local anaesthesia Flashcards
What is paraesthesia?
Altered sensation.
What is analgesia?
Loss of pain sensation only.
What is anaesthesia?
Loss of all modalities of sensation (pain, touch etc.)
Which 4 factors does the action of LA depend on?
- Time of the exposure.
- Concentration.
- Volume in the vicinity of the nerve.
- Size of the nerve fibres.
8 contraindications to LA
- Lack of cooperation.
- Acute infection
- Hypersensitivity.
- Haemophilia.
- Radiotherapy.
- Antidepressants.
- Age.
- Pregnancy.
Explain how acute infection impacts local anaesthetic.
(think more biologically)
- Infection causes pH to be lowered.
- Less anaesthetic molecules are in an uncharged state SO less can cross the phospholipid bilayer.
- Means less can bind to sodium channels.
- Leads to a reduction in LA potency.
Why is the use of local anaesthetic contraindicated in patients with hepatic or renal impairment?
Because reduced kidney and liver function can affect the metabolism of anaesthetic agents.
LOWER ANAESTHETIC DOSES to be considered.
Why should lower doses be considered in the elderly?
Due to the reduced kidney and liver function.
Cardiovascular disease is also more common so limiting adrenaline use should also be considered.
How should LA use be adapted for patients with bleeding disorders?
Local infiltration techniques are preferred over blocks due to the risk of intramuscular haematoma formation with potential airway compromise.
Why is local anaesthetic use contraindicated during pregnancy?
There is a lack of evidence to say LA has an adverse effect on pregnancy but there is a risk that it may cross the placenta and enter the foetus.
Max dose and duration for BUPIVICAINE.
2 mg/kg
Duration of 120-140 mins.
Max dose and duration of LIDOCAINE.
4.4 mg/kg
Duration of 15-60 mins.
Max dose and duration for MEPIVOCAINE.
7 mg/kg
Duration of 45-90 mins
Max dose and duration for PRILOCAINE.
7 mg/kg
Duration of 30-90 mins.
6 things to check for in an LA cartridge.
- Date
- Any cloudiness?
- Has the cartridge been partially used?
- Air bubbles
- Unbroken seal
- Glass or plastic
Which needle is used for blocks?
LONG NEEDLE - 27G, 35mm
Which needle is used for infils?
SHORT NEEDLE - 30G, 21mm
Which needle would be used for an intraligamentary?
VERY SHORT - 30G, 12mm
When would a palatal infiltration be given?
XLA
Multirooted Endo
Rubber Dam Placment
Between which two teeth is the mental block delivered?
Between the lower 4 and 5.
(this will spread to the 1)
When would a long buccal be administered?
- As a supplemental injection for XLA.
- In the event of a failed IDB.
- Placement of a rubber dam clamp.
- Matrix band.
Which group of local anaesthetic is more likely to cause an allergic reaction?
Ester group (e.g: benzocaine topical anaesthetic).
What are the 2 types of sensitivity to local anaesthetic?
Type 1 and Type IV
What is the compound that possesses an allergenic potential associated with ester-type LAs?
PABA
What is type IV hypersensitivity mediated by?
- immune component *
T cells
Describe the presentation of a type IV reaction to LA.
- delayed reaction
- localised to the site of injection
- localised swelling / angioedema
- localised rash / vesicle / blister
Describe the presentation of a type I reaction to LA.
- immediate reaction
- uticaria / erythema / itching
- swelling, difficulty breathing, wheezing, loss of consciousness.
- anaphylaxis
What is type I hypersensitivity mediated by?
IgE antibodies
What is the most common reason for angioedema after dental procedures?
Trauma to the area - not due to LA.
What is the bung of the LA cartridge made of that can trigger an allergic reaction?
(think rubber)
Latex
What is the action of adrenaline in LA?
- Delays the absorption by increasing local blood flow.
- Prolongs the duration of action.
- Vasoconstrictor reduces the risk of toxic side effects.
What could a patient be sensitive to that is present in LA but doesn’t necessarily mean they are allergic?
The pt may have a reaction to adrenaline due to having sulphite sensitivity.
What is the most common reason for adverse reactions to LA?
Psychogenic Response
Why do toxic reactions occur with the use of LA?
Due to high levels of LA entering the bloodstream.
What class of drug are local anaesthetics?
Sodium Channel Blockers
What are the 2 types of symptoms associated with toxic adverse effects of LA?
CNS and cardiovascular symptoms
Describe possible CNS symptoms associated with toxic adverse effects on LA.
minor side effects:
- paraesthesia
- slurred speech
- diplopia
- tongue numbness
major:
- tonic clonic seizures
- decreased consciousness
Describe the possible cardiovascular symptoms associated with toxic adverse effects of LA.
early signs include hypertension and tachycardia.
late signs include:
- hypotension
- sinus bradycardia
- AV blocks and dysrhythmias
- cardiac arrest
What are 3 investigations that can be carried out for an LA allergy?
- skin prick test
- intra-dermal test
- subcutaneous challenge (provocation)
How would you investigate a delayed reaction to LA?
Patch test.
How would you manage an adrenaline overdose?
- position the pt upright
- give oxygen
- reassure the pt
- monitor and call 999 if symptoms persist more than 5 mins.
How would you calculate Max Dose?
- weight = (age+4) x2
- 4.4 mg/kg x weight = max dose (mg)
- divide max dose by 44 to get number of cartridges
Why would you not give an IDB with 4% articaine?
Due to increased lingual nerve parasthesia.
Which type of vasoconstrictor should be avoided during pregnancy due to risk of stimulating uterine smooth muscle contraction?
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