Local Anesthetics

Question 1

Local anesthetics (6)

* for amides, rest are esters

Answer 1

• 1. Benzocaine
• 2. Bupivacaine *
• 3. Cocaine
• 4. Dibucaine
• 5. Lidocaine *
• 6. Procaine

Question 2

Allergic reactions to what type of local anesthetics is most common due to metabolism of allergy-causing compounds?

How can you tell the type of local anesthetic based on its name?

Answer 2

Ester ( benzocaine, cocaine, procaine, and tetracaine)

*Will only have one ‘i’ in the name; while amides will have at least two ‘i’s

Question 3

Local anesthetics that are amides

Answer 3

2 I’s

1. Lidocaine
2. Bupivacaine

Question 4

Which local anesthetics are more prone to hydrolysis and as a result generally have a shorter duration of action?

Answer 4

-Esters

Question 5

Use of which drugs will reduce systemic absorption of local anesthetics and is useful for those drugs with intermediate or short durations of action (ie., prolongation of action)?

Answer 5

Vasconstrictors (i.e., epinephrine) => helps to prolong action

Question 6

Which type of local anesthetic is widely distributed after IV bolus administration?

Answer 6

Amide-type

Question 7

How does the metabolism of ester-type local anesthetics differ from the amide-type?

Answer 7

1. Ester-type = are metabolized in plasma
2. Amide-type are metabolized in liver and then e_xcreted in urine as charged substances (CYP450)_

Question 8

What is the MOA of local anesthetics?

Where is their receptor site located?

Answer 8

- Block VGNa+ channel currents => stop spread of AP’s.

• Receptor site is at inner vestibule of the sodium channel

Question 9

What structural properties of some local anesthetics cause a faster rate of interaction with the Na+ channel and more potent actions?

Answer 9

Smaller and more lipophilic (Bupivacaine) => more potent and faster rate of AXN

Question 10

How does fiber diameter and degree of myelination affect the action of local anesthetics?

List an example

Answer 10

Preferentially block

1. Small fibers
2. Myelinated nerves (vs. unmyelinated nerves of the same diameter)

* Type A delta (pain/temp fibers) more susceptible to being blocked than larger Type A Alpha fibers (propioception/motor).

*Type B (preganglionic autonomic) fibers are blocked before smaller/unmyelinated C fibers

Question 11

How does firing frequency affect the action of local anesthetics, which are preferntially blocked?

List an example

Answer 11

Higher frequencies of depolarization = blocked first

• i.e., type A delta (pain and temperature) and C (dorsal root/sympathetic) fibers are blocked earlier than large (propioveption/motor) A alpha fibers

Question 12

Sensory or motor: Which is affected first by local anesthetics when injected into a bundle of large mixed nerves?

Answer 12

MOTOR

Question 13

How does the position of sensory fibers within the extremites change from proximal to distal limbs?

Answer 13

• Proximal sensory fibers = located in outer portion of nerve trunk (will be affected first by local anesthetic)
• Distal sensory fibers = located in the core of the nerve trunk (motor fibers will be affected first)

Question 14

Local anesthetics can be administered topically, injection OR IV regional anesthesia (Bier Block).

What are the 4 types of injections

Answer 14

1. Infiltration anesthesia
2. Block anesthesia
3. Spinal anesthesia
4. Epidural anesthesia

Question 15

What is block anesthesia and its purpose?

Answer 15

• Injection in major nerve trunks
• Purpose is the anesthetize a region distal to the injection site
• * femoral block = surgery distal to knee
• * brachial plexus block = procedure of UE or shoulder

Question 16

What is IV regional anesthesia (Bier block) used for?

How is it done?

Answer 16

• Used for short surgeries (<60 min) involving UE and LE’s
• IV injection of LARGE dose of local anesthetic in a distal vein + proximal tourniquet to isolate circulation of limb
• Keep tourniquet on prevent high circulating drug levels causing systemic effects

Question 17

What in infiltration anesthesia

Answer 17

inject directly into tissue next to a peripheral nerv_e,_ without taking into consideration the course of cutaneous nerve; can be superficial enough to include only skin or deep enough to include intraabdominal organs.

Question 18

What is spinal anesthesia

Answer 18

• Inject into CSF in lumbar space => causes anesthesia over big part of body with a dose of local anesthestic that negligable in plasma

Question 19

What ROA is best for cathetiers that placed in epidural space , allowing continous infusion or repeated bolus admin

Answer 19

Epidural anesthia

Question 20

How does co-admin of vasoconstrictors + local anesthetics affect shit

Answer 20

1. decreases rate the anesthesia is absorped into circulation and metaboliszed
2. dec systemic toxicity

Question 21

Epinephrine administration to prolong the action of local anesthetics should never be injected into what tissues?

What could this result in?

Answer 21

Those supplied by end arteries

• Fingers, toes, nose, and penis
• Vasocontriction could cause gangrene

Question 22

1. Which local anesthetic potentiates the effect of NE on α-adrenergic receptors by blocking NET and results in localized vasoconstriction?
2. What does this do?

Answer 22

1. Cocaine
2. *Eliminates need for combining the drug w/ epinephrine

Question 23

What are the early signs of CNS toxicity caused by local anesthetics?

Answer 23

1. Circumoral and tongue numbness
2. Metallic taste

Question 24

High concentrations of local anesthetics in the CNS may have what adverse effects?

Answer 24

1. Nystagmus
2. Muscular twitching
3. Convulsions
4. Death by respiratory failure

Question 25

When large doses of local anesthetics are need, what can be given to **prevent CNS toxicity** by raising the the seizure threshold?

Answer 25

**Parenteral Benzodiazepine** (_diazepam_ or _midazolam_)

Question 26

**Undesired effects** of local anesthetics on the **CV system** are the result of direct effects on ___________ and from indirect effects on the \_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 26

Undesired effects of local anesthetics on the CV system are the result of **direct** effects on **cardiac** and **smooth muscle** and from **indirect** effects on the **ANS**

Question 27

**Local anesthetics** block which ion channels in the _heart_ =\> cause AE on the _\<3_ and _BP_?

Answer 27

- Block **cardiac Na+ channels** 1. - ↓↓↓ electrical excitability, conduction rate, force of contraction 2. - Arteriolar dilation ---\> **systemic hypotension**

Question 28

**Cocaine** is an exception to the local anesthetic effects on the heart, and instead can cause what?

Answer 28

1. - **Vasconstriction** --\> **local ischemia** 2. - **HTN** 3. - **Cardiac arrhythmias**

Question 29

Which local anesthetic is the **most cardiotoxic?** ## Footnote **Why?**

Answer 29

**Bupivacaine =\>** longest duration of action

Question 30

Which local anesthetic is a **Class Ib antiarrhythmic?**

Answer 30

**Lidocaine**

Question 31

What are the effects of **Lidocaine** on the heart?

Answer 31

1. - **DEC automaticity of condunction tissue** by **increasing threshold of electrical stimulation** of ventricle, His-Purkinje system, and spontaneous depolarization of the ventricles during diastole 2. - **Blocks** both the **initiation/** **conduction** of AP by _decreasing the neuronal membrane's permeability to Na+ ions, =\>_ no depolarization & blocks conduction

Question 32

What is **Benzocaine** used for?

Answer 32

Only as **topical agent** 1. **Dermatologic conditions**, 2. **Hemorrhoids** 3. **Premature ejaculation** 4. **Anesthetic lubricant** (NG an e_ndoscopic tubes/catheters_)

Question 33

**Bupivacaine** has a tendency to provide more of a (sensory or motor) block? What else can it do due to its duration of action?

Answer 33

**Sensory block** _Long duration of action = **prolonged anesthesia**_

Question 34

**Cocaine**, as a local anesthetic, is used primarily how?

Answer 34

**_Topical_ anesthtic** of the u**pper respiratory tract**

Question 35

1. What is **Lidocaine** used for clinically? 2. How does it compare to _procaine_?

Answer 35

- A**lternative pt's with allergy** to ester local anesthetics - **Antiarrythmic agent** \*_Faster_, _more intense_, _longer acting_, and _more extensive_ anesthesia than an equal dose of Procaine

Question 36

What is **Procaine** used for clinically? _How does it compare to newer drugs?_

Answer 36

Only for **infiltration anesthesia** (local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings) \*_less_ potent, _slower_ onset, _shorter_ duration of action\*

Question 37

Which local anesthetic is metabolized to a **para-aminobenzoic acid,** which i**nhibits** the action of **sulfonamide ABX?**

Answer 37

**Procaine**

Question 38

**_Low concentrations_ of local anesthetics** may cause what adverse effects on the CNS?

Answer 38

1. **- Sleepiness (\*CIS Q)** 2. - Restlessness 3. - Light-headedness 4. - Visual / auditory disturbances

Question 39

Which **local anesthetic** is for surface use only? Why?

Answer 39

**Benzocaine =** poor solubility in H20 \*i.e., someone comes in with bad road rash or something

Question 40

Which 3 local anesthetics have **long durations of action?**

Answer 40

1. **Bupivacaine** 2. Ropivacaine 3. Tetracaine

Question 41

Which local anesthetic has a **short duration of action**; used only for infiltration anesthesia?

Answer 41

Procaine

Question 42

What is the **most poten**t local anesthetic vs **least**?

Answer 42

* **Most = Bupivacaine** = long duration * **Lease = Procaine** = short duration