1 - intro to anaesthesia Flashcards
Give the definition of anaesthesia
A state in which an animal is insensible to pain resulting from trauma or surgery (means without feeling)
Define the term analgesia
The absence of pain
Define the term general anaesthesia
The reversible controlled drug induced intoxication of the CNS in which the patient neither perceiver or recalls noxious stimulation
Define the term local anaesthesia
Lack of sensation of a localised part of the body
Why under GA do patients not perceive or recall pain?
Because pain is a conscious sensation so if unconscious you dont feel it
What are the 3 things in the triad of anaesthesia - explain it
- Hypnosis (being unconcious)
- Analgesia
- 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
Give the definition of balanced anaesthesia
The use of a number of different drugs to produce a state of general anaesthesia
Describe what balanced anaesthesia is and why we use it
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.
Why does the ‘ideal anaesthetic’ need high lipid solubility?
So that it can cross lipid bilayers - like cell membranes to get into cells to have its effect
Why does the ‘ideal anaesthetic’ need to have a water soluble formulation?
So it can be injected
Give 5 properties of the ideal anaesthetic - comment on whether any anaesthetic agent will have all the properties and why
- Rapid onset
- High lipid solubility
- No pain on injection
- Water soluble formulation
- 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.
Discuss the relationship between sedation and anaesthesia
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
Give the definition of sedation
A rousable state of CNS depression
Name and say what happens in each of the stages of anaesthetic depth (not including clinical signs)
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
Which anaesthetic agent was first used to describe the stages of anaesthesia? Whats the relevance of this
Ether anaesthesia
Due to its slow induction you see all the stages
What is movement through the stages of anaesthesia associated with?
Increase in CNS depression
With modern anaesthetic agents which stage of anaesthesia do we usually start at?
Stage 3 plane 1
In stage 3 of anaesthetic depth what plane do we aim to be in and what is the relevance if we arent?
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
What are the 6 general steps of the GA process?
- Patient prep
- Pre-anaesthetic assessment
- Lab tests (if indicated)
- Physical status classification
- The GA itself
- Post GA care
Describe the patient prep stage of the GA process
- 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 - 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
How long should you fast dogs and cats for before GA?
6-8 hours
When should you withhold water from cats and dogs before GA?
Why?
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
Describe the pre-anaesthetic assessment stage of the anaesthetic procedure.
- 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.
- Physical exam of animal: focus on organ systems important to anaesthetic - CV, Resp, CNS
Which body systems are important in GA and why?
- CV and resp - because thats where the drugs have their main adverse effects
- CNS - this is where the drug has its target effect
When are lab tests done before GA?
If:
- there has been an abnormality identified in the history or clinical exam
- If elderly
- If its an emergency status
Why do we not to lab tests on all animals undergoing GA?
Most conditions affecting health and welfare during GA should be picked up at clinical exam.
You may identify undetectable abnormalities - encourages overdiagnosis.
Describe the categories in the physical status classification step of the GA procedure.
- Normal healthy patient
- A patient with mild systemic disease (that doesnt limit normal function)
- A patient with severe systemic disease (that does limit normal function)
- A patient with severe systemic disease thats a constant threat to life
- A moribund patient not expected to survive without the procedure
Why do we assign patients for GA a physical status classification?
Why may this be useless
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.
What are the phases of the GA journey?
- Premedication
- Induction
- Maintenance
- Recovery
In what phase of the anaesthetic journey is there greatest risk of complications?
During induction and recovery
What 5 things does post anaesthesia care include?
- Monitoring - of the same parameters and same frequency as anaesthesia
- Patient warming
- Fluid therapy - should be continued until animal is eating and drinking normally
- Analgesia
- Sedation - may be needed in some cases
Why is the post operative period so important to monitor patients in?
Most anaesthetic related deaths occur in the early post op period - probably due to lack of monitoring in a physiological abnormal patient.
What are some causes of prolonged recovery from GA?
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)
