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Continuous Peripheral Nerve Block: A Novel Technique Laura Zarucco, DMV, PhD Facoltà di Medicina Veterinaria dell’Università degli Studi di Torino, Italy University of Pennsylvania
Bernd Driessen, DVM, PhD, DECVPT, DACVA University of Pennsylvania
About This Column Leading Edge is published by Compendium Equine in par tnership with Morris Animal Foundation. The column highlights the cutting-edge work and insights of leading veterinar y researcher s who are working with the foundation. For each column published, Compendium Equine makes a donation to the foundation in suppor t of its impor tant research programs. Studies funded by Morris Animal Foundation have led to new diagnostic, surgical, treatment, and prevention techniques, some of which are now the standards in animal health care. For more information, visit the foundation’s Web site at www. MorrisAnimalFoundation.org.
Managing pain effectively is one of the most important tasks that veterinarians perform on a daily basis in clinical practice. Successful treatment of pain affecting the forelimbs in horses is complicated, not only because responses to injuries vary among individual animals but also because horses put a high load on their forelimbs for most of the day (30% to 33% of their body weight per forelimb), predisposing them to overloading the contralateral limb after either a severe injury to or major orthopedic surgery in one forelimb. Alleviation of pain is an important aspect of equine orthopedic treatment because it significantly decreases physiologic stress on the animal and reduces perioperative complications. Systemic administration of opioids and NSAIDs has been widely accepted for short- and long-term analgesia in horses with severe tissue injury but often is not very effective or is associated with multiple adverse events.1 Only continuous-rate infusion (CRI) of butorphanol, a κ-opioid receptor agonist and µ-receptor antagonist, has been reported recently as lacking major side effects while significantly improving behavior scores during the first 24 hours after exploratory celiotomy; the investigators interpreted these results as being consistent with effective analgesia provided by the prolonged intravenous butorphanol administration.2,3 Further studies are needed to characterize the potential advantages of a butorphanol CRI in alleviating orthopedic pain. The relatively low cost and minimal systemic absorption of local anesthetics (LAs) make them optimal alternatives or adjuncts to opioid- and/or NSAID-based analgesia. In recent years, applications of peripheral nerve blocks in humans have increased considerably and have gained much popularity among clinicians for the treatment of virtually all types of severe surgical and procedural pain. Regional analgesia/anesthesia has been applied in awake and anesthetized patients. Two discoveries fueled the exploration of regional analgesia/anesthesia techniques in pain management, especially lower-extremity nerve blocks: 1. Peripheral and central sensitization play a major role in prolonging postoperative pain and can be effectively inhibited only by peripheral nerve blockade, not by opioid-based analgesia, if they can be inhibited at all.1,4 2. When discontinued or used over longer periods, opioids may even exhibit pronociceptive effects, depending on the doses administered and duration of treatment.5
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cavitary infusion, and, more recently, nerve blocks in almost all types of single-dose local wound lavage (splash regional anesthesia/analgesia proceblock) and perineural techniques.1,6–8 In dures. In addition, such complications horses, a local/regional technique of as intraneuronal and intravascular injecanalgesia, such as epidural analgesia for tion can be avoided.16 9 Continuous perineural block often pain originating in the hindlimb, is currently not available for treating provides much better pain control with severe pain in the forelimb. fewer side effects than systemic analgeAlternative methods of postoperative sia and may not impair normal motor analgesia, such as single-dose or confunction in the affected extremity—a tinuous peripheral ner ve blockade feature of particular importance in the (CPNB), have long been introduced in standing horse. The CPNB technique, human medicine with great success10–14 when used as part of a multimodal and hold considerable promise in small anesthetic regimen, also may substananimals, where they have more recently tially reduce the amount of general been tested to minimize intra- and anesthetic needed to maintain a surgipostoperative discomfort in surgical cal plane of anesthesia, thus helping patients.6–9 In humans, numerous benpreserve adequate cardiovascular and efits of the CPNB technique have been respirator y functions in the anesrecognized, including reduced hospital thetized patient undergoing surgery. stay and duration of convalescence as EXPERIMENTAL well as improved functional rehabilitaTECHNIQUES tion and postoperative outcome. 11–15 These benefits also emphasize the To provide alternative methods of importance of integrating regional pain management in the distal equine analgesia into multimodal pain treatforelimb and digit, our research group at ment regimens and more sophisticated the University of Pennsylvania investirehabilitation programs. gated the feasibility of instrumenting The CPNB method entails continu- Figure 1. The following anatomic the palmar, median, and ulnar nerves ous or intermittent low-volume infu- landmarks—some of which are with perineural catheters in standing sion of LAs by placing catheters along specified—for the palmar sedated horses. Continuous perineural continuous peripheral nerve 15 or close to peripheral nerves. Three palmar blocks (proximal or distal to the blockade (CPNB) technique are techniques have been proposed to place used to determine the insertion communicating branch) are recomperineural catheters: the nonstimulat- point for the lateral (Lat) and mended primarily in patients in which ing needle technique, the stimulating medial (Med) CPNB needle: severe pain is anticipated to occur as a Accessory carpal bone (ACB)— needle technique, and ultrasound-aided result of palmar fetlock, pastern, or foot needle/catheter placement. A fourth distal margin; proximal sesamoid surgery and in which early functional bone (PSB)—proximal margin; technique, which is no longer used, is communicating branch of palmar rehabilitation can be facilitated. Major the periarterial placement of axillary nerves (CB); interosseous muscle surgery, such as phalangeal arthrodesis, catheters under direct vision after cut- (suspensory ligament); superficial or severely painful conditions that put digital flexor tendon; and deep down during local anesthesia.15 the contralateral digit/foot at risk for With the support of ultrasound digital flexor tendon and developing laminitis (e.g., sesamoid/ imaging, nonstimulating perineural accessory ligament. phalangeal osteomyelitis, severe deglovcatheters can be placed with great accuing injuries/trauma, septic interpharacy, allowing imaging and assessment of all anatomic langeal joints, puncture wound with sepsis of navicular structures and the position of the catheter tip relative to bone, bursa, joint, or deep digital flexor tendon) are the nerve and the LA spread.15,16 In humans, it has been examples of possible indications for CPNB of the palmar demonstrated that ultrasound guidance, more than any nerves. In addition, horses undergoing total or partial other technique, can significantly improve the quality of hoof wall resection may benefit from CPNB. COMPENDIUM EQUINE
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Figure 2. Instrumentation used for horses with CPNB catheters.
Reusable, lightweight, ambulatory infusion pumps (Ace Medical Automed 3400, Curlin Medical).
We first developed a simple and reproducible technique for placing catheters along the palmar nerves. In preparation for the first in vivo instrumentation of horses and to avoid inaccurate catheter placement and/or catheter dislodgment, a number of different studies aimed at identifying anatomic landmarks, potential risk for damage to surrounding tissues during catheter placement, satisfactoriness of the catheter–skin fixation, and incidence of complications (e.g., dislocation/kinking, infection) were conducted.17 Forty-two forelimb specimens were dissected to locate the anatomic landmarks for safe percutaneous CPNB catheter insertions along the medial and lateral palmar nerves, and the potential for catheter dislodgment was investigated in vitro using fluoroscopy during passive carpal flexion and dye injection following November/December 2007
Local anesthetic drug-containing infusion bags transferred into horse boots (Ice Horse insulated leg wraps, Mackinnon Ice Horse).
The pumps are connected to the CPNB catheters using proprietary tubing and are then mounted on the lower extremity.
Afterward, the boots are secured in place with an outer bandage.
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simulated limb motion.17 Landmarks for palmar CPNB catheter placement were identified and are shown in Figure 1. The studies followed an initial in vivo feasibility study testing the efficacy of CPNB for long-term regional analgesia in the distal equine forelimb. The catheter placement along the palmar nerves in the standing horse as we recommend it has been described in detail elsewhere.18 Ultrasound imaging before and at the end of the instrumentation procedure helps the operator to become familiar with the local anatomy and confirm correct placement after catheter insertion. The feasibility of CPNB catheter instrumentation was tested in five standing, sedated pilot horses using ultrasound control. A Perifix epidural catheter set (B. Braun) was used. The set contained a 20-gauge, 8.9-cm Tuohy-
Schliff–style tip needle that served as an introducer for the enclosed closed-tip, radiopaque polyamide catheter (20 gauge, 0.80-mm internal diameter, 104 cm), which was flushed with heparin solution before insertion. After subcutaneous tunneling over 2.0 to 2.5 cm, the Tuohy needle was cautiously pushed through the palmar fascia and advanced over its entire length along the nerve. Subsequently, medial and lateral CPNB catheters were inserted through the needle and advanced for approximately 7 and 10 cm, respectively, to place their tips just proximal to the communicating branch of the palmar nerves. The free endings of the CPNB catheters were later connected to reusable, lightweight, battery-driven ambulatory infusion pumps (Figure 2; Ace Medical Automed 3400, Curlin Medical) by means of proprietory tubing (AM-360/370, Curlin Medical). Pump sets and extension tubing were primed with LA solution before attachment to the CPNB catheters, and the legs were bandaged at the insertion site of the catheters (Figure 2). Subsequent CRI of LAs (lidocaine 2%, mepivacaine 1%, bupivacaine 0.5%) through the CPNB catheters significantly increased pain thresholds and hoof withdrawal response latencies to electrical and mechanical noxious stimulation, while saline infusion did not.17 This initial study and a subsequent study showed that the in vitro– developed technique of placing and securing palmar CPNB catheters in the equine forelimb can be successfully applied under ambulatory conditions in the standing horse. 17,18 Catheters were well tolerated for up to 10 days in saline-infused limbs. However, in the initial experimental series, LA infusion caused limb swelling, thus calling for further exploration of drug and infusion regimens lacking this side effect, although this effect was not observed in a clinical patient in which the technique was applied over 3 weeks.18 Therefore, additional in vivo studies are under way to refine drug concentrations, infusion regimens, COMPENDIUM EQUINE
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and the instrumentation technique itself (i.e., catheter advancement beyond the communicating branch of the palmar nerve). Because the treatment of severe pain in other areas of the forelimb, including the carpus, as well as painful surgical procedures performed in the digit remain a therapeutic challenge in equine patients, we currently are also evaluating a technique for placing peripheral catheters in the antebrachium along the ulnar and median nerves.
FUTURE WORK AND APPLICATIONS Many horses could profit from CPNB techniques. Only clinical studies will eventually reveal more about the usefulness of CPNB techniques for specific clinical conditions in horses. However, not all questions can be readily answered by studies alone, and only long-term experience with CPNB techniques in clinical practice will prove the efficacy of these techniques. The frequency of complications that occur with the multiple regional anesthetic techniques in use today is largely unknown. Thus, large studies are necessary to prove the superiority of CPNB techniques over other methods of
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Reviewer Comment This article represents the best in equine research. It is focused on the day-to-day management, wellness, and care of horses. The technique is described in clear detail and can be adapted quickly to clinical cases. I applaud the authors and will be happy to share this article with my students.
pain management in horses. Future studies should address drug and infusion protocols, possible improvements to the instrumentation technique, and the critical timing of treatments to maximize pain relief in the affected limb while preventing overloading of the contralateral limb. Ultimately, the goal is to minimize adverse events associated with the administered drugs while maintaining an optimal level of analgesia. CPNB techniques in the equine forelimb offer the advantage of more safely carrying out sophisticated surgical procedures with less risk for complications during convalescence and better managing pathologic conditions with recurrent intractable pain.
317 ACKNOWLEDGMENTS The above-mentioned studies were conducted with the generous support of Morris Animal Foundation (Grant D05EQ-024; P.I. B.D.). As members of our research group, Dr. Massimiliano Scandella provided excellent assistance during development and implementation of the CPNB technique, while Drs. Olga Seco and Francesca Cozzi assisted during the development of the instrumentation technique by performing ultrasonography and nerve conduction measurements, respectively.
REFERENCES 1. Driessen B: Pain—Systemic and local/regional drug therapy. Clin Tech Equine Pract 6:135–144, 2007. 2. Sellon DC, Monroe VL, Roberts MC, et al: Pharmacokinetics and adverse effects of butorphanol administered by single intravenous injection or continuous intravenous infusion in horses. Am J Vet Res 62:183–189, 2001. 3. Sellon DC, Roberts MC, Blikslager AT, et al: Effects of continuous rate intravenous infusion of butorphanol on physiologic and outcome variables in horses after celiotomy. J Vet Intern Med 18:555–563, 2004. 4. Driessen B: Pain—From sign to disease. Clin Tech Equine Pract 6:120–125, 2007. 5. Koppert W, Schmelz M: The impact of opioid-induced hyperalgesia for postoperative pain. Best Pract Res Clin Anaesthesiol 21(1):3–13, 2007. 6. Wenger S: Brachial plexus block using electrolocation for pancarpal arthrodesis in a dog. Vet Anaesth Analg 31:272–275, 2004. 7. Wolfe TM, Bateman SW, Cole LK, et al: Evaluation of a local anesthetic delivery system for the postoperative analgesic management of canine total ear canal ablation—A randomized, controlled, double-blinded study. Vet Anaesth Analg 33:328–339, 2006. 8. Rasmussen LM, Lipowitz AJ, Graham LF: Development and verification of saphenous, tibial and common peroneal nerve block techniques for analgesia below the thigh in the nonchondrodystrophoid dog. Vet Anaesth Analg 33:36–48, 2006. 9. Campoy L: Fundamentals of regional anesthesia using nerve stimulation in the dog, in Gleed RD, Ludders JW (eds): Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals. Ithaca, NY; International Veterinary Information Service; www.ivis.org; A1416.0506. 10. Natalini CC, Driessen B: Epidural and spinal anesthesia and analgesia in the equine. Clin Tech Equine Pract 6:144–153, 2007. 11. Ansbro FP: A method of continuous brachial plexus block. Am J Surg 71:716–722, 1946. 12. Seelander D: Catheter technique in axillary plexus block. Presentation of a new method. Act Anaesthesiol Scand 21:324–329, 1977. 13. Chelly JE, Delaunay L, Williams B, et al: Outpatient lower extremity infusions. Best Pract Res Clin Anaesthesiol 16:311–320, 2002. 14. Dalens B: Lower extremity nerve blocks in pediatric patients. Tech Reg Anesth Pain Mgmt 7:32–47, 2003. 15. Boezaart AP: Perineural infusion of local anesthetics. Anesthesiology 104: 872–880, 2006. 16. Marhofer P, Greher M, Kapral S: Ultrasound guidance in regional anaesthesia. Br J Anaesth 94:7–17, 2005. 17. Driessen B, Scandella M, Zarucco L: Development of a technique for continuous perineural blockade of the palmar nerves in the distal equine forelimb. Vet Anaesth Analg 2007; in print. 18. Zarucco L, Driessen B, Scandella M, et al: Continuous perineural block of the palmar nerves: A new technique for pain relief in the distal equine forelimb. Clin Tech Equine Pract 6:154–164, 2007.
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