Anesthetic Agents - Theory Flashcards
what is the aim of premedications?
calm the patient /stress reduction
enable easier handling
reduce anaesthetic drugs
reduce side effects of anaesthetic drugs
- balanced anaesthesia
- improved safety
- small amounts of many drugs balances side effects
relieve pain - often contains opioids
smooths recovery
what makes for an ideal premedication?
reliable sedation
minimal CV and respiratory effects
analgesic
reversible
cheap
what are the common side effects of premeds?
relaxation of smooth muscle including oropharynx
- not ideal for brachies
vomiting
- especially using dexmed
thermoregulatory effect
- especially using ACP
some have excitatory effects
some may string
what considerations do you need to make when giving a premed?
quiet/dark room
gentle handling
use pet-remedy/feliway
cat only rooms?
what is the definition of anaesthetic induction?
What is the best route to administer them?
the administration of drugs or agents, either injectable or inhaled, that bring about a state of unconsciousness
I/V best
- rapid effect - easier to monitor GA
- allow amount to effect - so better balanced
- IM or SC require specific amount - not how works
what makes for an ideal induction agent?
fast acting
can be used to effect
smooth induction
rapid metabolism
not an irritant
cheap
no side effects - eg. apnoea (common with propofol)
no strange recovery - eg. alfaxan in cats can cause seizure-like activity
what are examples of induction agents?
propofol
- only suitable in cats for 30 mins as cause accumulation and toxicity
- suitable for dogs for prolonged periods
- cause respiratory depression
- no analgesia
ketamine
- common for cat spays - IM with dexmedetomidine +/- butorphanol
- is an analgesic
alfaxalone
- can top up and use for continuous rate infusion
- has recovery side-effects
what considerations should you make during the induction period?
should be administered slowly and to effect
the dose needed will be significantly reduced if the patient has been pre-meded
it’s a dangerous time, particularly in sick patients, due to side effects
to minimise danger the process must be
- rapid
- stress-free
- cause minimal physiological changes
- followed by rapid intubation
- closely monitored
what are inhalant agents?
can be used for induction (avoid but common with smallies) and maintenance
liquid at room temperature and need conversion in an anaesthetic vaporiser for delivery to the patient
carried into the body by a carrier gas (usually oxygen) into the pulmonary circulation
it then crosses the blood-brain barrier to affect the CNS
what are the different types of inhalant agents?
what are their pros and cons?
nitrous oxide - banning
halothane - used in developing countries
desflurane - used in humans
isoflurane
- causes respiratory and cardiovascular depression
- irritant to the respiratory tract
- no/minimal effect on kidneys and liver
- hypotension ++
- reduced TV ++
- strong smell
- cheaper than sevo
- MAC 1.3% (dogs), 1.6% (cats)
sevoflurane
- very rapid induction and recovery
- no odour and non-irritant
- minimal effect on liver and kidneys
- hypotension +
- reduced TV +
- weak smell
- more expensive
- may react to soda lime
- MAC 2.3% (dogs), 2.6% (cats)
what makes for an ideal inhalant?
fast acting
reversible
provide muscle relaxation and unconsciousness
not an irritant to mucus membranes
no side effects
no cumulative/toxic effect
metabolised quickly/fast recovery
odourless (esp. if using to intubate)
safe with other drugs
non-flammable
environment friendly
what is TIVA? what are its pros and cons?
TOTAL INTRAVENOUS ANAESTHESIA
- of induction agents
- no inhalant needed
achieved by top-up bolus injection or continuous infusions from a syringe driver
pros:
- produces a much lower anaesthesia stress response
- minimal equipment needed
- doesn’t need deliver of oxygen - but best to have
cons:
- not easy to alter level - and slower response
- drugs can be expensive
what makes drugs ideal for TIVA?
fast-acting/rapid effects
reversible
quick change of effect
metabolised quickly/quick recovery
no side effects
no cumulative/toxic effect
what is PIVA? why do we do it?
what are its pros and cons?
Partial Intravenous Anesthesia Technique
- the use of multiple anaesthetic drugs at once
lowers the use of inhalants
reduces undesirable side-effects
- eg blood pressure better maintained
- less CV depression
provides high-quality anaesthesia and analgesia
reduces environmental impact
requires hepatic metabolism and renal excretion
appear ‘lighter’ due to muscle relaxation
slower recovery
what drugs can we use for PIVA?
fentanyl or morphine
- causes respiratory depression and bradycardia
- good for anaesthetic and analgesia
add dexmedetomidine
- reduces MAC and maintains blood pressure
- additional pain relief
- still causes bradycardia
add ketamine
- increased blood pressure, no effect on cardiac output
- additional muscle relaxent
