Predictability of the duration of motor blockade induced by unique injection of intrathecal prilocaine - an observational study.

Prilocaine is widely used for spinal anesthesia. Its intermediate effect makes it a valuable choice for one-day surgery. The duration of the motor blockade (DMB) may have an impact on the length of stay. The goal of this study was to establish a correlation between the DMB and different parameters (hyperbaric prilocaine dose, puncture level, surgical position, age, patient weight, and patient height). We prospectively enrolled adult patients scheduled for ambulatory surgery (n = 384). Univariate and multivariate regressions (backward stepwise) were applied. A P value lower than 0.05 was considered significant. We performed first analyzes on the entire population. We achieved same on a subgroup only composed of patients who received 60 mg of hyperbaric prilocaine between L4 and L5 and staying on dorsal position during surgery. The univariate analyses of the entire population demonstrate a significant correlation between DMB and 1) the prilocaine dose (P < 0.001), and 2) the BMI (P = 0.011). On the same population, the multivariate analyses confirm these two independent parameters correlated to the DMB: the patient height (P = 0.03) and the hyperbaric prilocaine dose (P < 0.001). The second analyses performed on the subgroup (n = 65), demonstrate a wide variability in the DBM (mean ± SD): 90.12 ± 30.36 minutes. For this concern, univariate analyses illustrate that only the patient height was significantly correlated to the DMB (P = 0.005). The multivariate analyses confirm that patient height could be considered as an independent parameter of DBM (P = 0.005). Within our entire population, there exists a considerable variation in the duration of the motor block after a unique injection of hyperbaric prilocaine. The prilocaine dose and the patient height were the only independent factors of the extension of the DMB. However, this relation is extremely weak and only allows explaining the variability of the DMB in a minority of the patients. This unknown pharmacological property of hyperbaric prilocaine could restrict its use for day-care surgery.