Induction-Phase Peripheral Perfusion Dynamics and Rocuronium Neuromuscular Blockade Onset: A Retrospective Cohort Study

Background: Rocuronium onset time shows interindividual variability, yet its hemodynamic determinants remain incompletely characterized. The peripheral perfusion index (PI), derived non-invasively from pulse oximetry, reflects integrated cardiac output and peripheral vascular tone. We hypothesized that early PI dynamics during anesthesia induction are associated with rocuronium onset time. Methods: This single-center retrospective observational cohort study included 1377 adults who received rocuronium 0.6 mg/kg under a standardized induction protocol with quantitative electromyographic train-of-four monitoring. Baseline PI was categorized as low-PI (PI < 0.7), intermediate-PI (0.7 ≤ PI < 1.4), or normal-PI (PI ≥ 1.4), and patients were further stratified by anesthetic method (TIVA or volatile anesthesia), yielding six subgroups. The 60 s PI change after propofol bolus (ΔPI60) was selected as the primary dynamic variable and classified into equal-frequency tertiles (Slow-Rise, Mid-Rise, Fast-Rise). Sequential multivariable linear regression model was used to quantify independent contributions of induction-phase variables on onset time. Results: In the overall cohort, onset time differed significantly across baseline PI groups (p = 0.033), though this was not replicated within either anesthetic subgroup (TIVA: p = 0.200; volatile: p = 0.137). In contrast, ΔPI60 tertile was significantly associated with onset time in both subgroups (both p < 0.001), with median onset times of 211, 183, and 170 s in the Slow-Rise, Mid-Rise, and Fast-Rise groups, respectively. In the regression model, ΔPI60 tertile produced the largest single increment in model fit (adjusted R2 Δ0.060, p < 0.001); Slow-Rise and Mid-Rise groups had 32.7% and 18.8% longer onset times relative to Fast-Rise, respectively. Conclusions: ΔPI60 was most strongly associated with rocuronium onset time among the variables examined, independent of baseline characteristics and anesthetic method. These findings provide hypothesis-generating evidence that induction-phase PI dynamics may serve as a physiologically grounded, non-invasive marker of rocuronium delivery conditions, warranting prospective validation.