Local Anesthetics Flashcards
Esters
- cause more hypersensitivity reactions
- only 1 letter “i”
Ester durations and potency
Short: Procaine (1)
Long: Tetracaine (16)
Topical/Surface: Benzocaine, cocaine (2)
Amides
-2 letter “i”s
Amides duration and potency
medium: lidocaine (4), mepivacaine (2)
Long: bupivacaine (16), ropivacaine (16)
Esters: Onset and duration
- Procaine:
onset: 2-5min
duration: 25 min to 1 hour - Tetracaine
onset: <15 min
duration: 2-3 hours
Amides: onset and duration
- Mepivacaine
onset: 3-5 min
duration: ~1hr - Bupivacaine
onset: 5 min
duration: 2-4 hrs - Lidocaine
onset: <2min
duration: 30min - 1hr - Ropivacaine
onset: 10-30min
duration: ~30min
Local anesthesia MOA
block voltage-dependent sodium channels of excitable membrane from sending sensory info to the CNS
Which form of local anesthetic is better/faster at crossing the lipid membrane to reach the cytoplasm receptor site?
Non-ionized form
Which form of local anesthetic is the more effective blocking entity once inside the axon?
Ionized form
What effect does sodim bicarbonate have when added to a local anesthetic?
- Accelerates the onset of action
2. Decreases burning sensation
What effect does adding epinephrine (alpha agonist sympathomimetic vasoconstrictor) to a local anesthetic?
prolongs duration
long acting don’t need this - bupivicaine, ropivicaine, tetracaine and neither do topical local anesthetics
What is the difference in esters and amides when it comes to metabolism?
Esters - metabolized in the blood by plasma cholinesterases (very rapid)
Amides -metabolized by liver (so, higher risk of liver toxicity with liver dysfunction)
What type of fiber would be most easily blocked?
a small myelinated fiber
What type of fiber would be most difficult to block?
a large unmyelinated fiber
Which type of fiber is hardest to block?
Type A - Alpha (proprioception, motor)
Which type of fiber is easiest to block?
Types B, C and Type A - delta (pain, temperature)
Which would be blocked first a medium myelinated fiber or a small unmyelinated fiber?
the myelinated fiber
A-alpha fiber
- muscle proprioception
- Largest fiber type
- myelinated
A-beta fiber
- Second largest fiber
- Touch
- myelinated
A-delta fiber
- 3rd largest fiber
- pain and temperature
- myelinated
C-nerve fiber
- Not myelinated
- pain, temperature, itch
- Small fiber
Sequence of nerves to be blocked
- Sympathetic
- Temperature
- Pain
- Light touch
- Motor
Epidural block
-local anesthetic extradurally
Caudal block
-epidural block in the caudal canal via the sacral hiatus
