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Local Anaesthetics > ICP-31 LA: Pharmacology and Equipment > Flashcards

ICP-31 LA: Pharmacology and Equipment Flashcards

1
Q

What is the difference between anaesthesia and analgesia

A

Anaesthesia = loss of all sensation to a circumscribed area of the body by depression of excitation in nerve endings or an inhibition of the condition process in peripheral nerves

Analgesia = Loss of only ‘pain’ sensation (Nociception)

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2
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

A local anaesthetic injection should not be painful

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3
Q

What is a local anaesthetic

A

A local anaesthetic can be defined as a drug that reversibly prevent transmission of the nerve impulse in the region to which it is applied, without affecting consciousness

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4
Q

How do local anaesthetics work

A

By blocking the entry of sodium ions that are required for an action potential to occur

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5
Q

Describe the chemical structure of local anaesthetics

A
  1. A lipophilic aromatic portion
  2. An intermediate chain: amide or ester
  3. A hydrophilic amine portion
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6
Q

Where are amide LAs metabolised and give examples of amide LAs

A

Amides are stable in the blood and are metabolised mainly by the liver so patients with reduced hepatic function are predisposed to toxicity:

  • Lidocaine
  • Bupivacaine
  • Articaine
  • Mepivacaine
  • Prilocaine
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7
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

All local anaesthetics in dental cartridges in the UK are amides

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8
Q

How are Ester LAs broken down and give examples

A

Esters are rapidly broken down by pseudocholinesterase in plasma and consequently tend to have a very short duration of action:

  • Procaine (Novocain)
  • Benzocaine (topical)
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9
Q

How can you tell is an LA is an amide

A

If it has an “i” in the prefix of the name (before -caine)

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10
Q

Describe the mechanism of action of Local Anaesthetics

A
  • LAs in a cartridge contain charged and uncharged forms
  • Uncharged form can cross the nerve cell membrane
  • This then re-equilibrates to charged and uncharged forms in the nerve
  • Once inside cell, the molecule must be in charged form to bind to specific receptor to block Na+ entry
  • This ability to exist in lipid-soluble and charged states is possible as LAs are weak bases
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11
Q

What 2 factors affect the proportion of charged to uncharged molecules following injection

A
  • pH of the tissues

- The dissociation constant (pKa) of the LA molecule

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12
Q

Why are the factors that affect the proportion of charged to uncharged molecules clinically important

A
  • Infection within the tissues can reduce the pH and so reduce the effectiveness of the local anaesthetic
  • Agents with a lower pKa will be more effective
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13
Q

What are the constituents of a local anaesthetic cartridge

A
  • Local anaesthetic agent
  • +/- vasoconstrictor (adrenaline or felypressin)
  • Reducing agents (stabilises the vasoconstrictor by preventing its oxidation)
  • Isotonic solution (modified ringer’s solution
  • Preservatives (not common anymore)
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14
Q

Why do we add adrenaline to the LA cartridge

A
  • Local vasoconstrictor
  • Less bleeding at operative site
  • Reduce systemic absorption and consequently lower toxicity
  • Prolonged duration of action
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15
Q

What are the potential CVS effects of adrenaline

A

Increases heart rate and stroke volume and hence cardiac output:

  • potential to cause cardiac arrhythmia
  • caution needed in those with heart disease
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16
Q

Why should LA cartridges be stored carefully

A

Exposure to excess heat or light causes the breakdown of adrenaline

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17
Q

In which patients should we be cautious about the use of adrenaline in LAs

A

In patients with cardiac complications like unstable angina and uncontrolled arrythmias

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18
Q

Why do we need avoid the use of felypressin containing agents in patients in late stage pregnancy

A

Similar to Oxytocin hormone and Can produce uterine contractions - dose needed for labour is well beyond dose for LA - still avoid its use in pregnancy

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19
Q

What is felypressin

A

a Synthetic polypeptide

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20
Q

When is the use of felypressin use more acceptable and can be considered instead of adrenaline

A

When the patient has heart or blood pressure problems or has a tendency of fainting

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21
Q

What is the most widely used LA and in what conc is it used

A

Lidocaine 2% (20mg/ml)

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22
Q

What are advantageses of using Lidocaine 2% (20mg/ml)

A

Highly effective with low toxicity and good tissue clearance

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23
Q

Does Lidocaine contain a vasoconstrictor, if so what does it contain

A

Contains Adrenaline 1:80,000

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24
Q

How long does Lidocaine last for

A

Pulpal anaesthesia = 45-60 mins

Soft tissues may be numb for 3-5 hours after infiltration/block injections

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25
What are the trade names for lidocaine LAs
Lignospan/Xylocaine
26
What conc do we use Prilocaine in
3% (30mg/ml)
27
Which LA has the trade name Citanest
Prilocaine
28
Does Prilocaine contain a vasoconstrictor, if so which one
Yes it has Felypressin
29
AY BAWS CAN I HABE DE NOTE PLZ
Prilocaine is less effective at controlling haemorrhage than adrenaline containing solutions
30
What conc do we use Articaine in
4% (40mg/ml)
31
What LAs have trade names Septocaine/septanest
Articaine
32
Does Articaine contain a vasoconstrictor, if so which one
Adrenaline in 1:200,000 or 1:100,000
33
Why might articaine use be advantageous in longer procedures
it is more quickly metabolised than any other agent as it is partly metabolised in the plasma, so it is preferable if repeated injections are needed
34
What are the 3 components of equipment that are needed to deliver local anaesthetic
1. The local anaesthetic cartridge 2. The syringe 3. The needle The Dental Hospital uses "Safety Syringes" that combine the syringe and needle
35
What are the 3 components of a local anaesthetic cartridge
- Cylinder - Plunger - Cap
36
What information is found on local anaesthetic cartridges
- Contents - Conc of anaesthetic and vasoconstrictor - Expiry date - Manufacturer's name - Batch number
37
How much LA do UK cartridges tend to contain
2.2ml (1.8ml also available)
38
What are the 2 most commonly used type of syringe
- Conventional | - Safety Syringes
39
What types of syringe are there
- Conventional - Safety syringe - Intraligamental - Computerised - Powered injectors
40
What is the difference between conventional and safety syringes
Conventional = separate needle and syringe components Safety = Syringe and needle come as one unit
41
What are the 2 parts of a needle to be used with dental syringes
- Sterile stainless steel coated with silicon at the end - Beveled (chevron) These needles come in plastic sheaths
42
What needle lengths are there
- Short (25mm) | - Long (35mm)
43
What is the gauge of a needle
This refers to the thickness of the needle
44
When do we use finer gauge needles for LA administration
We use fine (30 gauge) needles fo infiltration anaesthesia
45
When do we use thicker gauge needles for LA administration and why
We use thicker gauge (27 gauge) needles for inferior dental blocks as they tend to deflect less when entering the tissues
46
Why are safety syringes becoming more commonly used
They are single use and have a protective sheath that is incorporated in the barrel of the syringe and this is slid over the needle at the end of the injection so avoid the need to resheath the needle and reduces chance of needle stick injuries
47
What 2 types of safety syringe are there and what are they used for
Blue - fine (30 gauge) short needle (25mm) used for infiltrations Yellow - thicker (27 gauge) long (35mm) needle used for inferior alveolar nerve blocks
48
What is the difference between black and white handle safety syringe tings
- Black handles can be sterilised and re-used | - White handles are disposable (single use
49
What is the first step of the assembly of an LA syringe
Preparation - ensure you got all the appropriate items: - Syringe handle - Safety syringe (check length and gauge) - Cartridge (checked and safe)
50
What is the second step of the assembly of an LA syringe
Check cartridge - unwrap the correct syringe and check for: - Correct type of anaesthetic - Cartridge isn't out of date or damaged - Fluid is clear - No air bubbles
51
What does a cloudy LA cartridge solution indicate
A bacterial contamination
52
What is the third step of the assembly of an LA syringe
Load the cartridge into open end of syringe with the cap end first and the grey silicone bung last
53
What is the fourth step of the assembly of an LA syringe
Push the handle onto the syringe: Grip the handle plunger and put your thumb behind the finger holder. Introduce the handle tip of the barrel to the back end of the cartridge
54
What is the fifth step of the assembly of an LA syringe
Slide the sheath protecting the needle backwards towards the handle until it clicks
55
What is the sixth step of the assembly of an LA syringe
Remove the needle cap and discard it Pull the protective sheath back over the needle until you are ready to use it Never leave a syringe down without the protective sheath covering the needle
56
Describe the disassembly of the LA syringe
- Ensure the safety sheath is fully engaged (2 clicks) | - Remove the handle and dispose of the syringe and cartridge into the yellow sharps bin
57
What are the types of LA administration
Topical Anaesthesia Infiltration Anaesthesia Nerve Block/regional anaesthesia
58
Describe Topical anaesthesia
Applied to the mucous membrane
59
Describe infiltration anaesthesia
Used when anaesthetic can be delivered adjacent to the apex of a tooth and the bone is porous enough for the solution to infiltrate and act on local nerve endings (submucosal)
60
Describe block/regional anaesthesia
The technique used when the cortical plate of bone is too thick to allow infiltration anaesthesia, requires deposition of LA at a site where the nerve is unprotected by bone
61
Name 2 topical anaesthetic and their concs
Benzocaine (gel) 20% | Lignocaine (spray/ointment) 5-10%
62
How are topical anaesthetics usually used
Prior to needle anaesthesia
63
What must you be careful of when using topical anaesthestics
Due to higher concentrations - be aware that excessive doses may lead to toxicity especially in children
64
What volume of LA is usually needed for infiltration, block, long buccal and palatal infiltrations for anaesthesia
Infiltration = 0.5-1ml (about 1/3 of cartridge) Block = 2ml Long buccal inf. = 0.2-0.5ml Palatal = 0.2-0.5ml
65
What is the onset and duration of action of an LA dependent on
- pH of tissue - pKa of drug - Time of diffusion from needle tip to nerve - Time of diffusion away from nerve - Nerve morphology - Conc of drug - Lipid solubility of drug
66
What is the duration of action for lidocaine with vasoconstrictor
Pulpal tissues = 60 mins | Soft tissues = 3-5 hours
67
What is the duration of action for prilocaine with vasoconstrictor
Pulpal tissues = 60 mins | Soft tissues = 2-3 hours
68
What is the safe Max dose of Lidocaine
4.4mg/kg
69
How many mg of lidocaine in average cartridge
44mg
70
What is the max dose of Lidocaine for a patient
300 mg
71
What is the safe Max dose of prilocaine with vasoconstrictor
10 mg/kg body weight
72
How many mg of prilocaine in average cartridge
66mg
73
What is the max dose of Lidocaine with vasoconstrictor for a patient
600 mg
74
How many cartridges is the most usually ever administered
2-3
75
What are some ideal properties for LAs
- Should not irritate tissues applied to - Not cause permanent change to nerve structure - Systemic toxicity should be low - Time of onset should be short as possible - Duration long enough to do operation without extended recovery time - free from allergic reactions
76
What is the first sensation to be blocked by LAs
Pain and then things like touch
77
What is the rationale for adding adrenaline to LAs
- Reduces LA systemic absorption - Increased LA conc near nerve fibres - Helps makes bloodless operation filed
78
Why is it important to know between amides and esters
``` Esters = plasma metabolism Amides = liver and kidney metabolism so may harm patients with hepatic issues ```
79
How does the presence of inflammation affects LAs
- Recues effectiveness of LAs - Inflammation and increased blood supply causes LA to be removed more quickly - Creates more acidic environment - LAs are weak bases

Local Anaesthetics (4 decks)

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