1 - intro to anaesthesia

Question 1

Give the definition of anaesthesia

Answer 1

A state in which an animal is insensible to pain resulting from trauma or surgery (means without feeling)

Question 2

Define the term analgesia

Answer 2

The absence of pain

Question 3

Define the term general anaesthesia

Answer 3

The reversible controlled drug induced intoxication of the CNS in which the patient neither perceiver or recalls noxious stimulation

Question 4

Define the term local anaesthesia

Answer 4

Lack of sensation of a localised part of the body

Question 5

Why under GA do patients not perceive or recall pain?

Answer 5

Because pain is a conscious sensation so if unconscious you dont feel it

Question 6

What are the 3 things in the triad of anaesthesia - explain it

Answer 6

1. Hypnosis (being unconcious)
2. Analgesia
3. Muscle relaxation
   These are the 3 components of anaesthesia, perfect anaesthetic agents provide these 3 things in the right amount which isnt possible so we use balanced anaesthesia

Question 7

Give the definition of balanced anaesthesia

Answer 7

The use of a number of different drugs to produce a state of general anaesthesia

Question 8

Describe what balanced anaesthesia is and why we use it

Answer 8

We can conduct anaesthesia with just an inhaled anaesthetic agent - they are all good hypnotics but only provide good muscle relaxation and analgesia at high doses, putting the patient into a deep plane of anaesthesia and risking side effects. Using balanced anaesthesia with more than one drug means we use lower doses of the drugs to get the desired effect, and less side effects.

Question 9

Why does the ‘ideal anaesthetic’ need high lipid solubility?

Answer 9

So that it can cross lipid bilayers - like cell membranes to get into cells to have its effect

Question 10

Why does the ‘ideal anaesthetic’ need to have a water soluble formulation?

Answer 10

So it can be injected

Question 11

Give 5 properties of the ideal anaesthetic - comment on whether any anaesthetic agent will have all the properties and why

Answer 11

1. Rapid onset
2. High lipid solubility
3. No pain on injection
4. Water soluble formulation
5. Rapid recovery
   No anaesthetic agent has all the ideal properties, some are mutually exclusive like being lipid soluble and water soluble. But all anaesthetics have some of the properties.

Question 12

Discuss the relationship between sedation and anaesthesia

Answer 12

They are on a continuum.
An animal may be conscious through to anaesthetised. Sedation is somewhere on this continuum of CNS depression.
You can have sedation with anaesthetic drugs, and anaesthesia with ‘sedative’ drugs - it depends on dose

Question 13

Give the definition of sedation

Answer 13

A rousable state of CNS depression

Question 14

Name and say what happens in each of the stages of anaesthetic depth (not including clinical signs)

Answer 14

Stage 1: Voluntary excitement
Stage 2: involuntary excitement
Stage 3, plane 1: Light surgical anaesthesia
Stage 3, plane 2: moderate surgical anaesthesia
Stage 3, plane 3: deep surgical anaesthesia
Stage 4: Paralysis
Stage 5: death

Question 15

Which anaesthetic agent was first used to describe the stages of anaesthesia? Whats the relevance of this

Answer 15

Ether anaesthesia

Due to its slow induction you see all the stages

Question 16

What is movement through the stages of anaesthesia associated with?

Answer 16

Increase in CNS depression

Question 17

With modern anaesthetic agents which stage of anaesthesia do we usually start at?

Answer 17

Stage 3 plane 1

Question 18

In stage 3 of anaesthetic depth what plane do we aim to be in and what is the relevance if we arent?

Answer 18

Plane 1 and 2.

If we are needing to use plane 3 or stage 4 the anaesthetic is deep so we probs arent using a balanced approach properly

Question 19

What are the 6 general steps of the GA process?

Answer 19

1. Patient prep
2. Pre-anaesthetic assessment
3. Lab tests (if indicated)
4. Physical status classification
5. The GA itself
6. Post GA care

Question 20

Describe the patient prep stage of the GA process

Answer 20

1. Stabilise pre-existing conditions - most patients are anaesthetised to either investigate or fix something wrong. Patient prep aims to optomise physiological function of the patient by treating/stabilising pre-existing conditions. This may be done through:
   - Medical management (e.g. of diabetes/hyperthyroidism)
   - Fluid therapy (i.e. to treat hypovolemia or dehydration)
   - Analgesia (if painful)
   - Anxiolysis
2. Withhold food and water - this is to prevent regurgitation and aspiration AND to reduce stomach size - because a full stomach presses on the diaphragm during GA which can lead to hypoventilation

Question 21

How long should you fast dogs and cats for before GA?

Answer 21

6-8 hours

Question 22

When should you withhold water from cats and dogs before GA?
Why?

Answer 22

When the first sedative/anaesthetic drugs are given

If we withheld water for longer it leads to hypovolaemia and dehydration which contributes to CV instability during GA

Question 23

Describe the pre-anaesthetic assessment stage of the anaesthetic procedure.

Answer 23

1. You need history. Important things to look for are: any previous anaesthetics, and any issues that happened, details of presenting complaint and any lab results from health conditions and also allergies.
2. Physical exam of animal: focus on organ systems important to anaesthetic - CV, Resp, CNS

Question 24

Which body systems are important in GA and why?

Answer 24

1. CV and resp - because thats where the drugs have their main adverse effects
2. CNS - this is where the drug has its target effect

Question 25

When are lab tests done before GA?

Answer 25

If:

• there has been an abnormality identified in the history or clinical exam
• If elderly
• If its an emergency status

Question 26

Why do we not to lab tests on all animals undergoing GA?

Answer 26

Most conditions affecting health and welfare during GA should be picked up at clinical exam.
You may identify undetectable abnormalities - encourages overdiagnosis.

Question 27

Describe the categories in the physical status classification step of the GA procedure.

Answer 27

1. Normal healthy patient
2. A patient with mild systemic disease (that doesnt limit normal function)
3. A patient with severe systemic disease (that does limit normal function)
4. A patient with severe systemic disease thats a constant threat to life
5. A moribund patient not expected to survive without the procedure

Question 28

Why do we assign patients for GA a physical status classification?
Why may this be useless

Answer 28

To integrate all clinical info you have into 1 sentence of how healthy they are.
Its subjective, and it doesn’t really matter as long as you think about the status of the animal.

Question 29

What are the phases of the GA journey?

Answer 29

1. Premedication
2. Induction
3. Maintenance
4. Recovery

Question 30

In what phase of the anaesthetic journey is there greatest risk of complications?

Answer 30

During induction and recovery

Question 31

What 5 things does post anaesthesia care include?

Answer 31

1. Monitoring - of the same parameters and same frequency as anaesthesia
2. Patient warming
3. Fluid therapy - should be continued until animal is eating and drinking normally
4. Analgesia
5. Sedation - may be needed in some cases

Question 32

Why is the post operative period so important to monitor patients in?

Answer 32

Most anaesthetic related deaths occur in the early post op period - probably due to lack of monitoring in a physiological abnormal patient.

Question 33

What are some causes of prolonged recovery from GA?

Answer 33

Hypothermia
If weve given drugs with long duration of action
If they have had prolonged anaesthesia
Animals with concurrent disease
The presence of intraoperative adverse effects (lie hypoxaemia or haemorrhage)