Chen X, Ling D, Cao J, et al. - Researchers focused on the correlations between the minimum effective volume (MEV) of lidocaine 1.5% for an ultrasound-guided popliteal sciatic nerve block and individual factors such as the cross-sectional nerve area, gender, age, body mass index, and the depth of the sciatic nerve, in this study with 40 patients. They also assessed whether combined femoral and sciatic nerve blocks were safe. For this purpose, they monitored the plasma concentration of local anesthetics. The participants were administered combined single-shot femoral and continuous sciatic nerve blocks. Experts performed the femoral nerve block with an in-plane technique and 15 mL of lidocaine 1.5%. They identified that the MEV of lidocaine 1.5% correlated significantly with the cross-sectional area of the sciatic nerve (r = 0.459), with a regression equation of the MEV (mL) = 5.969 + 0.095 × (the cross-sectional area of the sciatic nerve). The maximum concentrations of lidocaine, monoethylglycinexylidide, and glycinexylidide were reported to be 1672.9 (227.6), 265.7 (32.7), and 42.2 (22.4) ng/mL, respectively. So, findings revealed a positive correlation between the cross-sectional area of the sciatic nerve and the MEV. The ability of the regression equation to aid the prediction of MEV of lidocaine 1.5% for popliteal sciatic nerve blocks was also shown. Toxic threshold limits were not touched by the maximum concentrations of lidocaine and its metabolites reported in this study.