LA Flashcards
The most common type of nociceptor is the?
Polymodal nociceptor.
Stimulation of the substantial gelatinosa produces what?
Inhibition of pain conduction to the Thalamus.
Dysphoria and hallucinations are mediated by which opioid receptor?
Kappa
A∂ nociceptors terminate in what lamina of the dorsal horn?
I and V
Which are more easily blocked by local anaesthetics?
(a) Large, myelinated axons.
(b) Small, myelinated axons.
(c) Non-myelinated axons.
- (b)
- (c)
- (a)
What is meant by “narcosis”?
A stupour and mental clouding produced by high doses of opioid receptor agonists.
Why is pethidine (a strong opioid receptor agonist) safe to use during labour, but other strong agonists aren’t?
Because pethidine doesn’t reduce uterine contractions.
C-fibres terminate in what lamina of the dorsal horn?
I and II
Respiratory depression is mediated by which opioid receptor?
µ
A∂ mechanoreceptors terminate in what lamina of the dorsal horn?
II and III
When a local anaesthetic is applied, what are the nerve functions lost first and in what order?
- Autonomic
- Pain
- Temperature detection
- Touch
- Proprioception
- Deep pressure
- Motor
What is the most common cause of death in an opiate overdose?
Respiratory cessation.
Dextropropoxyphene and tramadol belong to which group of opioids?
Mild to moderate agonists, the same classification as codeine.
Which opioid receptor has the least amount of effects?
∂ receptor
Which symptom tends to disappear with repetitive dosing and which symptom tends to remain even in opioid-dependent users?
Nausea and vomitting tends to disappear.
Pupillary constriction is found even in dependents.
Where or what is the substantial gelatinosa?
The second lamina of the dorsal horn.
The descending inhibitory pathways have what kind of effect on the substantial gelatinosa?
Excitatory.
What receptor mediates histamine release in opioid use?
Gotcha! None of them. It’s a direct effect on mast cells.
Lignocaine is used for something other than local anaesthesia, what is it?
To treat arrythmias.
Which are more stable, amide or ester local anaesthetics?
Amide.
Ester local anaesthetics are rapidly inactivated in the plasma and tissues.
Within what time frame does opioid tolerance develop?
12-24 hours
What are some strong opioid agonists?
Fentanyl, heroin, morphine and oxycodone.
What long-acting LA has cardiotoxicity? What does it do to the heart?
Bupivicaine.
AV block.
Vent. arrythmias.
Decreased cardiac contractility.
Smooth muscle relaxation => Hypotension
How is opioid tolerance developed (celullarly)?
µ-receptor desensitisation.
If a local anaesthetic is systemically circulated, what effects does it have?
CNS toxicity
Cardiotoxicity
Which has more pharmacologically active metabolites, amide or ester LAs?
Amide LAs.
Which is a more important factor for opioid dependence, physiological effects or psychological ones.
Psychological ones.
What are the antagonists of the opioid receptors?
Naltrexone and naloxone.
What is a moderate opioid receptor agonist?
Codeine
What’s the average half-life of an opioid drug?
3-6hrs.
A ‘bier block’ is also known as? How does it work?
An IV block. You torniquet the patient’s arm, then IV inject the LA. Anaesthetises the whole arm.
Epidurals usually contain what two types of drug?
Local anaesthetic and an opioid.
Diamorphine is also known as?
Heroin
Nociceptive neurons are what kind of fibre?
C-fibres.
Why do local anaesthetics promote themselves being systemically circulated?
Because they promote vasodilation.
Why is buprenorphine so good for treating opioid addiction?
Has high binding to µ receptors.
Antagonises the kappa receptors (responsible for hallucination and dysphoria).
Has a long half-life (24-37hrs).
Has a ceiling on its dose-response effect.
Less sedation and less euphoria.
What are the two chemical types of local anaesthetics?
Amide and ester anaesthetics.
Nalbuphine and pentazocine are what kind of opioid/opiate?
Mixed agonist and antagonists.
Why don’t local anaesthetics work very well in inflamed tissues?
Because inflamed tissues have a low pH (acidic) and hence tend to ionise a large proportion of the local anaesthetic weak base – reducing its effectiveness.
What is a partial/mixed agonist of the opioid receptor?
Buprenorphine
Naltrexone, although used for opioid overdose is also useful for:
Treating the craving for alcohol in alcoholics.
Opioid receptor binding leads to what neuronal effect?
Decreaed neuronal excitability.
What are the effects on the CNS from LA drugs?
Depressant effect at low doses
Excitation effect at high doses
Profound respiratory depression at high doses
Why is methadone used to treat opioid dependence?
Weaker, long-acting, blocks the euphoric effect of other opioids, allows for tapering and diminishes abstinence symptoms.
In the resting state, what are the statuses of the two gates?
v = closed t = open
Why is adrenaline co-administered with local anaesthetics?
It produces vasoconstriction, counteracting the vasodilation of the local anaesthetic.
It also produces a relatively bloodless surgical field.
If a local anaesthetic has an increased affinity to plasma proteins, what does that mean for its duration of action?
It will have a longer duration of action.
Local anaesthetics bind the receptor in what states?
The active state or the inactive state, but not the open state.
What are the two gates in the sodium voltage-gated channel?
‘v’ and ‘t’.
If a local anaesthetic is ionised, is it more or less clinically effective?
Less clinically effective. Needs to be lipid soluble in order to diffuse through membranes and act.
In the inactive state of the sodium voltage-gated channel, what are the statuses of the gates?
v = open t = closed
Which lamina of the dorsal horn conduct signals to the thalamus via the spinothalamic pathway?
I and V
Euphoria is mediated by which opioid receptor?
µ
What kind of pain are opioids useful for and not useful for?
Useful: Visceral, deep pain.
Not useful: Neuropathic pain.
Respiratory depression is mediated by which opioid receptor?
µ
