ICP L31: LA Pharmacology and equiptment Flashcards
Define anaesthesia
The loss of all sensation to a circumscribed area of the body by depression of excitation in nerve endings/ inhibition of conduction process in peripheral nerves
Define analgesia
The loss of pain sensation ONLY (nociception)
What is LA
Drug which reversibly prevents transmission of the nerve impulses to a region in which it is applied without affecting consciousness like GA
How does LA work
Produces loss of sensation as it prevents pain in a defined area by
- Blocking conduction of APs along nerve fibres
- Blocking entry of Na+ ions needed for membrane depolarisation (and so APs) meaning that the pain sensation from the tooth is not transmitted to the brain
Outline the structure of LA
- Aromatic lipophilic part
- Intermediate amide/ester chain
- Hydrophobic amine portion
What is the metabolism of LA dependant on
The intermediate carbon chain between aromatic lipophilic and amine hydrophobic portions (whether it is an ester or amide)
How do amide intermediate carbon chains affect LA metabolism
These remain stable in the blood and are metabolised in the liver therefore if the patient has reduced hepatic function it will predispose toxicity
Give examples of amide LAs
- Lidocaine
- Bupivacaine
- Articaine
- Mepivacaine
- Prilocaine
All UK LA dental cartridges are amides
How do ester intermediate carbon chains affect LA metabolism
These are rapidly broken down by pseudocholinesterase in the plasma so have a short duration of action and an increased allergy potential
Give examples of ester LAs
- Procaine (Novocaine)
2. Benzocaine (used as a topical anaesthetic gel)
Describe the mechanism of action of LAs in regards to charges
They are weak bases so in solution some molecules are charged and others uncharged -
Uncharged molecules pass through nerve cell membranes which re-equilibriates to charged/uncharged molecules inside the nerve
Inside nerve cells the molecules must be charged to bind to specific receptors and block sodium entry
List the constituents of LA
- LA agent
- Vasoconstrictor (adrenaline/epinephrine/felypressin)
- Reducing agents (stabilise vasoconstrictor by preventing oxidisation)
- Isotonic solution (modified Ringer’s solution)
- Preservatives
Why is adrenaline included in LA (3)
It is a local vasoconstrictor which controls blood flow by reducing the vessel size - thus ensuring less bleeding at the operative site (local infiltration) and less systemic absorption (lowers toxicity which allows higher dosages) and it also prolongs the duration of action
When can the vasoconstrictor part of LA be contraindicated
- Adrenaline in unstable angina and uncontrolled arrhythmias
- Felypressin in late-stage pregnancy because it causes uterine contraction
What are the adverse effects of adrenaline in LA
Adverse effects occur due to B1 adrenergic stimulation
- Increases HR + stroke volume = increased CO
- this can cause cardiac arrhythmias
- take caution with those who have heart disease - Exposure to XS hear/light causes adrenaline breakdown so needs to be stored carefully
- Plain solution LAs don’t contain vasoconstrictor
Describe what lidocaine contains, its advantages and its duration
2% sol (20mg/ml) aka. Linospan/Xylocaine
1:80000 Adrenaline
- most widely used LA
- highly effective and low toxicity
- has good tissue tolerance
Infiltration/block injections
Pulpal analgesia = 45-60mins
Soft tissues = 3-5hrs
Describe what prilocaine contains and its duration
3% sol (30mg/ml) aka Citanest
Felypressin vasoconstricter (less effective at haemorrhage control than adrenaline)
Available as 4% plain solution
Pulpal analgesia = 45-60 mins
Soft tissues = 2-3 hours
Describe what articaine contains, its usage and why
4% sol (40mg/ml) aka Septocaine/Septanest
1:200000/1:100000 Adrenaline
This is used when repeated injections are needed for a long procedure because it is partially metabolised in plasma and has a half life of 20 mins
What is included in an LA cartridge and what should be checked before use
3 components = cylinder, plunger, cap (contains 2.2ml)
Check the
- [anaesthetic]
- [vasoconstrictor]
- expiry date
- manufacturers name
- batch number
What are the different types of syringe
This is what accepts the LA cartridge and can be
- Conventional (separate needle and syringe)
- Safety syringe = reduces chances of injury by avoiding the need to resheath the needle
- Intraligamental
- Computerised
- Power injections
White handles = disposable
Black handles = sterilised and reused
What should the cartridge be checked for
Shouldn’t contain air bubbles and should be cloudy (indicates bacterial contamination)
Describe the LA needle
Sterile stainless steel (coated silicon) Beveled (chevron) Plastic sheath - Short = 25mm - Long = 35mm
When is a finer gauge (30) needle used (BLUE)
For infiltration anaesthesia
When is thicker gauge (27) needle used (YELLOW)
Inferior dental blocks
What is topical anaesthesia and what does it contain
Applied to the mucus membrane = Benzocaine ester gel or Lignocaine spray/ointment
What is infiltration anaesthesia
A submucosal injection to act on local nerve endings adjacent to the tooth apex and where the bone is porous enough to allow for this
What is a nerve block/ regional anaesthesia
Used for blocking the passage of pain along nerve trunks by injecting anaesthetic solution around it at a site where the nerve is normally unprotected by bone
Why would a nerve block/regional anaesthesia be used
When the cortical plate of bone is too thick to allow for infiltration anaesthesia
When is topical anaesthesia used
- Prior to needle penetration
- Reduces the discomfort of infiltration anaesthesia
- Makes no difference when used for nerve vlocks
What does the volume of LA required depend on
The administration route of LA
How much LA is needed for an infiltration
0.5ml
How much LA is needed for a block
2ml
How much LA is needed for a long buccal injection
0.2-0.5ml
How much LA is needed for a palatal injection
0.2-0.5ml
What does the onset and action of LA depend on (6)
- pH of tissue
- pKa of drug
- Time of diffusion from needle tip to nerve
- Nerve morphology
- Drug concentration
- Lipid solubility of drug
