Local Anaesthetics Flashcards
1
Q
LA
Classification
A
- First one was cocaine 1884
- Synthetic derivates:
- esters (e.g.procaine 1905)
- generally less stable
- higher incidence of allergic reactions
- amides (e.g. lidocaine 1943 bupivacaine 1963)
- generally more stable
- longer plasma half life
- esters (e.g.procaine 1905)
2
Q
LA
Effects
A
- systemic absorption after intraarticular or intralesional injection is slow/small
- produce a reversible abolition of nerve conduction
- small diameter, nonmyelinated fibres most easily blocked - nociceptors and sympathetic
- order of blockade:
- pain
- temperature
- touch
- proprioception
- motor
- Duration varies with type of LA
- penetrates nerve sheath in non-ionised (lipophilic) form
- once inside cell, some molecules become ionised and then block sodium channels in cell membrane by binding to receptor site within channel
- opening and closing of sodium channels is required for depolarisation and repolarisation for initiation and transmission of impulses
3
Q
LA
uses
A
Usually used in combination with steroid in MSM
- to give pain relief during and after an injection
- to increase volume of injection
- to distribute steroid
- maybe distension effect
- diagnostic use
- re-examine after injection to see if signs reduced or abolished
4
Q
LA
Side effects/complications
list
A
- CNS
- Cardiovascular
- Allergic
- Type A reactions
- Type B reactions
- Contraindications
5
Q
LA
Side effects/complications
CNS
A
- Initial stimulation
- lightheadedness
- circumoral paraesthesia
- restlessness / tremor / twitching
- confusion / agitation
- convulsions
- Further increases leads to depression
- sedation leading to coma
- respiratory depression
6
Q
LA
Side effects/complications
A
- Cardiovascular
- myocardial depression, arrhytmias, reduced cardiac output
- peripheral vasodilatation
- hypotension and circulatory collapse
7
Q
LA
Side effects/complications
allergic
A
- urticaria / allergic dermatitis
- angio oedema
- ANAPHYLAXIS - MAY BE FATAL
8
Q
LA
Side effects/complications
Type A and B reactions
A
Type A:
- dose dependant
- can potentially affect anyone
- do not exceed recommended dose
- avoid inadvertent IV injection - aspirate
Type B:
- allergy
- ask about previous exposure (dentist)
- other history of allergy/anaphylaxis
- be prepared to treat!
9
Q
LA
Contraindications / cautions
A
Contraindications:
- allergy to LA (ask about previous exposure or anaphylaxis
Cautions:
- heart block or other conduction abnormalities
- use of cardiosuppressant / anti arrythmic drugs
- epilepsy
- pregnancy
- breast-feeding ok
10
Q
LA
Commonly used
A
- lidocaine hydrochloride 1%
- Non-proprietary
- 10 mg/ml
- Rapid onset
- duration 1,5 hrs.
- Bupivacaine hydrochloride
- Marcaine
- 2,5 mg/ml 5 mg/ml
- slow onset
- duration 4-6 hrs.
- Procaine hydrochloride 2%
- non proprietary
- 20 mg/ml
- low duration: 30 min. Rarely used
11
Q
Lidocaine
Potency and duration of action
maximum dose
A
- Rapid rate of onset
- Medium duration t 1/2 of 2 hours
- maximum dose 200mg
- medium potency
- side-effects-risk
12
Q
Bupivacaine
Potency and duration of action
maximum dose
A
- Slow rate of onset
- Medium duration t 1/2 of 3 hours
- maximum dose 150mg
- 4 times as potent as lidocaine
- side-effects-risk
13
Q
Procaine
Potency and duration of action
maximum dose
A
- Moderate rate of onset
- Short duration t 1/2 of 30 min.
- maximum dose 1g (1000mg)
- low potency
- side-effects-risk
