Evaluation of the Impact of a Mobile App (LoAD Calc) on the Calculation of Maximum Safe Doses of Local Anesthetics: Randomized Controlled Trial

Background: Local anesthetics (LAs) are widely used in clinical practice, but their administration carries the risk of LA systemic toxicity, a potentially fatal complication. Calculating maximum safe doses is complex and error-prone when considering multiple patient-specific factors. Most existing tools and mobile apps have not been scientifically validated and may propose unsafe doses. The Local Anesthetics Dose Calculator (LoAD Calc) mobile app was developed at the Geneva University Hospitals to calculate maximum safe doses by integrating comprehensive patient parameters. Objective: The primary objective was to evaluate the overdose rate using the LoAD Calc app compared with traditional calculation methods. Secondary objectives were calculation time, user confidence, app usability, and interpractitioner variability. Methods: This single-center unblinded randomized controlled trial recruited 50 anesthesiologists to use either LoAD Calc or their usual calculation methods. Assessment was conducted in-person using a web-based platform. Participants completed 10 clinical vignettes featuring various patient characteristics, comorbidities, and medication interactions requiring maximum safe dose calculations for lidocaine, levobupivacaine, and ropivacaine. The primary outcome was the overdose rate, defined as exceeding the maximum safe doses calculated using a comprehensive set of rules incorporating all patient-specific factors. Secondary outcomes included overdose rates using 2 simplified weight-based methods, underdose rates, calculation time, and self-reported measures of confidence and app usability. Overdose rates were compared using chi-square tests with 95% CIs; calculation time and confidence were assessed using Student t test. Results: All 50 participants completed the study. Using the full set of calculation rules, the overdose rate was significantly lower when LoAD Calc was used (30/250, 12.0% vs 198/250, 79.2%; relative risk [RR] 0.15, 95% CI 0.11-0.21; P<.001). This was consistent across all 3 LAs: ropivacaine (5/100, 5% vs 64/100, 64%; P<.001), levobupivacaine (19/100, 19% vs 90/100, 90%; P<.001), and lidocaine (6/50, 12% vs 44/50, 88%; P<.001). When considering simplified weight-based methods, overdose rates remained significantly lower when LoAD Calc was used (actual weight: 8/250, 3.2% vs 95/250, 38.0%; RR 0.08, 95% CI 0.04-0.17; P<.001; ideal body weight: 10/250, 4.0% vs 151/250, 60.4%; RR 0.07, 95% CI 0.04-0.12; P<.001). Underdose rates were similar (25/250, 10.0% vs 27/250, 10.8%; P=.77). Calculation time was also similar (mean 111, SD 56 s vs mean 115, SD 89 s; P=.53). LoAD Calc users reported higher confidence (mean 8.5, SD 0.9 vs mean 6.3, SD 1.7; P<.001), and the app achieved a median System Usability Scale score of 98 (IQR 95-100). Conclusions: LA overdoses were significantly less likely when the LoAD Calc app was used in simulated clinical vignettes, without increasing calculation time or underdose rates. Given its high usability score and the improvement in practitioner confidence, clinical implementation could be considered and may contribute to improving patient safety and dose calculation standardization.