Treating Severe Forelimb Pain With a Continuous Nerve Blockade (AAEP 2010)

Veterinarians can reduce a horse's severe forelimb pain by administering a continuous, low-dose infusion of the local anesthetic bupivacaine, but this method is not suitable for every case, according to researchers from Cornell University's College of Veterinary Medicine.

"Severe forelimb pain can occur with fractures, joint or tendon sheath infections, or traumatic injuries," explained Ashlee E. Watts, DVM, Dipl. ACVS, a graduate student pursuing a PhD and a part time large animal surgeon, who presented a study on this subject at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md. "In response to the reluctance to bear weight on a severely painful limb, increased weight bearing stresses are placed on the opposite forelimb, which can lead to support limb laminitis."

Veterinarians can administer epidural medications in the hind limb to drastically reduce pain. Since an epidural cannot be used for forelimb pain, Watts and colleagues assessed the use of a continuous peripheral nerve blockade (CPNB). This technique is performed by inserting a catheter in the mid-metacarpal (cannon bone) region between the suspensory ligament o the deep digital flexor tendon and continuously administering bupivacaine to the palmer nerves. These nerves are responsible for transmitting pain signals from the tissues of the distal cannon bone, fetlock, pastern and foot to the spinal cord and brain.

Watts and colleagues compared the effect of administering bupivacaine via CPNB at a rate of 0.14 mL/hour to that of injecting bupivacaine only intermittently (0.85 mL every six hours). They studied 14 horses with experimentally induced forelimb pain over three days.

Key findings:

  • CPNB can be performed using a single catheter and a low volume of bupivacaine that does not cause complete nerve block;
  • Catheters were easily placed and did not dislodge with normal limb movements; and
  • CPNB effectively decreased severe, short term lameness compared to intermittent low-dose injections. No adverse effects of the injections were noted.

"One catheter did culture positive for Staphylococcus aureus, suggesting that although this technique can reduce lameness from short-term, severe, forelimb pain, clinicians need to consider the risk of microbial contamination to the tissues when selecting cases in which to use this technique," concluded Watts.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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