Page 2214 - Cote clinical veterinary advisor dogs and cats 4th

Epidural Analgesia/Anesthesia 1100.e3

needles, and instruments are opened on • After the ligamentum is penetrated, the hub • After the catheter is advanced to the appropri-
the sleeve around the gloves. of the needle is inspected for presence of ate space, the needle is then withdrawn over
VetBooks.ir a syringe. Dosages: most clinicians prefer ○ If blood is seen, the needle tip is partially • A section of skin adjacent to the site of
blood or cerebrospinal fluid (CSF):
the catheter.
• Epidural drugs are aseptically drawn into
local anesthetic bupivacaine (motor sparing
entry is then penetrated with the needle.
redrawn and redirected.
at 0.5%) 0.1-0.3 mg/kg canine or 0.1 mg/
probably within the subarachnoid space
kg feline, +/− morphine 0.02-0.05 mg/ ○ If CSF is encountered, the needle is The needle is tunneled parallel to the surface
of skin for 1.5-2 cm and then exits the skin.
kg. This combination can be diluted to a and should be withdrawn slightly. • The catheter’s free end is then fed retrograde
total volume of 0.1-0.15 mL/kg with saline ○ If no blood or CSF is seen, confirmation up the needle.
if advancement of the solution into the of epidural space is made by • The needle is then withdrawn, and the
thoracic area is needed (e.g., thoracotomy, ■ Loss-of-resistance technique: the syringe catheter is effectively tunneled away from
forelimb amputation, diaphragmatic repair), containing the saline and air is attached the epidural site. This provides for decreased
but dilution might reduce efficacy. Total to the hub of the needle. The syringe chances of iatrogenic bacteremia/infection in
volume rarely exceeds 6 mL of saline, local, plunger is then depressed. If there is the epidural space.
and opioid combined for canine patients no increase in resistance to pushing the • Excess catheter length is cut from the catheter
for an injection made from the LS space. plunger, the needle is correctly posi- using sterile scissors. Procedures and Techniques
Injections made more cranially are reduced tioned in the epidural space. If the air • The filter and injection port are secured.
in volume by 25% per four to five vertebral bubble in the syringe is compressed or • The epidural medications are then adminis-
bodies. Saline addition to the mixture is pushed against the saline as the plunger tered through the catheter, with the amount
dictated by need for cranial spread of the is depressed, the needle tip likely lies reduced to accommodate for placement of
agents. in the ligament, and further insertion catheter tip.
• Both species: 0.3-1 mL saline with same is indicated. • The catheter cap and filter are secured with
volume of air is drawn into another syringe, ■ Hanging drop technique: when the suture. A protective sterile covering is placed
which will act as an epidural space tester or ligamentum flavum is encountered— over the catheter and LS space.
identifier. the first sign of resistance—the stylet • Catheter position can be confirmed through
is withdrawn, and the hub is filled injection of contrast material.
TECHNIQUE OF EPIDURAL INJECTION with saline so the liquid forms a
• Clinician approaches the patient from behind meniscus. As the epidural space is Postprocedure
(facing in the same direction as the patient) if entered, its negative pressure will • Onset of analgesia varies from immediate
is in sternal recumbency or from the side of cause aspiration down the needle for lidocaine epidurals to 30-60 minutes for
the table (clinician’s hip against the patient’s shaft, and the fluid meniscus will bupivacaine epidurals to 2-4 hours for opioid
back, facing caudally) if the patient is in disappear. epidurals.
lateral recumbency. • After the correct positioning is confirmed, • Duration of analgesia varies from 1 hour
• Brace the hand holding the needle on the the injection proceeds over a 30-60 second for lidocaine epidurals to 3-6 hours for
patient’s back. Use the other hand to identify time frame. Often, respiratory and cardiac bupivacaine epidurals to 12-15 hours for
the LS space as outlined above. rate increase during injection. opioid/local epidural.
• The needle is then advanced transcutaneously • Pain of injection is severe with local anesthet-
at a 90° angle to the skin surface over the TECHNIQUE OF EPIDURAL CATHETERIZATION ics and ketamine. Some clinicians strongly
LS site. • After the needle enters the space, the bevel suggest using each as diluted solutions only
• The primary source of resistance is the dorsal of the needle must face cranially. and administering bupivacaine only if the
spinous ligament, the ligamentum flavum. • The catheter is then threaded down the animal is under the influence of heavy
This is the hardest layer to penetrate and needle; the needle does not move. sedation/analgesia or is anesthetized.
millimeter-depth pushes are required to • Catheter advancement should proceed • Vomiting, nausea, and ptyalism are common
realize 1) entry into the ligament and 2) without resistance. The catheter should never when catheters are placed in the thoracic
the classic loss of resistance or pop as the be withdrawn into the needle because of the spinal canal, when large volumes or con-
epidural space is entered under the ligament. possibility of shear/breakage. centrated morphine is used, or when pain/

EPIDURAL ANALGESIA/ANESTHESIA Finding the epidural space: the
operator’s right forefinger is in the depression caudal to the L7 spinous process;
thumb and middle finger of the same hand are on the most craniodorsal aspects EPIDURAL ANALGESIA/ANESTHESIA Epidural catheter in a dog with a
of each ilial wing. Epidural needle is ready to be placed immediately caudal to the surgically repaired ilial fracture. Note that the radiopaque catheter (short arrows)
forefinger (depression) to access the epidural space. This clinician is right-handed, enters the lumbosacral space and is visible on the floor of the vertebral canal at
but some left-handed clinicians prefer this orientation. L6 and L7 (long arrow). (Courtesy Dr. Peter Scrivani, Cornell University.)

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