Local and Regional Anaesthesia: Clinical Anaesthesia and Analgesia (incl. Farm)

Question 1

1. What is regional anaesthesia?
2. What is local anaesthesia?

Answer 1

1. • Often called ‘nerve blocks’.
     - Block a region of the body (e.g. whole leg).
     - Specific nerve / nerves blocked (e.g. brachial plexus).
2. Anaesthesia where the agent is injected.
   **both terms used interchangeably.

Question 2

1. What is one of the most important safety considerations associated w/ LA use?
2. How can side effects of LAs be minimised?

Answer 2

1. Total dose.
2. Use of multimodal analgesia which entails use of 2 or more analgesics w/ different modes of action to optimise analgesia w/o using too much of the same LA agent.

Question 3

1. Day 1 skills associated w/ anaesthesia in SA.
2. Skills associated w/ anaesthesia in SA that are not day 1 skills.

Answer 3

1. Topical anaesthesia e.g. larynx (intubeaze) , skin (EMLA), eye and splash blocks. Also infiltration of LA in a specific area like wound, lump, testicle.
2. Most regional techniques (e.g. dental blocks and brachial plexus blocks) and epidural analgesia.

Question 4

1. % lidocaine in Intubeze.
2. Alternative method to Intubeze for laryngeal LA.

Answer 4

1. 2%.
2. Lidocaine (10 or 20 mg/ml) in a 1ml syringe w/ catheter (w/o stylet) taped to the end. 0.2-0.3ml directed onto each side of the larynx.

Question 5

1. Depth of skin anaesthetised by EMLA.
2. LAs contained in EMLA.
3. Time for effective desensitisation.
4. Method of EMLA application.
5. When is EMLA most commonly used?

Answer 5

1. 1-2mm.
2. Prilocaine and lidocaine.
3. 45-60 mins.
4. Cover area of skin w/ EMLA thickly and place an occlusive dressing over the top of it.
5. In rabbit for auricular intravenous catheterisation. Or in cat or kittens for cephalic catheters. Also for arterial catheters.

Question 6

1. What LA would you use to anaesthetise eyes for examination?
2. Storage of this LA?
3. Onset and duration of action?
4. Post procedure consideration.

Answer 6

1. Proparacaine.
2. Fridge.
3. Quick onset and short duration of action (20-45 mins).
4. Remind owner that they do not have a blink reflex for protection so do not put rabbits back into hay immediately or walk dog in long grass etc.

Question 7

1. Care w/ LA infiltration.

Answer 7

1. Care w/ total dose and care w/ tissue trauma w/ needle. Be lighter handed and use a smaller gauge needle.

Question 8

Benefits of dental blocks in dental procedures such as tooth extractions.

Answer 8

• Reduces maintenance anaesthetic requirements.
• Improves post-operative pain management.
• May improve speed of recovery.

Question 9

1. Site of epidural injection.
2. Epidural provides analgesia to which areas?
3. What agent used for epidural?
4. Duration of action as analgesia?
5. Duration of motor effect?

Answer 9

1. L7-S1.
2. Pelvis, HLs, caudal abdomen.
3. Preservative free morphine and bupivacaine.
4. Up to 24hrs.
5. 6-8 hrs.

Question 10

Why use LA techniques in FA practice?

Answer 10

• Takes away the need for GA, which has a high risk of complications in ruminants (gas in rumen).
• Allows procedures to be carried out pain free “on farm”.
• Temperament of spp, allows for procedures to occur under local.
• Requires less expensive drugs and equipment.
• Animals can remain standing.

Question 11

Very common LA blocks used in FA practice.

Answer 11

• Cornual nerve block.
• Sacrococcygeal epidural.
• Paravertebral.
• L block.
• Local infiltration.

Question 12

Less common LA blocks in FA practice.

Answer 12

• Lumbosacral epidural.
• Retrobulbar block.
• Intravenous Regional Anaesthesia (IVRA).

Question 13

Uncommon LA block used in FA practice.

Answer 13

Pudendal nerve block.

Question 14

1. What is the only LA drug licensed for use in food producing animals? – What animals is this agent licensed for?
2. What administration route is this agent licensed for?
3. What is beneficial about this block agent?
4. Onset of action?

Answer 14

1. 5% procaine hydrochloride with adrenaline. – cattle, pigs (and horses). Nothing licensed for sheep and goats.
2. Subcutaneous only.
3. No milk and meat withdrawal.
4. 10 mins.

Question 15

1. What nerve block is used for disbudding / dehorning?
2. What spp. is this block used in?

Answer 15

1. Cornual nerve block.
2. Calves and goats.

Question 16

Cornual nerve block technique in cattle?

Answer 16

Block the cornual nerve as it runs ventral to the lateral ridge of the frontal bone, approx. half way between the lateral canthus of the eye and the horn bud.
- For calves:
– 1 inch 19G needle.
– 3 to 5 ml each side.
– Nerve superficial so don’t inject too deep (half inch).
- Adult cattle and bulls also require local infiltration to caudal aspect of the horn base.

Question 17

Cornual nerve block technique in goats.

Answer 17

As in the calf.
But also need to block the cornual branch of the intratrochlear nerve which is dorsomedial to the eye close to the orbit.
Be aware of toxicity levels in kids.
- X use >0.5ml of 5% procaine on each side.
- Dilute LA w/ sterile water of injection to allow diffucsion.
– Add 3ml sterile water to 1ml procaine to create 1.25% procaine injection. Then can use 1ml on block site.

Question 18

What LA block technique is used for castration in FA practice?

Answer 18

1. Intratesticular local infiltration.

Question 19

Give examples of abdominal flank surgeries in the ruminant?

Answer 19

Displaced abomasum surgeries, caesarean section surgeries.

Question 20

FA abdominal flank block techniques.

Answer 20

Paravertebral, inverted L block, local infiltration along incision site.

Question 21

Indications of paravertebral nerve block.

Answer 21

Caesarean section, LDA, RDA, rumenotomy, ex lap.

Question 22

Advantages of paravertebral block.

Answer 22

• Simple and safe technique.
• Produces wide uniform analgesia pf a;; layers of the abdominal wall.
• Small volume LA needed.
• Looks professional.
• Good muscle relaxation.
• Allows for increased incision intra operatively if required.

Question 23

Disadvantages of paravertebral?

Answer 23

Landmarks can be difficult in obese/heavy muscled animals.

Question 24

What sites should the block be applied to?

Answer 24

• T13.
• L1.
• L2.
  *need to block both cranial and caudal regions of these to get a full block.

Question 25

Equipment needed to perform paravertebral block.

Answer 25

- Clippers or razor. - Surgical scrub and spirit. - Local anaesthetic. - Scalpel blade. - 20ml syringe. - 18G 1.5 inch needle. - Paravertebral or spinal needle. -- dairy cow 18G 3.5 inch. -- beef cows 16G 5 inch. -- Sheep 19G 2 inch.

Question 26

How can you locate the sites that you want to apply the block to for paravertebral block?

Answer 26

Locate first transverse process. -- Often difficult to feel in well conditioned cows and easily missed as shorter and narrower than the second. -- Locate by counting back from last palpable transverse process -- L5. -- If L5 not palpable, position can be found by measuring the same distance forward from L2 as the L3 to L2 distance.

Question 27

Method of paravertebral block.

Answer 27

Clip a window over L1 and L2 -- midway along the length of the lumbar process. Surgically scrub windows with spirit. Inject 5ml LA subcutaneously in each window. Stab incision through the skin in centre of each window with a small scalpel blade.

Question 28

Signs of a successful block.

Answer 28

Anaesthesia of the skin. Increase skin temperature at the surgical site due to hyperaemia from the paralysis of the cutaneous vasomotor muscle. Relaxation of the flank muscles. Scoliosis of the lumbar spine towards the desensitised side.

Question 29

What is the inverted L method of abdominal flank block?

Answer 29

Inject subcutaneous and muscle layers in an inverted L cranial and dorsal to the incision site.

Question 30

Advantages of inverted L block.

Answer 30

LA is away from the incision site. Easy to perform.

Question 31

Disadvantages of inverted L block.

Answer 31

Requires large amount of LA -- >100ml. Not as effective analgesia as paravertebral block. Incision length set by block w/ no option to extend quickly during op.

Question 32

Local infiltration block of the abdominal flank.

Answer 32

- Infiltrate along line of wound. - Skin and muscle blocked.

Question 33

1. Advantages of local infiltration block. 2. Disadvantages.

Answer 33

1. Quick and easy to perform. 2. Relatively poor analgesia of deeper tissue. Large volume of local anaesthetic required -- ~100ml. Trauma to skin at site of incision.

Question 34

Sacrococcygeal epidural anaesthesia.

Answer 34

AKA caudal or low epidural. Commonly used in sheep and cattle. Indicated for: - Obstetrical manipulations. - Uterine / vaginal prolapse. - Tail amputation.

Question 35

1. Site of injection for sacrococcygeal blocks. 2. Where does the spinal cord terminate in cattle and sheep.

Answer 35

1. S5 to co1 or co1 to co2. Pump the tail head up and down. Most movable space will be injected into. 2. L6/S1.

Question 36

Technique for sacrococcygeal block?

Answer 36

Clip and clean site. Cattle - Insert a 1.5-2 inch 18G needle. - Perpendicular to the skin. Sheep - Insert 19G 1 inch needle. - 10 degree angle to the skin. Advance into the intra articulate ligament. Inject slowly.

Question 37

1. Dose of anaesthetic for sacrococcygeal block. 2. How do you know the position for injection is correct?

Answer 37

1. 4-5ml LA in cattle. 1-2ml in sheep. +/- xylazine which prolongs the duration of LA action. Higher doses increase risk of causing ataxia. 2. No resistance to injection. Negative pressure in the extradural space causes air/liquid to be sucked in. Sounds like a hiss.

Question 38

Lumbosacral epidural.

Answer 38

High or anterior epidural. Not day 1 skill. Used in sheep, goats or calves only. Indicated for: - Vasectomy. - Deep scrotal surgery. Technique very similar to dogs. Results in HL paralysis.

Question 39

IVRA. Risk?

Answer 39

Intravenous Regional Anaesthesia. Indicated for: - Surgery. - Exploration of foot. Sedation recommended. Principle: - Tourniquet distal limb. - Inject LA into isolated blood vessels to desensitise region. Risk of lack of circulation so ensure not too long but ensure long enough not to risk to LA going into other blood vessels and causing other issues elsewhere in the body.

Question 40

Retrobulbar.

Answer 40

Used to enucleate eye. Desensitise ocular tissue and associated nerves. Sedation recommended.