Local anaesthetic blocks

Question 1

What are the 2 types of local anaesthetics and how are they metabolised?

Answer 1

Amides: Metabolized by liver (e.g. lidocaine, bupivacaine)

Esters: Metabolized by plasma cholinesterases (e.g. procaine)

Question 2

How do local anaesthetics work?

Answer 2

Local anesthetics are weak bases that exist in equilibrium between:
- Non-ionized (neutral), lipid-soluble form (B): Penetrates lipid membrane
- Ionized (charged), water-soluble form (BH+): Binds to sodium channel receptor within channel pore, blocking nerve signal transmission

Question 3

Why are local anesthetics formulated as acidic hydrochloride salts?

Answer 3

To increase water solubility & ionization (pH 4–7), ensuring effectiveness in their water-soluble, charged form

Question 4

Answer 4

Question 5

What is the purpose of adding vasoconstrictors (e.g., adrenaline) to local anesthetics?

Answer 5

To prolong duration of action by reducing systemic absorption

Question 6

What is the purpose of a testicular block during castration?

Answer 6

Provides intraoperative nociception & postoperative pain relief by diffusing to spermatic cord & associated structures

Reduces pain from surgical crushing of tissue at castration site

Question 7

How is a testicular block performed?

Answer 7

1. Use sterile hypodermic needle (25- to 22-Ga, length depending on patient size)
2. Insert needle into testicular body, directing tip toward spermatic cord
3. Aspirate to ensure needle is not in blood vessel
4. Inject recommended dose of local anesthetic (bupivacaine, ropivacaine, or lidocaine) until testicle becomes slightly turgid or volume limit is reached

Question 8

How do we inject local anaesthetic for a testicular block for castration?

Answer 8

Cats: Inject local anesthetic as needle exits testicle to block skin & subcutaneous tissue over incision

Dogs: Inject anesthetic into skin & subcutaneous tissue at prescrotal incision site

Question 9

How is local anaesthetic used during an ovariohysterectomy?

Answer 9

Direct infiltration of mesovarium ligament

Alternatively, splash block can be applied to the ovaries

Additional step:
- lavage of peritoneal cavity with local anaesthetic to provide additional analgesia (careful with dosage)

skin & subcutaneous tissues at incision site should also be infiltrated with local anaesthetic.

Question 10

What is retrobulbar anaesthesia, and when is it used?

Answer 10

Retrobulbar anaesthesia involves injecting local anaesthetic behind eye to block nerves & provide pain relief during ophthalmic procedures, such as enucleation

Question 11

What are the indications for lumbosacral and sacrococcygeal epidurals in veterinary medicine?

Answer 11

Tail amputations (canine and feline).
Perineal urethrostomies.
Anal sacculectomies.
Catheterisation for relief of urethral obstruction.
Perineal relaxation for the delivery of puppies/kittens.
Other surgeries involving the penis or perineal region.

Question 12

What anatomical regions are targeted with lumbosacral and sacrococcygeal epidurals?

Answer 12

Lumbosacral epidural: Provides analgesia & anaesthesia for hindlimb and pelvic region surgeries

Sacrococcygeal epidural: Focused on the tail and perineal region

Question 13

What is the purpose of a rostral maxillary (infraorbital) dental block?

Answer 13

It provides analgesia for rostral maxillary soft tissues only (not teeth or bone)

Question 14

Where is the local anaesthetic injected for a rostral maxillary (infraorbital) block?

Answer 14

injection made near infraorbital foramen, targeting infraorbital nerve

Question 15

What nerve block is this?

Answer 15

Rostral maxillary (infraorbital)

Question 16

Label the nerves

Answer 16

Question 17

What does the superior alveolar nerve (SAN) innervate?

Answer 17

teeth & bone adjacent to the teeth within the maxilla

Often classified along with infraorbital nerve (ION), but it actually branches from this nerve caudal to them entering maxillary foramen at caudal aspect of maxilla

It can be blocked intraorally or extra- orally

Question 18

What are the 2 methods of blocking the caudal maxilla?

Answer 18

Question 19

Describe extra oral technique of blocking the maxilla

Answer 19

1. Needle inserted below cranioventral border of zygomatic arch, between caudal border of maxilla & cranial border of mandibular ramus
2. Needle advanced parallel to plane of hard palate & 1cm caudal to lateral canthus of eye
3. needle is advanced until bone is felt, aspirate! ++ risk of venepuncture

Question 20

What are the 2 methods of blocking the mandible?

Answer 20

Question 21

What kind of block is this?

Answer 21

Mandibular block (rostral)

Question 22

What is Intravenous Regional Analgesia (IVRA), and when is it used?

Answer 22

IVRA, also called Bier block, provides short-term anaesthesia for distal limb procedures, such as toe amputation

Question 23

How is IVRA performed for toe amputation?

Answer 23

1. Insert IV cannula into distal vein (e.g., cephalic or saphenous)
2. Desanguinate limb using Esmarch bandage
3. Place & tighten a proximal tourniquet
4. Remove Esmarch bandage & inject lidocaine via cannula
5. Remove cannula, inflate BP cuff, & prep limb for surgery

Question 24

How does the tourniquet aid IVRA?

Answer 24

prevents systemic distribution of anaesthetic, ensuring localised effect & safety

Question 25

What anaesthetic is commonly used for IVRA?

Answer 25

Lidocaine is injected to provide regional analgesia

Question 26

What block is this?

Answer 26

Bier block in cattle

Question 27

What is a RUMM block, and what does it involve?

Answer 27

RUMM stands for Radial, Ulnar, Median & Musculocutaneous nerve block

It involves:
- Blocking the radial nerve from a lateral approach.
- Blocking ulnar, median & musculocutaneous nerves from medial approach

Question 28

What are soak catheters?

Answer 28

large bore catheters with tiny holes for distributing local anaesthetic into surgical site

Used for analgesia in limb amputations, extensive reconstructive surgeries, mammary strips & total ear canal ablation (TECA)

Placed before closing incision & secured to skin at end of surgery

Question 29

What is a nerve locator, and what is it used for?

Answer 29

delivers small electrical impulses to identify nerves during regional anaesthesia

helps precisely locate target nerve by eliciting muscle twitches, improving block accuracy & minimising complications

Question 30

What are the benefits of femoral and sciatic nerve blocks (PNBs) compared to epidurals?

Answer 30

Reduced risk of urine retention

Decreased perioperative & postoperative opioid consumption

Less impact on mean arterial blood pressure (MAP) during anaesthesia.

Question 31

How do PNBs contribute to multimodal anaesthesia?

Answer 31

Reduce inhalational anaesthetic requirements, sparing isoflurane

Minimise side effects of opioids (e.g., nausea, dysphoria, inappetence)

Lower risk of perioperative hypotension in high-risk patients

Question 32

How is lidocaine used intravenously for pain management in veterinary practice?

Answer 32

Lidocaine is used as CRI (Continuous Rate Infusion) for soft tissue pain in dogs & equines, such as in colic cases.

Question 33

What are the benefits of IV lidocaine as a CRI?

Answer 33

Reduces inhalational anaesthetic requirements (decreases MAC).
Lowers opioid doses required.
Contributes to balanced anaesthesia.
Can be useful postoperatively.

Question 34

What precautions should be taken when using IV lidocaine?

Answer 34

Only use pure lidocaine (no adrenaline).
Avoid use in cats due to their sensitivity to lidocaine.

Question 35

What are the signs of local anaesthetic toxicity?

Answer 35

Signs include airway compromise, seizures, and arrhythmias

Question 36

How can local anaesthetic toxicity be managed?

Answer 36

Support patient (e.g., secure airway, treat seizures & arrhythmias).
Administer intralipid if needed.

Question 37

How can local anaesthetic toxicity be prevented?

Answer 37

Carefully calculate the dose.
Always aspirate before injecting.
Use proper technique to minimise risks.