11b. Drugs used in radiology II: anaesthetics and analgesics - Anasthetics Flashcards
what is anasthetics
controlled and reversible loss of conciousness, loss of pain perception and/or amnesia
what 5 reversible effects do general anaesthesia typically require
immobility analgesia amnesia unconciousness supression of stress response
what is local anasthesia
blockade of pain perception from peripheral nerves
what are the 2 ways that GA is administered
IV or inhalation
what 4 agents does GA require
induction
maintenance
analgesia
+/- paralysis
what is induction of GA
going off to sleep
what is maintenance of GA
staying asleep
how is GA induced - 2 ways
what is the most common way
IV or inhalation
generally IV as in inhalation you get agitation which is hard to deal with in adults
how is GA maintained - 2 ways
IV or inhalation
do acute patients get GA via IV or inhalation
IV
do paeds patients get GA via IV or inhalation
inhalation
how does GA work
no unifying theory of how GA works
are current GA agents selective for a single ion channel
no
many IV anesthetics do what to the inhibitory effects
what is an exception
enhance inhibitory effects by acting on GABA receptors leading to unconsciousness and amnesia
ketamine is an exception
what receptors does ketamine target
NMDA receptors
how do inhalation anaesthetics work in terms of where does it act
act on both brain and spinal cord
what does inhalation anaesthetics do to inhibitory pathways and how
increase inhibitory pathways through GABA neurotransmitter release and increased GABA receptor activity
what does inhalation anaesthetics do to excitatory pathways and how
suppress excitatory pathways through reduced glutamate release and increased GABA receptor activity
what is the IV anaesthetic agent for propofol
diakeylphenol
what is the most widely used IV anaesthetic
propofol
what is propofol used for in terms of anesthesia
induction or maintenance and sedation
propofol’s action is mostly via what
GABA
how is propofol formulated
formulated in lipid emulsion as it has low water solubility
what is propofol’s onset time and return to consciousness time like following bolus dose
fast for both
can propofol be used as infusion and why
yes due to rapid clearance via kidney resulting in reasonable recovery times
what does propofol appear white
poor solubility
what happens to the time it takes to wear off if you give propofol as an infusion
accumulates in body so if you give it as infusion eg for 8hrs, itll take 40 mins to wear off
can you give GA as intramuscular, what is the downside of this
yes but will only transiently cause anaesthesia and will need something else to keep it going
does propofol offer analgesia
no
what are the 5 side effects of propofol
pain on injection and increase in microbial growth
respiratory depressant
loss of airway reflexes
lowered BP
HR effects as rate drops with bolus, increased with low BP
why do you need to give propofol slowly
due to its BP effects
what does propofol do to your breathing and is this intentional
stops breathing and is intentional
how can propofol help heart functions
it increases HR with low BP
what is thiopentone’s IV anaesthetic agent
barbituate
what is thiopentone used for
induction
no longer used for maintenance
why is thiopentone no longer used for maintenance
metabolism is slow and repeated doses have a cumulative effect and recovery is much slower
has very long recovery time if given as infusion
what kind of mixture is thiopentone and what form is more potent
racemic mixture
S form is 2x as potent as R form
what does thiopentone cause - 4 things
sedation and hypnosis
EEG slowing but this is dose dependent
anticonvulsant effects
respiratory depression
what is thiopentone’s lipophilicity
highly lipophilic
what is the speed of thiopentone’s onset of action
occurs quickly after bolus dosing
lose consciousness within 30-50sec
what dies thiopentone do to neural output and seizures
decreases both
what are the 4 side effects of thiopentone
respiratory depressant
loss of airway reflexes
lowered blood pressure
heart rate effects = drops rate with bolus and increases with low BP
does thiopentone have analgesia properties
no
what kind of sedation does ketamine provide
dissociative sedation
does ketamine provide analgesia
yes
what does ketamine do to NMDA receptors
antagonist at NMDA receptors in spinal cord and brain to mediate analgesia
most anaesthetics do what to sympathetic tone
decreases it
what does ketamine do to CO and vasc resistance
increases CO and vascular resistance
what does ketamine do to resp drive and muscle tone
maintains respiratory drive and muscle tone with bronchodilation
in what conditions should ketamine be avoided and why
neuroanaesthesia due to cerebral blood flow (theoretical risk of increasing intracerebral pressure that can worsen injury)
what are 3 side effects of keetamine
intense dreams/nightmares/hallucinations/delirium
dose related increase in HR and BP
hypersalivation, nausea and vomiting
is there loss of airway reflexes and respiratory depression in ketamine use
no, less respiratory depression than other drugs
why is ketamine a commonly used field and emergency dept anaesthetic - 4 reasons
can be given intramuscularly via injection if no IV access
increases HR and BP by sympathetic stimulation = good for the bleeding unstable patient
doesnt depress respiration and maintains airway reflexes
provides analgesia
provides analgesia
what are the 3 classes of inhalational agents
esthers
alkanes
gases
what is the potency of inhalational agents
potency is related to lipid solubility
how are inhalational agents taken in body
lungs alveolus -> blood -> brain
what is inhalational agents’ onset wash in related to
4 things
conc delivered
flow rate of gas delivered
ventilation
cardiac output
how is ventilation related to an inhalational agents’s onset
increased vent = increase speed of onset
how is cardiac output related to an inhalational agents’s onset
Low CO = slow delivery blood to lungs = blood has more time to pick up agent = fast onset
metabolism of inhalation agents is via what
P450s and metabolised by liver
inhalation is commonly used for maintenance for which people
children
inhalation agents have an effect on where
brain and spinal cord
what is sedation
drug induced state of reduced level of consciousness that allows tolerance of an uncomfortable or painful procedure
what is sedation a continuum of
minimal to general anasthesia
what are 4 examples of sedative agents
benzodiazepines
ketamine
Propofol
opioids
what do benzodiazepines bind to
receptor sites in GABA system
what is the most commonly used benzodiazepines
midazolam
what are 3 uses of benzodiazepines - midazolam
anxiolysis
sedation
amnesia
what are the 5 side effects of benzodiazepines midazolam
no analgesia respiratory depressant loss of airway reflexes lowered BP HR effects
