Prepare and monitor anaesthesia in animals

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Prepare and monitor anaesthesia in animals

• STAGES OF ANAESTHESIA

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4 Stages

• Voluntary excitement
• Involuntary excitement
• Surgical anaesthesia
• Light
• Medium
• Deep
• Apnoea/Cardiovascular depression
• Death

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An old summary
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Monitoring depth

• Voluntary movement
• Muscle tone
• Heart function
• rate pulse strength
• Resp function
• rate depth pattern
• MM CRT
• Reflexes
• Pulse oximetery
• Capnography

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Voluntary movement

• Should be obvious!?

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Muscle tone

• Assess either
• Jaw tone (ability to open mouth)
• Test 2-3 x
• A good reflex to test before intubation
• Should be absent in light surgical anaesthesia
• Limb flexion or extension

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Jaw tone

• Lost with muscle relaxation
• Useful but not reliable

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Heart Function

• HR ?
• Pulse strength ?

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Respiration

• Check rebreathing bag
• Patent airway
• Adequate ventilation
• Check movement of chest wall
• Respiration rate
• ? RR indicates
• Deeper GA
• ? RR indicates either
• Lighter GA, or
• Hypoxia, or
• Pain stimulus
• Respiration pattern
• Should be regular

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Some Reflexes

• Eyelid (palpebral, blink)
• Medial palpebral reflex lasts longer than lateral
• Absent in normal surgical anaesthesia (i.e.
  StageIII, plane2)
• Eyeball (corneal, blink retract)
• Should always be present in surgical anaesthesia
• Gag (oro-pharyngeal)
• Laryngeal (cough/spasm when touched)
• Ear flap touch (pinnal)
• Toe web pinch (pedal)
• Should withdraw the leg
• Should be absent in light surgical anaesthesia
• Knee jerk (patellar)
• Tail pinch

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Eyelid blink reflex

• Palpebral reflex
• Absent or Sluggish in surgical anaesthesia

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Remember

• It is ok for eyelid (palpebral) reflex to
  disappear but not for eyeball (corneal) reflex to
  disappear!

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Corneal blink reflex

• Corneal reflex

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If no corneal reflex

• ALWAYS Too deep!
• Better tested with drop of cold saline than with
  finger
• Only perform if necessary (no palpebral)

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Eye position pupil size
Excitement
Light (skin Sx)
Moderate (most Sx)

• Deep (v painful Sx)

Near Death
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If Central Pupil watch out!

• Too light- about to wake up!

Too deep- about to die!, or Too light- about to
wake up!
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Toe pinch reflex

• Pedal withdrawal reflex

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Righting reflex

• Ability to bring forequarter into upright posture
• A measure of consciousness

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Stage 1. Voluntary excitement

• Still conscious
• Possible fear/apprehension, then disorientation
• ? RR ? HR but possible breath holding
• Pupils dilated
• Possible defaecation/urination
• Strong muscle tone and struggling activity
• More likely to see this stage with mask
  inductions
• If induction smooth may not see this stage
• Premedication usually reduces/eliminates this
  stage

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Stage 2. Involuntary excitement

• Unconscious
• Reflex struggling (paddling)
• Eyes rotate ventromedially during this stage
• All cranial nerve reflexes intact
• Toe pinch reflex intact
• Swallowing, Vomiting or Retching
• Seen at recovery also
• This stage reduced if premed. good

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Stage 3a. (Light Surgical)

• No voluntary limb movement but toe pinch reflex
  still present
• Eyes ventromedial, but possible nystagmus
• RR ?? according to stimulation
• Palpebral reflex sluggish, but corneal reflex
  still brisk
• Pharyngeal Laryngeal reflexes intact
• Muscle tone strong
• Light anaesthesia OK for superficial (skin)
  surgery

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Stage 3b. (Medium Surgical)

• Respiration ? depth
• Eyes ventromedial (if visible pupil small)
• R depth ?, RR ?? according to pain stimuln
• HR ?
• Palpebral reflex sluggish or absent, corneal
  reflex still intact
• Muscle relaxation (slackening jaw tone)
• Pharyngeal Laryngeal reflexes gone (easier
  intubation)
• Toe pinch reflex sluggish or absent
• Suitable for most surgery

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Stage 3c. (Deep Surgical)

• Central eyes, medium pupils, eyelids opening
• R depth ?, RR ?, breathing mainly diaphragmatic
  with pause at end inspiration
• More muscle relaxation (slack jaw tone)
• Toe pinch palpebral reflexes absent
• Corneal reflex now sluggish, but still present
• Suitable for very painful surgery (thoracotomy)

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Stage 4. Dangerous anaesthetic

• Corneal reflex absent
• Pupils Dilated Central
• HR ??
• RR slow and shallow then absent
• After respiratory failure get a jerky irregular
  respiration
• No reflexes at all
• Ends with cardiac arrest

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For most surgery, want

• Ventro-medial eye position
• Sluggish palpebral reflex
• Moderate corneal reflex
• Mild jaw tone
• Mild or absent toe pinch reflex

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Balanced anaesthesia

• Too light too much patient stress
• Too deep too much depression of cardio
  respiratory and other body systems function

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Tissue Hypoxia

• The major concern in anaesthesia
• Causes include
• ? O2 supply (poor respiration)
• ? blood O2
• ? blood supply (poor perfusion)
• ?cardiac output
• Possibly results in organ failure esp kidneys

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The End