A prospective randomised controlled trial of ultrasound guided versus nerve stimulation guided distal sciatic nerve block at the popliteal fossa

The direct visualisation of nerves and adjacent anatomical structures may make ultrasonography the preferred method for nerve localisation. In this prospective randomised study, we investigated whether, for distal sciatic nerve block in the popliteal fossa, an ultrasound guided technique would result in the use of less local anaesthetic without changing block characteristics and quality. Using electrical nerve stimulation or ultrasound guidance, the nerve was identified in two groups of 20 patients scheduled for lower limb surgery. Hereafter lignocaine 1.5% with adrenaline 5 mu g/ml was injected. The attending anaesthesiologist assessed the injected volume. Significantly less local anaesthetic was injected in the ultrasound group compared to the nerve stimulation group (17 vs. 37 ml, P <0.001), while the overall success rate was increased (100% vs. 75%; P=0.01 7). We conclude that the use of ultrasound localisation for distal sciatic nerve block in the popliteal fossa reduces the required dose of local anaesthetic significantly, and is associated with a higher success rate compared to nerve stimulation without changing block characteristics.