Defining the minimal effective volume and amount of lidocaine to perform a femoral nerve block under ultrasound control

Abstract BackgroundThe application of the combination of local anesthetics (LA) in some parts of the body increases the amount of LA and plasma concentration. 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. MethodsFemoral nerve blockade was performed with the following lidocaine solutions: 0.75% -10 ml, 7.5 ml; 1% -20ml, 15ml, 10ml, 7.5ml, 5ml; 1.5% -5ml, 4ml; 2% -5 ml, 4 ml; 3% -5ml, 4ml, 3ml; 4% -5 ml, 4 ml, 3 ml, 2.5 ml. 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. The quality of motor and sensory blocks was assessed after 45 min of administration of the femoral nerve block. ResultsA total of 181 femoral nerve blocks, in combination with sciatic nerve blocks, were used via the help of electrostimulation of the peripheral nerves (EPN), and under ultrasound (US) control. The femoral nerve blockade was effective with the following lidocaine solutions: 0.75% -10 ml (75mg); 1% -20ml, 15ml, 10ml, 7.5ml (75mg); 1.5% -5ml (75mg); 2% -5 ml (100 mg); 3% -5ml (150mg); 4% -5 ml (200mg). Femoral blockade was ineffective when using the following solutions of lidocaine: 0.75% - 7.5ml (56.25 mg); 1% - 5ml (50mg); 1.5% - 4ml (60mg, No spread along the entire circumference of the nerve - NSAECN); 2% - 4 ml (80mg, NSAECN); 3% - 4ml (120mg NSAECN), 3 ml; 4% - 4 ml (160 mg, NSAECN), 3 ml, 2.5 ml. ConclusionFor 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.