Methods of Anaesthesia

Question 1

anaesthesia vs analgesia?

Answer 1

anesthesia
- general: whole body - reversible depression of the CNS
- local: reduces sensation in a specific location

analesgia
- systemic: opiods modulate pain once reaching CNS
- local: prevents pain from reaching CNS BY reversibly binding to sodium channels to prevent influx of sodium

Question 2

what is the triad of anaesthesia?

Answer 2

narcosis (unconscious)
relaxation
analgesia

Question 3

why do we need to consider the triad of anaesthesia?

Answer 3

it’s necessary to balance the triad appropriately

this is procedure dependent
- eg non-painful procedure (eg imagine thorax) will need less analgesia
- eg. procedures such as dental, biopsies or ear flushes don’t need as much muscle relaxation as an abdominal surgery

Question 4

what is topical anaesthesia?

examples?

Answer 4

type of local
causes superficial desensitisation of an area

examples:
- ocular - proxy eye drops
- larynx - intubeaze
- skin - EMLA cream

Question 5

what is local anaesthesia?

examples?

Answer 5

eliminates pain and nociception at the targeted region

so signal won’t enter CNS

examples:
- epidural
- nerve blocks
- wound soaking catheter
- intra-articular injection

Question 6

what are the advantages and disadvantages of local anaesthesia?

Answer 6

advantages
- reduction in systemic analgesia
- reduced need for inhalant - improved anaesthetic safety
- reduced recovery time
- shorter hospital stay

disadvantages
- not always fully effective
- prolonged duration
- adverse reaction (eg anaphylaxis)
- infection
- nerve damage

Question 7

what is the order of nerves being blocked during local analgesia?

why do we need to consider this for recovery?

Answer 7

myelinated sensory fibres (detect pain)
autonomic nervous system
larger pressure fibres
unmyelinated chronic pain fibres
motor fibres

recovery is reversed order
- may be able to move but not feel pain - cause damage

Question 8

what are the possible adverse effects of local analgesia?

Answer 8

if given IV can cause neurological and CV signs
- esp. bupivacaine
- cats known to die from this

anaphylaxis can occur but rare

methemoglobinemia
- damage to RBCs causing anaemia
- eg benzocaine in cats

nerve damage/injection site-related effects

Question 9

what is an epidural?
what can it be used for?

Answer 9

the complete sensory, motor and autonomic block produced by local anaesthetics

used for:
- tail, hind limb or pelvic surgery/injury/post-op
- abdominal or thoracic surgery
- acute pancreatitis
- aortic-iliac thrombosis (cats)

Question 10

advantages and disadvantages of an epidural?

Answer 10

advantages
- used for a range of indications
- can provide up to 24 hours of analgesia
- can be topped up with a catheter
- reduces analgesic and anaesthti need
- provides good muscle relaxation
- avoids central sensitisation
- decreases hospitalisation time

disadvantages
- sympathetic blockade - causes hypotension and hypothermia due to vasodilation
- can be inefficient compared to other techniques - increases GA time
- causes urine retention
- not suitable if patient has:
-> coagulapthy
-> hypovolemia/hypotension
-> infection/neoplasm in epidural

Question 11

Describe the different locations a nerve block be administered

Answer 11

field
- directly into incision/wound

oral
- various areas of mouth
- for dentals
- block bone, teeth and soft tissue

testicles
- directly into base of testes
- migrates up spermatic cord

intraperitoneal
- diluted with saline and bathes entire abdominal cavity
- can be given pre (better analgesia but absorbed by swabs) or post (more nociception during but good recovery analgesia)

radial-ulnar-median/circumferential ring
- near carpal
- for digital amputation

bier
- IV lidocaine to limb
- use esmarch bandage and tornique to stop travelling beyond limb

brachial
- shoulder region
- for forelimb surgery or pain distal to elbow

intercostal
- 3 consecutive ribs are blocked
- for rib fractures, thoractomoy or thoracentesis

Question 12

what is a wound catheter?

Answer 12

placed in large surgical wounds
- left under the skin stitched

allows for local anaesthetic to be administered during hospitalisation

can cause disconnection, seroma or toxicity

Question 13

What precautions need to be considered when using topical anaesthesia?

Answer 13

Can damage RBCs causing anaemia in large quantities

Question 14

What precautions need to be considered when using regional nerve blocks?

Answer 14

May not work in the designated area

Infection is a risk

Can’t use adrenaline - reduces perfusion to the limb from vasoconstriction