Local anesthetics were once the singular mainstay of analgesia in medicine, and the modality now finds itself newly resurgent as a valuable and often integral part of the multimodal approach to pain management. Furthermore, recent evidence reveals local anesthesia is not only antinociceptive, it also elicits a constellation of positive immunomodulating, antimicrobial and tissue-healing effects.1,2
Following are six loco-regional blocks that deserve a second look and the recommended steps for administration.
1. Topical prilocaine/lidocaine cream
Familiar to many as the commercial product EMLA (AstraZeneca Pharmaceuticals), this cream also comes in generic form with 2.5% of each local anesthetic (lidocaine and prilocaine). The prilocaine penetrates skin and makes placement of an intravenous catheter painless, resulting in numerous benefits such as faster placement and diminished frustration. Topical lidocaine/prilocaine cream also can be used to ease the experience of phlebotomy in sensitive "touch-me-not" patients and to facilitate subcutaneous injection of microchips, fluids, local anesthetics, and so on. To administer, follow these steps:
2. Topical 5% lidocaine patch
Available only as the trade product Lidoderm (Endo Pharmaceuticals), the 10-x-14-cm patch is used to relieve the pain of post-herpetic neuralgia, also referred to as after-shingles pain, in people. However, lidocaine has many potential veterinary uses as a dermal differential blockade, meaning it will prevent pain but not the sense of touch or pressure. Common uses include postoperative application around larger or potentially more painful surgical or trauma sites and on limbs at the site of osteosarcoma or other metastatic bone cancers. In people, the lidocaine patch has been used for breakthrough osteoarthritis pain.3 The lidocaine, all 700 mg of it, is embedded in the self-adhesive patch, which can be cut to the desired size and shape. Studies in both dogs and cats reveal negligible plasma concentrations, even when the entire patch is placed for several days on normal skin4,5 (concentrations may be higher on inflamed skin). Here's how best to administer this local anesthetic:
3. Line and infiltrative blocks
These blocks are sublime, but far too often overlooked, parts of a multimodal perioperative protocol. Human medical studies show that these local blocks improve pain scores and decrease the need for other analgesics such as opioids. The veterinary literature, however, is more sparse on this matter, with three studies demonstrating a positive effect6-8 and one recent study that could not detect a difference in pain scores with the use of line blocks in elective spay/neuter procedures.9 The latter study's results may have been complicated, in part, by errors in technique. More important, the pain-scoring systems used in that study may not have been sensitive enough to detect differences with the use of local anesthetics, since all of the patients also received NSAIDs and opioids. Nevertheless, line blocks and subcutaneous infiltrative blocks are simple, safe, inexpensive and widely accepted as effective means of contributing to postoperative patient comfort.
4. Intravenous regional anesthesia
This technique, also known as the Bier block after the physician who developed the technique 100 years ago, is extremely useful for procedures on the distal limb, such as biopsy, mass removal, trauma repair and digit amputation. Intravenous regional anesthesia uses lidocaine only (without epinephrine, and not with bupivacaine). The utility of this procedure has been described in dogs,12 and safety has been established even in cats,13 with minimal plasma lidocaine concentrations detected. Following are some administration tips:
5. Intratesticular block
This technique is indicated, as the name implies, for orchiectomy. That the local anesthetic does in fact move up the spermatic cord and associated structures has been well-established in piglets14,15 and horses.16
6. Retrobulbar block
This technique is indicated for procedures involving the globe, especially enucleation. This is an intimidating-looking procedure but is simpler and safer than you might expect and is now well-described in the veterinary literature.17.18
Impaired immune function, increased risk of sepsis and delayed wound healing are just a few of the deleterious effects associated with pain. As part of a multimodal approach to pain management, the use of these six loco-regional anesthetic techniques can greatly improve your ability to provide complete and compassionate care.
1. Johnson SM, Saint John BE, Dine AP. Local anesthetics as antimicrobial agents: a review. Surg Infect (Larchmt) 2008;9(2):205-213.
2. Cassuto J, Sinclair R, Bonderovic M. Anti-inflammatory properties of local anesthetics and their present and potential clinical implications. Acta Anaesthesiol Scand 2006;50(3):265-282.
3. Grammaitoni AR, Galer BS, Onawola R, et al. Lidocaine patch 5% and its positive impact on pain qualities in osteoarthritis: results of a pilot 2-week, open-label study using the Neuropathic Pain Scale. Curr Med Res Opin 2004;20 Suppl 2:S13-S19.
4. Weiland L, Croubels S, Baert K, et al. Pharmacokinetics of a lidocaine patch 5% in dogs. J Vet Med A Physiol Pathol Clin Med 2006;53(1):34-39.
5. Ko JC, Maxwell LK, Abbo LA, et al. Pharmacokinetics of lidocaine following the application of 5% lidocaine patches to cats. J Vet Pharmacol Ther 2008;31(4):359-367.
6. Duffield TF, Heinrich A, Milman ST, et al. Reduction in pain response by combined use of local lidocaine anesthesia and systemic ketoprofen in dairy calves dehorned by heat cauterization. Can Vet J 2010;51(3):283-288.
7. Carpenter RE, Wilson DV, Evans AT. Evaluation of intraperitoneal and incisional lidocaine or bupivacaine for analgesia following ovariohysterectomy in the dog. Vet Anaesth Analg 2004;31(1):46-52.
8. Sawas, I, Papazoglou LG, Kazakos G, et al. Incisional block with bupivacaine for analgesia after celiotomy in dogs. J Am Anim Hosp Assoc 2008;44(2):60-66.
9. Fitzpatrick CL, Weir HL, Monnet E. Effects of infiltration of the incision site with bupivacaine on postoperative pain and incisional healing in dogs undergoing ovariohysterectomy. J Am Vet Med Assoc 2010;237(4):395-401.
10. Candido KD, Winnie AP, Ghaleb AH, et al. Buprenorphine added to the local anesthetic for axillary brachial plexus block prolongs postoperative analgesia. Reg Anesth Pain Med 2002;27(2):162-167.
11. Bazin JE, Massoni C, Bruelle P, et al. The addition of opioids to local anesthetics in brachial plexus block: the comparative effects of morphine, buprenorphine and sufentanil. Anaesthesia 1997;52(9):858-862.
12. Webb AA, Cantwell SL, Duke T, et al. Intravenous regional anesthesia (Bier block) in a dog. Can Vet J 1999;:40(6):419-421.
13. Kushner LI, Fan B, Shofer FS. Intravenous regional anesthesia in isoflurane anesthetized cats: lidocaine plasma concentrations and cardiovascular effects. Vet Anaesth Analg 2002;29(3):140-149.
14. Ranheim B, Haga HA, Ingebrigtsen K. Distribution of radioactive lidocaine injected into the testes in piglets. J Vet Pharmacol Ther 2005;28(5):481-483.
15. Haga HA, Ranheim B. Castration of piglets: the analgesic effects of intratesticular and intrafunicular lidocaine injection. Vet Anaesth Analg 2005;32(1):1-9.
16. Haga HA, Lykkjen S, Revold T, et al. Effect of intratesticular injection of lidocaine on cardiovascular responses to castration in isoflurane-anesthetized stallions. Am J Vet Res 2006;67(3):403-408.
17. Accola PJ, Bentley E, Smith LJ, et al. Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs. J Am Vet Med Assoc 2006;229(2):220-225.
18. Myrna KE, Bentley E, Smith LJ. Effectiveness of injection of local anesthetic into the retrobulbar space for postoperative analgesia following eye enucleation in dogs. J Am Vet Med Assoc 2010; 237(2):174-177.