Optimizing Local Anesthetic Concentration for Continuous Popliteal-Sciatic Nerve Blocks

The investigators therefore propose a volunteer-based clinical trial testing the hypothesis that providing ropivacaine at different concentrations and rates (0.1% at 8 mL/hour vs. 0.4% at 2 mL/hour)-but at an equivalent total basal dose (8 mg/hour)-produces comparable effects when infused for a continuous popliteal-sciatic nerve block. The primary endpoint will be tolerance to cutaneous electrical current applied on the plantar aspect of the foot. This is an objective endpoint that has been validated in multiple previous publications and correlates with intra- and post-operative pain.

This investigation will be a randomized, observer-masked, controlled, split-body, human-subjects clinical trial.

Enrollment. Subjects will be volunteers of both sexes, age 18 and older. Volunteers will be solicited using newspaper advertisements, fliers, and an existing database of volunteers (IRB approved). If a volunteer meets inclusion/exclusion criteria and desires study participation, written, informed consent will be obtained. Selection for inclusion will not be based on race or socioeconomic status. The study population of interest includes men and women of all races and socioeconomic status. A urine pregnancy test will be administered to all women of childbearing age following written informed consent but before any study interventions. This urine test will be administered by CTRI nursing staff using standard, FDA-approved urine pregnancy testing devices.

Inclusion criteria for the trial will be: (1) age ≥ 18 years; and (2) willing to have bilateral femoral perineural catheters placed with a subsequent ropivacaine infusion and motor/sensory testing for 6 hours, requiring an overnight stay in the UCSD GCRC/CTRI to allow dissipation of local anesthetic infusion effects by the following morning. Exclusion criteria for the trial will be: (1) current daily analgesic use; (2) opioid use within the previous 4 weeks; (3) any neuro-muscular deficit of either femoral nerves and/or quadriceps muscles; (4) morbid obesity [weight > 35 kg/m2]; (5) pregnancy (as determined by a urine pregnancy test prior to any study interventions); and (6) incarceration. We expect to recruit a maximum of 30 healthy volunteers; with a target goal of 24 for the analysis. Selection for inclusion will not be based on gender, race, or socioeconomic status. The study population of interest includes men and women of all races and socioeconomic status. There will be no participants from vulnerable populations, such as pregnant women, children, or prisoners

Perineural catheter insertion. Following written, informed consent, subjects will be admitted to the UCSD CTRI and have demographic/morphometric data recorded (e.g., age, weight, height). An intravenous line will be placed in an upper extremity, followed by external monitors (pulse oximeter, blood pressure, and EKG), and oxygen by nasal cannula. Sedation will be provided with intravenous fentanyl (50 mcg) and/or midazolam (1 mg), or oral valium (10 mg) and/or dilaudid (4 mg), as necessary. Subjects will then have bilateral popliteal-sciatic perineural catheters placed using standard UC San Diego techniques as previously published by the current P.I.7,8