Minimum Anaesthesia Concentration of Lidocaine Required for Sciatic Popliteal Block

Successful Popliteal Block Using Lidocaine; What is the Minimum Effective Anesthesia Concentration (MEAC90)

using a biased-coin design up-down sequential method, different concentration of lidocaine will be used for popliteal block After 45 successful block (positive response), the data will be used to calculate the minimum lidocaine concentration that can result in successful popliteal block in 90% of patients

The response of a patient determined the lidocaine concentration given to the next patient (a biased-coin design up-down sequential method). If a patient had a negative response, the lidocaine concentration was increased by 0.1% w/v in the next patient. If a patient had a positive response, the next patient was randomized to receive the same lidocaine concentration (with probability of 0.89), or to receive a concentration 0.1% w/v less (with probability of 0.11).

Inclusion Criteria:

• orthopedic foot or ankle surgery
• day case surgery

Exclusion Criteria: patients

• <18y,
• ASA class greater >III,
• obese (BMI >30),
• patients with low body weight, who required lidocaine dose is of more than 4.5mg.kg-1
• peripheral neuropathy,
• motor weakness,
• infection at the injection site
• any contraindications for medications in the study.