Treating Phantom Limb Pain Using Continuous Peripheral Nerve Blocks: A Department of Defense Funded Multicenter Study
Condition: Phantom Limb Pain
MeSH terms: Phantom Limb
Intervention: Perineural infusion [continuous peripheral nerve block(s)]
Intervention description: Electronic, programmable, portable infusion pumps will be used to administer perineural study solution at fixed rates for over 6 days. Subjects will receive a total of 1,100 mL of study fluid from either one (upper extremity) or two (lower extremity) pump and external reservoir combinations. The continuous basal infusion rate will be determined by catheter location: femoral 2.5 mL/h; popliteal-sciatic 5 mL/h; and infraclavicular 7.5 mL/h (37.5 mg/h for both upper and lower extremity subjects). No patient-controlled bolus dose will be included. Subjects will have the option of returning 4-16 weeks later for a second infusion of the alternate treatment solution.
Phase: Phase 4
Study type: Interventional
Primary purpose: Treatment
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Masking description: The investigators originally planned to unmask the treatment groups following the completion of the statistical analysis ("triple masked"); but following the analysis using "treatment A" and "treatment B" labels, opted to wait to unmask the groups until the manuscript was drafted ("quadruple masking").
Enrollment: 144.0
Sex: All
Minimum age: 18 Years
Healthy volunteers: No
Keywords: phantom pain; traumatic limb amputation; amputees

Summary:

      When a limb is traumatically severed, pain perceived in the part of the body that no longer
      exists often develops. This is called "phantom limb" pain, and is different from "stump"
      pain, which is pain within the part of the limb that remains intact. Unfortunately, phantom
      pain resolves in only 16% of people, with the rest experiencing this pain for the remainder
      of the lives. There is currently no reliable treatment for phantom limb pain.

      The exact reason that phantom limb pain occurs is unclear, but when a nerve is cut-as happens
      with a traumatic amputation-changes occur in the brain and spinal cord that actually worsen
      with increasing phantom pain. These abnormal changes may often be corrected by putting local
      anesthetic-termed a "peripheral nerve block"-on the injured nerve, keeping any "bad signals"
      from reaching the brain, with resolution of the phantom limb pain. However, when the nerve
      block ends after a few hours, the phantom pain returns. But, this demonstrates that the brain
      abnormalities-and phantom pain-that occur with an amputation may be dependent upon the "bad"
      signals being sent from the injured nerve(s), suggesting that a very long peripheral nerve
      block-lasting many days rather than hours-may permanently reverse the abnormal changes in the
      brain, and provide lasting relief from phantom pain.

      Until recently, extending a peripheral nerve block beyond 16 hours was unrealistic. However,
      a treatment option called a "continuous peripheral nerve block" is now available. This
      technique involves the placement of a tiny tube-smaller than a piece of spaghetti-through the
      skin and next to the nerves supplying the amputated limb. The tiny tube may be placed with
      minimal discomfort in about 15 minutes. Numbing medicine called local anesthetic is then
      infused through the tube, blocking any signals that the injured nerve sends to the spinal
      cord and brain. Using a small, portable infusion pump, this prolonged nerve block may be
      provided in individuals' own homes.

      The ultimate objective of the proposed research study is to determine if a 6-day continuous
      peripheral nerve block provided at home is an effective treatment for persistent phantom limb
      pain following a traumatic limb amputation. The primary hypothesis (what the researchers
      predict) is that phantom limb pain intensity will be significantly decreased 4 weeks
      following treatment with a 6-day continuous peripheral nerve block.
    

Eligibility criteria:

        Inclusion Criteria:

          -  18 years of age or older

          -  Upper or lower limb traumatic or surgical amputation at least 12 weeks prior to
             enrollment at or distal to the mid-humerus or hip (femoral head remaining),
             respectively; and including at least one metacarpal or metatarsal bone, respectively.

          -  Experiencing at least moderate phantom limb pain (defined as 2 or higher on the
             numeric rating scale, NRS 0-10), at least three times each week for the previous 8
             weeks.

          -  Accepting of an ambulatory continuous peripheral nerve block for 6 days.

          -  Willing to avoid changes to their analgesic regimen from 4 weeks prior to and at least
             4 weeks following the initial catheter placement (preferably 4 weeks following the
             second/crossover catheter insertion as well).

          -  Having a "caretaker" who will transport the subject home following the catheter
             insertion(s), and remain with the subject for the first night of the infusions.

        Exclusion Criteria:

          -  Known renal insufficiency

          -  Allergy to study medications

          -  Pregnancy

          -  Incarceration

          -  Inability to communicate with the investigators

          -  Morbid obesity (BMI greater than 40)

          -  Comorbidity that results in moderate-to-severe functional limitation (ASA greater than
             2)

          -  Possessing any contraindication to ambulatory perineural catheter placement or
             perineural local anesthetic infusion:

               -  Current infection

               -  Immune-compromised status of any etiology

               -  Uncontrolled anxiety/panic disorder

               -  Inability to contact investigators during the perineural infusion