Introduction to Anaesthesia Flashcards
What is General Anaesthesia?
It is the controlled reversible production of unconsciousness through pharmacological means.
What is the aim of General Anaesthesia?
Controlled depression of the CNS to produce lack of awareness of painful inputs (nociception).
Where do we want minimal depression during anaesthesia?
Of the hind brain region - cardiovascular centres.
Where do we want to depress during GA and why?
Front brain so that the patient is not aware.
Name 5 methods to introduce local anaesthesia into the body?
- Topical
- Infiltrative
- Conductive
- Epidural
- Subarachnoid
Name 3 reasons we anaesthetise our patients?
- Unconsciousness- pain free
- Restraint - immobilisation (patient and practitioner safety)
- Relaxation - surgical access (this will improve the access)
When were barbiturates developed?
1920s
What is the triad of anaesthesia?
Hyponosis, Anti-nociception (analgesia), muscle relaxation
What do we mean by hypnosis?
Artificially induced sleep - cannot wake up therefore different wave form of sleep.
What are the 4 areas involved with anti-nociception?
- Perception (cerebral cortex)
- Modulation
- Transmission (sensory nerves)
- Transduction (sensory nerve endings, nociceptors)
What can block transduction?
NSAIDs
What can block perception?
Opioids.
Give an example of a muscle relaxant?
Diazepam or a specific neuromuscular junction blocking agent e.g. curare (plant extract)
Why is it important to use muscle relaxants?
It is very difficult intubating patients that have not recieved muscle relaxants.
What are the outdated 4 stages of anaesthesia?
- Induction
- Excitement
- Operative
- Danger
What are the signs of the induction stage?
- pupil normal size
- reaction to light
- irregular pulse
- normal resp.
- normal BP
What are the signs of the excitement stage?
- normal pupils
- exaggerated response to light
- Increased resp rate
- pulse irregular and fast
- BP high
What are the signs of the operative stage?
- Small pupils
- No reaction to light
- steady resp rate
- steady, slow pulse
- normal BP
What are the signs of danger stage?
- dilated pupils
- No response to light
- no resp rate
- weak to thready pulse
- low BP
What are the modern three classes to monitor anaesthesia?
- Conscious
- Unconscious
- Dead
What are the specific signs of CNS depression related to?
Muscle relaxation
What happens to the eye during anaesthetic?
It rolls ventrally and inwardly.
What happens to the eye as the patient nears death?
The eye returns more central, pupil is fixed, non-responsive and dilated.
What do we need to be aware of in horses regarding eyes?
We need to check both eyes at the same time during GA because they tend to do different things.
What are the levels of CNS depression related to?
The level of brain stem depression e.g.
- respiratory rate - decrease
- heart rate - decreased
- Blood pressure - increase
What are the three risks associated with anaesthesia?
- Direct toxicity
- Indirect toxicity e.g. liver damage
- ‘Accidents’ - 90% anaesthetic deaths
what does CEPEF mean?
Confidential Enquiry into Perioperative Equine Fatalities
How many horses die in relation to anaesthesia?
1 in 100 (1.9%)
What is the death rate of dogs under anaesthesia?
0.17%
What is the death rate in humans?
1 in 100,000
Why is it higher in animals?
- species differences
- training
- monitoring
What marks a successful anaesthetic?
One where there is no cerebral hypoxia, not just about death.
What is the ASA?
America Society of Anesthesiologisys - Physical Status Classification - 2012
What is a category I patient?
- Normal healthy patient
- No discernible disease
- Elective ovariohysterectomy, castration, dentistry
What is a category II patient?
- Pre-existing disease
- No discernible systemic signs
- Skin tumour, fracture without shock, uncomplicated hernia, localised infection, compensated cardiac disease.
What is a category III patient?
- Pre-existing disease
- Mild systemic signs
- Fever, dehydration, mild anaemia, mild cachexia, mild hypovolaemia
What is category IV?
- Pre-existing disease
- Severe systemic signs
- Uraemia, toxaemia, severe dehydration and hypovolaemia, severe anaemis, cardiac decompensation, emaciation, high fever.
What is category V?
- Moribund patient (at the point of death)
- Not expected to survive with or without intervention
- Extreme shock and dehydration, terminal malignancy or infection, severe trauma
What is category IV?
- declared brain-dead patient whose organs are being removed for donor purposes.
Name 5 ways in which the risk of anaesthesia can be minimised?
- Evaluation and planning
- Support e.g. oxygen, fluids, warmth
- Monitoring (during anaesthesia and recovery)
- Anaesthesia record sheet (legal record), allows you to spot trends
- The trained anaesthetist
Tranquilisation definition?
Relief of anxiety
Sedation definition?
Central depression, drowsiness - less aware of surroundings.
Narcosis ?
- drug induced sleep produced by narcotics e.g. opium like drugs
Dissociative anaesthesia?
Induced by drugs like ketamine that dissociates the thalamo-cortical and limbic systems.
Name two other effects of anaesthesia?
- Stress response
2. Thermoregulation
name three things that general anaesthesia increases?
- BP
- Insulin
- Cortisol - stress response
Name the 7 steps of a normal anaesthesia induction?
- Administer premedication
- Induce anaesthesia - injectable agent
- Intubate
- ABC - airways, breathing, circulation
- Connect to anaesthetic machine and supply volatile anaesthetic and oxygen
- Alter inspired concentration in response to physical signs
- Supply analgesia separately - ALWAYS
Why use combinations of agents?
To achieve all three desired effects of the triad - muscle relaxation, anti-nociception, hypnosis.
What happens if ketamine is used alone?
- poor muscle relaxation
- good analgesia and unconsciousness (dissociative state)
What other drug would you add with ketamine to induce muscle relaxation?
Medetomidine (improve analgesia and muscle relaxation)
