Regional anesthesia and pre-existing neurological disease--II.

To the Editor: Dhir et aL ~ should be congratulated for successfully administering regional anesthesia to a small series of patients with Charcot-Marie-Tooth disease. In reading the aforementioned case reports, it not only becomes apparent that dissimilar approaches to the brachial plexus were utilized but also that different local anesthetic solutions and volumes were employed. 1 Universally absent from these local anesthetic solutions was epinephrine. 1 Epinephrine possesses a complex pharmacodynamic profile and exerts dose dependent changes in peripheral nerve blood flow. 2 For example, a 1:200,000 concentration o f epinephrine has been demonstrated to decrease peripheral nerve blood flow. 2 Unsurprisingly, this reduction in regional blood flow is well tolerated in patients without vascular compromise or peripheral nervous system disorders. 2 However, patients afflicted with peripheral nervous system disorders, including Charco t -Mar ie -Tooth disease, may be more susceptible to nerve damage following periods o f diminished blood supply. Maintaining blood flow to a partially demyelinated nerve may eliminate one etiology involved in the "double-crush p h e n o m e n o n " ) Remote from these vascular properties, epinephrine may also enhance local anesthetic induced nerve toxicity. 2 Given the possible injurious consequences o f epinephrine, the authors x should be applauded for omitting this vasoconstrictor from their local anesthetic solutions. Given the equivocal patient responses to nerve stimulation, ultrasound guidance allowed these practitioners to strategically place local anesthetic circumferentially around the brachial plexus) The authors do not mention in their article whether the epineurium was violated or if the local anesthetic was placed outside the epineural barrier and allowed to diffuse inward.1 When placed underneath the epineurium, local anesthetics may diminish peripheral nerve blood supply secondary to edema or a mass effect. 4 By not breeching the epineurim and allowing the local anesthetic solution to diffuse inward, it is possible that nerve fascicles in the endoneurium are exposed to a lower concentration o f local anesthetic. In general, higher concentrations o f local anesthetics produce increased cytotoxic effects. 5 These cytotoxic effects are typically proportionate to duration of exposure to local anesthetic, s It is worth mentioning that Dhir et al. 1 did not incorporate bupivacaine into any of their local anesthetic solutions. Also, the authors did not chronicle tourniquet use in their case reports2 To further eliminate etiologies implicated in the "double-crush phenomenon" ,3 I believe it is a reasonable request to ask our orthopedic colleagues to forgo tourniquet inflation in patients with known peripheral nervous system disease.