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Anaesthesia Belinda Farnfield Some definitions and terms Anaesthesia & Analgesia Anaesthesia State of controllable, reversible insensibility general - loss of consciousness local - loss of sensory and motor function confined to a specific region Analgesia

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anaesthesia

Anaesthesia

Belinda Farnfield

anaesthesia analgesia
Anaesthesia & Analgesia
  • Anaesthesia
    • State of controllable, reversible insensibility
      • general - loss of consciousness
      • local - loss of sensory and motor function confined to a specific region
  • Analgesia
    • Temporary abolition or diminution of pain perception
sedatives tranquillisers
Sedatives & Tranquillisers
  • Sedatives
    • Drowsiness
    • Reduced fear & apprehension
  • Tranquillisers
    • Calming effect
    • No sedation
  • Overlap, species variation
  • Think of them as one group
muscle relaxants
Muscle relaxants
  • Muscle relaxant
    • Many drugs used as part of an anaesthetic regimen produce varying degrees of muscle relaxation
    • Specific term “muscle relaxant” refers to
      • neuromuscular blocking agent
      • produce paralysis of skeletal muscles
premedication
Premedication
  • Historical
    • drugs given before anaesthesia to reduce side effects
    • eg excess secretions, ether anaesthesia
  • Modern
    • pre-emptive analgesia
      • before painful stimulus occurs
    • sedate/ tranquillise (in larger species)
an anaesthetic regimen includes
An anaesthetic regimen includes
  • Induction
  • Maintenance
  • Recovery
induction
Induction
  • Refers to general anaesthesia
  • Animal loses consciousness
  • Should be
    • Calm, stress free (and so humane)
    • Safe for animal and handler
maintenance
Maintenance
  • Keeping animal asleep
  • The animal should be
    • Unable to perceive painful stimuli
    • Relaxed muscles
    • Asleep (or immobile)
  • This is called the anaesthesia triad
recovery
Recovery
  • Rapid return to normal physiology & behaviour
  • Abnormal physiology leads to poor animal model
anaesthetics may be given by various routes
Anaesthetics may be given by various routes
  • Possible routes are
    • Inhalation
    • Injection
    • Local
  • Routes may be combined
    • Injectable agent for induction
    • Then inhalational anaesthesia for maintenance
inhalational anaesthesia principles
Inhalational anaesthesia: principles
  • Animal breathes in anaesthetic vapour delivered in a carrier gas (oxygen +/- nitrous oxide)
  • Crosses from alveoli to blood stream
  • Reaches CNS and has anaesthetic effect
  • Side effects
  • Recovery process
    • animal breathes off anaesthetic vapour
    • minimal metabolism
practicalities
Practicalities
  • Two main agents used
    • Isoflurane
    • Halothane
  • Both are liquids at room temperature, placed in a vaporiser
  • Oxygen passed through the vaporiser
  • Vapour delivered in oxygen to the animal
induction chambers
Induction chambers
  • Induction chambers
    • Useful for small species
    • Minimal restraint needed
face masks
Face masks
  • Facemasks
    • Need close restraint
    • Or
      • Induction chamber first
    • Or
      • Injectable agents first
the anaesthetic machine
The anaesthetic machine
  • Take some time with this
  • Well before you are first due to use the machine
the anaesthetic machine20
The anaesthetic machine
  • Find the oxygen cylinder
    • learn to change cylinder, ask about alarms
  • Find the vaporiser
    • learn how to fill it
  • Learn where to connect a breathing system/ chamber
  • Learn how to connect up and use scavenging equipment
slide21
Oxygen cylinder
  • Vaporiser
  • Breathing system/ chamber
  • Scavenging equipment
other equipment you may see use
Other equipment you may see/ use
  • Endotracheal tubes
    • Protect and maintain airway
    • Can control ventilation
    • Essential for some species
    • Skill needed to place
isoflurane in the mouse
Isoflurane in the mouse
  • Video: isoflurane in the mouse (6 minutes)
injectable anaesthesia principles
Injectable anaesthesia: principles
  • Drug is administered
  • Absorption and circulation
    • depending on route
  • Anaesthetic effect once it reaches the central nervous system (CNS)
  • Recovery process
    • Metabolism (liver) & excretion of drug (kidneys)
practicalities26
Practicalities
  • Routes of injection
    • Intraperitoneal
    • Intramuscular
    • Intravenous
slide28
And
  • Lots of dose tables and “Recipes”
  • Species differences
  • Strain differences
why are combinations of agents used
Why are combinations of agents used?
  • One agent can be used to produce induction and all 3 desired effects of the triad (unable to perceive painful stimuli, relaxed muscles, asleep)
    • Eg isoflurane
  • Injectable agents are often used in combination
    • “Balanced anaesthesia”
    • Eg ketamine: if used alone, poor muscle relaxation
    • Add xylazine: improved analgesia and muscle relaxation
information overload
Information overload?
  • Invest some time
  • Get to know the basic drug families
    • plus key examples of each
  • “Laboratory Animal Anaesthesia” - vital reading
  • Which agents are you likely to be using
  • In which species
  • Get familiar with one protocol at a time
one common combination is xylazine and ketamine
One common combination is xylazine and ketamine
  • Video: mouse xylazine and ketamine (5 minutes)
selecting a regimen33
Selecting a regimen
  • May be done for you
    • Join another research group
    • Evaluate & question
  • Based on a publication
    • Essential to contact the authors if you are adapting something reported in a journal
species procedure
Species & procedure
  • Species, strain, age, sex, weight
  • Procedure
  • Depth & duration
  • Experience/ skill
  • Equipment available
  • Legal permission
during all parts of the regimen
During all parts of the regimen
  • A minimum of side effects
  • Normal physiology maintained
    • All body systems
  • This is impossible
    • Desirable effects and side effects must be balanced
make a list
Make a list
  • Which routes are practical?
  • Make a list of possible agents/ combinations
  • Likely interactions with your procedure?
  • Cross off undesired agents
  • Now have one or two left
    • Recovery time
    • Familiarity
    • Cost