Induction of anaesthesia Flashcards
Name 3 induction methods that can be used?
- injectable agents (IM,IV, IP, SC)
- Induction chamber/ masks (birds)
- Immersion/ contact (Fish - passes over gills or absorbed by skin)
Name 12 things that make the ideal anaesthetic?
- Water soluble
- Long shelf-life
- stable when exposed to light
- small volume reuired
- no local toxicity
- no effect on vital organ function
- Minimal individual variation
8, safe therapeutic ratio (ketamine 10x induction dose kills paient, propofol -2-3x will kill the patient) - onset
- short duration - patients should recover well
- non-toxic metabolites
- no histamine release
Which is the most commonly used anaesthetic in the UK for cats and dogs?
Propofol ‘milk of amnesia’
what is propofol and what is its drug content?
Alkyl phenol, white emulsion, 10mg/ml
name 5 things in propofol?
- soyabean oil
- glycerol
- egg lecithin
- no preservative
- NaOH (changes pH)
Name one promlem with propofol?
It supports bacteria and endotoxin
How quickly to use the vial once opened?
Within 24 hours
what was the problem with propoflo plus (zoetis) which lasted for 28 days?
More pain on injection
How quickly does propofol work?
Very rapid onset of action (30-40 seconds head down)
How long is the period of unconsciousness?
5-8 mins
what is the pharmacokinetic features of the drug?
Highly lipophilic and high Vd. Will cross the BBB.
What is the recovery like with propofol and why?
rapid, smooth emergence due to redistribution and efficient metabolism - metabolites inactive (Hepatic metabolism)
What does propofol do to ventilation?
Respiratory depression IPPV
What do you need to do if you suspect post induction apnoea?
Half the speed of injection
What is the recovery like with propofol?
Rapid and smooth recovery
is propofol suitable for top-ups and TIVA and when would you use this?
Yes, if you don’t want to put the animal on gas.
What does propofol do for muscle relaxation?
Usually okay
Is propofol an analgesic?
NO - no analgesic properties - does reduce ICP (intra-cranial pressure) - use if head trauma or ocular ulcer.
Why hold the animal tightly when administering propofol?
Because it stings a lot.
What dose of propofol would you administer?
1-7mg/kg - depends on pre-meds
In what animals should you be very careful when using propofol?
In patients with shock or sepsis.
What should you do in old dogs and cats using propofol?
Decrease the dose
Name two diseases in which propofol is fine to administer?
renal compromise and hepatopathy
What can propofol be combined with to dilute?
5% dextrose
In what animals is propofol licensed?
Dogs and cats
Name 8 problems associated with using propofol?
- Rigidity, twitching
- Apnoea
- Profound bradycardia
- Care in hypoproteinaemia
- Heinz body anaemia in cats (clumped RBCs)
- Use for patients with pancreatitis/ hyperlipoproteinaemia or diabetic hyperlipidaemia.
- pain on injection
- . Local reaction (clear formulation, discontinued)
Name a common thiobarbituate used?
Thiopentone sodium
What is thiopentone sodium?
A sodium salt powder
What is the property of thiopentone sodium
Highly lipophilic and highly alkaline solution (pH 14)
Is thiopentone sodium commonly used?
No, difficult to source and no longer licensed in cats, dogs or horses.
Name 4 effects of thiopentone sodium?
- rapid loss of consciousness
- respiratory depression
- cardiovascular depession
- peripheral vasodilation
What is the length of time the thiopentone works?
Ultra short-acting
What does thiopentone sodium do in the blood?
highly protein bound and displaced by flunixin and phenylbutazone
Why does pH affect the response?
Because the unionised fraction can penetrate the cell.
What else is important in terms of fraction unbound of thiopentone sodium?
The plasma protein concentration
What is the danger of administering to pregnant animals?
Thiopentone sodium crosses the placenta
Where is thiopentone sodium metabolised?
In the liver
In what species is there a long recovery from thiopentone and why?
Sighthounds - metabolism and body fat.
What is the dosage of thiopentone and when would you reduce?
10-25mg/kg - reduce more if pre-med was alpha 2 agonists.
How quickly should you administer thiopentone?
Give 1/2-1/3 dose over 30 seconds
What is its primary use today and why?
Used in horses to ‘top up’ - can use in horses that are kicking on the table.
works faster than ketamine top-ups.
Name a contraindication of using thiopentone and how is this prevented?
Fractious animals with minimal IV access - can cause enormous sloughing of the skin if injected around the vein –> always administer with a catheter and not a needle.
Name 6 illnesses in which it would NOT be appropriate to administer thiopentone?
- Hypoproteinaemic patients
- CHF, arrythmias (unless lidocaine given)
- liver disease
- Renal disease (increases potassium –> worsen arrythmias)
- anaemia/ hypovolaemia
- Hypothyroid/ hypoarenocorticoid patients (hypotension can be difficult to control)
What is NTK?
Oxybarbiturates (pentobarbitone)
What is NTK similar to in structure?
Thiopentones.
What is the solution of NTK?
6% (60mg/ml)
What is the onset like using NTK and why?
Slower onset of action than thiopentone due to less plasma protein binding and less lipid solublility.
is pentobarbitone commonly used?
No longer available!
Name 4 reasons why NTK is no longer used?
- slow recovery
- difficult to source
- CVS and respiratory depression
- Irritant
Name another form of anaesthetic?
Injectable steroid anaesthetics - saffan
Are injectable steroid anaesthetics used common?
No longer available in the UK in this form.
Name 2 examples of an injectable steroid anaesthetic?
Alphaxalone (6mg/ml) and alphadonolone (3mg/ml)
How do the two compare?
Alphaxolone is more potent and alphadonolone
By what are injectable steroid anaesthetics solubolised by?
Cremaphor EL
In what species were injectable steroid anaesthetics used?
Pigs and ruminants
What is a major contraindication of using injectable steroid anaesthetics?
They cause a massive histamine release
What do injectable steroid anaesthetics cause in some cats?
anaphylaxis.
Name two side effects of the massive histamine release associated with injecatble steroid?
Swollen larynx and swollen paws.
What is the formulation of alphalaxone without cremaphor?
A HPBCD (hydroxypropyl-beta-cyclodextrin) - donut shaped molecule (hydrophillic on the outside and lipophilic on the inside.
what is the trade name of alfaxalone?
alfaxan
In what species is alfaxalone used?
Dogs and cats.
How does alfaxalone cause anaesthesia?
By inhibiting the GABA receptor.
What does alfaxalone look like?
Clear, colourless solution - neuroactive.
How quickly is alfaxalone cleared from the body and why?
Very rapidly - short plasma elimination hald-life.
How can alfaxalone be used to maintain anaesthesia?
Repeated boluses or as TIVA
How quickly is the induction agent given if an injectable steroid anaesthetic?
Over 60 seconds.
Does alfaxalone or propofol lead to better recovery?
Propofol
What is occassionally seen with alfaxalone recovery and what is required?
Occasional apnoea and IPPV might be needed.
Name 3 good properties associated with alfaxalone?
- cardiovascularly stable
- NO HISTAMINE RELEASE
- good muscle relaxant
Why should animals not be disturbed during recovery with alfaxalone?
Because excitement can occur.
Name two dissociative agents?
Ketamine and Tiletamine (Europe and USA)
What is the pH of the dissociative agents and what does this mean?
Weak organic acid (pH 3.5_ therefore stings on injection, especially IM.
Describe dissociative agent composition?
Racemic 10% solution (100mg/ml)
How can dissociative agents be administered?
IV, IM, SC, IP, PO, epidural space
Why do you normally have to combine ketamine with something else?
Causes rigidity therefore combine with something that causes muscle relaxation e.g. benzodiazepines.
What is the induction rate of ketamine?
Very rapid
What does ketamine cause when introduced?
Minimal respiratory effects, bronchodilation (good for asthma!)
What is a very beneficial property of ketamine?
GOOD ANALGESIA!
what do CVS effects of ketamine depend on?
Dose
name 4 things that are increased following ketamine administration?
- jerky movements
- muscle tone
- salivation
- lacrimation
What is the recovery process for ketamine?
Stormy if disturbed or not adequately pre-medicated
What effect does ketamine have on eyes?
Depth assessment is different because eyes open.
What is an issue associated with the eyes being open?
Corneal drying - use lacrilube.
What is common in patients when combined with alpha 2 agonists?
Vomiting - avoid in patients with GI obstruction.
Name 4 conditions in which you should avoid the use of ketamine?
- Increased ICP
- Occular surgery
- Fever
- Hyperthyroids
What type of drug is ketamine legally?
Schedule 2
What is zoletil 100?
250mg tiletamine and 250mg zolazepam
how much sterile water needs to be added to zoletil 100?
5ml sterile water.
what is zoletil 100 used for?
Dog and cat anaesthesia.
Give an example of an imidazole anaesthetic?
Etomidate (not licensed)
What are 3 things that remain stable when using etomidate?
- HR
- ABP (arterial blood pressure)
- CO
Name 4 contraindications of etomidate?
- Myoclonus
- Phlebitis
- Pain on injection
- Addision crisis
Is etomidate (imidazole anaesthetic) commonly used ?
Not in the UK
What kind of induction agent would you use for horses?
IV induction agent.
Name three ways anaesthesia can be topped up in horses?
IV Top-ups
inhalation
TIVA
How can anaesthesia be induced in foals?
Inhalation - associated with increased death rates.
What is the most common induction agent used in horses?
Ketamine
How does ketamine have to be used and why?
In combination with something else - causes seizures if used alone.
What is the safety margin of ketamine?
Very wide.
What is ketamine commonly used in combination with in horses?
. ACP
Alpha 2 agonists (sedative)
BZDs (not licensed)
Guaifenesein
In what species is Guifenesein (GGE) licensed?
In horses.
What is the function of guifenesein?
It is a centrally acting muscle relaxant
What is it used as part of?
TIVA - called ‘triple drip’
What is the best solution of guifenesein to use?
5% or 10%
What does guifenesein substitute?
The use of benzodiazepines (midazolam or diazepam)
can guifenesein be used in horses alone?
Good in foals alone, do not use in adults alone.
What does giufenesein cause if not injected correctly?
Causes sloughing of the skin - always use a catheter.
Name a common induction combination for horses?
Acepromazine, detomidine, ketamine and isoflourane
How is most anaesthesia done in ruminants?
With the animal standing
How is anaesthesia administered in ruminants?
IV - calves could use a mask
What might some cows drink?
Chloral hydrate
Why do ruminants require cuffed intubation?
regurgitation
Where are most anaesthetic agents administered in the pig? what are the other options?
deep IM in the neck
- could use IV or mask
Name three induction agents used in pigs?
- ketamine
- Propofol
- Alfaxalone
What can occur in pigs after exposure to an anaesthetic inhalant and how is it treated?
Malignant hypothermia
Treated with dantrolene.
Why is intubation of pigs difficult?
Larynx angle and mouth does not open far
What is the main risk when inducing exotics?
Hypothermia or hyperthermia (increased SA to BW ratio)
What is the death rate for rabbits under anaesthetisa?
1/72
Name 4 problems of rabbit anaesthtsia?
- hypothermia
- prolonged recovery - GI disturbances
- difficult intubation
- respiratory obstruction leading to cyanosis.
What two things are advisable in rabbit anaesthesia?
Pre-medication and pre-oxygenate
Name two licensed induction agents in rabbits?
Fentanyl/ fluanisone
Alfaxalone
Name 4 induction examples in rabbits?
- Fentanyl/ fluanisone recipie
- Ketamine, medetomidine, Opioid
- BZD and opioid, followed by alfaxalone or propofol 15 mins later
- alfaxalone
Name 3 pieces of equipment which can help with rabbit intubation?
Laryngeal masks, V-gels, nasal intubation,
‘Fleknell laryngoscope’
What is common in birds and what is a good idea?
High GA mortality, IPPV is a good idea.
What means that conditions change quickly in birds?
they have high metabolism
How long should birds be fasted for?
Not too long (especially budgies and small pet birds). Raptors and waterfoul - 4-6 hours to make sure crop is empty.
What is unique about birds and intubation - what kind of tube should be used?
They have complete tracheal rings.
Use Cole intubation tubes.
What happens if birds are put onto their backs - what is beneficial?
they become bradycardic - IPPV beneficial.
What two positions can birds not breath very well and why?
If you lie birds on their sternum or on their backs - they do not have a diaphragm.
How are most bird injections performed?
Using an inhalant e.g. isoflurane in oxygen.
Why is intubation reccomended in birds?
Apnoea common
What is another technique used to intubate birds?
Can use air sac cannulation - push ET tube inside air sac.
How many different species of reptiles?
6400 - need to know anatomy
What makes reptiles so difficult to anaesthetise and maintain?
Blood shunting
What happens to heart rate in reptiles under GA?
It does not really change.
What is needed to aid respiration in reptiles?
IPPV - respiration is abolised at surgical planes.
What type of reptiles are particularly difficult to induce with gas?
Chelonia
What response is used in large, fractious lizards to restrain for injection?
vagal-vagal response.
What is used for gas induction of reptiles?
Isoflurane or sevoflurane
what are the injectable agents used in reptiles?
Alfaxalone or propofol
What works alone as TIVA for chelonia?
Alfaxalone
Name two combinations which can be used to sedate large fractious patients?
Ketamine/ midazolam
ketamine/ medetomidine
What can be used for analgesia in reptiles?
Butorphanol +/- NSAID
buprenorphine in some too
Why is intubation difficult in chelonia?
Fleshy, large tongue.
What remains closed when reptiles are not breathing?
Glottis.
In what order to snakes induce and recover?
They induce from head to tail and recover from tail to head.
What is a reptiles response to gas concentrations?
They respond very slowly to gas concentrations
How do we test to see if a reptile is recovering from anaesthsia?
Toe and tail pinch and tongue retraction reflexes.
corneal and palpebral reflexes.
What is an invaluable monitoring system in reptiles?
Doppler flow monitor.
What is unique about ECG and the heart in reptiles?
Heart can still contract after death and you could get an ECG reading for about 3 days after death.
If administering an injectable anaesthetic to lizards, which vein would be used?
Central coccygeal vein e.g propogol 3-5mg/kg
Where is the tracheal opening in lizards?
The base of the tongue, on the floor of the oral cavity.
How often is IPPV administered in lizards?
1x2 times a minute
What can cause cardiac arrest in reptiles?
any sudden change in position
What needs monitoring throughout reptile GA?
Temperature
How long does recovery take for some reptiles?
24-48 hours
What also helps reptiles wake up?
Intraosseous or IV access and fluids (1-2ml/kg/hour)
Why do reptiles wake upquicker when ventilated with room air before recovery?
Because high pCo2 stimulates ventilation and is suppressed by high O2.
Where is blood best sampled from in chelonians?
Jugular vein - avoid lymph contamination
Name 5 induction routes for chelonia?
- oral
- IV
- Intracoelomic
- Epicoelomic
- Intraosseous
Is anaesthesia well tolerated in chelonians?
yes
Where is the rima glottis in chelonians?
2/3 along the tongue mid line
What kind of circuit would you use for chelonians?
A T piece circuit - deliver iso/sevo and oxygen
- also use IPPV
What are the 2 most common types of captive snakes?
Colubridae
boidae
When might sedation be needed in snakes?
Blood samples and detailed examination
How is blood usually collected from snakes?
Cardiocentesis or from the tail vein
How can fluids be administered to snakes?
SC or intracoelomic
How often should IPPV be administered to snakes?
1-4 X a minute
What is commonly used as an injectable agent in fish and amphibians?
MS-222 in water
-tricaine methanesulphonate
Which species of fish might require injectable agent?
Lungfish
What is MS-222 buffered with?
Sodium bicarbonate
Why does tricaine mehanesulphonate need to be removed from the tank once anaethetised?
because it is cumulative
When can you remove amphibians and fish from water?
When surgery less than 5 mins and keep moistured.
What is required in fish and amphibians for longer procedures?
Oxygenated water over gills +/- anaesthetic solution (1ml every 30 secs to keep them anaesthetised)
What dilution of MS-222 is used for amphibians?
1:25 000 dilution in sterile water
Name 5 methods of anaesthesia in amphibians?
- Phenoxyethanol
- Benzocaine (in acetol)
- Ketamine IM (50mg/ml)
- Bubble iso or sevo through water)
- iso in KY jelly
How can the plane of anaesthesia be changed in amphibians?
- water + anaesthetic to deepen
- just water to lighten
