Clinical Observation of Bupivacaine Liposome for Lower Extremity Nerve Block

This prospective clinical observational, sequential dose-finding study is designed to determine the effective concentrations of liposomal bupivacaine for ultrasound-guided femoral nerve block in patients undergoing lower limb surgery or related procedures.

All patients receive ultrasound-guided femoral nerve block performed by an experienced anesthesiologist using a standardized technique. A fixed injection volume of liposomal bupivacaine is administered, while the drug concentration is adjusted according to a modified up-and-down sequential method. The concentration for each subsequent participant is determined based on the response of the preceding participant. Following a positive response, the concentration is decreased; following a negative response, the concentration is increased by a pre-specified step size. The study is terminated after eight reversal points (crossovers) are observed.

To independently characterize sensory and motor block dose-response relationships, participants are allocated into two endpoint-specific observation groups:

Sensory block group

Sensory function in the femoral nerve distribution is assessed 30 minutes after block placement using standardized sensory testing. Complete loss of sensation at 30 minutes is defined as a positive response, while preserved sensation is defined as a negative response.

Motor block group

Motor function of the quadriceps muscle is evaluated 30 minutes after block placement using a standardized motor strength assessment. The successful (positive) quadriceps motor block is defined as a decrease of ≥1 grade in the muscle strength of the quadriceps compared with that before the block.

The primary objective of this study is to estimate the EC50 and EC95 of liposomal bupivacaine for:femoral nerve sensory blockade, and femoral nerve motor blockade, based on sequential allocation data and appropriate dose-response modeling.

Secondary objectives include describing the differential sensory-motor block profile of liposomal bupivacaine and evaluating its clinical feasibility and safety for femoral nerve block applications. All patients are monitored for block-related adverse events, including signs of local anesthetic systemic toxicity, nerve injury, and other complications throughout the perioperative period.

Inclusion criteria

• Adults aged 18 to 85 years
• Scheduled for elective unilateral lower limb surgery
• Unilateral ultrasound-guided femoral nerve block clinically indicated as part of routine perioperative anesthesia and analgesia management
• Ability to clearly distinguish between the blocked (operated) limb and the contralateral (non-blocked) limb for sensory and pain assessments
• Ability to understand the study procedures and provide written informed consent
• Ability to cooperate with sensory and motor assessments, including visual analog scale (VAS) scoring and quadriceps muscle strength testing

Exclusion criteria

• Known allergy or hypersensitivity to bupivacaine, amide-type local anesthetics, or any component of liposomal bupivacaine
• Infection at or near the planned injection site
• Coagulopathy or clinically significant bleeding disorder, or anticoagulant/antiplatelet therapy incompatible with peripheral nerve block
• Pre-existing neurological deficits, neuropathy, or motor weakness affecting either lower limb that could interfere with sensory or motor assessments
• Severe hepatic dysfunction or other conditions that increase the risk of local anesthetic systemic toxicity
• Pregnancy or breastfeeding
• Emergency surgery
• Inability to complete study assessments or comply with study procedures