Anaesthetic Types

Question 1

Define General Anaesthesia

Answer 1

’ A state of controlled and reversible unconsciousness characterised by a lack of pain sensation, lack of memory and relatively depressed reflex responses’

Question 2

What the advantages of local anaesthetics?

Answer 2

• Targeted analgesia - e.g. nerve blocks
• Can be used in high risk patients where GA is not an option (they have minimal effects on CNS, CVS and respiratory system)
• Can be part of a multi-modal analgesia approach intra-op so reduces dose of other drugs needed
• Pre-emptive analgesia

Question 3

How do local anaesthetics work?

Answer 3

Block sodium channels at nerve endings, blocking the conduction of nerve impulses - producing local analgesia.

Question 4

What sensations are lost when local anaesthetic administered? in order

Answer 4

1. Pain
2. Cold
3. Warmth
4. Touch
5. Pressure

Question 5

Name the 5 methods of administration of local anaesthetics

Answer 5

• Injection (local infiltration)
• Regional anaesthesia (injected into the nerve that supplies a region)
• Spinal
• Transmucosal (absorbed via MM)
• Transcutaneous (e.g. EMLA cream)

Question 6

Name some examples of Local anaesthetic drugs

Answer 6

Lidocaine- IV analgesic (10-20m), especially for superficial pain. Blocks sodium channels. Rapid onset. Short-acting. Excreted via kidney.

Bupivicaine - shouldn’t be given IV as more toxic than lidocaine. Slow onset. Long duration. Excreted via kidney.

Mepivicaine - Rapid onset. Medium duration of action.

Question 7

How do Local anaesthetics wear off?

Answer 7

They are redistributed to the liver where they are inactivated

Question 8

Why is adrenaline sometimes added to a lignocaine local anaesthetic?

Answer 8

It causes vasoconstriction which keeps the local anaesthetic in the desired area, decreases the rate of drug absorption therefore increasing its duration of action, and reduces the concentration of drug entering the circulation therefore reducing toxicity.

Question 9

When would using lignocaine with adrenaline be contraindicated?

Answer 9

In a patient with CV disease where the heart couldn’t cope with an increased HR associated with adrenaline

Question 10

Name three types of regional anaesthetic techniques

Answer 10

Epidural
Spinal
Topical

Question 11

What does an epidural do?

Answer 11

Blocks the sensation to the caudal abdomen, pelvis, tail, hind limbs, perineum and obstetrics
Injected between dura and vertebrae

Question 12

Where is a spinal regional anaesthetic injected

Answer 12

Subarachnoid space

Question 13

Give some examples of topical anaesthetics

Answer 13

Skin - EMLA cream - lidocaine
Larynx - lignocaine spray
Lignocaine gel for urinary catheterisation

Question 14

What should be careful with when using topical local anaesthetics?

Answer 14

1. Give plenty of time to actually work! 20-30 mins minimum!
2. Care not to overdose! E.g. don’t give a tiny kitten a lignocaine throat spray and then lignocaine EMLA cream for their catheter

Question 15

What are 5 risks of using local anaesthetics?

Answer 15

1. May cause nerve damage or permanent loss of function when injected into nerve fibres
2. Tissue irritation - slow wound healing, may be painful
3. Can chew area following recovery
4. Allergic reactions
5. Hypotension can occur - especially after epidural

Question 16

What can an overdose or incorrect route of local anaesthetics cause?

Answer 16

CNS stimulation - may lead toseizures
CNS depression - may lead to respiratory failure
Heart contractility reduced - myocardial depression

Question 17

What animals should you take extra care with when using local anaesthetics?

Answer 17

Cats and exotics

Question 18

What are muscle relaxants?

Answer 18

Neuromuscular blocking agents (NMBAs)

Question 19

What do NMBAs do?

Answer 19

Interrupt the transmission of impulses from motor nerve to muscle synapse. Block the release of Acetyl choline

Question 20

Name and describe the 2 types of NMBAs

Answer 20

1. Depolarising
   - Bind to receptors on the muscle side causing an initial surge of muscle activity and then nothing
   - e.g. succinylcholine
   - have rapid onset and are VERY short acting (a few minutes)
2. Non-depolarising
   - compete with Acetyl choline for receptors so block the receptors at the muscle plates
   - no initial surge
   - roughly 30-40minutes duration
   - can be reversed
   - e.g. Vecuronium

Question 21

Can NMBAs be topped up?

Answer 21

Yes

Question 22

How are NMBAs administered?

Answer 22

Slow IV

Question 23

Do NMBAs affect consciousness? How?

Answer 23

They do not affect consciousness as they do not cross the blood-brain barrier

Question 24

Why are NMBAs not used much in veterinary practice?

Answer 24

The only paralyse skeletal muscle therefore the patient is unable to move or respond to inadequate anaesthesia. A patient on these is very difficult to monitor e.g. eye position doesn’t change

Question 25

What MUST you do if NMBAs are administered to a patient?

Answer 25

Provide adequate IPPV

Question 26

What circuits can be used for IPPV?

Answer 26

Bain, Ayres T-piece and Circle (ADE)

Question 27

What are the disadvantages of using muscle relaxants?

Answer 27

• Hypothermia due to decreased muscle tone (can’t shiver)
• Difficult to assess anaesthetic depth
• Some may cause hypotension
• increased effects if used with aminoglycosides
• Increased susceptibility if used alongside halothane, isoflurane, corticosteroids, some diuretics and epinephrine

Question 28

Why would we use muscle relaxants?

Answer 28

• To administer prolonged IPPV - e.g. during thoracic surgery
• During intraocular surgery to avoid change in eye position
• Where muscle relaxation required for surgery
• As part of balanced anaesthesia for high-risk patients

Question 29

Give examples of drugs used to reverse NMBAs

Answer 29

Neostigmine

Edrophorium

Question 30

What may happen when reversing NMBAs? What’s done to counteract this?

Answer 30

May lead to bradycardia and excess salivation. Reversal agents are often given with atropine or glycopyrrolate to counteract this