Induction and intubation

What are Guedel’s 4 stages of anaesthesia?

Stage I = induction (analgesia)

Stage II = delirium (excitement)

Stage III = surgical anaesthesia

Stage IV = respiratory and medullary paralysis/depression

Properties of propofol, including side effects

• lipid soluble

• hypnotic

• hepatic and extra hepatic metabolism

• inhibits GABA receptors

• neuroprotective

• may cause excitation on induction

• respiratory depression

• cyanosis

• hypotension

• vasodilation

• does not maintain0 baroreceptor reflex

Properties of alfaxalone, including side effects

• hepatic metabolism

• similar onset and duration to propofol

• respiratory depression depends on dose

• moderate vasodilation

• hypotension

• maintains baroreceptor reflex - less CV depression than propofol

• inhibits GABA

• less drug accumulation than propofol

• needs to be given after sedatives, otherwise agitation, stiffness, dysphoria

Properties of ketamine, including side effects

• liver metabolism

• give alongside mucle relaxant as increases muscle tone

• norketamine metabolite accumulation may occur

• dysphoria

• hypersensitivity to noise, light and handling

• respiratory depression, apneustic breathing

• hypersalivation

• increased cerebral blood flow

• increased heart rate, cardiac output and blood pressure (careful with heart disease)

Avoid in cats with hypertrophic cardiomyopathy

Characteristics of Etomidate

human drug

preserves cardiovascular function

suppression of adrenal function can lead to Addisons crisis

Discuss usage of thiopental

no longer licenced

causes tissue necrosis if peri-vascular injection

can occasionally be given to horses to top up

List 3 drugs used for co-induction of anaesthesia

midazolam

ketamine

fentanyl

Name these 2 laryngoscopes

A - straight Miller blade

B - curved Macintosh blade

How to confirm correct placement of ET tube? (5)

• visualisation with laryngoscope

• capnography to check adequate ETCO2

• condensation inside ET tube

• movement of reservoir bag

• squeeze reservoir bag and watch for chest movement

4 limitations of supraglottic airway devices

• risk of aspiration not eliminated

• hard to completely seal

• ,may be harder to ventilate

• easier to dislodge

List 5 alternative intubation techniques and when they may be used

• nasotracheal = common in large animal

• pharyngotomy = if having oral surgery

• retrograde intubation = if hard to open oral cavity

• one lung intubation = for specific thoracic surgeries

• tracheostomy = if obstructed upper airway

Considerations when intubating ruminants and camelids

Large ruminants need a bite block, as hand must be placed into mouth

All have regurgitation risk

Considerations when intubating pigs

Difficult due to S-shape larynx, so use a stylet to help

Considerations when intubating birds

use uncuffed tubes due to complete tracheal rings