisciplinary team reviewed charts simultaneously to assist with the reliability and validation of the data abstracted from the charts. The chart review process was completed with all research team members present in 1 day to ensure consistency of data abstraction. Data obtained from the chart included ethnicity, gender, age, estimated weight, actual weight, and IV rt-PA dose received. The emergency department in this study did not have a mechanism to weigh patients on admission, so all documented weights at the time of the rt-PA administration were estimated. Estimations of weight were provided by nurses, physicians, family members, or patients. Actual weight was defined as the first inpatient weight upon admission to the critical care unit. The standard of care in this hospital includes scales in all critical care beds, and patient weights are obtained on admission to the unit.

Recorded (prescribed) dosing of IV rt-PA was compared with the suggested dosing using the admission weight. The standard of practice, 0.9 mg/kg with a maximum dose of 90 mg for patients greater than 100 kg, was used for dosing calculations. Differences in the dose the patient received based on the estimated weight and the dose calculated using the admission rate for dosing were calculated. The differences between the weights and the doses were then analyzed and further categorized as being underdosed or overdosed. Underdosed was defined as the dose of IV rt-PA calculated using the admission weight that was greater than the dose the patient received in the emergency department because of a lower estimated weight. Overdosed was defined as the dose of IV rt-PA calculated using the admission weight that was less than the dose the patient received in the emergency department because of a higher estimated weight. A standard estimation of acceptable accuracy discrepancy for weight-based dosing was not found in the literature. However, previous studies defined dose error to be ±10% from the optimal weight-based dose of rt-PA, and this definition was used in this study (Breuer et al., 2010; Messe et al., 2004, 2011).

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Results

Twenty-six charts met the inclusion criteria and were analyzed in this study. Data were entered into SPSS 19 (IBM) and were analyzed using descriptive statistics and tests of difference (t test; IBM Inc., 2010). Alpha was set at 0.05. Table 1 provides the demographics of the patients included in this study. The mean estimated weight was 79.9 kg (± 3.92 kg), and the mean actual weight was 78.5 kg (± 3.86 kg); four patients had an estimated weight discrepancy of ≥5 kg. Two of these individuals weighed more than 100 kg; thus, the estimated weight error did not influence rt-PA dosing. For the other two patients with a weight error of ±5 kg, the rt-PA dosing discrepancy based on weight did not exceed the threshold of 10% error. Estimated weights of patients with stroke seen in this emergency department were more likely underestimated rather than overestimated, but this weight estimation error did not appreciably impact rt-PA dosing (±10% drug administration error).

Table 1
Table 1
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Six patients had the correct estimated dosing in the emergency department; however, all of these patients were greater than 100 kg in body weight and received the maximum dose of 90 mg. Eleven patients’ estimated weights were underestimated that resulted in the underdosing of IV rt-PA. Two of these patients received a dosing error of ≤10% of the desired rt-PA dosing. Slightly fewer patients’ (n = 9) estimated weights were overestimated leading to overdosing of the drug, but none of the dosing overages exceeded 10% nor did the overage exceed 0.95 mg/kg. The mean difference in the calculated dose of IV rt-PA administered based on the incorrect (estimated) weight was −0.319 mg (± 2.9 mg). No statistical significance was found between the two groups’ estimated weights or dosing errors, t(26) = 0.69, p = .79. Two patients had a documented ICH; neither patient received an inaccurate dose of rt-PA ± 10% based on estimated or actual body weight. One patient’s weight was underestimated, and the other patient received correct dosing of rt-PA. Table 2 provides a summary of the study findings of estimated and actual weight and IV rt-PA dosing.

Table 2
Table 2
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Agreement of the estimated and actual weights was completed using a Bland–Altman plot (see Figure 1). The estimated and actual weights observed in this study were within a 5-kg difference with a mean −0.2 (bias). Two subjects had their weights overestimated or underestimated by more than 10 kg; however, both of these patients were greater than 100 kg, and the weight estimation error did not impact rt-PA dosing decisions.

Figure 1
Figure 1
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Discussion

Accurate IV rt-PA dosing is essential in the care of patients having a stroke. The results of this study found that estimated weight was close to the patient’s actual weight. For best practice, the emergency department nurse should strive to obtain the most accurate weight possible with the first option being a scale weight. Emergency departments face many obstacles when administering weight-based medications, specifically when administering IV rt-PA for a patient presenting with symptoms consistent of an acute ischemic stroke. Most emergency departments do not have access to convenient weighing devices for a patient experiencing stroke symptoms, and these patients may not be candidates for using a standing scale (Messe et al., 2011). Timing is crucial when treating a patient with stroke, and thus, using an estimated weight when dosing IV rt-PA has become the practice norm (Breuer et al., 2010; Messe et al., 2011). Rapid assessment, diagnostics, and administration of antithrombolytic agents are essential links in the sequence of treatment toward decreasing risk for further neurological damage. Designing practice procedures to obtain actual weights to safely administer rt-PA are desired to prevent underdosage and overdosage of this thrombolytic agent.

In this study, it was assumed, based on current standard practice, that the estimated weight was obtained in collaboration with the patient or family when possible. It is not known which clinician (e.g., nurse or prescribing provider) determined the estimated weight for weight-based drug dosing. Results from this study found that the documented estimated weights were not significantly different from the actual weights and the bias and precision of the estimated weight were similar to weights obtained using a scale. The findings suggest that, in this study, the documented estimated weights correlated well with scale weights.

Results also found that weights were more consistently underestimated; (42%) the mean underdosing of IV rt-PA was less than 0.3 mg (SD: ±2.9 mg). It is unclear as to the clinical impact of underdosing of rt-PA and optimal neurological outcome (Messe et al., 2004). Evidence has explored rt-PA dosing ranges from 0.6 to 0.9 mg for effective treatment, and the outcomes of the NINDS trail suggest that 0.9 mg/kg is the optimal dose (Menon & Kell, 2005). Overestimation of weight and subsequent higher dosing was found to occur less often in this study.

Overestimating in weight (± 5 kg) did not result in an rt-PA dosing error (± 10%) or negative clinical events such as ICH. The greatest errors (weight estimation of ±10 kg) occurred in two patients, both of whom were over 100 kg. Consistent with other studies, providers and patients are less accurate in estimating weights in individuals at higher weighs (Breuer et al., 2010; Hall et al., 2004; Menon & Kell, 2005).

Overall, the documented estimated weights in this study were found to be close to the actual patient weights obtained with a scale. Although the absolute dosing of rt-PA was different when comparing estimated and actual weight, the dosage difference did not exceed 10% in 24 of the 26 patients in this study, and few errors (n = 4) in estimated weights had a discrepancy of ±5 kg. The results of this study support the findings from the larger study conducted by Messe et al. (2011), which suggested that weight estimation was acceptable for calculating rt-PA dosing and estimating weight did not have major adverse patient outcomes.

Despite evidence suggesting that estimated weights may not negatively impact rt-PA dosing and patient outcomes, methods for obtaining actual weights in the emergency department for high-risk patient and high-risk weight-based medication administration should be explored. A prospective observational study, “Weight Approximation in Stroke Before Thrombolysis,” concluded that unreliable body weight estimations resulted in dosing errors in one third of patients with stroke and recommended standardizing weighing practice (Breuer et al., 2010). Clinical efforts to obtain accurate weights using a scale are needed to continually improve accuracy of the IV rt-PA administration as emergency departments strive to improve rapid and effective treatment of stroke victims and achieve goals for practice excellence.

In this study, providers estimated patient weights within 5 kg of their actual weight. Possible solutions that should be explored to enhance the ability to obtain an accurate weight in the emergency department include providing stretchers with built-in weighing device, floor-based scales that a stretcher is directly placed upon, or a pneumatic device that lifts the stretcher to obtain a weight. At the emergency department involved in this study, the decision was made to purchase a bed scale installed in the shared ambulance entrance and hallway to the CT scanner. Current practice is to weigh patients on arrival by emergency medical services or enroute to the CT scanner to obtain a scale weight for dosing rt-PA more accurately.

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Limitations

This study has several limitations with the primary limitation being the small sample size and the retrospective chart review as the method for data abstraction and analysis. In addition, it is not known how the documented estimated weight was obtained (e.g., in collaboration with patient, family, nurse, provider, etc.).

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Implications for Emergency Nurses and Conclusions

Many emergency departments have scales that require the patient to stand, but in the case of a patient with a potential ischemic stroke, it is recommended that the patient should not stand and instead position the head either flat or up to 30° depending on the individual (Summers et al., 2009). This allows for maximal cerebral perfusion taking into account the potential for increased intracranial pressure. To ensure accurate patient weights are obtained quickly for the patient presenting with stroke symptoms, the emergency department should have devices that easily facilitate access to current patient weights rather than relying on estimated weights for IV rt-PA dosing. It is imperative for accurate IV rt-PA dosing that the emergency department nurse strive to obtain the most accurate weight possible. Given the urgency of the situation, the nurse is faced with many tasks. While preparing for possible IV rt-PA administration, if the nurse cannot weigh the patient, asking the patient for the weight may be more accurate than the nurse or provider estimating the patient’s weight for IV rt-PA dosing (Breuer et al., 2010; Menon & Kell, 2005).

Obtaining the most accurate weight in emergency departments poses a challenge for the patient with stroke and healthcare providers. To maximize patient outcome, overcoming barriers to allow for obtaining accurate weights is needed in emergency departments to ensure that correct dosing of IV rt-PA is administered to all patients experiencing an ischemic stroke.

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References

Acheampong P., Forg D. A. (2012). Pharmacokinetics of alteplase in the treatment of ischaemic stroke. Expert Opinion on Drug Metabolism and Toxicology, 8 (2), 271–281.


Breuer L., Nowe T., Huttner H. B., Blinzler C., Kollmar R., Schellinger P. D., Kohrmann M. (2010). Weight approximation in stroke before thrombolysis. The WAIST-Study: A prospective observational “dose-finding” study. Journal of Stroke and Cardiovascular Diseases, 41, 2867–2871

Hacke W., Kaste M., Bluhmki E., Brozman M., Dávalos A., Guidetti D., Toni D.ECASS Investigators. (2008). Thrombolysis with Alteplase 3 to 4.5 hours after acute ischemic stroke. New England Journal of Medicine, 359, 1317–1329.

Hall W. L., Larkin G. L., Trujillo M. J., Hinds J. L., Delaney K. A. (2004). Errors in weight estimation in the emergency department: Comparing performance by providers and patients. Journal of Emergency Medicine, 27 (3), 219–224.

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Summers D., Leonard A., Wentworth D., Saver J. L., Simpson J., Spilker J. A., Mitchell P. H.American Heart Association Council on Cardiovascular Nursing and the Stroke Council. (2009). Comprehensive overview of nursing and interdisciplinary care of the acute ischemic stroke patient. Journal of the American Medical Association, 40, 2911–2944.

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Keywords:

estimated weight; rt-PA; stroke; weight

© 2013 American Association of Neuroscience Nurses

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