Bupivacaine-Lidocaine vs Bupivacaine for Ultrasound-Guided Popliteal Sciatic Nerve Block

Background and Rationale

Peripheral nerve blocks have become an increasingly preferred technique for both anesthesia and analgesia in distal lower extremity surgery, offering advantages such as reduced opioid consumption, stable intraoperative hemodynamics, lower rates of postoperative nausea and vomiting, and enhanced early mobilization. The popliteal approach to the sciatic nerve provides effective surgical anesthesia for foot, ankle, and distal leg procedures, with high patient satisfaction and a low complication profile. Ultrasound guidance further improves block success rates by enabling direct visualization of perineural anatomical structures.

The choice of local anesthetic plays a critical role in determining block onset time, duration of sensory and motor blockade, and overall analgesic duration. Lidocaine offers rapid onset and short-to-intermediate duration, while bupivacaine provides prolonged sensory and motor blockade, thereby reducing postoperative opioid requirements. The combination of these two agents theoretically enables simultaneous achievement of rapid onset and prolonged analgesia; however, the net effect of this combination on block characteristics remains inconclusive in the current literature.

Study Design

This is a prospective, randomized, double-blind, single-center, two-arm parallel-group clinical trial conducted at Ataturk University Research Hospital, Department of Anesthesiology and Reanimation, Erzurum, Turkey.

Participants

A total of 60 adult patients scheduled for elective distal lower extremity surgery will be enrolled. Inclusion criteria: age 18-65 years, ASA physical status I-III, body mass index (BMI) 18-35 kg/m², and written informed consent. Exclusion criteria include inability to provide informed consent, coagulopathy, sepsis, hepatic or renal insufficiency, known allergy to local anesthetics, prior surgery or significant scar tissue in the popliteal fossa, pregnancy, and chronic opioid use at home.

Randomization and Blinding

Eligible patients will be randomized in a 1:1 ratio using a computer-generated random number list into two groups of 30. Study solutions will be prepared by a dedicated investigator not involved in block performance or outcome assessment. Patients and the outcome assessor will be blinded to group allocation (double-blind). The anesthesiologist performing the block will be aware of the group allocation. Block procedures will be performed by an anesthesiologist with a minimum of two years of experience in ultrasound-guided regional anesthesia who is not involved in patient care.

Intervention

All patients will receive an ultrasound-guided popliteal sciatic nerve block using a total volume of 20 mL local anesthetic solution. Patients will be positioned prone or in lateral decubitus with the operative limb uppermost and the knee in slight flexion. Under aseptic conditions, a high-frequency linear ultrasound probe will be placed transversely over the popliteal fossa to visualize the popliteal artery and the tibial nerve. The probe will be advanced proximally to identify the tibial and common peroneal nerve bifurcation. A 100 mm echogenic block needle will be advanced in-plane from lateral to medial. After confirming circumferential perineural spread of 1-2 mL test injection under ultrasound guidance, the study solution will be incrementally injected with repeated aspiration checks.

Group BL (n=30): 10 mL 2% lidocaine + 10 mL 0.5% bupivacaine (administered sequentially in separate syringes)

Group B (n=30): 20 mL 0.5% bupivacaine (administered in two 10 mL syringes) In cases involving the medial malleolus or medial leg surface, an additional adductor canal block will be performed using 10 mL of the respective study solution.

Intraoperative Management Conscious sedation will be maintained intraoperatively with intravenous dexmedetomidine (loading dose: 0.5-1 µg/kg over 10 minutes; maintenance: 0.2-0.7 µg/kg/hour). Continuous monitoring of heart rate, non-invasive blood pressure, oxygen saturation, and electrocardiography will be performed throughout the procedure.

Postoperative Analgesia Protocol All patients will receive intravenous paracetamol 1000 mg 30 minutes before the end of surgery, repeated every 8 hours postoperatively. Intravenous dexketoprofen 50 mg will be administered intraoperatively and repeated every 12 hours. Rescue analgesia with intravenous tramadol 100 mg will be administered for NRS ≥ 4, with a maximum of 3 doses per day and a minimum interval of 4-6 hours between doses.

Outcome Measures Primary Outcome: The primary outcome is the duration of sensory block. It is defined as the time to return of sensation in the postoperative period, i.e., the time at which the patient first reports regaining sensation in the toes. Sensory function will be assessed at 1, 2, 4, 8, 12, and 24 hours postoperatively. The time of sensory recovery will be confirmed by in-person visit or telephone interview at 24, 48, and 72 hours after block performance.

Secondary Outcomes:

Block onset time: Time elapsed from completion of local anesthetic injection to first achievement of block success criteria.

Block success rate: Proportion of patients achieving a total sensorimotor score ≥12/14 with a sensory score ≥7/8 within 60 minutes of injection.

Adequacy of surgical anesthesia: Completion of surgery without the need for supplemental general anesthesia or local infiltration at the surgical site.

Duration of motor block: Time to return of motor function in the postoperative period, i.e., the time at which the patient is first able to move the toes. Motor function will be assessed at 1, 2, 4, 8, 12, and 24 hours postoperatively.

Duration of analgesia: Time to first reported pain after block performance. Postoperative pain scores: Pain intensity assessed using the Numeric Rating Scale (NRS 0-10) at 1, 2, 4, 8, 12, and 24 hours postoperatively. The highest NRS score will additionally be recorded at 24, 48, and 72 hours.

Quality of recovery: QoR-15 score (0-150; higher scores indicate better recovery) assessed preoperatively (baseline) and at 24 hours postoperatively.

Incidence of rebound pain: Defined as NRS ≥7 within 24 hours after resolution of the sensory block.

Neurological complications: Presence of paresthesia, numbness, or motor deficit in the blocked extremity, assessed by telephone interview or outpatient clinic visit on postoperative day 7.

Block Assessment

Sensory block will be assessed using the pinprick test across four nerve territories: tibial (plantar aspect of the foot), deep peroneal (first web space), superficial peroneal (dorsum of the foot), and sural (lateral border of the fifth metatarsal). Each territory will be scored from 0 to 2 (0 = normal sensation; 1 = analgesia, i.e., the patient perceives touch but not pinprick; 2 = anesthesia, i.e., the patient perceives neither touch nor pinprick), giving a maximum score of 8.

Motor block will be evaluated across three nerve territories: tibial (ankle plantar flexion), deep peroneal (ankle dorsiflexion), and superficial peroneal (foot eversion). Each territory will be scored from 0 to 2 (0 = normal; 1 = paresis; 2 = paralysis), giving a maximum score of 6.

The total maximum sensorimotor score is 14. Successful block is defined as a total score ≥12/14 with a sensory score ≥7/8. Blocks not achieving success criteria within 60 minutes will be considered failed. Patients with a successful block will then be transferred to the operating room.

Statistical Analysis Continuous variables will be assessed for normality using the Shapiro-Wilk test. Normally distributed variables will be compared using the independent samples t-test; non-normally distributed variables using the Mann-Whitney U test. Categorical variables will be analyzed using Fisher's exact chi-square test. A p-value <0.05 will be considered statistically significant. Statistical analyses will be performed using SPSS (IBM, Armonk, NY) or R (v4.2, Vienna, Austria).