LA Flashcards

• When may a dental hygienist/therapist administer LA?

  • PMPR
  • RSD
  • restoring primary and secondary dentition
  • extraction of deciduous teeth
• What is the responsibility of the DHT when administering LA?

  1) review medical history, obtain informed consent from the patient.

  2) third person present that is competent in Cardio-pulmonary resuscitation
• What is informed consent?

  • clinician must explain to patient the procedure terms which the patient is able to understand
  • the patient must give their consent to this procedure
  • children may consent for themselves providing that they are Gillick Competent
  • Verbal consent is acceptable for LA.
• What cranial nerve is the trigeminal nerve?

  5th Cranial nerve - large sensory root & smaller motor root
• What are the three divisions of the trigeminal nerve?

  1st Division Ophthalmic

  2nd Division Maxillary - sensory only

  3rd Division Mandibular
• What is the mode of action of local anaesthetic agents?

  • Blocking nerve conduction
  • action is the same for all types of anaesthetic solutions
  • L.A. solution prevents the normal passage of ions through the nerve membrane
  • by binding reversibly to specific receptors in the sodium channels.
• What happens when LA is introduced around a nerve fibre?

  The nerve membrane gets stabilised, thereby not permitting any ion passage through the membrane. Thus the action potential cannot be generated and no conduction of impulses can take place

  
• Why does LA need to be soluble in both water and fat?

  The solution needs to be able to diffuse inside the nerve membrane in order to act on the sodium channels and prevent them opening
• What two factors govern the proportion of charged to uncharged molecules following injection?

  · The pH of the region· The dissociation constant of the local anaesthetic molecule (pKa)
• What is Lidocaine so effective?

  Has a lower pKa than older anaesthetics

  The lower the pKa the more uncharged molecules exist
• What fibres of the nerves does LA work on?

  • A delta fibres are responsible for transmitting pain.
  • LA agent works on the A fibres at the nodes of Ranvier.
  • Type C fibres are postganglionic fibres of the autonomic nervous system, unmyelinated and the local anaesthetic solution acts on the entire length.
  • C fibres are slow in response and responsible for transmitting dull, throbbing pain.
  • C fibres can shut off noxious stimuli from A fibres.

  
• How is pulp anaesthesia obtained?

  diffusion of the solution into the bone tissue - concentration level required is high
• What is Analgesia?

  loss of pain sensation unaccompanied by loss of other forms of sensibility
• What is Anaesthesia?

  Loss of all forms of sensation including pain, touch, temperature and pressure perception and may be accompanied by impairment of motor function.
• The larger the gauge number....

  the narrower the needle 27 gauge - 0.4 mm diameter 35 mm (long)30 gauge - 0.3 mm diameter 20 mm (short)
• What two parts do a needle have?

  Point & Butt-end, separated by the hub

  
• What do LA cartridges consist of?

  - a cylinder - a plunger - a cap
• What must the user check when using LA cartridges?

  · Content, Concentration of anaesthetic and vasoconstrictor, Expiry date, Batch number, Damage e.g. cracked, cloudy, large bubble.
• What is the commonest volume of cartridge?

  2.2ml (Mepivacaine is 1.8ml)
• What type of syringes are currently used in the Dental Hospital?

  needle and barrel pre-fixed together.The Septodont Safety plus syringe
• What is aspiration?

  technique that allows material at the tip of the syringe to be drawn into the cartridge before and during injection. Mandatory to use an aspiration technique, aids in determining whether or not the tip of the needle is in a blood vessel. Intravascular injection has adverse systemic effects and must be avoided.
• How can administering a drug intravascularly be avoided?

  Aspirate twice in 2 planes by turning the bevel of the needle before injecting A negative aspiration does not necessarily mean you are not in a blood vessel because the wall of the blood vessel may have collapsed onto the needle. The pressure of injected liquid may then open up the vessel and the drug is given intravascularly
• What are the advantages of the Septodont safety plus system?

  The needle is pre-attached to the cartridge holder by the manufacturer. A protective sheath is incorporated with the barrel and the syringe which slides over the needle at the end of the injection.
• What does each LA cartridge contain?

  • local anaesthetic agent
  • vasoconstrictor
  • reducing agent
  • preservative
  • fungicide
  • vehicle.
• What are the ideal properties of an LA agent?

  1) Potency & reliability

  2) Reversibility of action within a predictable time

  3) Wide margin of safety from the poisonous side effects

  4)Lack of irritation, isotonic and pH compatible

  5) Rapidity of onset

  6) Duration of effect

  7) Sterility

  8) Adequate shelf life

  9) Penetration of mucous membrane
• What is the therapeutic ratio?

  Lethal Dose (LD50) = Dose which kills 50% of a group ofexperimental animals-------------------------------------------------------------Effective Dose (ED50 = Dose which produces the desired effect in50% of a group of experimental animalsThe higher the value of this ratio, the greater the safety margins
• What has the highest therapeutic ratio?

  Procaine, followed in descending order by mepivacaine, prilocaine, and lidocaine.
• What are the two classes of LA agent

  Esters - Esters are metabolised rapidly in plasma. An example of an ester is the topical agent benzocaine Amides - more complex and slower than that of Esters All the local anaesthetic drugs available in dental cartridges in the U.K. are amides
• What LA agent is generally used in dentistry?

  2% Lidocaine Hydrochloride with the vasoconstrictor of 1 in 80,000 adrenaline
• What are the advantages of vasoconstrictors?

  1. It reduces toxic effects by retarding the absorption of the constituents .2. By confining the anaesthetic agent to a localised area, it increases the depth and duration of anaesthesia .3. It produces a relatively bloodless field of operation for surgical procedures.
• What are the vasoconstrictors in general use?

  1. Adrenaline (epinephrine), a synthetic alkaloid almost identical with the natural secretion of the adrenal medulla. The pH of LA with adrenaline is 3.5 therefore it stings on injection .2.Felypressin (Octapressin), a synthetically produced polypeptide similar to that secreted from the human posterior pituitary gland.
• The lower the concentration of vasoconstrictor......

  the less the depth and duration of anaesthesia Both the depth and duration of anaesthesia may be modified by the amount of vasoconstrictor in the solution. Lidocaine solutions containing adrenaline in concentrations of 1:50,000, 1:80,000 or 1:100,000
• What can Octapressin (vasoconstrictor) cause?

  Arrhythmias, angina and decreased blood glucose in susceptible patients. It is less effective in controlling haemorrhage than adrenaline.
• Why is sodium meta-bisulphite included as a reducing agent to LA solution ?

  Competes for available oxygen, more readily oxidised than adrenaline Vasoconstrictors are unstable in solution and may oxidise especially on prolonged exposure to sunlight. This results in the solution turning brown and this discoloration is an indication that such a solution must be discarded.
• What is an example of a preservative in LA?

  caprylhydro-cuprienotoxin, which is included in Xylotox.
• What is the shelf-life of modern LA solutions?

  2 years
• What is a fungicide used in LA solutions?

  Thymol
• What is Ringer's solution?

  An isotonic solution which minimises discomfort during injection
• What are the components of modified Ringer's Solution?

  Sodium Chloride 8.6 mg Potassium Chloride 300 mg Calcium Chloride 330 mg+ Boiled and purified water to yield 1000 ml
• Who is responsible for the LA agent used?

  The prescribing Dentist However: Always review patient medical history before giving LIA