Analgesia 1 Flashcards
What are the 4 areas of the conduction of pain that analgesics can act at?
- Sit of injury e.g. NSAIDs (decrease the inflammation)
- Alter nerve conduction (Local anaesthetics)
- Modify transmission in the dorsal horn (opioids and some antedepressants)
- Central competent and emotional aspects of pain e.g. opioids and antidepressants.
What is appropriate pain?
Pain that lasts whilst the injury is still present
What is chronic pain?
Pain that remains past the time of the injury.
With pre-emptive analgesia, what does not occur at the time of injury?
Pain or hypersensitivity.
What are the 4 opioid receptors?
- mu
- delta
- kappa
- nociception
Name 4 things that affects the success of opioids?
Route, species, dose and stimulus.
name 10 clinical side-effects associated with the use of opioids?
- mania
- respiratory depression
- CVS effects
- Pancreatic duct
- Ileus
- Nausea and vomiting
- urinary retention
- pruritus
- miosis
- mydriasis
What is the name of our own endogenous opioids?
Endorphins
Which is the most efficacious opioid at relieving pain?
Morphine
What is morphine?
A full agonist at mu, delta and kappa receptors.
What is the duration of morphine?
4 hours
What is the oral availability of morphine and how much will an increased dose extend its action by via this route?
25% bioavailability - can be extended to 8 hours duration.
Is morphine licensed and what class of drug is it?
Not licensed. class II drug.
What is methadone?
It is a full mu agonist with affinity for the NDMA receptor.
What does it inhibit?
Inhibits epinephrine and serotonin reuptake.
What is the duration of action of methadone and how can it be extended?
about 4 hours, can be extended with SC administration.
What is the bioavailability of methadone and what class drug is it?
Poor oral bioavailability - class II drug.
Is methadone licensed?
Licensed for dogs and cats.
What is an advantage of methadone over morphine?
Morphine sometimes causes sickness, methadone can, but very rare.
What is the NDMA receptor involved in?
Chronic pain.
What is Pethidine (Meperidine)?
Short acting agonist of the mu receptor and shown to block sodium channels.
Agonist at alpha 2 B sub types.
What impact does pethidine have on the heart?
Negative inotrope, however increases heart rate therefore cardiac output is maintained.
Why should you not give pethidine IV?
Can induce histamine release.
Which drug should pethidine not be administered with and why?
Selegiline in dogs - combination of a monoamine oxidase inhibitor and pethidine should be avoided to prevent a serotonin like syndrome from occurring.
Is pethidine licensed and what category drug is it?
Licensed for dogs, cats and horses (spasmodic colic).
Category II drug.
What is fentanyl?
It is a short acting mu agonist.
What drug class is fentanyl
Class II.
When is the peak fentanyl effect following bolus administration?
3-5 mins later
Can be used for what?
Induction with BZD in compromised patients.
What kind of transfermal administration can be used for fentanyl?
Transdermal patches - never send an animal home with these on in case they eat them and overdose.
What is a negative impact of fentanyl and why dangerous?
Fentanyl causes significant bradycardia and if there is an overdose, the animal can stop breathing for 2/3 mins.
What kind of solubility is fentanyl?
it is really lipid soluble - only lasts about 20-30 mins.
Name another opioid which has been used in dogs for mild-moderate pain?
Codeine
Name another opioid which is used post-operatively in dogs?
oxycodone
What is the reversal agent/ antagonist of pure opioids?
Naloxone.
What is tramadol?
It is a pro-drug that is metabolised in only about 5-10% dogs. It is a low potency mu selective partial agonist.
What does tramadol increase and what is the result of this?
increases serotonin and therefore looks like analgesic effects.
Why should tramadol not be used as a sole drug analgesic?
Because they might still be in pain, despite showing signs that they are not.
Is tramadol licensed in animals?
NO - it is used mainly in humans.
What does tramadol inhibit?
5HT re-uptake (serotonin)
What else does tramadol cause?
Alpha 2 adrenergic effect
In what species does tramadol work better?
Works better in cats.
Give an example of partial and mixed agonist/ antagonist opioids and where it targets?
Buprenorphine - partial agonist with a strong affinity for mu receptors and kappa antagonist properties.
What is an important feature of buprenorphine when using with other drugs?
It will displace other drugs, even full agonists. Does not matter how much full agonist you administer, will not be able to displace buprenorphine.
Is buprenorphine highly efficacious?
it is highly potent, but not as efficacious as other opioids.
When is the peak effect of buprenorphine after IV administration?
45-60 mins
In which species is buprenorphine licensed?
Dogs, cats and horses
What is the most effective routes of administration of buprenorphine?
OTM - oral transmucosal.
What is butorphanol?
A kappa agonist and a mu antagonist
What is it used for?
Analegsia and sedative/ anaesthetic (only 10 mins)
What is the duration of butorphanol?
Short-medium duration
In cardiac patients, what is it used in combination with for sedation?
Acepromazine.
In what species is butorphanol licensed in?
Dogs, cats and horses
Why is butorphanol good at relieving coughs, what is it?
Antitussive
Name 5 routes of administration of opioids?
- Epidurally
- Intra-articularly
- Locally at site of injury
- Nasal spray
- Rectally (1st pass metabolism)
What are the two methods LA block pain?
They affect the neurone directly or they block channels.
What type of drugs are LA’s?
Weak bases and ionised at physiological pH.
In what kind of tissue does it take longer for local anaesthetics to start working and why?
Longer in inflammaed tissue because there is a higher degree of ionisation.
What is a local anaesthetic’s duration of effect directly related to?
Their degree of protein-binding.
What is a local anaesthetics potency related to?
Their lipid solubility.
Name 4 types of local anaesthetics available?
- bupivicaine
- lidocaine
- Etidocaine
- Cocaine
Which type of local anaesthetic is good for occular anaesthetic?
Proparacaine.
What is the therapeutic window for local anaesthetics and how to we avoid problems?
It is very narrow and we need to aspirate before injecting local anaesthetic because most issues come from injecting the LA intravenously.
Name 3 effects of toxicity of LA?
- CNS toxicity
- cardiovascular toxicity
- methaeglobinaemia
What is ED 90?
The dose of a drug which eliminates 90% of the target pathogen.
What is the most commonly used local anaesthetic?
Lidocaine (0.5-2.0%)
How is anaesthesia produced?
Several intradermal injections 0.3-0.5ml with a 22-25G needle.
In what kind of animals is local anaesthetic best administered?
Sedated/ anaesthetised animals.
What is used for intubating cats?
Lidocaine spray (intubeeze) - 2%, 2-4ml
What do we use for catheterising and urethra?
Lidocaine jelly 2% 20mg/ml
What is EMLA?
It is a lidocaine cream useful for IV catheter placement
What can be used to de-sensitise to cornea and for how long?
Proparacaine 0.5% and butacaine 2% can de-sensitise cornea for 10-20 mints.
What is used to treat post-herpetic neuralgia in humans? How does this work?
Lidocaine transdermal patches. The patch delivers lidocaine to the topical superficial nociceptors.
Are lidocaine patches licensed in animals?
No.
Which is the only local anaesthetic which we can use IV?
Lidocaine.
Which species can lidocaeine be used as an infusion?
Dogs and horses with colic.
When is lidocaine most useful?
Post-operatively
In which species should lidocaine be avoided in?
Cats - very sensitive and toxic at 4-5mg/ml
Name two methods which will enable us to identify the location of a nerve?
Electro-stimulation and ultrasound.
Where would you block if you wanted to block sensation to the elbow and distal limb and how would you find this?
Brachial nerve plexus - located between C7- and C8
Name 4 scenarios when an intercostal nerve block might be necessary?
Rib fractures
Flail chests
Chest drain
Thoracic surgery
When would you use intra-articular local anaesthetics?
Following arthroscopy, ligament repair or arthrotomy for removal of cartilage debris.
What anaesthetic would you use intra-articularly?
Bupivicaine 2mg/kg
What could be used for total ear canal ablations (TECA), limb amputations or reconstructive surgery?
Soaker catheters
What are soaker catheters?
relatively large bore (6-12 French) catheters with tiny holes.
When are these placed and what happens with them?
They are placed just before closing of surgery and are secured into the skin. Allow distribution of anaesthetic into the surgical site.
What is IVRA and how is it performed?
Intra-venous regional anaesthesia.
A tonriquet and esmarch bandage applied to a limb and when the esmarch bandage is removed, the torniquet is still in place. This is when you inject the lidocaine (0.25-0.5%, 2.5-5mg/kg) and can leave the torniquet in place for 90 mins.
What is IVRA used in conjunction with?
Sedation or general anaesthesia
What is the difference between epidural and a spinal?
An epidural is the placemen of a catheter induction and a spinal is a single needle injection.
What do NSAIDs inhibit?
Prostaglandins (COX, LOX)
What are the COX receptors?
COX 1, 2 and maybe 3
Which part of the spinal canal do NSAIDs target?
Dorsal horn, not central.
What is unique about NSAIDs in terms of MAC?
NSAIDs are the ONLY group of drugs which do not reduce MAC therefore if you administered carprofen, you would not turn down the iso or sevo.
Which drugs stop the production of arachidonic acid?
Steroids
Which drugs stop the production of prostaglandins, blocking COX and LOX receptors?
NSAIDs.
