Local Nerve Blocks

Chapter 3 Local Nerve Blocks



EYE BLOCKS IN HORSES



Features



▪ Specific nerve blocks useful for sensory functions, motor functions, or both

▪ Allow easier examination of eye

▪ Allow treatment of some eye conditions without anesthesia

▪ Eye(s) must be protected from injury, corneal desiccation, and so on, after procedure is finished, especially after motor blocks


image Nerve supply to horse eye.


image Injection sites for sensory and motor eye blocks in the horse.


image Desensitized areas of eyelids of horse after blockade at the corresponding nerve sites.


Drug(s) to Use



▪ Lidocaine 2%

▪ Lidocaine 2% + bupivacaine 0.5% (for longer duration)

▪ When mixing drugs, use ratio of 1:1 by volume

▪ Bupivacaine alone requires longer time for onset; not always practical


Technique



Supraorbital Nerve



▪ Supraorbital foramen

▪ Palpate supraorbital process of frontal bone, dorsal to eye

▪ Foramen is palpable approximately 5 to 7 cm dorsal to medial canthus
□ Inject 1 ml into foramen, then another 2 ml as needle is withdrawn into subcutaneous tissue (22-gauge needle)


Infratrochlear Nerve



▪ Infratrochlear foramen

▪ Dorsal rim of orbit, almost at medial canthus

▪ Inject 1 ml into foramen, then another 2 ml as needle is withdrawn


Lacrimal Nerve



▪ Dorsal rim of orbit, approximately 1 cm dorsal to lateral canthus

▪ Inject 1 ml into foramen, then another 2 ml as needle is withdrawn


Zygomatic Nerve



▪ Ventral rim of orbit, approximately 0.5 cm ventral to lateral canthus

▪ Inject 1 ml into foramen, then another 2 ml as needle is withdrawn


Auriculopalpebral Nerve



▪ Two sites between eye and base of ear, along zygomatic arch

▪ Can inject at each site or use single injection to cover both sites and area between them

▪ Useful for examinations, temporary relief of spasm

▪ With addition of topical anesthesia, useful for removal of foreign bodies and for subconjunctival injections

▪ No sensory block occurs with this nerve block

▪ Protect cornea from desiccation after procedure is completed

▪ Locate zygomatic arch

▪ For dorsal site, inject 2 ml of drug approximately 3 cm ventral to highest point

▪ For ventral site, inject 2 ml of drug at dorsal rim of supraorbital process

▪ For single injection, inject at dorsal site and redirect needle to cover area between locations, using 5 ml total


DENTAL BLOCKS IN DOGS AND CATS



Materials Required for All Dental Blocks



▪ Syringe containing 1 to 2 ml of the following:
□ 2% lidocaine

□ or 0.5% bupivacaine

□ or 1% mepivacaine

▪ 25- to 27-gauge needle, 1½ to 1¾ inches for infraorbital block

▪ Volume (1 vs 2 ml) depends on size of animal

▪ Use chosen volume as the total volume for all blocks that will be performed at the same time

▪ Epinephrine (1:200,000) may be added to the local anesthetic to prolong the block

▪ An aspiration syringe is convenient and accommodates commercially available ampules of local anesthetic*

▪ Commercially available ampules can be purchased either with or without epinephrine


image Aspiration syringe.


image Ampules of local anesthetic for use in aspiration syringe.


Drug Comparisons




image


Technique



▪ Always aspirate after needle placement

▪ If blood is aspirated, withdraw the needle and redirect, then reaspirate

▪ Inject only if blood is no longer aspirated

▪ Blocks can be repeated at the end of long procedures to provide longer duration of analgesia during recovery from anesthesia


Upper Teeth



Infraorbital Nerve Block


This unilaterally blocks the following:


▪ Upper teeth anterior to the infraorbital foramen

▪ Upper lip

▪ Nose

▪ Roof of nasal cavity

▪ Skin anterior to infraorbital foramen

Inject at infraorbital foramen on lateral side of maxilla, anterior to the orbit. To find the infraorbital foramen, do the following:


▪ For dogs, press on the gum just above and slightly anterior to the mesial root of the fourth premolar tooth and feel for a depression just above the junction of lip and gum

▪ For cats, press on the gum and feel for a depression at the anterior aspect of the zygomatic arch, just above the third premolar tooth


image A, Infraorbital nerve block in a dog. B, Infraorbital nerve block in a cat.


image A, Injection site for infraorbital foramen in a dog. B, Injection site for infraorbital foramen in a cat.


Lower Teeth



Mental Nerve Block


This unilaterally blocks the following:


▪ Lower teeth anterior to the mental foramen

▪ Lower lip

▪ Skin anterior to mental foramen

Inject at mental foramen on lateral side of anterior portion of ramus of mandible. Feel for a depression in the gum below the first premolar and just below the junction of lip and gum.



image A, Mental nerve block in a dog. B, Mental nerve block in a cat.


image A, Injection site for mental foramen in a dog. B, Injection site for mental foramen in a cat.


Mandibular Nerve Block


This unilaterally blocks the following:


▪ Lower teeth

▪ Lower lip

▪ Tongue

▪ Skin anterior to mandibular foramen

Inject at mandibular foramen on medial side of posterior portion of ramus of mandible. Insert the needle medial to the lower molars and direct it posteriorly to “skim” along the bone. The foramen has a bony lip at its anterior border. Continue just past this point and inject.



image A, Mandibular nerve block in a dog. B, Mandibular nerve block in a cat.

An alternative technique is to start from the ventral aspect of the ramus of the mandible and inject medially.



image A, Injection site for mandibular foramen in a dog. B, Injection site for mandibular foramen in a cat.


image A, Alternative mandibular nerve block in a dog. B, Alternative mandibular nerve block in a cat.


image A, Alternative injection site for mandibular foramen in a dog. B, Alternative injection site for mandibular foramen in a cat.


DEHORNING OF CATTLE, SHEEP, AND GOATS



Features



▪ Specific nerve block is more useful in cattle than in sheep and goats

▪ Ring block may be more practical in sheep and goats because of more variable location of nerves; an arc is injected near anterior border of horn to affect all nerves that supply horn

▪ Occasional failure may result in some animals because of nerve supply from deep branch of the nerve to the frontal sinus, which cannot be blocked

▪ Sedation may be necessary in some animals


Nerve Supply to the Horn



▪ Trigeminal nerve
□ Ophthalmic division
• Frontal nerve (innervates the horn in only a small number of animals)

□ Ophthalmic division
• Zygomaticotemporal (lacrimal) portion
▪ Cornual nerve

▪ Infratrochlear nerve
□ Cornual branch


image Sites for injection of local anesthetic for dehorning of cattle. The frontal nerve innervates the horn in only some animals.


image Sites for injection of local anesthetic for dehorning of goats. Because of the variable nature of the nerve supply in goats, supplementary injections may be necessary around the base of the horn to ensure complete block.


Drugs to Use



▪ Lidocaine 2%

▪ Lidocaine 2% + bupivacaine 0.5% (for longer duration)

▪ When mixing drugs, use ratio of 1:1 by volume

▪ Bupivacaine alone requires longer time for onset; not always practical


Suggested Total Volume of Local Anesthetic to Use per Horn





















Anesthetic Adult Cattle (ml) Calves, Sheep, and Goats (ml)
Lidocaine 10–15 3–5
Bupivacaine 5–8 2–3
Lidocaine + bupivacaine 5–8 2–3


Technique



To Block Individual Nerves



▪ Frontal nerve
□ Dorsal rim of orbit near lateral canthus

▪ Cornual nerve
□ Halfway between eye and orbit, immediately ventral to lateral edge of frontal bone

▪ Cornual branch of infratrochlear
□ Halfway between eye and orbit

□ An alternative site along nerve is at dorsal rim of orbit near medial canthus


Using Single Injection to Block All Nerves



▪ Use long needle (10 cm, 18 gauge) for cattle; use shorter needle (5 cm, 22 gauge) for sheep and goats
□ Halfway between horn and lateral canthus, level with lateral border of frontal bone

□ Direct needle dorsomedially and withdraw slowly while injecting approximately two thirds of total volume

□ Redirect 2 to 3 cm ventrally, close to frontal crest, and inject remaining volume


BRACHIAL PLEXUS BLOCK



Overview


Brachial plexus block is suitable for analgesia for surgery on the front limb, within or distal to the elbow. Although in some patients the block may extend above the elbow, it does not do so reliably, and adjunct analgesic techniques should be used in such cases.



▪ The technique should be performed in a well-sedated or anesthetized animal

▪ Bupivacaine is the local anesthetic agent of choice because of its longer duration of action compared with lidocaine

▪ Onset time for motor block is 6 to 15 minutes

▪ Onset time for sensory block is 18 to 30 minutes

▪ Duration of analgesia is 2 to 6 hours

▪ Blocks can be repeated at the end of long procedures to provide longer duration of analgesia during recovery from anesthesia


Species



▪ Dogs, cats, small ruminants, foals


Anatomy


The brachial plexus is derived from the cervical roots C5, C6, C7, and C8 and the thoracic root T1. The plexus runs from the neck to the axilla, passing between the clavicle and the first rib, forming the median, ulnar, radial, and musculocutaneous nerves. Alongside the axillary artery runs the axillary vein, and care must be taken not to inject into either vessel via aspiration before injection of drug.



Equipment and Considerations



▪ Syringe containing 1 to 6 ml (depending on size of patient) of local anesthetic

▪ 18- to 22-gauge spinal needle or 18- to 27-gauge syringe needle depending on size of patient (1 inch for cats and small dogs; 3 inches for large dogs, ruminants, and foals)

▪ Volume to use depends on size of animal (e.g., for bupivacaine use 0.5 ml for cat or small dog; administer up to 10 ml in large dog, ruminant, or foal)

▪ Ensure that dose administered is below toxic dose based on patient weight (see table below)

▪ Epinephrine (1:200,000) may be added to the local anesthetic to prolong the block


Drug Comparisons




image


Technique



▪ Place animal in lateral recumbency with affected limb up

▪ Clip and prepare area using sterile technique

▪ Insert needle medial to shoulder joint and direct it parallel to vertebral column toward the costochondral junction

▪ Attach syringe containing local anesthetic

▪ Aspirate to check for presence of air or blood (withdraw and redirect if either is present)

▪ Inject as the needle is withdrawn and remove needle and syringe together


Nerve Stimulator Technique



▪ Large motor neurons may be stimulated with the aid of an electrical current

▪ By observing for muscle twitches, through electrical stimulation of the nerve, the practitioner can position a needle extremely close to the nerve; the accuracy of local anesthetic blocks can be improved through this technique


image Needle placement for canine brachial plexus block. A, Sixth cervical nerve. B, Seventh cervical nerve. C, Eighth cervical nerve. D, First thoracic nerve. E, Greater tubercle of humerus. F, First rib.

Related posts:

  1. Blood and Blood Substitutes
  2. Case Management
  3. Fluids
  4. Drug Combinations

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Oct 14, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Local Nerve Blocks

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