Defining the minimal effective volume and amount of lidocaine to perform a femoral nerve block under ultrasound control.
Abstract Background. The aim of our research was to define the minimal effective volume and amount of lidocaine with added adrenaline (1:200,000) to perform a femoral nerve block under ultrasound control and with neurostimulation.Methods. The chosen starting concentration of lidocaine was 1%, as the most widely applied solution for the peripheral blocks. Subsequently , depending upon the acquired results, we applied 0.75%, 1.5%, 2%, 3%, and 4% solutions in volumes that were defined in accordance with the results of the research. All blocks were performed with added adrenaline (1:200,000). In all, 181 blocks of the femoral nerve, in combination with sciatic nerve blocks, were carried out with the help of the electrostimulation of peripheral nerves, and under ultrasound.Results. While measuring the cross-sectional area of the femoral nerve, no valid intergroup differences were observed (p = 0.98). The cross-sectional area of the femoral nerve within the region of the performed block was 0.27 cm2 (range: 0.24–0.3 cm2). Our research indicated that the minimal efficient volume of lidocaine that was necessary for the development of a complete block of the femoral nerve was 5 ml, and the amount of 75 mg. Conclusion. For a complete motor and sensory block of the femoral nerve: the minimum effective volume of local anesthetics was 5 ml; and the minimum effective amount of lidocaine was 75 mg. А complete block of the femoral nerve was achieved only with the spreading of local anesthetic along the whole circumference of the femoral nerve.