6. Locoregional Anesthesia LA

Question 1

What is a general overview of locoregional anesiasia for LA?

Answer 1

• Need to know important anatomical structures in area of interest
• Always aspirate prior to injection
• Avoid intravascular local anesthetic injection
• Always perform sterile preparation of area for injection
• Approx. volumes for adult cattle/equine nerve blocks = 5-15 mL per site
• Most common local anesthetic used = lidocaine
• Sheep/Goats/Camelids = 4-5 mg/kg
• Horses = 8 mg/kg
• Cattle = 8 mg/kg

Question 2

What is the cornual nerve block?

Answer 2

• Desensitizes horn
• Blocks ophthalmic branch of trigeminal nerve: cornual nerve, +/-
  supraorbital and infratrochlear nerves
• Uses: Dehorning or horn injury repair

Question 3

What is the technique for the cornual nerve block?

Answer 3

• Young cattle: palpate upper 1/3rd temporal ridge approx. 2-5 cm down
  from horn based – insert needle SQ, aspirate and inject 3-5 mL local
  anesthetic
• Adult cattle (well-developed horns) = ring block around entire base of
  horn or three-point block to completely desensitize horn

Question 4

What is the technique for a cornural nerve block for a goat?

Answer 4

• Goats: TWO branches of cornual nerve
• Must block BOTH to completely desensitize the horn
  Technique: insert needle SQ at each site, aspirate and inject 2-3 mL
  lidocaine per site
• Zygomaticotemporal (aka. lacrimal) branch: behind root of supraorbital
  process, halfway between lateral canthus of eye and lateral base of horn
• Infratrochlear branch: dorsomedial margin of orbit, midway between
  medial base of horn and medial canthus of the eye

Question 5

What is the large animal opthalmic block?

Answer 5

• Sensory denervation of eyelid = must block 4 separate
  nerves
• Upper eyelid: Supraorbital (frontal), lacrimal nerves
• Lower eyelid: zygomatic, infratrochlear nerves
• Motor innervation to eyelid:
• Palpebral nerve (branch of auriculopalpebral nerve) = must
  block to prevent blinkin

Question 6

What is the technique for the LA ophthalmic upper lid blocks?

Answer 6

Technique for Upper eyelid
* Insert needle SQ at each site, aspirate and inject desired
volume of local anesthetic
1. Supraorbital nerve: Dorsal to medial canthus of eye,
medial to supraorbital ridge
* Also Blocks part of palpebral nerve
2. Lacrimal nerve: Palpate lateral canthus and place needle
pointing medial along dorsal orbit rim

Question 7

What is the technique for the LA ophthalmic lower eyelid blocks?

Answer 7

3. Infratrochlear nerve: dorsal orbital rim near medial
   canthus (bony notch)
4. Zygomatic nerve: lateral aspect of lower orbit rim
   and supraorbital part of zygomatic arch (direct
   ventral)

Question 8

What is the LA retrobulbar block?

Answer 8

• Retrobulbar block: desensitizes ocular surface, globe
  and intraocular structures
• Optic, oculomotor, trochlear, maxillary and abducens nerves
• Surgical preparation should be done with iodine 1.25% solution and sterile eye wash
• Complications:
• Eye penetration, IV or intraneural injection, retrobulbar hemorrhage, proptosis, oculo-cardiac reflex, increased IOP, chemosis
• Use: enucleation +/- evisceration, orbectomy

Question 9

What is the technique for the retrobulbar block for cattle?

Answer 9

1. Bend 20-gauge, 9-cm needle into circular angle
2. Insert needle at 4 points around orbit (12, 3, 6, and 9 o’clock positions) and advance through soft tissues until bone of orbit is hit
3. Advance needle along orbit bone until needle is located behind the orbit (feel ‘pop’ sensation when entering retrobulbar cone)
4. Aspirate, then inject 5mL lidocaine per site (20 mL total)

Question 10

What is the technique for the retrobulbar block for the horse?

Answer 10

1. Palpate orbital fossa just caudal to posterior aspect of dorsal orbital rim
2. Insert 22-gauge, 3.5-inch spinal needle perpendicular to skin, advance until eye rolls dorsally in orbit and a ‘pop’ is felt (entering retrobulbar cone)
3. Insert needle 2-3mm more, aspirate then inject 10mL
   lidocaine or bupivacaine

Question 11

What is the maxillary nerve block?

Answer 11

• Desensitizes maxilla bone, intraoral soft tissues, upper dental arch, upper lip and nostril, hard and soft palate
• Uses: Extraction of maxillary teeth, maxillary sinus trephination, nasal
  cavity surgery
• Complications: salivary gland or maxillary artery damage, nerve damage

Question 12

What is the technique for the maxillary nerve block?

Answer 12

1. Palpate infraorbital foramen
2. Insert needle approx. 3-4 cm into foramen
3. Aspirate then inject approx. 5mL local anesthetic

Question 13

What is the inferior alveolar nerve block?

Answer 13

Mandibular block
* Desensitizes entire ipsilateral mandible bone and soft tissues,
lower lip and lower dental arcade
* Complications: tongue desensitization
* Uses: dental extractions for molars/premolars,
mandibulectomies, mandibular fracture repairs, mass
removals, etc

Question 14

What is the extraoral mandibular block technique?

Answer 14

1. Estimate mandibular foramen location by imagining
   two intersecting lines: vertically down from caudal aspect of orbit AND horizontal line parallel to
   occlusal surface of lower cheek teeth
2. Insert 18 gauge, 8 – 10-inch spinal needle along caudal mandible until you hit the bone
3. Walk off the end of the mandible heading medially, insert needle by scraping along inner aspect of mandible until you reach intersection of lines previously discussed
4. Aspirate, then inject desired volume of local anesthetic

Question 15

What is the intraoral technique for the mandibular block?

Answer 15

1. Attach 20-gauge, 1.5-inch needle (bent 20-30
   degrees) to IV fluid extension set, and guide insertion
   into oral cavity with 12-inch pliers
2. Insert needle into mucosa just caudal and above
   occlusal surface of 3rd mandibular molar (lateral to
   palate)
3. Aspirate and inject desired volume of local anesthetic

Question 16

What is the mental nerve block?

Answer 16

• Lower lip desensitization only (A)
• Local anesthetic injected around mental foramen
• Lower incisors to 3rd premolar desensitization =
  mandibular alveolar nerve block (B)
• Insert needle into mental foramen and advance into
  mandibular canal (ventromedial direction)

Question 17

What is purpose of the distal limb locoregional anesthesia?

Answer 17

• Purpose: specific nerve blocks used to
  diagnose lameness but also to provide analgesia
  to lower limb for surgical procedures

Question 18

What is the digital nerve block and technique?

Answer 18

Distal Limb Locoregional Anesthesia
* Purpose: specific nerve blocks used to
diagnose lameness but also to provide analgesia
to lower limb for surgical procedures

Question 19

What is the abaxial sesamoidean nerve block and technique?

Answer 19

• Desensitizes medial and lateral palmar (plantar) nerves
• Palpate nerves as they pass proximal sesamoids
• Blocks entire foot, back pastern and distal sesamoidean ligaments
• Can result in partial numbing of fetlock

Question 20

What is the low palmar/plantar nerve block? and technique?

Answer 20

• Desensitizes: structures distal to fetlock and fetlock joint
• Does not block small area dorsal to fetlock joint
• Approach: 4-point block (patient should be bearing weight on the limb of choice)
• Medial and lateral palmar (plantar) nerves: between flexor tendon and suspensory ligament
• Medial and lateral palmar (plantar) metacarpal nerves: between suspensory ligament and splint
  bone

Question 21

What is the high plantar/palmar nerve block and technique?

Answer 21

• Desensitizes palmar metacarpal (metatarsal) region and all digits distal to fetlock
• Does not block dorsal fetlock metacarpal (metatarsal) region
• Approach: level of the proximal quarter of metacarpus (metatarsus)
  proximal to communicating branch of medial and lateral palmar
  (plantar) nerves
• Limb can be elevated or weight bearing
• Needle (perpendicular to skin): 4.5 cm distal to carpometacarpal joint into groove between suspensory ligament and deep flexor tendon
• Medial and lateral sides

Question 22

What is the proximal forelimb block and techniques?

Answer 22

• Desensitizes 3 nerves: median, ulnar, and musculocutaneous
  nerves
  Proximal Forelimb Block
  Technique:
• Median nerve: medial aspect forelimb, 5 cm ventral to elbow
• Needle inserted between border of radius and internal flexor carpi radialis muscle belly, deep
  to superficial pectoral muscle
• Ulnar nerve: 10cm proximal to accessory carpal bone between flexor carpi ulnaris and ulnaris lateralis muscles
• Medial cutaneous antebrachial nerve (branch of musculocutaneous) Anteriomedial
  aspect of forelimb
• Halfway between elbow and carpus, palpate cranial to cephalic vein

Question 23

What is the proximal hindlimb block

Answer 23

• Desensitizes: tibial, saphenous, superficial peroneal
  (superficial fibular), deep peroneal (deep fibular) nerves

Question 24

What is the tibial nerve technique?

Answer 24

• Tibial nerve: medial aspect of limb, 10 cm proximal to point of tarsus
• Between combined gastrocnemius muscle tendons and superficial digital flexor tendon
• Desensitizes posterior metatarsal area, foot except anterolateral region

Question 25

What is the saphenous nerve technique?

Answer 25

* Saphenous nerve: medial aspect of limb, proximal to tibiotarsal joint * Can have two nerve trunks: caudal AND cranial aspect of medial saphenous vein → inject on either side of vein * Desensitizes medial aspect of thigh and part of metatarsal region

Question 26

What is the superficial and deep peroneal nerve block technique?

Answer 26

* Superficial and deep peroneal nerves: 10cm proximal to lateral malleolous of tibia * Between long and lateral digital extensor muscles * Deposit local anesthetic SQ around superficial nerve branch * Advance 2-3 cm (enter deep fascia) and deposit local anesthetic around deep branch * Desensitizes anteriolateral tarsal and metatarsal regions and tarsus joint capsule

Question 27

What is a caudal epidural block?

Answer 27

Site = S5 – Co1 or Co1 – Co2 * First midline depression caudal to sacrum palpated when tail is moved up and down * Prepare area aseptically, as in small animal epidural procedures * Volume = DIFFERENT FROM SMALL ANIMALS * 6-8 mL total (450 kg horse) = perineum, rectum, vulva vagina, urethra and bladder * 10 mL MAXIMUM for standing procedures * Complications: ataxia, motor paralysis to hindlimbs, excitement, infection, hypotension

Question 28

What is the caudal epidural block technique?

Answer 28

1. Prep area and instill 1-2 mL lidocaine in soft tissues where you will place epidural needle 2. Insert needle at 30o angle to skin, fill hub with sterile saline 3. Advance needle through tissues until epidural space is entered = sub- atmospheric pressure sucks in drop of saline 4. Attach syringe with epidural solution and inject slowly – there should be NO resistance

Question 29

What is the inverted L block?

Answer 29

* Similar to simple line block, except injecting local anesthetic in TWO long lines 1. Behind the last rib (R13) 2. Below transverse process of vertebrae (L1 – L5) * Total volume = up to 100mL lidocaine (adult cow) evenly distributed * Blocks skin but not peritoneum * Advantage over line block: no anesthetic agent in incision line (minimized edema, hematoma and healing interference)

Question 30

What is the proximal paravertebral block?

Answer 30

* Block T13, L1, L2 nerves exiting intervertebral foramen near dorsal aspect of transverse process * Desensitizes skin, muscle and peritoneum * Animal will bend towards the opposite side (scoliosis) and flank will be warm (vasodilatation) * Standing laparotomy procedures: C-section, rumenotomy, cecotomy, intestinal obstruction, displaced abomasum, volvulus, etc. * Use 10-20 mL lidocaine per site (onset 10 min, duration of block 90 min) * Complications: aorta puncture, vena cava puncture, ataxia and loss of hindlimb motor function

Question 31

What is the technique for the proximal paravertebral block?

Answer 31

1. Prep skin overlying area T12 – L3 transverse processes 2. 2.5-5 cm from midline, along cranial aspect of transverse spinal process 3. Inject 2-3 mL lidocaine under skin along cranial border for local anesthesia in order to perform needle insertion 4. Insert 16 - 18-gauge 1.5 – 6-inch needle until you hit cranial aspect of transverse process bone, walk off cranially until you pop through intertransverse ligament 5. Aspirate, inject 10-15mL lidocaine, withdraw needle 1-3 cm and repeat by injecting 5mL lidocaine above intertransverse ligament 6. Repeat steps at L1 and L2 transverse processes Sheep/goats = only use 2-3 mL lidocaine per site!

Question 32

What is the distal paravertebral block?

Answer 32

* Desensitizes T13, L1, L2 but in more distal position (ends of L1, L2 and L4) * Used for similar reasons as proximal block * Advantages over proximal blocks: * Minimal risk of penetrating vascular structures * Not as much scoliosis * Minimal risk of ataxia and pelvic limb paralysis * Disadvantages: * Large volume required * Variable efficacy for skin desensitization

Question 33

What is the technique for distal paravertebral block?

Answer 33

1. Prepare and desensitize skin similar to proximal paravertebral block but at L1 – L4 2. Insert 18-gauge, 1.5-inch needle until you hit the lateral aspect of L1 transverse process 3. Walk needle ABOVE transverse process, aspirate and inject in fan infiltration pattern 15 mL lidocaine 4. Back needle up until you hit the lateral aspect of the transverse process again 5. Walk needle BELOW transverse process, aspirate and inject in fan pattern 5 mL lidocaine Sheep/goats = only use 2-3 mL lidocaine per site!

Question 34

What is the intratesticular block and technique?

Answer 34

* Desensitizes spermatic cord and soft tissue structures * Used for castration * Local anesthetic used = lidocaine Technique: 1. Insert needle directly into testicular body and aspirate 2. Inject until you feel increased ‘pressure’ within testicle or desired volume is reached ** Can infiltrate incision line (pre-scrotal or scrotal) with small amount of local anesthetic *

Question 35

What is the teat locoregional anesthesia

Answer 35

Dairy cattle, sheep and goats for surgical procedures of the teat

Question 36

What is the inverted V block technique for the teat locoregional anesthesia

Answer 36

Inverted V Block: 25-gauge, 1.5-cm needle inserted into skin and musculature dorsal to surgical site in inverted V patter. Aspirate and inject 2.5 mL local anesthetic in each site

Question 37

What is the ring block technique for the teat locoregional anesthesia

Answer 37

25-gauge, 1.5-cm needle inserted into skin and muscle encircling entire base of teat and injecting 5mL total equally around entire teat

Question 38

What is the Teat cistern infusion technique for the teat locoregional anesthesia

Answer 38

Teat Cistern Infusion: milk out cistern then place tourniquet on teat base (prevent local anesthetic from entering udder). Sterile teat cannula inserted into teat cistern and inject 10mL local anesthetic. Remove cannula and milk out any extra local anesthetic. * At end of procedure, remove tourniquet

Question 39

What is intravenous regional anesthesia? Whats its other name?

Answer 39

Bier's block * Tourniquet applied to limb proximal to planned surgical area, lidocaine injected IV distal to tourniquet * Local anesthetic spread from vessels to nearby nerves and tissues * Time and area dependent: short procedures (< 90 minutes) on distal extremities (distal to elbow or hock) * Alternative to ring block, minimal blood loss * Potential for tissue necrosis and ischemic pain

Question 40

What is the technique for the intravenous regional anesthesia?

Answer 40

1. Place loose tourniquet on limb and ID palpable arterial pulse in area of interest 2. Insert IV catheter in distal vein, then exsanguinate distal limb using flexible bandage 3. Inflate/tighten tourniquet > 50-100 mmHg higher than SAP – document time! (Complete procedure within 90 min form this time) 4. Remove bandage used to exsanguinate the limb 5. CHECK for PULSE 6. Inject 20 mL lidocaine IV slowly (2-3 min) – document time!**** 7. At end of procedure, slowly remove tourniquet while surgical site is closed ** Sheep/goats = only use 3-4 mL lidocaine!