11a. Drugs used in radiology II: anaesthetics and analgesics - Analgesics Flashcards
what is the definition of an analgesic
medications and actions that act to relieve pain
what are the 5 types of analgesia
non pharmacological paracetamol NSAIDS opiates adjuvant agents
what is the definition of anaesthesia
to be without pain
what are the 3 types of anaesthesia
local
regional
general
what is local anaesthesia
small area
what is regional anaesthesia
block nerve and numb a body part
what is general anaesthesia
go to sleep
what is the 3 points of general anaesthesia
analgesics
muscle relaxation
hyponosis
what is the clinical context of anathesia use
ED/ICU/interventional
paeds
how is anaesthesia involved in radiology
radiological and interventional procedures can cause pain, anxiety, psychological and physical distress
this can be improved with sedation and anaesthesia, good pain relief gives good images
what is the definition of pain
an unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage
is pain objective
no its subjective
is pain the same for everyone
no its highly variable
what are the 2 types of pain
nociceptive pain
neuropathic pain
what is nociceptive pain
pain from physical damage or potential damage to tissues
what is neuropathic pain
due to inflammation, irritation compression or damage to nerves and is often associated with chronic pain
pain lasts after the tissue injury has resolved
what is potential damage in terms of pain
no damage yet but nearly damaged and needs to get away from damage
what are nocioceptors
specific pain receptors
nerve endings in most body tissues that only respond to damaging or potentially damaging stimuli
where in the body are there no nociceptors
brain
what are the 3 types of stimuli that can activate pain receptors
mechanical
heat
chemical
what is transmission in terms of pain
nociceptive message transmitted from periphery to central nervous system
what is the nociceptive message transmitted from periphery to central nervous system via
via axon of primary afferent nociceptor
what is the structure of a neuron
cell body in dorsal root ganglion and long process called the axon that divides and sends one branch out to the periphery and one into spinal cord
what are the 2 main types of pain fibres
non mylienated C fibres
thinly mylienated fast conducting A fibres
what do the primary afferent nociceptors activate
second order pain transmission cells that run up the spinothalamic tracts in the spinal cord and transmit message to primary somatosensory region of brain
what type of pain is Cfibres responsible for
slow burning pain
what type of pain is Dfibres responsible for
sharp pinching pain
who is analgesics prescribed and administered by
prescribed by doctor and administered by dr or nurse
what is the WHO ladder in terms of analgesics
Start with non-pharmaceutical then weak opioids then opioids then adjuvant agents
what is multimodal analgesia
Aim to use multimodal analgesics, use lots of diff receptors to manage pain
what is paracetamol’s drug type
analgesics/pain killers
can you buy paracetamol over the counter
yes
how effective is paracetamol
surprisingly effective
what are the side effects like for paracetamol
minimal
what is the action of paracetamol thought to be
mainly central action acts via the peroxidase site of COX 2
how is paracetamol similar and different from NSAIDs
similar analgesics and antipyretic effects to NSAIDS
lacks anti-inflammatory and anti platelets effects
when can paracetamol be toxic
normal metabolism is overwhelmed and results in increased toxic byproduct produced leading to liver damage
what 4 things can increase risk of paracetamol toxicity
high paracetamol dose
chronic alcohol/drug use
pre-existing hepatic failure
malnutrition
what are NSAIDs
non steroidal anti inflammatory drugs
how does NSAIDS work
work by selective or non selective blockade of COX1/2 enzymes resulting in decreased prostaglandin production
what is broken down into COX 1/2 in terms of NSAIDs
arachidonic acids
what does prostaglandins do
mediate inflammation, transduction of pain signals and fever
what is NSAIDs action thought to be
mainly peripheral
what 2 things does COX 1 affect
gastric protection
platelet function
what 3 things does COX2 affect
pain
fever
bone formation
what are 3 of NSAIDs uses
analgesia
anti-inflammatory
anti-pyretic
what are the side effects of COX1 targeted NSAIDs
5 things
gastric ulcers increased bleeding tendency decreased renal blood flow bronchoconstriction effects binding of other deugs
what are the 3 side effects of COX 2
increased risk of MI or stroke
similar renal risks
increased anaphylaxis risk
what are opiates
naturally occurring compounds derived from poppy plants
what are 3 examples of opiates
morphine
codeine
heroin
what are opiods
overarching terms including natural synthetic and semi synthetic drugs
what are 3 examples of opiods
oxycodone
fentanyl
tramadol
what are opiod receptors
G protein coupled receptors
why do opioids act at multiple levels
they are widespread
what are the 4 levels that opiods work at
peripherally
spinal cord
central activity
activate reward signalling pathway
how do opiods peripheral receptors work
modulate nociceptive transmission in the dorsal horn through descending pathways
how do opiods spinal cord receptors work
inhibit release of substance P from primary sensory neurons
what system does opioids also activate and how is this linked to drug abuse
reward signaling pathways -> addiction
what are the 3 types of classical opioid receptors
M, delta, k
what are common CNS side effects of opioids - 4 things
sedation
delirium/confusion
dizziness
physical dependence and tolerance
what are 4 GIT side effects of opioids
nausea
vomiting
constipation
dry mouth
what are 2 respiratory side effects of opioids
respiratory depression and arrest
what are 2 skin side effects of opioids
itch
sweating
what is tolerance to opioids and what does it result in
needs escalating doses to get same outcome
what are 2 common weak opioids
tramadol and codeine
where does tramadol act
centrally acting partial opioid agonist
what is the potency of tramadol in comparison to morphine
5-10 x less potent
how does tramadol work
inhibits neuronal uptake of noradrenaline and increases serotonin release
what is the respiratory and GI side effects of tramadol like in comparison to morphine
much less resp depression and consitpation
tramadol cant be used for patients with what condition and why
epilepsy
tramadol results in a lowered seizure threshold
where does codeine act
centrally acting opioid agonist
what is the potency of codeine in comparison to morphine
10x less potent
how is codeine a prodrug and what does this mean
prodrug that is metabolized to morphine
20mg of codeine -> 1mg morphine
why cant some people not feel effects of codeine
genetic differences
cannot metabolize codeine into morphine so get minimal pain relief (codeine itself doesnt provide pain relief - has to be in morphine form)
what is the respiratory side effects of codeine like in comparison to morphine
less resp depression than morphine
what are 3 types of strong opioids
morphine
fentanyl
oxycodone
what can morphine do in terms of histamine release
can cause histamine release that can cause skin rashes and low BP
how potent is fentanyl compared to morphine
100x more potent
what is the onset and duration of action for fentanyl
fast onset
short duration of action
what are the 2 ways that fentanyl can be administered
patches or IV
how potent is oxycodone compared to morphine
mildly stronger than morphine
how long does morphine to set in and how long does it stick around for
5mins to set in
2hrs duration
why cant you give fentanyl orally
its fully broken down in the stomach
why does oxycodone give high
kicks in faster
what are 3 examples of anticonvulsants
gabapentin
pregabalin
carbamazepine
how do anticonvulsants work
via central neurotransmitter effects
what are the 4 side effects of anti convulsants
sedation
nausea
vomiting
ataxia
what are 2 examples of antidepressants
TCAs and SSRIs
how do antidepressants work
via noradrenergic and seroternergenic pathways
blocking spinal pathways
what are the 3 side effects of antidepressants
sedation
dry mouth
cardiac toxicity
what is an example of NMDA antagonists
ketamine
how do NMDA antagonists work
noncompetitive inhibitor at NMDA receptor
what are 5 side effects of NMDA antagonists
dysphoria increased secretions addiction hallucinations anesthetics at high doses
how do GABA agonists work
activates GABA receptors decreasing neurotransmitter release in pain pathways
what are the 4 side effects of GABA agonists
sedation
nausea
vomiting
decreased blood pressure
how do A2 agonists work
decrease central sympathetic nervous activity and inhibits pain transmission peripherally
what are the 3 side effects of A2 agonists
low blood pressure
sedation
weakness
how are local anesthetics IV given
as IV infusion
how do local anesthetics IV work
blocks sodium channels when used IV it decreases pain transmissions peripherally and centrally
what are the 2 side effects of local anesthetics IV
cardiac and neurological toxicity (LAST)
what is the therapeutic window like for local anesthetics IVs
narrow
how are local anesthetics regional adminsitered
injected around nerves, subcutaneously or into epidural/thecal space
how do local anesthetics regional work
blocks sodium channels -> blocks transmission of pain through nerves
what are the 4 side effects of local anesthetics regional
LAST
motor blockade
insenate limb
local nerve toxicity or damage
