Abstract TP494: Estimated tPA Dosing Weight on a Mobile Stroke Unit: Comparison between Estimated and Hospital-measured Weights

Introduction: The purpose of the Houston Mobile Stroke Unit (MSU) is to expedite stroke care by treating patients in the pre-hospital setting where obtaining a measured body weight, critical for accurate pre-hospital tPA dosing, is challenging and impossible. The paramedic and nurse on the MSU subjectively estimate by assessment (with patient report if possible) the weight for calculating tPA dosing. We aimed to determine the accuracy of the estimated weight method compared to the actual weight of patients treated with tPA on the MSU. Methods: Data were prospectively collected for MSU tPA-treated patients as part of the BEST-MSU study comparing MSU to standard EMS management. We collected the first-documented hospital-measured weight (bed scale) within 24 hours of hospital arrival, and the estimated weight used on the MSU for treatment. Mean absolute and percent difference in weights were calculated; less than 10% difference in weights was considered acceptable. To compare the estimated and measured weights, we conducted a Wilcoxon signed-rank test. Differences between weights were set as 0 if both weights were above 100kg. Fisher’s exact test was used to explore association between weight difference > 10% and patient outcomes. Results: Among 337 patients, mean age was 67.8 (15.6) and average measured weight was 81.2 kg (SD 22.3). Median absolute difference in measured versus estimated weight was 2.70 kg (IQR 0.55-7.60), and both weights were significantly different from each other (p value < 0.0001). The average absolute percent difference in weight was 7.04% (SD 9.11%). The absolute mean difference in tPA dosage was 3.49 mg (SD 6.06). Among patients whose estimated and measured weights were not both ≥100 kg, 56 (16.6%) had weight difference >10%. In patients with overestimation of weight by >10%, there were no symptomatic intracerebral hemorrhages. There was no association between weight difference and discharge modified Rankin score (p value = 0.5921). Conclusion: Weight estimation on a mobile stroke unit can lead to similar tPA dosing for 82% of subjects compared to if dosing were determined based on actual weight. Weight over- or under-estimation had no detected significant impact on tPA outcomes.