Lecture 11.1: Local Anesthetics

Question 1

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

Answer 1

Amide-type

Question 2

What is the MOA of local anesthetics?

Where is their receptor site located?

Answer 2

- Block voltage-gated Na⁺ channel currents and stop spread of AP’s across nerve axons

• Receptor site is at inner vestibule of the sodium channel

Question 3

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

Answer 3

Smaller and more lipophilic

*Tetracaine, bupivacaine, and ropivacaine

Question 4

What is block anesthesia and its purpose?

Answer 4

• Injection in major nerve trunks
• Purpose is the anesthetize a region distal to the injection site

Question 5

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

How is it done?

Answer 5

• Used for short surgeries (<60 min) involving UE and LE’s
• IV injection of agent is placed in a distal vein while circulation of limb is isolated w/ a proximally placed tourniquet
• Large doses of local anesthetic used; tourniquet remains in place to prevent high circulating drug levels causing systemic effects

Question 6

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

What could this result in?

Answer 6

• Those supplied by end arteries
• Fingers, toes, nose, and penis
• Vasocontriction could cause gangrene

Question 7

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

Answer 7

• Vasconstriction –> local ischemia
• HTN
• Cardiac arrhythmias

Question 8

What is Benzocaine used for?

Answer 8

• Only as topical agent
• Dermatologic conditions, hemorrhoids, premature ejaculation, and as anesthetic lubricant (i.e., NG an endoscopic tubes/catheters)

Question 9

Bupivacaine has a tendency to provide more of a (sensory or motor) block?

Answer 9

Sensory

Question 10

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

Answer 10

Topical anesthtic of the upper respiratory tract

Question 11

What is Lidocaine used for clinically?

Answer 11

• Alternative choice for pt’s with allergy to ester-type local anesthetics
• Antiarrythmic agent

*Faster, more intense, longer acting, and more extensive anesthesia than an equal dose of Procaine

Question 12

What is Procaine used for clinically?

Answer 12

Only for infiltration anesthesia (local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings)

Question 13

Which local anesthetic is for surface use only?

Answer 13

Benzocaine

*i.e., someone comes in with bad road rash or something

Question 14

Propofol

Answer 14

allergic reactions possible

May cause hypotension

Respiratory depressant

Question 15

Etomidate

IV anasthetic

Answer 15

Minimal cardiovascular and respiratory depression; useful in patients with impaired CV and/or respiratory systems

Endocrine adverse effects •Adrenocortical suppression by inhibition of 11β-hydroxylase (cholesterol to cortisol)

4-8 hr suppression after induction limits usefulness for continuous infusion

Extensive liver and plasma biotransformation

Question 16

Ketamine

Answer 16

Unpleasant emergence reactions after administration are the main factor limiting ketamine’s use (e.g., vivid colorful dreams, hallucinations, out-of-body experiences, increased and distorted visual, tactile, and auditory sensitivity)

Only IV anesthetic to produce profound analgesia

Question 17

Common side effects of inhaled anasthetics

Answer 17

nausea and vomiting

Question 18

Halothane may cause what?

(inhaled)

Answer 18

hepatitis (halothane hepatitis) • May occur with or without prior halothane exposure (more rare) •

Symptoms develop 2 days to three weeks after exposure (nausea, myalgias, rash, eosinophilia, jaundice, elevated liver enzymes)

Question 19

enflurane and sevoflurane may cause what?

Answer 19

Agents metabolized to products including fluoride ions may cause renal toxicity

Question 20

In combo with succinylcholine, inhaled anasthetics may cause what?

Answer 20

May cause malignant hyperthermia, which consists of rapid onset tachycardia and hypertension, severe muscle rigidity, rhabdomyolysis, hyperthermia, hyperkalemia, and acid-base imbalance with acidosis