ANAESTHESIA - Anaesthesia for Reproductive Surgery Flashcards
Which should you advise owners before neutering surgery in regards to anaesthetic risk?
It is important to advise owners that there is always a risk of mortality with general anaesthetic, however it is low for neutering (1 in 10,000 in most recent studies)
Which factors should you consider before anaesthetising a patient for neutering?
Age
Breed
Temperament
Body condition score
Analgesia required
Health status
Although anaesthesia for neutering surgery is often viewed as routine it is always good practice to think about your patient as an individual and ask yourself if there are any factors that might affect the patient’s response to anaesthesia and that might therefore warrant a change in the anaesthetic plan
Which factors should you consider in regards to age before anaesthetising a patient for neutering?
It is mostly young adults that you are neutering, however be aware you may have to neuter older patients who will have an increased anaesthetic risk, or even very young patients (i.e. feral kittens) who will not yet be physiologically mature and thus have a higher anaesthetic risk
What are the steps of pre-anaesthetic preparation?
Fasting
Clinical examination
Pre-anaesthetic blood sampling (if appropriate)
Patients under 7 with no abnormalities on clinical exam don’t require bloods
Why is it so important to fast patients prior to general anaesthetic?
It is important to fast patients prior to general anaesthetic to reduce the risk of regurgitation and aspiration
How should you fast adult animals prior to general anaesthetic?
Traditionally adult animals are fasted overnight (minimum 8 - 12 hours), however you should allow for free access to water
How should you fast puppies and kittens prior to general anaesthetic?
If puppies or kittens are less than 8 weeks old, do not fast them for more than 2 hours, and allow for free access to water
What are the most common sedatives used in premedication for neutering surgery?
Medetomidine
Dexmedetomidine
Acepromazine
Pick most appropriate based on your individual patient
What are the most common opioids used in premedication for neutering surgery?
Methadone
Burpenorphine
Butorphanol
Pick most appropriate based on your individual patient
Which routes of administration are most commonly used for premedication for neutering surgery?
IM
IV
Pick most appropriate based on your individual patient
Which anaesthetic agents are most commonly used for induction for neutering?
Propofol
Alfaxalone
Pick most appropriate based on your individual patient
Which route of administration is used for induction for neutering?
Administer IV until the drug takes effect
Which inhaled anaesthetic agents are most commonly used for maintenance for neutering?
Isoflurane
Sevoflurane
Which factors should you consider when determining an anaesthetic plan for neutering an animal with an excitable/anxious temperament?
- Select a sedative dose at the higher end of the range
- Choose a more reliable sedative (i.e. α2 is more reliable than ACP)
- Combined sedation is also useful (e.g. ACP, metetomidine and methadone)
- IM for premedication may be preferable
Which factors should you consider when determining an anaesthetic plan for neutering an animal with an aggressive temperament?
- It can be useful to combine the sedative and opioid for the premedication with an injectible anaesthetic such as ketamine or alfaxalone (in cats)
- IM administration is preferable
e.g. metetomidine, methadone and low dose ketamine (get a strong sedation), or metetomidine, methadone and high dose ketamine (get an anaesthetic effect, used for cats only)
Which factors should you consider when determining an anaesthetic plan for neutering an animal at ASA grade II (i.e. older, less healthy animal)?
- Select a sedative dose at the lower end of the range (consider temperament)
- Select the most appropriate sedative considering the pharmacodynamics, side effects etc.
Which factors should you consider when determining an anaesthetic plan for neutering an animal at ASA grade III (i.e. systemically unwell animal)?
- Stabilisation
- Pre-anaesthetic blood testing
- Consider using an opioid only premedication
- Consider co-induction to reduce individual anaesthetic doses
- Aim for balanced anaesthesia
e.g. methadone premed, co-induction of propofol and alfaxalone, maintenance with iso or sevo
Use local anaesthetic technique ± infusion of fentanyl ± ketamine
What is balanced anaesthesia?
The use of a combination of drugs to achieve an anaesthetic effect, allowing for synergy and lower dose requirements for each drug
What are the three key components of multimodal analgesia used in neutering surgery?
Opioids
NSAIDs
Local anaesthetic
Which NSAIDs are licensed and safe for peri-operative use?
Meloxicam
Carprofen
Robenacoxib
Remember low blood pressure under anaesthesia can increase the risk of NSAID induced renal injury, so important to choose drugs that have been tested to be ‘safe’ under anaesthetic
When may you want to administer NSAIDs in more high risk patients?
You can withhold giving the NSAID until after anaesthesia and this might be preferred if there are other risk factors
What are the key differences between lidocaine and bupivicaine?
Lidocaine is licensed in dogs and cats, with a rapid onset and short duration of action. Bupivicaine is not licensed in cats and dogs, with a slow onset and long duration of action and is more cardiotoxic than lidocaine
What should you be aware of when administering local anaesthetic to cats?
Cats are more sensitive to the toxic effects of local anaesthetic and thus you should use lower doses and avoid intravenous route of administration
Which local anaesthetic blocks can you use in a castration?
Incisional block
Testicular block
Which local anaesthetic blocks can you use in an ovariohysterectomy?
Incisional block
Infiltration of ovarian pedicle
Intraperitoneal lavage
What is an incisional block?
An incisional block is the administration of local anaesthetic into the subcutaneous tissues where you intend to incise
What is the typical post-operative analgesia following neutering surgery?
Oral NSAIDs for 3 - 5 days
Repeat opioid before discharge if the patient is particularly painful
± Paracetamol (in dogs)
± Tramadol (in cats)
± Oral transmucosal buprenorphine (in cats)
Use same NSAID as the one you used perioperatively
What are the most common anaesthesia related complications?
Bradycardia
Tachycardia
Hypotension
Poor quality/prolonged recovery
When is a dog classified as bradycardic under anaesthesia?
Heart rate less than 60bpm
When is the cat classified as bradycardia under anaesthesia?
Heart rate less than 100bpm
Which factors should you consider when determining if bradycardia under anaesthesia requires concern?
How low is the heart rate?
How quicky did the bradycardia develop?
What is the rhythm?
What is the blood pressure?
Could this be drug related?
What are the main causes of bradycardia under anaesthesia?
Increased vagal tone (most common)
Hypothermia
Pre-existing disease
What are the potential causes of increased vagal tone and consequential bradycardia under anaesthesia?
α2 agonists
Opioids
Young, athletic dogs
Brachycephalic breeds
Visceral traction
Deep anaesthesia
Light anaesthesia (vasovagal reactions)
How can you manage bradycardia under anaesthesia?
Address inciting cause of bradycardia (i.e. assess what the surgeon is doing, adjust anaesthetic depth, reverse drugs etc.)
Administer antimuscarinic drug
Which drug can be used to reverse α2 agonists if they are causing bradycardia?
Atipamezole
What should you be aware of if administering atipamezole during surgery?
Be aware that administering atipamezole during surgery can cause an abrupt lightening in anaesthetic depth
Which antimuscarinic drugs can be used to treat bradycardia under anaesthesia?
Atropine
Glycopyrrolate
What are the risk factors for hypothermia under anaesthesia?
Open body cavities
Small patients
How can you prevent/manage hypothermia under anaesthesia?
Minimise heat loss (maintain ambient temperature)
Active warming (warm air blankets etc.)
Be aware some active heating devices can cause burns
When is a dog classified as tachycardic under anaesthesia?
Heart rate over 160bpm
HR around 130, 140 do suggest a problem
When is a cat classified as tachycardic under anaesthesia?
Heart rate over 220bpm
Which factors should you consider when determining if tachycardia under anaesthesia requires concern?
How low is the heart rate?
How quicky did the tachycardia develop?
What is the rhythm?
What is the blood pressure?
Could this be drug related?
What are the main causes of tachycardia under anaesthesia?
Increased sympathetic tone
Hyperthermia
Pre-existing disease
What are the potential causes of increased sympathetic tone and consequential tachycardia under anaesthesia?
Light anaesthesia
Inadequate analgesia
Hypovolaemia/Hypotension
Drug mediated
Hypercapnia
Hypoxaemia
How can you manage tachycardia under anaesthesia?
Address inciting cause of tachycardia (i.e. assess what the surgeon is doing, adjust anaesthetic depth.)
Administer vagomimetic drug
Which vagomimetic drugs could you administer to treat tachycardia under anaesthesia?
Opioids
(T/F) You can administer a beta blocker to manage tachycardia under anaesthesia
TRUE. However!! You must rule out hypotension and hypovolaemia as causes of tachycardia before administering beta blockers
What are some of the main anaesthetic recovery problems?
Prolonged recovery
Excitement
Dysphoria
Which factors can contribute to a prolonged anaesthetic recovery?
Hypothermia
Hypotension
Hypoventilation
Can contribute to reduced rate of drug elimination
What is dysphoria?
Dysphoria is a profound sense of unease or dissatisfaction accompanied by anxiety or agitation
Which factors can contribute to an excitable or dysphoric recovery?
Pain
Opioid induced dysphoria
Ketamine
Alfaxalone
Post-operative atipamezole
Full bladder
How can you manage excitable or dysphoric recovery?
Analgesia if animal in pain
Sedative if dysphoric
Alpha 2 can be useful if unsure as has analgesic and sedative effects
