Evaluation of Automated Vasopressor Administration Algorithms Using Lower-Limit Control for Intraoperative Hypotension: A Simulation Study

<b>Background/Objectives:</b> The aim of this study was to develop evaluation metrics for lower-limit vasopressor control, a strategy intended to prevent prolonged intraoperative hypotension under noninvasive blood pressure monitoring. <b>Methods:</b> Using general-purpose simulation software, we developed a blood pressure generation model with one-minute intervals and an automated vasopressor administration model with five-minute intervals. The latter delivered drugs according to predefined rules when systolic blood pressure (sBP) fell below a threshold. Four dosing strategies were constructed by combining bolus, repeated low-dose bolus, and continuous infusion approaches. Simulations were performed, and the following evaluation metrics were calculated: (1) proportion of time below threshold (PTBT), (2) mean value below threshold (MVBT), (3) average sBP, and (4) median performance error (MDPE) and median absolute performance error (MDAPE). <b>Results</b>: PTBT and MVBT analyses showed that incorporating continuous infusion reduced both the duration and severity of hypotension. Moreover, adding MVBT to the average sBP after subtracting the threshold quantified the extent to which sBP exceeded the threshold on average. In contrast, MDPE and MDAPE varied substantially with the assumed target pressure, highlighting their limitations in evaluating lower-limit control without a fixed target. <b>Conclusions</b>: For lower-limit control, metrics such as PTBT, MVBT, and average sBP offer useful insights into control stability and hypotension avoidance, whereas MDPE and MDAPE may be unsuitable for quantitative assessment when the primary goal is to exceed a threshold rather than achieve a fixed target pressure.