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Local and regional anesthetic techniques (Proceedings)

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Apr 01, 2010

Epidural analgesia/anesthesia

      Technique
Patients are typically sedated or anesthetized and placed in sternal or lateral recumbency. Next, the cranial edge of the wings of the ilia are palpated. Once located, a 10 cm by 10 cm area of hair directly over the lumbosacral junction is clipped and the skin is surgically prepared. Needle insertion is made directly over the depression formed by the lumbosacral junction with the needle initially positioned perpendicular to the skin. It is important the stylet is correctly positioned within the needle to prevent transplantation of skin into the epidural space. Following insertion, the needle is observed for flow of cerebral spinal fluid or blood. Once the tip of the needle is confirmed to be in the epidural space, the syringe is attached to the hub of the epidural needle and a slow injection of the analgesic agent is begun. Signs indicating correct needle placement may include twitching of the tail muscles and a change of respiratory pattern during injection.

      Complications and contraindications
Sterile technique is mandatory.
Inflammation, coagulopathy, or other pathology in the area of the lumbosacral junction may be a contraindication to epidural placement.
Local anesthetics should not be given by epidural route when animals are hypotensive. Sympathetic blockade may worsen hypotension.

Epidural catheter placement

      Indications
Used for procedures where repeated epidural administration of analgesic drugs is anticipated such as pancreatitis or orthopedic surgery of the hind limb or pelvis.

      Complications and contraindications
Remember that application of local anesthetics to the cranial thoracic or cervical spinal cord can cause motor blockade to the respiratory muscles and block sympathetic nerves responsible for regulation of cardiovascular function.
Repeated injection of drugs which contain preservatives may result in damage to the spinal cord and neurological dysfunction.
The same complications and contraindications apply as for epidural drug administration with the addition of possible hind limb weakness and prolonged urinary retention.

It is important to reposition the animals ever 2 to 4 hours since normal sensation to a significant part of the body may be reduced or absent. Prolonged pressure on nerves and muscles may result in temporary or permanent dysfunction.
The risk of serious infection will usually increase over time; therefore the catheter should be removed as soon as it is no longer needed.
Aseptic technique is essential for placement of the catheter and for handling during subsequent injections.
Catheter insertion and removal may be associated with epidural hematoma development. Animals should be carefully monitored for development of this serious complication.

Brachial plexus block

Technique
An area cranial and dorsal to the point of the shoulder is clipped and prepared with surgical scrub. This is often done during the preparation of the leg for surgery. With the neck in a natural position, the cervical transverse processes will form a line that, if continued, will usually traverse the proximal brachial plexus. It is important the needle be guided beneath the scapula, but outside the thorax. Then the syringe is attached and aspiration is attempted to check for accidental puncture of a blood vessel. After confirmation of correct needle placement, 1 or 2 mls of the analgesic solution is injected. Then the needle is withdrawn approximately 1 cm, and the process of aspirating and injecting is repeated until the needle is just ready to exit the skin.

Complications and contraindications
Brachial plexus blocks are relatively safe and easy to perform. Accidental insertion of needle tip into thoracic cavity should be guarded against.
Contraindications would include infection in the nearby tissues or history of sensitivity to the drugs being used.