Background and Aims Sciatic nerve block(SNB), a well-established and widely used for lower limb surgeries. The distal SNB (popliteal fossa block) is used peripheral nerve block for below knee surgeries. Popliteal fossa block with bupivacaine provide 12-24 hours of analgesia, irrespective of the nerve localisation technique used, complete sensory and motor block is associated with slow onset time(20-60 mins). To evaluate and compare the onset of action of sciatic nerve block proximal to its bifurcation and immediately after bifurcation using ultrasound with local anaesthetic injection inside the paraneural sheath.
Methods After Ethical Committee Approval, USG sub paraneural popliteal SNB performed in 50 patients undergoing lower extremity surgeries and were randomly divided into 2 groups (A & B). Group A recieved 20ml 0.5% bupivacaine 8 cm above the bifurcation into tibial and common peroneal nerve. Group B recieved 20ml 0.5% bupivacaine immediately after its bifurcation. Performance time, adverse events, onset of sensory, motor blockade of sciatic nerve were recorded.
Results SNB proximal to the bifurcation had a shorter onset of sensory and motor block than distal bifurcation. Time taken for scanning was more, whereas needling time was less in the pre bifurcation group. Total time taken to perform pre bifurcation and post bifurcation SNB was (4.5+0.9) min and
4.5+1.0) min respectively, P=0.766 which is comparable. Demographic data, ASA grade, BMI were comparable in both the groups.
Conclusions In conclusion, SNB administered at pre bifurcation has faster onset of action compared to post bifurcation. Block performance time was comparable and independent of BMI in both the groups
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