Estimated versus actual weight when dosing rt-PA in acute ischemic stroke: is there a difference?

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.

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.

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.

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.