local anesthesia Flashcards
What is local anaesthesia (local analgesia)?
local and temporary (reversible) state of loss of pain sensation in a localised area of the body without loss of consciousness
Method of producing local anaesthesia?
by using local anaesthetic
Are local anaesthetics safe and effective?
yes and they are most effective for the management of peri-operative and post-operative pain in dentistry
What are the substances used for local anaesthesia?
Cocaine
What are other derivatives for cocaine?
Procaine (ester type) and Lidocaine (amide type)
What are other derivatives of Procaine?
Tetracaine and Chloroprocaine (ester type)
What are other derivates of Lidocaine?
Bupivacaine, Mepivacaine, Articaine and Prilocaine
Bupivacaine is can be either Ropivacaine or Levobupivacaine
What is the first local anaesthesia to be made?
Cocaine
What are long-acting local anaesthesia?
Ropivacaine and Levobupivacaine
Articaine breakdown?
90% by pseudo-cholinesterase enzymes in blood plasma
10% in liver
What local anaesthesia should be used if a patient has allergy from amide AND ester types?
general anaesthesia
Which is the most commonly used local anaesthesia?
Articaine
Which is the most known local anaesthesia?
Lidocaine
How does local anaesthesia cause local analgesia
by preventing depolarisation of nerve as it prevents Na+ influx by blocking Na+ channels (local anaesthesia are Na+ channel blockers). Therefore, it temporarily interrupts and blocks conduction of nerve impulses
Local anaesthesia are …………. compounds?
synthetic compounds
Local anaesthesia have chemical structure almost similar to cocaine but differ in…
- local anaesthesia don’t have abuse potentials (addiction)
- local anaesthesia are vasodilators while cocaine is a vasoconstrictor
- local anaesthesia are synthetic compounds but cocaine is natural
What is the chemical structure of local anaesthesia?
tertiary amines
in each ammonia molecule (NH3) the 3 hydrogen molecules are replaced by radicles to form local anaesthesia (NR3) and the three radicals can be similar or dissimilar in chemical structure
How are local anaesthesia prepared?
in carpule in the form of hydrochloride salt of tertiary amines
lidocaine + hydrochloric acid –> lidocaine hydrochloride
Is local anaesthesia soluble in water?
No, it is insoluble in water but its hydrochloride salts are soluble in water
What is another name for carpule (ampule)?
cartridge
Is there only ionised local anaesthesia in anaesthetic carpules?
No, there is ionised (water soluble) and non-ionised (lipid soluble) forms in anaesthetic carpules
What is the importance of ionised form of local anaesthetics?
- water soluble
- essential for diffusion of local anaesthetics through tissue toward the nerve
- essential for blocking the Na+ gated channels at receptor sites (from inside)
What are the chemical groups that local anaesthesia consists of?
- hydrophilic group (amino group)
- lipophilic group (aromatic group “benzoic”)
- intermediate linkage (ester or amide linkage)
What is the importance of the lipophilic group?
- essential for lipophilic properties
- essential for penetration of local anaesthetics to phospholipid bilayer of nerve cell membranes
What is the importance of hydrophilic group?
- essential for hydrophilic properties
- essential for diffusion of local anaesthetics through interstitial tissue fluid towards nerve to be anaesthetised
- essential for preparation of water soluble salts when local anaesthetics combined with strong acid during preparation
What is the difference between ester and amide types of local anaesthesia?
intermediate linkage
What is local anaesthesia classified into according to intermediate linkage?
ester type of local anaesthesia
amide type of local anaesthesia
What is the biotransformation of ester type?
metabolised in plasma by pseudo cholinesterase enzyme and for some extent in liver by liver esterase enzyme
What is the biotransformation of amide type?
metabolism in liver by liver microsomal enzymes
What are the contraindications of using ester type?
- patients with deficiency of paeudo cholinesterase enzyme (1:2500)
- patients with history of prolonged life-threatening apnea (respiratory arrest) when using succinylcholine (short-acting muscle relaxant) during induction phase of general anaesthesia
- patients allergic to ester type
What are the contraindications to using amide type?
- patients allergic to amide type
- patients with liver failure or impaired liver function
What is the incidence of allergy of ester type?
rare (allergic reactions are usually related to metabolic product of ester type known as PABA - para amino benzoic acid)
What is the incidence of allergy of amide type?
nearly absent
What is the duration of action of ester type?
short
What is the duration of action of amide type?
longer than esters
Why is the duration of action of ester shorter than amide type?
ester links are more prone to hydrolysis than amide links
What is the cross allergy of ester type?
patients allergic to one member of ester type is usually allergic to any other members of the same group
What is the cross allergy of amide type?
patients allergic to one member of amide type is usually allergic to any other member of the same group
What are some examples of ester type?
- procaine
- chloroprocaine
- tetracaine
- benzocaine
- unacaine
- intracaine
What are some examples of amide type?
- lidocaine (xylocaine or lignocaine)
- articaine
- mepivacaine (mepicaine)
- prilocaine ( lcitanest)
- bupicacaine
- etidocaine
- ropivacaine
What are the two chemical forms of local anaesthesia?
- topical (surface) anaesthetics
- injectible local anaesthetics (loval anaesthetic carpules)
What are topical anaesthetics?
- insoluble in water
- not suitable for injection into tissues as they have only lipophilic group and have no hydrophilic group
- have many forms: gels, cream, ointment or spray
What is injectable local anaesthesia?
- soluble in water
- suitable for injection into the tissue as they have both hydrophilic and lipophilic groups
What are local anaesthesia classified into according to presence of VC
- with VC
- without VC (plain anaesthesia)
What does a carpule of local anaesthesia without VC contain?
- local anaesthetic agent
- saline (0.9% NaCl)
What does a carpule of local anaesthesia contain with a vasocontrictor?
- local anaesthetic agent
- saline (0.9% NaCl)
- vasoconstrictor agent (vasopressor)
- antioxidant (as preservation for vasoconstrictor agent)
Does local anaesthetic catridges contain preservative and bacteriostatic agent (methyl paraben)?
No, but multi-dose vials of local anaesthetic contains methyl paraben
What is the main component and what is the purpose of other additional components of local anaesthetic cartridge?
- local anaesthesia is the main component
- other components are added to potentiate the action of local anaesthetic afent and prevent deterioration of local anaesthetic solution
What are the ideal properties of LA?
- rapid onset (induction period)
- adequate duration of action
- selection action on sensroy nerves
- reversible action on nerve tissue
- compatible with salts as saline to form isotonic solution
- have vasoconstrictor action or compatible with vasoconstrictors can be added by manufactures
- soluble in water
- hydrolysed according to type of LA
- no systemic complications (side effects) like toxicity, allergy and idiosyncrasy
- no local complications like burning sensation
- does not interfere with healing of injected tissues
- potent enough to avoid use of toxic concentration or overdose
- sterelised without deterioration
- not expensive
- long shelf life (high stability)
What happens when sodium bicarbonate reacts with local anaesthesia?
it causes slight tissue alkalinity (7.2-7.4)
What does the free base (non-ionised) of local anaesthesia do?
it will be released and will affect nerve tissue to be anaesthetised
What is succinylcholine?
- short acting muscle relaxant that is used during induction of general anaesthesia
- produces respiratory arrest for a period of 3 minutes during induction of general anaesthesia
- in normal pseudocholinesterase enzyme patient, they hydrolyse succinylcholine with rapid recovery from respiratory apnea to normal respiration
- patients with atypical pseudo-cholinesterase enzyme are unable to hydrolyse succinylcholine resulting in prolonged life-threatening respiratory apnea under general anaesthesia (respiratory arrest)
How is local anaesthesia excreted?
- both types of local anaesthetics and their metabolites are excreted through the kidneys
What happens in a patient suffers from kidney dysfunction?
the patient may be unable to eliminate local anaesthetics and their metabolites from metabolite with risk of toxicity
what are contraindications of local anaesthetics regarding its excretion?
-significant renal disease (ASA class 4 or 5) like chronic glomerulonephritis or pyelonephritis
- patients undergoing renal dialysis
What is the elimination half life of local anaesthetic?
time required to decrease blood or plasma level or concentration of local anaesthetic by 50% by its elimination through excretory organs (kidney)
What is the half life elimination known for local anaesthesia?
6 half lives where the blood level or concentration of local anaesthetic in blood will be decreased by 98.25% at 6 half lives
Which type of anaesthetic has a high elimination of half life?
elimination of half lives of amide is more than that of esters
What are the drugs to avoid and alternative drug to a patient suffering from local anaesthetic allergy?
-drugs to avoid: all local anaesthetics in the same chemical group
-alternative drugs: any local anaesthetics in different chemical class provided that there is no allergy to there alternative drugs
What are the drugs to avoid and alternative drug to a patient suffering from bisulfite allergy?
bisulfite is preservative anti-oxidant to VC of local anaesthetic carpules
-drugs to avoid: all local anaesthetic carpules containing VC
-alternative drug: any local anaesthetics without VC (plain anaesthesia)
What are the drugs to avoid and alternative drug to a patient suffering from significant kidney dysfunction?
-drugs to avoid: esters or amides of local anaesthetics
-alternative drugs: amides or esters of local anaesthetics but judiciously
What are the drugs to avoid and alternative drug to a patient suffering from significant CVD?
-drugs to avoid: high concentrations of VC
-alternative drugs: local anaesthetics with epinephrine 1:100,000 or 1:200,000 or plain anaesthesia
What are the drugs to avoid and alternative drug to a patient suffering from clinical hyperthyroidism?
-drugs to avoid: all local anaesthetic carpules containing VC especially epinephrine
-alternative drugs: plain anaesthesia
What are absolute medical contraindications?
- local anaesthetic allergy
- bisulfite allergy
- atypical or deficient plasma pseudocholinesterase
- clinical hyperthyroidism
What are relative medical contraindications?
- significant liver dysfunction
- significant kidney dysfunction
- significant CVD
What are vasopressors?
sympathomimetics mimic the effects of sympathetic nervous system on the human body
Sympathomimetics are classified according to presence of catechol nucleus into…
-catecholamines
non-catecholamines
What does sympathomimetics act on?
Adrenergic receptors (alpha and beta)
What are the advantages of adding VC in local anaesthetic carpules?
it produces VC of BV resulting in…
- slow rate of absorption of LA which prolongs its duration of action, decreases its toxicity and decreases the volume of LA solution needed during surgery
- decreases blood flow to injected area resulting in local tissue ischaemia and increases local anaesthesia effect
- reduce bleeding during surgical procedure (produce haemostasis)
- stimulates the heart which counteracts the depressant effect of LA agent on the heart
What are the disadvantages of using VC in local anaesthetic carpules?
relative contraindications to VC
- uncontrolled diabetics because VC counteract the action of insulin
- significant hypertension because VC results in increased BP
- significant CVD because it stimulates the heart (tachycardia)
- pregnancy because VC leads to uterine contraction followed by abortion (felypressin has a potential oxytocic actions and induce abortion in pregnant females)
- patients receiving MAO inhibitors, tricyclic, antidepressants and phenothiazines to avoid development of dysrhythmias with epinephrine administration
absolute contraindications to VC
- clinical hyperthyroidism or toxic goiter as using VC may lead to thyroid crisis and may end with sudden death
- bisulfite allergy as it is added to carpules containing VC with LA acting as antioxidant and bisulfite may cause allergy to some patients (allergy may lead to life-threatening anaphylactic shock)
What are some common types of VC?
- epinephrine
- nor-epinephrine
- levonordefrin
- phenylephrine
- felypressin (octapressin)
Do we need preservative for LA agent?
No
Do we need preservative for VC agent?
Yes, an antioxidant (sodium bisulfite)
What is the vehicle (solution) needed to make LA solution isotonic?
saline solution (0.9%NaCl)
Does carpule have lidocaine only?
No
What is sodium bisulfite?
added to local anaesthetic carpules to prevent oxidation of VC agent (therefore acting as antioxidant to VC agent)
What is methylparaben?
- added to LA carpules to preserve LA agent and to prolong its shelf life
- may cause allergy to patients (especially patients with para-group allergy such as sulfa and procaine)
- nowadays, no preservative is added to LA carpules to avoid this type of allergy
What is plain anaesthesia?
carpule with LA agent and saline only (no VC agent)
How is ester type hydrolysed?
by liver enzymes
If the liver isn’t working (liver disease), do we give the patient ester or amide type?
amide
If a patient has liver disease, is articaine a good option?
no
