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
- You can infiltrate the local anesthetic postoperatively subcutaneous to the surgical site, if the opportunity was not taken