Development of a technique for continuous perineural blockade of the palmar nerves in the distal equine thoracic limb

Authors

  • Bernd Driessen DVM, DrMedVet, Diplomate ACVA, Diplomate ECVPT,

    1. Department of Clinical Studies, New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, PA, USA
    2. University of California-Los Angeles, David Geffen School of Medicine, Department of Anesthesiology, Los Angeles, CA, USA
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  • Massimiliano Scandella DMV, PhD,

    1. Scienze Cliniche Veterinarie, Sezione di Clinica Chirurgica Veterinaria, Facoltà di Medicina Veterinaria, Università degli Studi di Milano, Milan, Italy
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  • Laura Zarucco DMV, PhD

    1. Department of Clinical Studies, New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, PA, USA
    2. Dipartimento di Patologia Animale, Facoltà di Medicina Veterinaria, Università degli Studi di Torino, Torino, Italy
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Bernd Driessen, Department of Clinical Studies, New Bolton Center, 382 West Street Rd., Kennett Square, PA 19348, USA. E-mail: driessen@vet.upenn.edu

Abstract

Objective  To develop a technique for placing continuous peripheral nerve block (CPNB) catheters adjacent to palmar nerves in horses and to evaluate the effect of low-volume local anesthetic (LA) infusion on nociception in the distal equine thoracic limb.

Study design In vitro and in vivo laboratory investigation.

Study material and animals  Forty-two thoracic limbs from 22 equine cadavers and five horses.

Methods  Thoracic limb specimens were dissected to find landmarks for catheter insertion adjacent to medial and lateral palmar nerves. Based on the anatomy of the proximal metacarpus, a technique for placing palmar CPNB catheters was developed and the potential for catheter dislodgement studied in vitro by fluoroscopic visualization during passive carpal flexion and dye injection following simulated limb motion. The feasibility of CPNB catheter instrumentation in standing, sedated horses was tested in five animals, with ultrasound control. Electrical and mechanical stimulation thresholds and response latencies for hoof withdrawal responses (HWR) were determined following saline or LA infusion.

Results  Medial and lateral CPNB catheters were inserted percutaneously 2 and 4–5 cm, respectively, distal to the accessory carpal bone and advanced for ∼7 and 10 cm, respectively, to place the tip just proximal to the communicating branch of the nerves. Catheters were placed correctly in 88% and 85% of cadaver limbs. In the standing horses, LA infusion not only increased HWR thresholds and latencies to noxious mechanical or electrical stimulation but also caused vasodilation and limb swelling over time.

Conclusion  The technique, developed in vitro, for placing and maintaining palmar CPNB catheters in the equine thoracic limb was successfully applied in vivo. Catheters were well tolerated but LA infusion may cause limb swelling, suggesting a need for further exploration of drug and infusion regimens.

Clinical relevance  Continuous perineural LA infusion along palmar nerves may develop into an effective analgesic technique in horses suffering from lower limb pain.

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