Prepare and monitor anaesthesia in animals

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Prepare and monitor anaesthesia in animals

• INTUBATION

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Why intubate?

• Airway protection
• Oral-Laryngeal patency
• Anaesthesia removes muscular supports
• Worse than sleeping/snoring!
• Saliva
• Regurgitations
• Reduce anatomic dead space
• Reduce gas pollution
• For forced/controlled ventilation

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Why not intubate?

• Maybe risk of laryngeal injury
• Cats
• Often no intubation done with short term
  ketamine-valium anaesthesia
• Laryngeal reflexes preserved with this

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Minimizing airway obstruction

• DO use a rapid induction technique
• DO remove excretions from pharynx prior to
  extubation
• DO extend the neck and pull out the tongue if
  airway patency is compromised during recovery
• DO pre-oxygenate
• DO NOT extubate too early
• DO NOT excessively premedicate

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Positioning of intubation

• Varies
• Small animals best in sternal recumbency
• Larger animals (heavy to hold up) often in
  lateral recumbency

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Sternal recumbency
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Tube length ext. diameter
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Bulldog tiny tube diameter
Bulldogs have a very small larynx trachea in
this case a 5.5 mm tube for a 15 kg dog!
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Canine larynx
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Feline larynx
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Local anaesthetic

• For Cats
• Lignocaine
• (0.1 mL) 1-2 drops on epiglottis
• Wait 30 sec

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Laryngoscope
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Laryngoscope

• Most useful for
• Cats Small dogs
• Also man, rabbit, pig
• Brachycephalic dogs
• Oral mass/Saliva/FB blocking view
• Depress base of tongue
• This everts the epiglottis
• Dont touch the epiglottis!
• Wipe clean with alcohol swab

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Endo-Tracheal (ET) Tube
Securing method
Cuff
Connector
Cuff inflation valve
Cuff pressure indicator
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ET Tube Materials

• Made of
• Plastic (PVC)
• Red rubber
• Silicone

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ET Tube Cuffs

• No cuff
• Easiest to pass through larynx but very likely to
  leak
• Low volume / High pressure
• Smoother through larynx but easily cause pressure
  injury if over-inflated
• High volume / Low pressure
• Bulkier to pass through larynx but safer

High Volume / Low pressure
Low Volume / High pressure
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Cuffed or Un-Cuffed?
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Cuffed or Un-Cuffed?

• Generally, Cuffed is better
• Better protection against r or v fluids
• Better delivery of anaesthetic gases
• But, Uncuffed used for
• Small kittens/puppies Ferrets
• Better internal diameter means less resistance to
  airflow and less likely to obstruct
• Birds
• Because complete cartilaginous tracheal rings
  means more risk with cuff inflation
• Reptiles

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ET tube stylets

• Soft wire placed inside soft tubes to make them
  more rigid

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Lubrication

• Optional
• Thin smear of sterile lubricant placed on tip
  cuff to make passage of tube smoother

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Intubation

• Have ready a range of possible tubes
• Check tubes
• Clean?
• Cuff holds pressure?
• Connector fits snugly?
• Head held straight
• Best in sternal recumbency
• By top jaw
• By ears?
• Mouth opened
• Tongue pulled forward (not too far)
• Care with laceration of underside
• Use laryngoscope if necessary to depress base of
  tongue
• Hold tube near connected end
• Curvature means that hand does not block view
• Wait for larynx to open
• Do not force down
• Pass through glottis
• Check placement

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Checking placement

• Visualise larynx
• Usually all you need to do
• Feel neck
• Sometimes useful
• Breath tests
• Inflate cuff
• Tap on thorax
• Look for cotton tissue or tuft of hair blown
• Listen
• Smell

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Visualise placement
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Feel placement
Feel here
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Secure tube

• String
• Cotton tape
• Rubber band
• Drip tubing

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Cuff inflation

• Connect tube to Circle
• Ensure bag is moderately filled
• Close pop-off valve
• Squeeze bag to check for audible leaks
• Ideally want only to hear leaks once pressure gt
  12 cm water
• Open pop-off valve
• Turn on Vaporiser

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Dont !

• Dont test for leaks with bag pressure whilst
  vaporiser is on
• Can easily overdose with anaesthetic gas when
  using positive pressure!

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Remember

• Use an appropriately sized syringe for the cuff
• Dont assume that the feel of an inflated cuff
  reflects proper fill or seal
• Close pop off valve, squeeze rebreathing bag
  inflate cuff to seal at pressure of 12 cm H2O
• Make sure that you are assessing (listening) for
  gas leakage at the time the chest is being
  inflated
• If it is difficult to inflate a cuff sufficiently
  to avoid leakage, the tube is in the esophagus or
  tube is excessively undersized
• Often 0.5-1.0 ml of air is added to the cuff
  after this test to ensure a good seal, allowing
  for some airway relaxation to occur as the
  patient deepens

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How far the tube?

• Too far gt passes into one bronchus gt lung
  collapses gt acts as an arteriovenous shunt
  because blood still flows through but doesnt
  pick up O2 gt cyanosis
• Ideally incisor teeth ? lower neck
• Midway between larynx and where trachea divides?
• Where crosses spine of scapula?

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Tube problems

• Endo-oesophageal placement
• Animal wakes up
• Dangerous regurgitation stomach bloating can
  result
• Trauma
• Cuff forced roughly through larynx
• Cuff over-inflated
• Obstruction
• Kinking
• More likely with red rubber (Plastic tubes mould
  to shape of trachea with body warmth)
• Dried Secretions clean properly
• Cuff Over-inflation
• Tip impaction
• Cuff herniation
• Endo-bronchial intubation
• Apparatus dead space (too long)
• Interference with oral procedures

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Endobronchial intubation

• Tube too far in
• Other lung collapses
• Blood flows through collapsed lung without
  picking up oxygen
• This oxygen poor (cyanotic) blood dilutes the
  oxygenated blood from the good lung causing
  patient cyanosis

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Endobronchial intubation
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Tip impaction

• If slanted opening lies flat against a bend in
  tracheal wall
• Overcome by a Murphy Eye

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Cuff over-inflation

• Immediate obstruction, or
• Later tracheitis (coughing, scarring)

• OR

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Cuff herniation

• Torn cuff covers end hole of tube
• Rare!

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Extubation

• Signs to look for extubation
• Swallowing
• Corrects the dorsal displacement of soft palate
  relative to epiglottis
• Reflexes
• Palpebral
• Jaw tone
• Withdrawal

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Extubation

• Animal has jaw tone swallowing reflex
• Cats earlier may take out before this much awake
• Cats have a very strong laryngeal protective
  reflex
• Brachycepahlic dogs late as possible
• Pulling tongue lightly can stimulate the
  swallowing reflex
• Untie tube
• Ensure any swabs/discharges removed (dentals)
• Ensure head positioned downwards
• In case there is regurgitated fluid in mouth
• Extend neck pull out tongue
• Deflate cuff with syringe
• Remove tube slowly but steadily
• Ensure the patient is moving air normally

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Extubation problems

• Laryngospasm (cats) after rough intubation then
  tube removal
• Larngeal obstruction (brachycepahlic dogs)

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Tube Maintenance

• Cleaning
• Disinfection or Sterilisation
• How sterile is the trachea anyway?
• What about infectious diseases (URTI)?
• Drying
• /-Repair (Silicone tubes)

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Tube cleaning

• Rinse under running water
• Soak in detergent
• Scrub residual mucus (esp. internal)
• Rinse-off detergent (thoroughly)

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Tube sterilisation

• Varies according to type of tube material

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Red Rubber ETT

• Chlorhexidine soak
• Rubber damaged by
• Repeated autoclaving (but, will tolerate 10-20
  times)
• Oils
• Sunlight

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PVC ETT

• Chlorhexidine soak
• Specifically cannot use ETO (Ethylene Oxide) gas

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Silicone ETT

• Can be autoclaved

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The End