Pharmacology and Equipment Flashcards
Define anaesthesia
- Loss of sensation to circumscribed are of body by depression of excitation in nerve endings or an inhibition of conduction process in peripheral nerves
- Includes all sensation
Define analgesia
Loss of only pain sensation
Define local anaesthetic
Drug which reversibly prevents transmission of nerve impulse in region to which it is applied, without affecting consciousness
How do LAs work?
Blocking conduction of action potentials along nerve fibres
Describe the 3 parts to the structure of a LA
- A lipophilic aromatic portion
- An intermediate chaine (Amide or Ester)
- A hydrophilic amine portion
What does the metabolism of an LA depend on?
Whether it is an amide of an ester
Give some examples of amide LAs (5)
- Lidocaine
- Prilocaine
- Articaine
- Mepivacaine
- Bupivacaine
How are amide LAs metabolised?
Metabolised mainly by the liver
How are ester LAs metabolised?
Metabolised by pseudocholinesterase to PABA and excreted in urine
What 2 factors affect proportion of charged to uncharged molecules following a LA injection?
- pH of tissues
- Dissociation constant (pKa) of the LA agent
Comment on the link between infection and LA
Infection within the tissue can reduce pH and reduce effectiveness of LA
What are the components of a LA? (5)
- LA agent
- Vasoconstrictor
- Reducing agents
- Isotonic solution
- Preservatives
What is the role of reducing agents in LAs?
Stabilises vasoconstrictor by preventing oxidation
What agents can act as vasoconstrictors in LA? (2)
- Adrenalin
- Felypressin
What are some advantages of adrenaline as a vasoconstrictor? (3)
- Less bleeding at site
- Less systemic absorption, consequently lower toxicity
- Prolonged duration of action
What are some disadvantages of adrenaline as a vasoconstrictor? (2)
- Potential to cause cardiac arrhythmia
- Caution needed in those with Heart Disease
Explain the relationship between heat/light and LA storage
Exposure to excess heat or light causes breakdown of adrenaline so LA cartridges should be stored carefully
When can felypressin be considered instead of adrenaline as a vasoconstrictor? (2)
- Patient has heart or blood pressure problems
- Patient has tendency to fainting
What is a disadvantage of felypressin?
Causes uterine contraction and initiates labour
very unlikely in such a small dose
What percentage lidocaine is used in practice?
2% (20mg/ml)
How much adrenaline is in lidocaine?
1:80000
What is the anaesthetic times provided by Lidocaine?
Pulp tissue?
Soft tissue?
- 45-60 mins pulp tissue
- 3-5 hours soft tissue
What percentage prilocaine is used in practice?
3% (30mg/ml)
What percentage articaine is used in practice?
What is its half life?
- 4% (40mg/ml)
- 20 mins
