6 practical loco-regional blocks you should be using

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:

• Clip the desired site, and apply the local anesthetic cream.

• Place an impervious covering, and wrap with bandage material of your choice. Commercial medical products are available. Some prefer to use clear plastic wrap. At our clinic, we use a small square of aluminum foil. Secure the site in a manner that disallows licking and cream ingestion.

• Wait about 30 minutes. A shorter, 15-to 20-minute wait period is usually sufficient.

• Unwrap, clean and prepare the site, now numbed, and proceed. For perioperative protocols, the shorter wait period allows for premedications to be administered, so that when returning to place the intravenous catheter, the patient is both sedated and pain-free at the site of vascular access. In properly premedicated patients, a skilled technician often can place an indwelling catheter without assistance.

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:

• Clip, clean and dry the site.

• Cut the patch to the desired shape and size; since it is not sterile, don't place the patch directly on top of incision lines, but rather to either side. In areas of severe swelling, for example, after cruciate repair, shape the patch to cover much of the affected region.

• Protect and secure the patch with bandage material so that there is no chance of ingestion (similar to the precaution given when applying fentanyl patches); the large amount of lidocaine present in an individual patch can be toxic if consumed.

• Leave the patch in place for a maximum of five days.

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.

• Before surgery, clip and prepare the animal in a customary manner.

• Inject the local anesthetic subcutaneously at the expected incision site. Lidocaine and bupivacaine can be mixed, but the onset and duration of both will be delayed due to the dilution. If the surgical incision will not be made for 15 minutes after infiltration (while the patient and surgeon are being prepped, for example), it is satisfactory to use bupivacaine only to take advantage of its full duration of action (about six hours). There are several published doses, but a customary one for bupivacaine is 2 mg/kg for dogs and 1 mg/kg for cats. Lidocaine doses are suggested at 5 mg/kg for dogs and 2.5 mg/kg for cats. If combining the two, then each drug should be drawn at half these doses. In people, the duration of bupivacaine has been shown to nearly double if small amounts of opioids are added (0.075 mg/kg morphine10 and 0.003 mg/kg buprenorphine11 ). This is a routine addition in our practice.

• If the surgical area is large (e.g., mass removal), you may have to dilute the local anesthetic 1:1 or 2:1 with saline solution to achieve the necessary volume. That will shorten the duration of action, but recall that, with the addition of opioids, the duration can be extended. When infiltrating, keep in mind that innervation of the site generally comes from the proximal or dorsal aspect and possibly cranial. So infiltrate these areas first, and use the remainder to move under the rest of the site (distally/ventrally).

• You can infiltrate the local anesthetic postoperatively subcutaneous to the surgical site, if the opportunity was not taken before incision.

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:

• Ideally, an indwelling intravenous catheter should be placed (use standard procedure). Note: A separate intravenous catheter must be placed in an unaffected limb for the administration of intravenous fluids.

• Gently exsanguinate the veins of the affected limb by encircling the paw with your thumb and forefinger and moving with pressure in a distal-to-proximal motion.

• Place one or two tourniquets proximal to the site of injection and firm enough to occlude veins but not arteries.

• In dogs, inject 3 mg/kg of lidocaine (no epinephrine). In cats, the dose should be reduced to 1 mg/kg.

• Although lidocaine's effects come on rapidly, one still must be patient for the block to reach peripheral nerves and take full effect, perhaps as long as 10 to 15 minutes. The tourniquet and block should be left in place for a minimum of 30 minutes and a maximum of 90 minutes.

• Once the tourniquet is removed, the lidocaine remaining in the vein will enter systemic circulation, but even in cats this results in very low plasma concentrations. The block will last about another 20 minutes. You can infuse the surgical site subcutaneously with bupivacaine (possibly with an opioid to extend duration) or apply a lidocaine patch to extend the loco-regional anesthetic effect beyond the time when the intravenous regional anesthesia will have worn off.

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

• Clip and prepare the scrotum and prescrotal areas in a customary manner.

• Use a 22- or 25-ga needle on the local anesthetic syringe, depending on patient size. Some clinicians prefer lidocaine only (2 mg/kg); others prefer a combination of lidocaine 1 mg/kg and bupivacaine 1 mg/kg. An opioid can be added as described above.

• Secure the testicle in the scrotum with one hand, and advance the needle with the other from the caudal pole to the cranial pole of the testicle. Apply aspiration, with the negative pressure held for several seconds to ensure no flashback (this tissue is more dense than most others).

• Inject the local anesthetic while withdrawing the needle caudally until the testicle is felt to be turgid; this will take about one-third of the volume. Then repeat in the other testicle. The rest of the local anesthetic can be used for a line block at the incision site.

• Despite the expected rapid onset of lidocaine, it takes several minutes (perhaps 10) for the block to move up the cord and achieve the maximum effect. If the block is successful, the absence of the expected cremaster muscle twitch when the clamp is applied will be notable.

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

• Clip and prepare the hair and skin ventral to the affected eye.

• Use a 22-ga, 1½-in needle on the syringe containing the local anesthetic. Place a slight (15-degree) bend in the middle of the needle.

• Place the needle perpendicular to the skin at the lateral aspect on the dorsal edge of the zygomatic arch, directed medially toward the retrobulbar area.

• Advance the needle in the caudomedial direction, sliding along the dorsal edge of the zygomatic arch. When the needle is about halfway inserted, direct it in a more dorsal manner to come up into the retrobulbar space. With the slight bend in the needle, advancing it will naturally follow this course.

• Once placed, aspirate. If you note no flashback, inject the local anesthetic. If the eye had vision and an intact pupillary light reflex, you'll observe rapid mydriasis if the block was placed correctly (this will not be apparent in a blind eye).

• For enucleation, after closure of the lids, administer a peri-incisional infiltration of bupivacaine with or without an opioid since the skin of the face won't have been blocked by the retrobulbar local anesthetic.

Conclusion

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.

REFERENCES

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.