local anaesthesia armamentarium

Question 1

anaesthesia

Answer 1

loss of sensation

Question 2

analgesia

Answer 2

selective loss of pain sensation

Question 3

how do local anaesthestics work?

Answer 3

block the conduction of nerve impulses in the peripheral nerves or spinal chord

Question 4

mode of action of general anaesthetics

Answer 4

block corticol neuronal activity underlying consciousness and all sensation

Question 5

historical background

Answer 5

1860
Albert Nieman in Germany
psychoactive alkaloid, cocaine

Question 6

definition of local anaesthetics

Answer 6

Loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.
Loss of sensation without inducing loss of consciousness.

Question 7

classifications of LA

Answer 7

esters
amides

Question 8

esters

Answer 8

procaine
cocaine
tetracaine

Question 9

why are they not used anymore

Answer 9

addictive

Question 10

amides

Answer 10

Bupivacaine ( Marcaine) general, long lasting
Mepivacaine (Carbocaine, Scandonest), long lasting, severe side effects
Prilocaine (Citanest) mimics birth hornmone, 7/8/9 month pregnancy
Lidocaine (Lignocaine, Xylocaine)
Articaine (Septocaine)

Question 11

ideal properties of LA

Answer 11

I = should not be irritating to tissue
N = should not cause any permanent alteration of nerve structure
S = systemic toxicity should be low
T = time of onset of anaesthesia should be short
E = should be effective regardless of it being injected or applied topically
D = Duration of action should be long enough to complete procedure
Have the potency to give complete anaesthesia without the use of harmful concentration solutions
Should not produce an allergic reaction
Should be free in solution and undergo biotransformation in the body (should be able to be broken down and excreted from the body)
Should be sterile or capable of being sterilized by heat without deterioration

Question 12

chemical structure of LA

Answer 12

the lipophilic aromatic ring- improves lipid solubility
whereas the tertiary amine end is relatively hydrophilic, making the molecule water-soluble
Intermediate hydrocarbon linkage – determines if the molecule is an ester or an amide

Question 13

mechanism of action of local anaesthetics

Answer 13

Local anaesthetics block voltage-gated sodium channels
Nocicepters on the surface

Question 14

conduction of nerve impulses

Answer 14

Nerve impulses begin in a dendrite, move toward the cell body, and then move down the axon.
depolarization → hyperpolarization → repolarization → resting potential
Local anesthetics prevent nerve impulse transmission by blocking voltage gated sodium channels without causing central nervous system depression or altered mental status

Question 15

composition of local anaesthetics

Answer 15

local anaesthetic agent
vasoconstrictors (epinephrine)
Vasoconstrictor preservative (Sodium bisulfite,/ metabilsulfite)
Sodium Hydroxide (Buffer adjusts pH)
Sodium Chloride (Buffer creates in injectable solution)

Question 16

what do you need to calculate maximum dosage?

Answer 16

1. pt’s weight
2. drug concentration
3. amount of LA in cartridge
4. maximum dose of anaesthetic based upon milligrams per kg

Question 17

pharmacodynamics

Answer 17

physiological effect to the body and mechanisms of drug action

Question 18

pharmacokinetics

Answer 18

body’s handling of the drug (absorption, distribution, metabolism and excretion; onset of action; duration; biotransformation)

Question 19

pharmacokinetics (esters)

Answer 19

amino esters metabolised primarily by plasma esterase
PABA metabolite - causes hypersensitivity reactions (procaine)

Question 20

pharmacokinetics (amides)

Answer 20

amino amides are metabolized primarily by hepatic cytochrome P450–linked enzymes (amidases)
Long half-life
No PABA in amides.
Metabisulphite or preservative agent, rubber stopper – allergic reaction

Question 21

Indications of LA

Answer 21

used to anesthetize a particular part or region of the body,
are given to patients undergoing surgery
during labour and delivery
for diagnostic procedures such as gastrointestinal endoscopy.

Question 22

failure of LA (pharmakinetic factors)

Answer 22

(1) increased local blood flow leading to accelerated removal of drug from perineural injection compartments;
(2) local tissue acidosis leading to a greater proportion of the drug in the hydrochloride form, which diffuses more poorly across biologic membranes (abcesses, must be drained or double dose); and
(3) local tissue oedema, which increases diffusion distances for drug into nerves and promotes further dilution.

Question 23

failure of LA (pharmadynamic factors)

Answer 23

the effects of inflammation on both peripheral sensitization of nerves and central sensitization.
Infected mandibular tooth, inferior alveolar nerve block (performed proximally at a site presumably remote from the infected area) also has an unexpectedly frequent failure rate. (DS Moodley)

Question 24

cocaine

Answer 24

first local anaesthetic to be discovered.
both local anaesthetic and CNS stimulant properties
significant vasoconstriction as a result of itssympathomimetic effect.(sympathetic nervous system, fight or flight response)
the nose, where its vasoconstrictive action highly needed.

Question 25

lidocaine (lignocaine)

Answer 25

Available in sol. 1,5%,2%,4% and 10% Topical and parenteral use Most widely used anaesthetic Cheap, autoclavable T1/2 = 1,5hrs Metabolised in the liver Excreted in urine antiarrhythmic and local anaesthetic (tachychardia and barychardia, adrenaline increases heart rate) blockade affects all nerve fibres sequence autonomic, sensory and motor  Loss of nerve function clinically is as follows: pain, temperature, touch, proprioception, skeletal muscle

Question 26

mepivacaine

Answer 26

Carbocaine 3% provide profound local anaesthesia without being formulated with a vasoconstrictor  shorter duration

Question 27

prilocaine

Answer 27

Widely available, cheap Short half-life, quick onset can provide excellent oral anaesthesia with or without a vasoconstrictor. provides a slightly shorter duration of surgical anaesthesia.

Question 28

bupivacaine

Answer 28

Slow T1/5 - 5hrs Expensive (4 x lignocaine) For obstetric anaesthesia Treatment of postsurgical pain. causes cardiac depression more frequently than do many other local anaesthetics.

Question 29

articaine

Answer 29

newest local anaesthetic arsenal approved by (FDA) in April 2000. Amide class of local anaesthetics, available in 4% strength with 1:100,000 or 1:200,000 epinephrine. Unique among the amide local anaesthetics The thiophene ring increases its liposolubility Additional ester group- biotransformation in the plasma as well as in the liver potency 1.5 times that of lidocaine faster onset increased success rate Dual metabolism

Question 30

local anaesthetics and adrenaline

Answer 30

Reduces the blood flow Long anesthetic time Reduce chances of toxicity Blue ring –adrenaline Green ring – plain

Question 31

metabolic effects of adrenalin

Answer 31

increases blood glucose levels Decreases plasma potassium level arrythmias (increase heart rate and blood pressure)

Question 32

unwanted effects of local anaethesia

Answer 32

Caused by local anaesthetic agent Intravenous injections (aspirate before injecting, toxicity if injected into a vessel, if you see blood – withdraw) Overdose CNS – cerebral stimulation Depression the medulla (resp & vasomotor centres CVS- direct action on the heart Action on the vascular bed

Question 33

psychomotor effects

Answer 33

Collapse at the sight of the needle Hysterical behavior Need sedation

Question 34

complications (CNS)

Answer 34

facial nerve paralysis Paresthesia (partial numbness) Ocular-diplopia, ptosis, mydriasis, miosis, enophthalmos, and even permanent blindness. Horner’s mydriasis, ptosis, and diplopia

Question 35

complications (CVS)

Answer 35

hypotension and cardiac depression. anaesthetics are vasodilators, and they also block vasoconstriction induced by the sympathetic nervous system. Most local anaesthetics have antiarrhythmic activity,  can cause tachyarrhythmia characterized by a wide QRS complex. (bradychardia – increase heart rate) (uncontrolled hypertension!)

Question 36

allergic reaction

Answer 36

allergies to amides is less than 1%. methylparaben – increase shelf life – 1980 removed esters - para-aminobenzoic acid-component (PABA)

Question 37

treatment of allergic reaction

Answer 37

Treatment of allergic reactions depends on the severity of the reaction. Mild form- oral or intramuscular antihistamines, such as diphenhydramine, 25 to 50 mg. Serious signs or symptoms develop, basic life support, intramuscular or subcutaneous epinephrine 0.3 to 0.5 mg, and Emergency transportation to the local hospital

Question 38

toxicity due to LA

Answer 38

starts with excitatory phase Manifest as tremors, muscle twitching, shivering, and tonic-clonic convulsions. This phase is followed by generalized central nervous system depression and possible life-threatening respiratory depression. Cardiac excitability and cardiac conduction decrease. The manifestations include ectopic rhythms, bradycardia and ensuing peripheral vasodilation, and significant hypotension.

Question 39

treatment of toxicity

Answer 39

Treatment should address respiratory depression and convulsions. Vital signs should be monitored basic life support administered, the emergency medical support Intravenous diazepam or midazolam

Question 40

emergency drugs and care

Answer 40

1. Routine vital sign monitoring equipment 2. An oxygen tank or wall oxygen outlet 3. Airway equipment, including a bag-mask circuit for delivery of positive-pressure ventilation 4. Drugs to terminate convulsions, should they occur, preferably midazolam, lorazepam, diazepam, or thiopental.