Prospective RCT Lidocaine & Levobupivacaine on Block Dynamics After Subparaneural Popliteal Sciatic Nerve Block

A Prospective Randomized Comparison of the Effects of Lidocaine and Levobupivacaine on Block Dynamics After a Subparaneural Popliteal Sciatic Nerve Block

Sciatic nerve block at the popliteal fossa is indicated for foot or ankle surgery, and the introduction of ultrasound guidance (USG) has improved the ease and accuracy of the performance of this block. Recent studies proved that subparaneural injection is associated with faster block onset, higher block success rate, and prolonged block duration suggesting subparaneural compartment of the sciatic nerve is a desirable site for local anaesthetic injection. Data from an ongoing trial in the investigator's institution comparing the block dynamics of subparaneural injection of 30ml 0.5% levobupivacaine (Chirocaine) above and below the bifurcation of the sciatic nerve at popliteal fossa has also shown that the time to 'readiness for surgery' was faster when the injection was performed below the bifurcation of the sciatic nerve. Lidocaine (Xylocaine) has a better pharmacokinetic and pharmacodynamics profile than levobupivacaine and is also widely used as local anaesthetic agent in clinical practice. Since there is no data comparing the block dynamics of lidocaine and levobupivacaine, this study aims to study and compare the block dynamics of lidocaine and levobupivacaine when given as a subparaneural injection below the bifurcation of the sciatic nerve at the popliteal fossa. In this study, the investigator hypothesizes that the use of lidocaine as the sole agent for this block will fasten the time to 'readiness for surgery' as compared to levobupivacaine when given as a subparaneural injection below the bifurcation of the sciatic nerve at the popliteal fossa.

This study will involve performing ultrasound guided subparaneural popliteal sciatic nerve block for 40 patients by using either Lidocaine or Levobupivacaine. Both are commonly used local anaesthetics for regional anaesthesia in daily clinical practice. Patients will be enrolled from the elective orthopaedic surgical list at Prince of Wales Hospital after informed consent.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status I-III
• adult and scheduled to undergo elective forefoot surgery under regional anaesthesia

Exclusion Criteria:

• patient refusal
• ASA physical status > III
• pregnancy
• neuromuscular disorder
• prior surgery in the popliteal fossa
• coagulopathy
• allergy to local anaesthetic drugs
• skin infection at the site of needle insertion