vation is lost but motor control of the hind limbs is
not affected. However, the tail should be tied over-
head to support the horse if ataxia develops. The
sacrocaudal or first intercaudal vertebral space is
selected as the site for injection for epidural anes-
thesia.
5 This location is found by grasping the tail
and moving it up and down. The first articulation
caudal to the sacrum is the first intercoccygeal
space. The site should be clipped and aseptically
prepared. The epidural should be administered
with the use of aseptic technique. There are vari-
ous injection techniques and drug combinations that
can be used. The horse should be sedated and re-
strained in stocks (if available) during administra-
tion of epidural anesthesia. A small skin bleb of
local anesthetic can be deposited at the proposed
injection site to facilitate placement of the spinal
needle. A 20-gauge, 7.5-cm spinal needle should be
positioned just cranial to the dorsal spinous process
of the second coccygeal vertebra. The needle is in-
serted through the skin at an angle 30 degrees rel- ative to the tail and inserted cranially. If bone is
encountered, the needle should be redirected. Once
the needle is placed, the stylet should be withdrawn
and the hub of the needle is filled with the local
anesthetic to be injected. If the needle is positioned
in the epidural space, the fluid will be aspirated
(hanging drop technique). Minimal resistance is
encountered during epidural injection. Horses that
have had previous epidural injections may develop
fibrous scar tissue over the intercoccygeal space,
making needle placement difficult.
5 After injec -
tion, the needle should be removed. Caution
should be exercised during placement of the spinal
needle because some horses will kick during the
procedure. An epidural catheter can be placed to
facilitate readministration of anesthetic agents if
needed during the surgery. Loss of anal sphincter
tone is common when epidural anesthesia is
achieved. The type of blockade (motor and/or sensory) and
the duration of effect is dependent on the type of
drug(s) and the volume that is administered. Local
anesthetics should produce motor and sensory block-
ade, whereas only sensory innervation is lost with
other drug treatments. The use of 5 to 7 mL of 2%
lidocaine hydrochloride per 500 kg body weight
should produce analgesia within 5 to 15 minutes,
and the duration of analgesia should be 60 to 90
minutes.
5 Two percent mepivacaine hydrochloride
given at the same dose will produce analgesia in 10 to 30 minutes and provide analgesia for 90 to 120
minutes.
4 Ataxia is a complication when local an -
esthetics are used. Epidural administration of
\42-adrenergic agonists
such as xylazine will provide profound analgesia
without the complication of ataxia.
6,7 The recom -
mended dose of xylazine is 0.17 mg/kg. The onset
of action is 10 to 30 minutes, and the duration of
analgesia is 2.5 to 4 hours.
5 The xylazine should be
diluted in saline to a total volume of 6 to 10 mL.
Epidural administration of detomidine (30 – 60
fi2g/
kg) provides analgesia lasting for 2 to 3 hours but
produces sedation and ataxia.
5,6 The combination
of lidocaine (0.22 mg/kg) and xylazine (0.17 mg/kg)
produces significantly longer analgesia (approxi-
mately 5 hours) with only mild ataxia when com-
pared with either agent used alone.
7
Ataxia and the potential for recumbency must be
considered when determining which drug or combi-
nation of drugs and the dosage that is to be
administered.
5. Conclusions
The successful outcome of the use of local anesthetic
drugs depends on the clinician to accurately deposit
an appropriate volume and type of drug at the cor-
rect anatomic site. This can be achieved by a thor-
ough understanding of the pharmacology of local
anesthetics and equine anatomy.
References
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and techniques. In: Muir WW, Hubbell JAE, editors. Equine
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JC, Grimm KA, editors. Lumb & Jones’ Veterinary Anesthesia
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souri: Elsevier; 2012:868.
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Assoc 1988;193:1405–1408.
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466 2013 fiVol. 59fiAAEP PROCEEDINGS
HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT