- CV depression (vasodilation and v BP) - respiratory depression > so give SLOWLY over one minute

Induction Flashcards by laura knight

Which inhalational agents can be used to induce anaesthesia?

isoflurane
sevoflurane
halothane
desflurane (not licensed)
N20 (nitrous oxide)
xenon (new, expensive, specialised equipment needed)

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Which injectable agents can be used to induce anaesthesia?

propofol
alfaxalone
ketamine
> thiopentone/thiopental (old, can’t get vet form anymore)
> etomidate (not licensed, human drug)

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What is the most common route of induction?

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What do GA agents cause?

Dose dependant CNS depression

continuum from sedation -> anaesthesia
eg. use of propofol as a sedative (michael jackson!)

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How is CV and respiratory system affected by anaesthetic agents?

> CV
- v CO
- vasodilation
- reduced BP 
- bad for kidneys etc. 
> resp
- v RR
- v TV (tidal volume)
= reduced minute volume
*dose-dependant*

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Do GA drugs provide analgesia?

No - so must administer analgesics eg. opioids

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What does uptake of GA depend on?

route of administration

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What does distribution into tissues depend on?

blood flow (eg. injecting into sublumbar fat)
may be influenced by disease
lowers blood levels if injected into muscle etc.

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Which species are particularly sensitive to a2 agonists?

Goats

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What is metabolism of drugs influenced by?

Species
Disease state (esp. liver and kidneys, lungs for inhalation agents)
> thiopental in a thin dog will maintain for a long time due to lack of body fat

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How does propofol’s action differ in cats?

take a long time to recover
- enzyme lacking to conjugate glucuronides
- problems metabolising triglyceride lipid carrier of drug
> cumulative effects of the drug, can be TOXIC if given repeatedly
> Oxidative injury, Heinz body production, anaemia and death

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Where does the induction agent ultimately act?

In the brain

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How does age affect amount of induction agent required?

extremes of age require less

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Should doses of GA drugs be learnt?

NO NOT FOR EXAMS!!! Know where to find them

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WHat type of drug is propofol? What is it’s appearance and ROA?

a phenol
white opaque liquid (rich medium for bacterial growth)
must be given IV (not IM)

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What can propofol be used for?

Induction AND maintainence eg. if cannot use inhalation agents (TIVA)

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Pharmacodynamics of propofol

rapid onset after injection
blood levels v by redisribution
rapid metabolism (hepatic and extra-hepatic eg. lungs)

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Effects of propofol

CV depression (vasodilation and v BP)
respiratory depression
> so give SLOWLY over one minute

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What is propclear?

Nanodroplet clear solution - no longer available

- caused extreme pain on injection

What is propofol plus?

Preservative (benzyl alcohol) means can be used once opened (doesnt have to be discarded on the day)
> benzyl alcohol toxicity ->
- prolonged recovery and hyperkinesia in cats
- tremors in dogs
* DO NOT USE FOR TIVA*

What type of drug is alfaxalone? What s it mixed with in preparations?

steroid - poorly soluable

- mixed with solubilising agent (cyclodextrin)

ROA alfaxolone?

IV or IM

How does alfaxolone differ to propofol?

rapid onset of action, short duration

- less CV and respiratory depression than propofol

Potential side effects and cons of alfaxolone?

More expensive

Can see excitement on recovery if not adequately sedated

What type of drug is ketamine?

- Dissociative anaesthetic | - Analgesic actions at sub-anaesthetic doses (NMDA receptors)

ROA ketamine

IM or IV

What can ketamine be used for?

Inuction and maintainence of anaesthesia

Why is ketamine NEVER GIVEN ALONE?

Excitation and muscle tension if given alone, always requires a sedative (benzodiazepine or a2 ag) - also need to lubricate eyes as will remain open

What situations is ketamine useful for?

- angry cats | - brachycephalic breeds

What is the triple combination? Which species is this commonly used in?

``` - Aggressive cats > Ketamine, medetomidine, opioid - IM - onset of action ~5 mins - single injection alone suitable for short procedures ```

Which species if ketamine commonly used in following sedation with a n a2 agonist?

Horses after PROFOUND sedation with an a2 ag | - given IV combination with a benzodiazepine (diazepam or midazolam)

How does ketamine affect the CNS, CB and resp systems?

> CNS reflexes are preserved (palpebral, jaw tone, swallowing) > CV: SNS stimulated -> hypertension and tachycardia mildly, but some direct CV depression also > resp: mild resp depression

Where is thiopental usually used nowadays?

Horses - not licensed for vet use anymore - used for induction (to effect) and as top up during maintainence

Effects and potential side effects of thiopental?

- irritant and necrosis if administered extravascualrly (alkaline) - CV and resp depression similar to propofol

Can thiopental be used once vial is opened?

Yes for ~5d (pH so high nothing can grow)

What drug or drug combination is best for high risk, sick patients? POtential problem with this drug?

*Etomidate - minimal CV and resp depression - problem: depresses adrenal gland function and cortisol production > NOT LICENSED * Fentanyl/midazolam combination - very potent opioid

Which inhalational agents are used for induction? Why would these be used over injectables?

- sevoflurane or ioflurance delivered in oxygen | > aggressive patients if IV impossible

What are the downsides to inhalational indcution?

- ^ risk pollution and personnel exposure | - may see excitement/stress during induction

Which inhalational agent is more irritating to respiratory passages and what effect may this have?

Isoflurane -> breath holding (but is cheaper)

How can the smell of isoflurane be disguised to prevent mask avoidance?

Smear food inside mask

What concentration roughly approximates brain concentration of anaesthetic drug?

ALveolar concentration

What does partial pressure mean?

Amount in blood

If an agent is very soluble in blood how is the partial pressure or tension of gas in the brain affected?

Lower in brain (doesnt ant to leave blood!)

What is the partition coefficient?

Blood:Gas partition coefficient = no. particles gas in blood vs. alveolus - high number means gas is very soluble in blood (and therefore induction and recovery will take longer, as moving agent from blood to brain and back takes long time) - eg. halothane 2.4 [long induction and recovery], N2O and desflurane ~0.4 [short induction and recovery]

Why is endotracheal intubation advocated?

- o2 delivery - inhalational anaesthetic if required - protect airway from occlusion or aspiration - allow ventilation to be supported if depressed