Optimizing Local Anesthetic Concentration for Continuous Popliteal-Sciatic Nerve Blocks
Condition: Relatively Healthy Volunteers
Intervention: Ropivacaine 0.1%; Ropivacaine 0.4%
Intervention description: A sciatic catheter was inserted and ropivacaine 0.1% was administered as a basal infusion for 6 hours.; A sciatic catheter was inserted and ropivacaine 0.4% was administered as a basal infusion for 6 hours.
Intervention MeSH terms: Ropivacaine
Phase: Phase 4
Study type: Interventional
Primary purpose: Treatment
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: This is a split-body study in which each study subject receives both treatments: one on each side of the body. Which treatment is applied to which side of the body is randomized (and masked).
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Masking description: The only individual aware of the treatment group assignments is the investigational pharmacist who has no interaction with the study subjects. Treatment group assignments were released by the investigational pharmacy only after completion of data collection.
Enrollment: 24.0
Sex: All
Minimum age: 18 Years
Healthy volunteers: Accepts Healthy Volunteers

Summary:

      A continuous peripheral nerve block-also termed "perineural local anesthetic
      infusion"-involves the insertion of a tiny tube (a "catheter") through the skin and adjacent
      to a peripheral nerve, followed by local anesthetic (numbing medicine) administration via the
      catheter, providing pain control following surgery. Continuous peripheral nerve blocks may be
      provided in the hospital setting, but the use of lightweight, portable pumps permits infusion
      at home as well. However, it remains unknown if the concentration of the local anesthetic
      influences the block effects; or, is it rather simply the total dose of medication that is
      important. If it is the latter, then the concentration of local anesthetic could be
      increased, allowing a decreased basal infusion rate, which would allow patients at home to
      receive twice the duration of potent pain control since their infusion pump local anesthetic
      reservoir would last twice as long as current practice. In addition, if one
      concentration/dose combination results in less muscle weakness, but with at least equivalent
      analgesia, then the risk of falling might be decreased as well.

      The investigators will test 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 (8 mg/hour)-produces comparable effects when used in a continuous popliteal-sciatic
      nerve block.
    

Eligibility criteria:

        Inclusion Criteria:

          1. age ≥ 18 years

          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:

          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)

          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.