Cryoneurolysis and Peripheral Nerve Stimulation: Reply

We would like to thank our colleagues for their thoughtful letter¹  regarding the use of percutaneous peripheral nerve stimulation to treat postoperative pain.²  We agree that combining a local anesthetic–based peripheral nerve block with percutaneous peripheral nerve stimulation will most likely prove the optimal management after painful surgical procedures, although we hesitate to describe it as “novel” given this combination was reported in multiple publications previously.^3–6  Several feasibility studies found that the acute pain from orthopedic procedures such as rotator cuff repair frequently required the addition of local anesthetic–based nerve block to percutaneous peripheral nerve stimulation in the recovery room.^3–6  Therefore, in a recently completed randomized, double-masked, sham-controlled trial (n = 66), we administered a single-injection ropivacaine peripheral nerve block after ultrasound-guided percutaneous lead insertion in all participants (NCT03481725). While the ropivacaine peripheral nerve block did provide effective postoperative analgesia as our colleagues suggest in their letter, the transition to stimulation during block resolution proved very challenging for the majority of participants—it was not a “smooth” transition from one modality to the next. The problem stems from the finding that current intensity requirements can vary dramatically—and unpredictably—preoperatively and postoperatively,^3–6  and that percutaneous peripheral nerve stimulation current can induce pain and muscle contractions with an intensity that is too high.³  Therefore, the pulse generator must be set to a relatively low intensity in the recovery room to ensure that the electrical current does not induce pain and/or contractions during block resolution 4 to 12 h postdischarge (and providing suboptimal analgesia until increased by the patient).

We agree with our colleagues that the cost of the available percutaneous peripheral nerve stimulation system may discourage its general adoption and that the (off-label) use of existing stimulating perineural catheters is enticing due to their availability and dramatically lower cost. This possibility certainly deserves investigation. However, we are somewhat pessimistic regarding the probability of providing adequate analgesia using a single stimulating catheter to deliver both perineural local anesthetic and, subsequently, electrical current. In general, perineural catheters must be inserted within the same fascial plane as the target nerve/plexus for adequate local anesthetic administration. In contrast—and as described in our review article—for percutaneous peripheral nerve stimulation, “…the optimal distance from the lead tip to epineurium of the target nerve was consistently 1.0 to 1.5 cm… A relatively remote distance theoretically promotes selective stimulation of the desired larger-diameter myelinated sensory neurons without activating motor or smaller-diameter sensory neurons that induce muscle contraction and discomfort, respectively… In addition, leads placed at this distance from the nerve are less sensitive to small changes in positioning due to movement which is critical in avoiding unpleasant sensations with purposeful muscle contraction.”³  Therefore, at more than 1.0 cm from the target nerve and rarely within the same fascial plane, it is improbable that a perineural local anesthetic infusion would provide significant analgesia.

The University of California at San Diego has received funding and product for other research projects of Drs. Ilfeld and Finneran from: Epimed (Farmers Branch, Texas); Infutronics (Natick, Massachusetts); and a manufacturer of percutaneous peripheral nerve stimulation devices, SPR Therapeutics (Cleveland, Ohio).