Complications of locoregional anesthesia include accidental IV administration of local blocks, hematoma formation or other tissue injury at the administration site, and nerve blockade failure.1,3,8,9
IV administration of bupivacaine can induce significant systemic toxicosis that can be fatal. Accidental administration is more likely when syringes are poorly labeled or not labeled in the perioperative period. Brightly colored labels or special syringe caps instead of a needle can be used (Figure). Waiting until right before administration to draw the solution can also help avoid accidental IV delivery. Blocks may be drawn for multiple patients in a clinic, so a conspicuous patient label on the syringe is recommended.
The incidence of complications associated with dental blocks in horses was <3% in a retrospective study.13 Complications included hematoma formation at the site of administration and failure to desensitize the desired nerve. Another retrospective study on equine dental blocks noted hematoma formation as the most common complication (3 of 270 cases); all cases resolved in 24 to 48 hours.5 A case report noted formation of retrobulbar hematoma following maxillary block in a dog that required immediate drainage to avoid damage to the eye.14
Hematoma formation following locoregional anesthesia does not always result in significant complications, but it can induce bruising that may be upsetting to the pet owner, significant swelling, and temporary disfigurement of the area that makes anatomic landmarks difficult to find. Hematoma formation also increases blood flow to the area, which can increase absorption of the local anesthetic and thus decrease the duration and efficacy of a nerve blockade.
Peripheral nerve injuries can occur when the nerve involved in a block is lacerated, stretched, or otherwise compromised due to poor technique. Most needles used in ultrasonography or nerve-stimulator–assisted techniques are designed with a rounded bevel and no bladed edges, making them less likely to cut or slice through nerve tissue. Although these needles are more expensive, they can help mitigate nerve or tissue damage.
It is important to note the pressure required when administering a block, as high resistance during injection may indicate the needle is in the nerve sheath; if this occurs, the needle should be redirected slightly and reassessed for lower resistance during administration.3,8
Blockade failure can occur with certain conditions (eg, inflammation or neoplasia at the blockade site), increased blood flow to the area being blocked (faster metabolism of the local anesthetic), or removal of the blockade (eg, flushing the abdomen after an intraperitoneal splash block). Timing, location, and clinician comfort level (eg, willingness to perform the block, willingness to use multiple attempts to achieve appropriate landmarks) should be considered when determining the cause of blockade failure.