Local Anesthesia

Question 1

Mechanism of Action of Local Anesthetics

Answer 1

1st: Non-Ionized Local Anesthetic (LA) Molecule penetrates the cell membrane
2nd: LA Ionized inside cell and binds to Na+ channel inactivation gate, Preventing opening of Na+ channel
3rd: Action Potential blocked, No Pain Transmission

Question 2

Local Anesthetics (LA) are commonly mixed with \_\_\_\_\_\_ to cause vasoconstriction to area of administration.
This will \_\_\_\_\_\_ the duration of action of the LA.

Answer 2

Epinephrine

Prolong

Question 3

What is the difference between Amino Ester LAs and Amino Amide LAs?

Answer 3

Amino Ester LA: metabolized by pseudocholinesterases in blood, causing SHORTER Duration of Actions
*Amino Esters can cause allergic rxns
Amino Amide LA: metabolized by the liver, causing LONGER Duration of Actions

Question 4

What group are the Local Anesthetics below classified as?
Cocaine
Procaine
Tetracaine

Answer 4

AMINO ESTERS

Hint: Amino Esters only have one ‘i’ in their name

Question 5

What group are the Local Anesthetics below classified as?
Lidocaine Prilocaine
Mepivacaine Ropivacaine
Bupivacaine Etidocaine

Answer 5

AMINO AMIDES

Hint: Amino Amides have two ‘i’ in their name

Question 6

Describe some difference between the LAs below:

Cocaine, Procaine, Tetracaine

Answer 6

Cocaine: used as LA in nasal passages
Procaine: First synthetic LA, Slow Onset, Low Potency
Tetracaine: used in LONG-acting Spinal Blocks, VERY potent (not used for peripheral blocks)

Question 7

Describe some differences between the LAs below:
Lidocaine
Prilocaine
Mepivacaine

Answer 7

Lidocaine: used for Regional Blocks and Pain Management
Prilocaine: Can cause Methemoglobinemia
(tx: methylene blue)
Mepivacaine: TOXIC to Neonates=NO OB Use!
*All are intermediate Duration of Action

Question 8

Describe some differences between the LAs below:
Ropivacaine
Bupivacaine
Etidocaine

Answer 8

Ropivacaine: Popular for Peripheral Nerve Blocks (Less toxic than Bupivacaine)
Bupivacaine: CardioTOXIC-dilute concentrations used
Etidocaine: Prolonged motor block that outlasts sensory block=BAD
*All are long Duration of Action

Question 9

As tissue pH _______, the amount of LA in the non-ionized form ________.

Answer 9

Decreased, Decreased

*LA unable to get into cell so unable to produce effects

Question 10

What is LAST?

Answer 10

Local Anesthetic Systemic Toxicity

Question 11

Local Anesthetic Systemic Toxicity is more likely to occur in an (acidotic/alkalotic) patient. Why?

Answer 11

Acidotic: less protein bound Local Anesthetic

aka MORE FREE Local Anesthetic

Question 12

Are small fibers or large fibers easier to block w/LAs?

Answer 12

Small Fibers

Question 13

Are un-myelinated or myelinated fibers easier to block w/LAs?

Answer 13

Myelinated (LA pools near the axonal membrane)

Question 14

Once a patient has lost the sensation to _____, you know they have lost the sensation of pain.

Answer 14

Cold

Question 15

REMINDER to Review Local Anesthetic Calculations

*Local Anesthetic Slides, Page 26

Answer 15

Review Local Anesthetic Calculations

Question 16

What is the Treatment for LAST?

Answer 16

1) Airway Management and Seizure Precautions
2) BLS and ACLS (Avoid Lidocaine, Ca2+ Channel Blockers, Vasopressin, Beta Blockers)
3) 20% Lipid Emulsion Therapy (Soaks up the LA)