Local anesthetics are ______ blockers
Calcium channl
How do local anesthetics work?
Prevent depolarization, blocks conduction of nerve impulses to inhibit pain
What nerve fibers are affected by local anesthesia, and what effect does that have?
A-delta & C fibers first > Provides analgesia
A-beta & A-alpha second > paralysis
Order of sensation disappearance with local anesthesia
Pain > Cold > Warmth > Touch > Joint pain > deep pressure > motor blockade (paralysis)
What are the 3 basic units of local anesthetics?
- Aromatic group (benzene ring) > Lipophilic
- Intermediate chain - Ester-linked or Amide-linked
- Tertiary Amine (amino tail) > Hydrophillic
How does lipid solubility affect local anesthetic efficacy?
- Higher solubility = Higher potency
2. Smaller lipophilic modules = faster onset of action
Ester-linked local aesthetics
Procaine, tetracaine, proparacane
Amine-linked local anesthetics
Lidocaine, bupivacaine, ropivacaine, mepivacaine
How does pKa influence local anesthetics?
More basic»_space; More rapid onset, greater potency
How does addition of vasoconstrictors (epinephrine, etc.) influence local anesthetics?
- Delays absorption & onset
- Prolongs duration
- May increase intensity of blockade
How does addition of bicarbonate influence local anesthetics?
Increases pKa (more basic)»_space; more rapid onset
List common adjuvants to local anesthesia
Opioids
Vasoconstrictors
Alpha-2 Agonists
How are opioids commonly used with local anesthetics?
- Enhance epidural anesthesia
- Improve analgesia without affecting motor blockade
- With lidocaine +/- ketamine for CRIs
How do alpha-2 agonists affect local anesthetics?
- Enhance epidural analgesia
- Enhance peripheral nerve blocks
- Increase duration
How does bupivacaine compare to lidocaine?
- Slower onset
- Longer duration
- May be more cardiotoxic
Tuohy needle
Curved, blunt tip needle used for epidurals.
Less likely to penetrate perineurium
Better tactile sensation
Spinal needle
Very sharp with short stylet. Used for spinal injections & CSF colection
Insulated nerve block needle
- Used with peripheral nerve stimulator
- Directs current to tip
- Helps identify target nerves before injection
How is ultrasound used for regional anesthesia?
- Used alone or with peripheral nerve stimulator
2. Allows for visualization of nerve for more precise placement
Peripheral Nerve Stimulator
- Used with nerve block needles
- As needle approaches target, less current is needed to stimulate response
- When response is elicit at 0.2 - 0.6 mA, okay to inject
When is the best time to use an incision block?
Pre-op; but sometimesat closure
Mepivacaine & Ropivacaine for IA block
Less chondrotoxic
What opioid can be used for IA block?
Preservative-free morphine; preservatives may play a role in chondrotoxicity
Why should steroids be used with caution for IA injection?
Can be chondrotoxic depending on dose & duration
