Epidural and Spinal Anesthesia and Analgesia in the Equine

In human and animal anesthesia, epidural and spinal administration of drugs is used to provide surgical anesthesia and/or postoperative analgesia. Several local anesthetic drugs are used to produce epidural anesthesia, such as lidocaine, bupivacaine, ropivacaine, and mepivacaine. Epidural analgesia is obtained with opioid agonists, alpha₂-adrenergic agonists, and ketamine. In horses, caudal epidural anesthesia is used to desensitize the anus, rectum, perineum, vulva, vagina, urethra, and bladder. The goal is to produce surgical regional anesthesia without losing motor function of the hind limbs. A combination of a local anesthetic drug with an alpha₂-adrenergic agonist or an opioid is the most popular option as this combination extends the period of action of the epidural anesthesia or analgesia in horses, humans, and small animals. Spinal analgesia and anesthesia has not been used in horses as an adjunct to general anesthesia as much as it has in small animals and human beings. The epidural administration of opioids with or without local anesthetics is commonly performed in dogs and cats before surgery to reduce general anesthetic requirements as well as to provide intraoperative and postoperative pain control. The perioperative use of epidural and spinal analgesia in horses is likely to increase in the future as recent studies have shown that administration of epidural or subarachnoid alpha₂-adrenergic agonists, phencyclidines, opioids, and low-dose local anesthetic produce intense antinociceptive effects.