How do we induce anaesthesia?

Question 1

Options for induction of anaesthesia.

Answer 1

Injectable.
- IV (Propofol/Alfaxalone).
- IM – Sedation / GA combinations.
Inhalant.
- Face mask.
- Gas chamber.

Question 2

Routes for injectable induction of anaesthesia.

Answer 2

• IV – Quickest w/ 2-10 mins onset of action.
  – Reliable, expected efficacy, less stress for animal.
  – But relies on IV catheter which can be tricky in some animals.
• IM – Fairly quick w/ onset of action 10-20 mins.
  – Reliable if hit a muscle (more difficult in obese animals.
  – But can be painful and has a slower onset of action than IV.
• SC – Fairly uncommon.
  – Easy administration.
  – Less painful than IM.
  – But still can cause pain and has a longer onset of action of 30-45 mins and has a lower efficacy than the others.

** always check licensing of drugs before administration as this also cover the route via which it can be given.

Question 3

1. Advantages of gas chamber for inhalational induction of anaesthesia.
2. Disadvantages of gas chamber for inhalational induction of anaesthesia.

Answer 3

1. • Great for smallies like mice and hamsters.
     - Easy to set up and use.
     - Cheap.
     - No technical skill needed.
2. • Very stressful for animal.
     - Difficult to observe the animal,
     - Risk of exposure to staff.
     - NOT a nice way to be anaesthetised.

Question 4

1. Advantages of face mask for inhalational induction of anaesthesia.
2. Disadvantages of face mask for inhalational induction of anaesthesia.

Answer 4

1. • Cheap.
     - Easy to set up and use.
     - Can give O2 / volatile agents quickly.
2. • Does not protect airway.
     - Increases dead space.
     - Human exposure to VA / waste gases.
     - Not always tolerated.

Question 5

1. Points about restraint for induction of anaesthesia.
2. Risks associated with physical restraint.

Answer 5

1. • As minimal as possible.
     - Be ready if need to apply more restraint.
     - Know when to consider chemical restraint.
     - Never scruff cats!
     - Ask for help where needed.
     - Optimise ventilation.
2. • Stress.
     - CATS are v stressy.
     - Can cause respiratory compromise.
     - Raised ICP, IOP, increased jugular pressure and coughing.
     ** Important to be aware of what is going on around you.

Question 6

Why is positioning so important?

Answer 6

Facilitates placement of ET tubes / catheters / blocks.
Ensures animals safety.
Ensures patient safety.
Prevents injury to all.
Good positioning during GA prevents stiff joints / skin sores, provides good ventilation and improves surgical access.

Question 7

Methods of airway management.

Answer 7

Face mask.
Laryngeal mask (LMA).
Supraglottic device (V-Gel).
Endotracheal tube (ETT).

Question 7

Laryngeal mask (LMA)…
1. Advantages.
2. Disadvantages.

Answer 7

1. Easy to use – sits over the larynx.
   Reduced complications compared to ETT.
   Reduced airway pollutants compared to face masks.
2. Not really designed for vet spp.

Question 8

1. Points about supraglottic airway devices. (V-GELs)
2. How does the V-GEL fit in the animal.

Answer 8

1. • Technology first used in humans.
     - Spp. specific design.
     - Weight specific design.
     - Training needed before use.
     – Online training available (docsinnovent).
     - Useful in rabbits.
2. Blind end sits in the oesophageal opening and open part of the V-GEL cups over the trachea.

Question 9

1. Advantages of ET tubes.
2. Types of ET tubes?

Answer 9

1. ‘Gold standard’.
   Complete airway protection.
   Prevent atmospheric exposure.
   Accurate provision of anaesthetic gases.
   Some with a cuff system for snug fit.
2. Silicone / PVC / red rubber.

Question 9

Name parts of the ET tube from tracheal end to buccal end.

Answer 9

Bevelled edge.
Murphy’s eye (safety feature in case end become obstructed).
Cuff.
Size label in mm (diameter).
Pilot balloon (to inflate cuff).
Adaptor.

Question 10

1. Advantage of a clear ET tube.
2. What type of ET tube used in procedure where neck moved a lot? – when would we absolutely not use this type of ET tube.

Answer 10

1. Can see debris in them.
   Can appreciate condensation when patient breathing.
2. Armoured ET tube. – MRI as metal contained.

Question 11

What is the point of a cuff?

Answer 11

• Allows tight seal in trachea.
• Safe if inflated correctly.
• Prevents gas leaking around tube for personnel safety.
• Prevents contents going into patient lung for patient safety.
• Accurate delivery of VA and O2.

Question 12

What are the 2 types of cuff and which one is preferred and why?

Answer 12

Low volume higher pressure and high volume low pressure.
High volume low pressure is preferred as it exerts less pressure on the airway therefore reducing risk of damage.

Question 13

1. Comparison of ET tubes.
2. Considerations for if reusing them.

Answer 13

1. Low volume high pressure.
   High volume low pressure.
   Clear or opaque (clear allows to see debris in tube and visualise condensation).
   Some have safety features e.g. Murphy’s eye.
2. Care when cleaning as can become brittle. Check ET tubes regularly and before use to ensure in good condition.

Question 14

Equipment for ET intubation.

Answer 14

Laryngoscope.
Tubes.
- Range of sizes (10mm = 20kg).
- Length (incisors to point of shoulder) (minimise dead space).
LA (cats) (i.e. Intubeaze).
Tie.
Cuff syringe.
Swab, suction, mask for pre-oxygenation, stylet / bougie.

Question 15

Confirmation of correct placement.

Answer 15

Gold standard = capnograph trace.
Visualisation of the tube between vocal folds.
Condensation inside the tube.
Appreciation of air movement (don’t use hair).
Don’t press the thorax.
- can result in false positives.
- reflux.
- reduces the functional residual capacity of the lungs.

Question 16

1. Common complications during induction of anaesthesia.
2. How can we reduce these complications?

Answer 16

1. • Injury – to staff or patient.
     - Lack of airway patency quickly enough.
     - Aspiration / regurgitation.
     - Hypothermia.
     - CV and respiratory effects – MUST MONITOR PATIENT!
     - Post-induction apnoea.
2. • Don’t assume someone else doing it, communicate.
     - Check peripheral pulses.
     - Confirm ventilation.
     - Attach up to monitoring equipment if not already done.
     - BE PREPARED!