Term
| When may injectable anaes. be given? |
|
Definition
-anaes. induction
-adjuncts to maintaining anaes
-maintain anaes. w/o volatiles |
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Term
What factors affect
-how rapidly effective plasma conc. are achieved
-what percentage of drug given is available to produce an effect
-duration of action? |
|
Definition
-dose
-route of admin
-volume of distribution
-protein binding
-ionisation
-metabolism and elimination |
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|
Term
| how does dose affect anaesthesia? |
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Definition
| a higher dose will prodce higher plasma conc. and for longer |
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Term
| Describe and compare IV, IM and SC anaes. admin |
|
Definition
-IV has rapid rise in plasma conc. w. highest plasma peak conc. and longest duration of effective dose in plasma
-IM has slower rise and peak in plasma conc. and shorter duration of effective conc
-SC rise in plasma conc is even slower and may not reach effective plasma conc |
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Term
| Use of IV, IM and SC anaes admin |
|
Definition
IV-most common
IM-esp. difficult aniamls e.g feral cats
SC-rare, used occasionaly in exotics |
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Term
| Why do some inj. drugs produce lower plasma conc. than expected? |
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Definition
| due to uptake and distrubution in other tissues |
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|
Term
| What does volume of distribution represent? |
|
Definition
the vol of water in which drug would have to be distributed to give its plasma conc
-gives comparision of drugs distribution |
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|
Term
| what is the relevance of plasma protein binding in injectable anaes. admin? |
|
Definition
if a drug is bound to plasma proteins it cannot exert its effect at a receptor site
-so if plasma protein is dec. e.g. hypoalbuminaemia, there will be a larger free-fraction of drug and so incr. effect of drug - relative OD
-if multiple drugs that bind in the same way are co-admin there may be competition for binding sites - again relative OD |
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Term
| Which drugs of anaesthetic importance are highly plasma protein bound? |
|
Definition
-barbiturates
-propofol
-NSAIDs |
|
|
Term
| What is the relevance of ionisation in injectable anaes. admin? |
|
Definition
Factors affecting ionisation of drugs may affect efficacy
-most drugs are ionised and exist in plasma in ionised and unionised forms
-unionised forms cross memb. more easily
e.g. inflammation decr. pH and so decr. unionised forms of LA - can't reach target organ |
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Term
| What can affect metabolism and elimination of anaesthetics? |
|
Definition
-dz. of liver / affecting BF to the liver will alter metabolism and so duration of many drugs
-drugs can affect other drugs metabolism
e.g. induce enzyme p450 and incr. metabolism of other drugs |
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|
Term
| Advantages of injectable anaesthesia |
|
Definition
-convenient
-rapid loss of consciousness (IV)
-rapid deepening of anaesthesia possible
-no airway irritation
-no pollution of environment
-some drugs have antagonists
-less equipment required - can perform "in field" |
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|
Term
| Disadvantages of injectable anaesthesia |
|
Definition
-requires restraint - stressful for animals
-pain of injection in some sites
-not easy to lighten anaesthesia or dec. effects
-rely on organ function for elimination in most cases
-may get drug accumulation
-no airway protection
-risk of self-admin |
|
|
Term
| Which anaesthetic agents can be administered by injection? |
|
Definition
-thiopentane
-propofol
-alphaxalone
-ketamine |
|
|
Term
|
Definition
-injectable GA
-rapid onset of action (depending on circulation time) - big advantage
-causes peripheral vasodil. and so dec BP
-myocard depression not marked at normal doses
-arrhythmias common in induction but usually innocuous and not observed
-not analgesic
-slow metabolism - recovery dependent on redistribution
-irritant if perivascular
-decr. intracranial and intraocular P
-effective anticonvulsant |
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|
Term
| Describe the metabolism and distribution of thiopentane - consequences? |
|
Definition
-slow metabolism
-recovery depends of reedistribution of drug to muscle and fat rather than excretion
-cumulation of drug w. repeated doses (as muscle / fat saturated) - can suddenly OD - do not give repeatedly
-recovry slow in sighthounds due to distrubution |
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|
Term
| Describe the use of thipentane |
|
Definition
-licensed in D+C and H
-now rarely used for induction
- still popular in horses due to rapid onset of action - if horse needs to be brought under control quickly |
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|
Term
|
Definition
-injectable GA
-rapid onset but not as rapid as thio
-rapid redistribution and metabolism
-not cumulative
-not irritant perivascular but can occ. cause pain on inj
-dec. intracranial P
-gr. myocardial depression than thio and peripheral vasodil w. decr. BP
-occasional muscl. twitching or rigidity
-can cause post-induction apnoea - less if administered slowly and to effect |
|
|
Term
| Describe propofol preparation |
|
Definition
-emulsion prep (i.e. white)
-some contain preservatives - vial can be kept for up to 28 days once opened
-use non-preservative containing emulsion if giving by long term infusion - to avoid accumulation or toxicity of the preservative (benzyl chloride) |
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|
Term
| Which spp is propofol licenced for? |
|
Definition
|
|
Term
|
Definition
-injectable anaesthetic
-mild CV effects, mild hypotension, mild resp. compression c.f. others
-can also be used to maintain anaesthesia
-expensive |
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|
Term
|
Definition
-should be given slowly and to effect - may require less than data sheet recommended doses
-generally IV (IM requires large volume) |
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|
Term
|
Definition
-dissociative anaesthetic (can also be used for sedation)
-induction slower after IV than thio
-little cumulation - can be given by infusion or repeat bolus inj
-little resp. depression
-mild INCR. in HR and BP due to sight sympathetic stimulatiomn of CV system
-good analgesia
-increases muscle tone
-incr. salivation
-convulsive activity poss. in dogs, esp. is used alone
-INCR. intracranial and intraocular P |
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Term
| What is unusual about ketamine anaesthesia? |
|
Definition
| although unconscious and unaware, may retain reflexes - swallowing, blinking |
|
|
Term
|
Definition
-most popular in horses / LA, also dogs and exotics, less in dogs
-rarely alone except some reptiles and birds |
|
|
Term
|
Definition
-repeated inj. in cats can result in Heinz body anaemia - not <10days between uses
-avoid repeated dosing of form w. benzyl chorlide (preservative) - can cause toxicity |
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