Clinical induction & maintenance

What are the options for induction agents?

• Propofol

• Alfaxalone

• Ketamine

• Inhalational agents (sevoflurane & isoflurane)

• Thiopental (large animal)

• GGE (Guaifenesin)

• Etomidate

• Potent opioids

What is choice and admin of an induction agent dependent on?

• Species

• Drugs available & their pharmacology

• Personal preferance

• Individual animal 

• Environment 

Dogs vs cats when inducing (things to consider)

Dogs —> obesity, brachycephalics, temperament variable, can induce to effect, IV access easy

Cats —> smaller in body mass, can be spicy, IV access more challenging, mask sub-clinical dx well, care with repeated doses of propofol (forming of Heinz bodies in the blood), can induce to effect 

What needs to be considered when inducing horses?

• Flight reaction to stressful situations

• Large body mass

• IV access easy

• Do not lie down after sedation / do not want to remain recumbent when recover

• Cannot easily administer to effect

What needs to be considered when inducing farm animals?

Must follow releavnt food safety legislation —> extremely limiting 

What are the licenced UK Induction agents?

What is the route of administration of the different induction/maintenance agents?

What are some examples of induction co-agents?

• Muscle relaxation

  • Benzodiazepines (not licenced in farm animals)

    • Midazolam

    • Diazepam

  • Guaifenesin (GGE)

• Analgesia

  • Ketamine

  • Opioids

What does anaesthesia do?

• Relaxation of laryngeal & pharyngeal tissues

• Abolishes the swallowing reflex

• Cause resp depression

  • Can lead to apnoea

What are the considerations you need to make regarding the pharmacology of the drug when choosing an induction/maintenance agent?

• Pharmacokinetics

  • Route of administration

  • Onset of action

• Pharmacodynamics

  • Quality of anaesthesia

  • Cardiovascular and respiratory effects

  • Other effects

  • Quality of recovery

  • Adjunctive drugs

• Formulation

  • Irritancy

  • Pain on injection

  • Shelf-life

  • Combine with other drugs

What are the considerations you need to make regarding the procedure when choosing an induction/maintenance agent?

• Procedure

  • Duration

  • Complexity

  • Safety of working personnel

• Anaesthetic environment

  • Hospital vs Field

  • Quiet and calm vs busy noisy

  • Facilities and equipment available

What are the different induction techniques in horses?

• 1 person

• 2 person

• Wall induction

• Gate induction

• ‘Free’ fall

What specific considerations do you need to make with ruminants?

• Licencing!!!!

• Safety

  • Handling variable

  • Most are in sternal recumbency post pre-medication

• Risk of aspiration

  • Quick induction preferable

  • Position to allow saliva to drain

• IV access can be challenging

What are the advantages of intubation?

• Protects airway from oesophageal/ gastric content

• Allows delivery of oxygen/ medical air +/- maintenance inhalant

What are the different options for airway management?

• Face mask

• Endotracheal intubation - cuffed and uncuffed

• Supraglottic airway devices-LMA/ V-Gel

What are face masks usually used for?

• Not commonly used for delivering inhalant agents due to large amount leaking into the working airspace

• Commonly used to deliver oxygen

How do you carry out intubation in small animals?

Use laryngoscope to visualise larynx and aid intubation

When would you use a cuffed and uncuffed ET tube in small animals?

• Cuffed in dogs

• Uncuffed in cats

  • Can use cuffed in cats but be cautious of laryngeal necrosis

How do you carry out Endotracheal intubation on equines?

• Large ETT tube

• Placement is blind

• Bite block used to keep jaw open to aid placement and prevent biting on the tube

How do you carry out Endotracheal intubation on ruminants?

• Cows- same technique as horse

• Sheep/ Goats- Like small animal but much longer laryngoscope blade

• Often need stylets to aid

What are the uses of Supraglottic airway device?

• Bronchoscopy

• Cats

• Rabbits

How do you deal with laryngeal spasm in cats?

• Intubeaze (lidocaine spray)

• Apply directly to larynx to prevent laryngeal spasm

• 1 spray = 0.14ml= 2.8mg lidocaine

What may you need to do when carrying out an emergency intubation?

Horses = urinary catheter, needle into trachea, tracheostomy

What are the different inhalational agents?

• Isoflurane

• Sevoflurane

What are the different intravenous maintenance agents?

TIVA (total intravenous anaesthesia) or PIVA (partial intravenous anaesthesia)

• Propofol

• Alfaxalone

• Ketamine

What are the inhalational agents administered with?

100% oxygen or medical air

How is TIVA achieved and when would you do this?

• Constant rate infusion or intermittent boluses

• Field anaesthesia

• Upper airway diagnostics or surgery

What species are the different maintenance agents licence in?

What are some MAC sparing techniques?

• PIVA

• Multimodal analgesia

• Locoregional techniques

What are the most commonly used induction/maintenance agents in different species?

• Cats/ Dogs- Propofol/ Alfaxalone induction with Isoflurane/ Sevoflurane maintenance

• Horses- Ketamine (+midazolam) induction with isoflurane inhalant maintenance or Ketamine boluses (TIVA)

• Large animal- Ketamine induction with isoflurane inhalant maintenance or Ketamine boluses (TIVA)

  • Majority of procedures under sedation and local anaesthetic