Induction Flashcards
Describe the ideal injectable induction agent
Water soluble Long shelf life Stable when exposed to light Small volume required No local toxicity No effect on vital organ function Minimal individual variation Safe therapeutic ratio Onset – one vein to brain circulation time Short duration of action Non toxic metabolites No histamine release
Describe the pharmacokinetics and dynamics of Propofol (include time and vd)
Rapid onset of action -rapid uptake by CNS
Short period of unconsciousness (5-8 mins)
Large volume of distribution (lipophilic)
Rapid smooth emergence due to redistribution & efficient metabolism (hepatic and extra hepatic) metabolites inactive
Describe the actions of Propofol on the patient
Respiratory depression (apnoea) - IPPV – can be affected by speed of admin – go slowly Cardiovascular depression Rapid and smooth recovery Suitable for top ups or TIVA Muscle relaxation usually ok Anticonvulsant
When is the use of propofol contraindicated?
Avoid in shock or sepsis
Decrease dose in old dogs
What are the side effects of propofol?
Rigidity, twitching
Apnoea- Profound bradycardia
Describe the action of Thiopentone sodium
Highly protein bound & displaced by other drugs e.g flunixin, phenylbutazone
Unionized fraction of the drug penetrates cells so pH can affect response
Plasma protein concentration also important
Crosses placenta
Metabolised in liver
Describe the use of alfaxalone
Alfaxalone has a short plasma elimination half life and is cleared from the body relatively quickly
Alfaxalone can be give as repeated boluses or as TotalIntraVenousAnaesthetic to maintain anaesthesia
Premedication is preferable/essential in order to ensure a smooth recovery
Anaesthesia induction is smooth, and the injection is given slowly over 60 seconds.
Describe the effects of sterious anaesthetics (e.g. alfaxalone) on the patient
Apnoea (temporary cessation of breathing during sleep) may be seen and IPPV may be necessary
The drug has good cardiovascular stability, causes no histamine release and produces good muscle relaxation
Animals should not be disturbed during recovery as excitement can occur
Name a dissociative agent
Ketamine
Give the uses of ketamine
Can be combined with BZD, alpha 2 agonists, acepromaine, opioids
Versatile induction agent
Invariably needs to be combined with something
Describe the properties of ketamine
Rapid induction
Respiratory effects are mixed – bronchodilation and RR usually preserved but may stop!
GOOD ANALGESIA
CVS effects depend on dose
Muscle tone ↑ and jerky movements
Salivation and lacrimation ↑
Ketamine can be diluted with sterile water or physiological saline
Describe the problems of using ketamine
Stormy recovery if disturbed or not adequately premedicated
Depth assessment is different (eyes open)
Corneal drying - use ‘Lacrilube’ or similar tears
Vomiting common with alpha 2 combinations avoid in patients with GI obstruction
Avoid in patients with ↑ ICP, ocular surgery, fever, hyperthyroids
Describe the process of induction in equine patients
Usually an intravenous agent is used
After an induction agent a horse becomes unconscious
The quality of induction is affected by the premedication
Anaesthesia is then maintained by incremental ‘top ups’ IV or by infusion (TIVA) or by inhalation agents
Anaesthesia can be induced with inhalants in foals
What can be the problems with using ketamine with horses
Must not be used alone (seizures)
Eyes remain open and central, less cumulative than thiopentone
Can be used as ‘top ups’ (don’t exceed induction dose)
Describe the intubation process with ruminants
Small ruminants are intubated by direct visualisation
Larger ruminants are intubated by palpation
Use cuffed tubes
Regurgitation
Describe the induction of anaesthesia in pigs (include drugs and potential problems)
Can be achieved with drugs given im (deep) on the neck near the ear, iv or via mask with inhalant
Ketamine, alfaxalone, propofol
Ketamine combinations
Malignant hyperthermia (rare condition of pigs will manifest itself soon after exposure to inhalant usually), rapidly fatal, can be treated with dantrolene
What differences are there in bird prep and GI?
Have a reputation for high GA mortality, they hide illness well, IPPV a good idea
They have a high metabolism meaning conditions will change quickly
Stabilise bird pre op, don’t fast for too long. Raptors and waterfowl should be fasted for 4-6 hours to ensure crop is empty
Care with body position (ventrolateral recumbency is best), IPPV, types of ET tubes (birds have complete tracheal rings, Cole tubes useful)
Describe the process of induction in birds
Most inductions are performed using an inhalant (e.g. isoflurane in oxygen)
Apnoea common, so intubation strongly recommended
Air sac cannulation is possible – air sac just behind the thigh
What is it about reptiles that make them hard to induce /maintain using gas?
Blood shunting (many can go through periods where send blood to the lungs or will send more blood to kidneys) can make gas induction and/or maintenance difficult or even impossible Chelonia especially difficult to induce with gas (may just stop breathing) Heart rate often does not change even from deep anaesthetic plane to very much awake!
Describe the process of inducing reptiles
Gas induction i.e. isoflurane or sevoflurane
Injectable i.e. propofol or alfaxalone
TIVA with alfaxalone works well in chelonia
Giant or fractious patients can be sedated with ketamine/midazolam or ketamine/medetomidine
Analgesia butorphanol +/- NSAID (buprenorphine in some too)
Intubation generally straight forward chelonia can be difficult due to large, fleshy tongue
Glottis remains closed when not breathing
