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
- 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.
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.