local anesthesia

Question 1

define local anesthesia

Answer 1

• loss of sensation limited to a local area or region of the body

Question 2

define local anesthetic

Answer 2

• drug that blocks generation and propagation of nerve impulse that results in reversible, regional loss of function (analgesia)

Question 3

what is the primary MoA of local anesthetics (LA)

Answer 3

- Blockade of voltage-gated sodium channeles

• decrease in genreation and conduction of action potentials

RESULT:

–> Increase in excitation threshold and slower impulse conduction

–> decrease in rate of action potential generation

–> decrease in amplitude of action potential

–> no ability to generate action potential

Question 4

amides vs esters

Answer 4

• Amides

–> metabolized by liver by P450s

–> longer half-life and longer duration of action

• Esters

–> rapidly metabolised by hydolysis in plasma

–> short plasma half-life –> short duration of action

Question 5

describe the influence of fiber size on local anesthetic onset/recovery

Answer 5

• Increase fiber size –> INcrease minimum anesthetic conc (Cm)
• B-fibers (first) and A-alpha fibers last

Question 6

describe the effect of pH on LA onset and recovery

Answer 6

• Increase in pH –> decrease on minimum anesthetic concentration (Cm)

Question 7

describe the effects of Calcium concentration on LA onset and recovery

Answer 7

• Increase in Calcium conc –> increase Cm

Question 8

describe the effects of vasconstrictors on LA onset and recoery

Answer 8

• Vasoconstrictors substances REDUCE local blood flow and reduce systemic absorption and REDUCE LA TOXICITY

** NEVER INJECT LA WITH CASOCONSTRICTOR INTO AREAS WITH END ARTERIOLES (DIGITS, TOES, EAR LOBES, NOSE, PENIS)

–> potential for gangrene or sloughing of tissue

Question 9

what are the 4 factors that affect reversal of local anesthesia

Answer 9

1) Dilution by extra-cellular fluid

–> reduces intracellular conc of LA (from high [LA] –> low [LA])

2) Absorption into circualtion (MOST IMPORTANT FACTOR)

–> depends on local blood supply, metabolism depends on this

3) redistribition to other areas

–> function of organ blood flow and plasma protein binding

4) Use of vasoconstrictors (epinephrine0

–> decrease in blood flow –> increase in duration of action

Question 10

Metabolism of Amides

Answer 10

- Metabolised in LIVER by P450s to INACTIVE metabolise

• longer laf-life and longer duration of action

**CAUTION: half-life is altered in pts with liver problems**

Question 11

metabolism of ESTERS

Answer 11

- Esters are metabolised in plasma by BChE into inactive metabolite (PABA moiety)

• Short plasma half-life –> short duration of action

**CAUTION: metabolite para-aminobenzoic acid (PABA) is prone to ALLERGIC REACTIONS**

Question 12

what are the 5 amides

Answer 12

• lidocaine
• bupivacaine
• ropivacaine
• articaine
• mepivacaine

** all end in caine and have 2 i’s**

Question 13

list the 5 esters

Answer 13

• cocaine
• procaine
• tetracaine
• benzocaine
• chloroprocaine

** all end in caine and only have one i**