Local Anesthetics Flashcards
1
Q
Local anesthesia general definition/mechanism
A
- = loss of sensation in circumscribed area of the body
- results from block of AP initiation or propogation @ nerves
- block voltage-gated Na+ @ peripheral nerves
2
Q
Chemical structure of local anesthetics
A
- lipophilic aromatic portion
- intermediate alkyl chain
- ester vs. amide group
- hyrdophilic amine portion
- naming
- “-caine”
- one i = intermediate ester (cocaine)
- two i’s = intermediate amine (lidocaine)
3
Q
Effect of pH on local anesthetic action
A
- local anesthetics = weak base
- pKa ~7.7 - 9.0
- thus, local anesthetics are partly ionized @ pH 7.4 ==> more drug molecules are charged vs. neutral
- both forms are needed for proper action
- changes in tissue pH ==> ratio of neutral/charged ==> alter effectiveness of local anesthetics
4
Q
MOA of local anesthetics
A
- binding site = @ wide region of water-filled pore of Na+
- route of access = intracellular pore entrance
- binding site accessed when channel is open
- cross plasma membrane when in neutral form
- lipophillic portion ==> membrane solubility
- charged (cationic) form of binds with more affinity w/in Na+ channel pore
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5
Q
Characteristics of use-dependent block
A
- more the channel is open, thre greather degree of local anesthetic binding and block
6
Q
Physiocochemical properties ==> potency, onset of drug action
A
- lipid solubility ==> potency
- pKa determines speed of drug to target ==> onset of action
- lipid solubility correlates w/pKa and onset
- protein binding ==> longer duration of action
7
Q
Procaine: potency, onset, duration, pKa, lipid solubility, protein binding
A
- low potency
- slow onset
- short duration
- high pKa
- low lipid solubility
- low protein binding
8
Q
Lidocaine: potency, onset, duration, pKa, lipid solubility, protein binding
A
- medium potency
- intermediate onset
- medium duration
9
Q
Etidocaine: potency, onset, duration, pKa, lipid solubility, protein binding
A
- high potency
- fast onset
- long duration
- low pKa (7.7)
- high lipid solubility
- high protein binding
10
Q
Methods of local anesthetic application
A
- topical anesthesia
- infiltration anesthesia
- nerve block anesthesia
- IV regional anesthesia
- Spinal anesthesia
- epidural anesthesia
11
Q
Topical anesthesia mechanism/disadvantage
A
- directly onto skin, cornea, mucous membranes of nose, mouth, etc.
- disadvantage: considerable amount can get into circulation ==> toxic effects
12
Q
Infiltration Anesthesia
A
- Injection of local anesthetic into tissue without consideration of the location of cutaneous nerves.
- advantage = very superficial anesthesia but function of underlying organs is unaffected
- Disadvantage is that large doses are needed and there may be significant absorption into the circulation.
13
Q
Nerve block anesthesia
A
- injection of a high concentration of local anesthetic near a peripheral nerve or nerve plexus
- advantage of this technique = larger body regions can be anesthetized as compared to infiltration anesthesia.
14
Q
IV regional anesthesia
A
- blood is squeezed out of a limb or part of a limb using a very tight elastic bandage, and a tourniquet is placed proximally.
- Local anesthetic is then injected via a catheter, and limb anesthesia develops within 5-10 minutes.
- Tourniquet pain and ischemic injury limit the use of this method to a maximum duration of 2 hours.
15
Q
Spinal anesthesia technique + advantages/disadvantages
A
- injection of a local anesthetic into the cerebrospinal fluid bathing the lumbar section of the spinal cord.
- advantage = large body regions can be anesthetized while maintaining a low plasma level of drug
- disadvantage = useful for surgical procedures of the lower abdomen, perineum and lower extremities.
