Local Anesthetics

define topical anesthesia

Aqueous solutions, sprays, ointments or gels intended for topical penetration

define ionophoresis

Inject though skin using an electrical current

define nerve block anesthesia

insert close to a nerve trunk but proximal to the intended area of anethesia

define infiltration anesthesia

Injecting directly into the area to be anesthetized

define field block anesthesia

Injected closer to a larger terminal nerve branch, subcutaneous or submucosal

mechanism of local anesthesia

reversible blockage of peripheral nerve conduction by inhibition of the movement of the nerve impulse

describe peripheral nerve conduction

myelin sheath prevents the local current from flowing across the membrane, and the current flows down the nodes of Ranvier. Upon stimulation, ion channels propagate the action potential to the next node

2 things resting potential and the ability to generate an AP depend on

1 - concentration of electrolytes in the ECF

2 - Permeability of nerve membrane to Na+ and K+ channels

Local anesthetic bind to ____ ____ ____ channels and ___ the generation and conduction of action potentials

voltage gated Na+; block

There are _____ alpha subunits with 6 segments each in the voltage gated Na+ channel. segment ____ senses the change in current along the membrane. This causes the segment to be _____. When all of the alpha subunits have a segment that has been displaced, the channel is considered open and ions can pass through.

4; 4; displaced

what is the Na+ inactivation region located?

between the PKC site and inactivation trimer

how to determine rapid onset of an anesthetic

pKA of local anesthetic is close to the pH of the tissue

ester type anesthetics are commonly used ____ and metabolism has a high association of ____ _____. It is metabolized in the tissue by _____

topically; allergic reactions; pseudocholinesterase

amide type LA are metabolized in the _____. They have better ____ solubility , _____, and ____ ____ ____. They also bind well to ____ ____

liver; lipid; potency, duration of action; plasma proteins

what structure of a LA contributes to lipophilicity and why is this important

aromatic residue; essential for drug to permeate the nerve sheath and nerve membrane

what structure of a LA contributes to hydrophobicity and why is this property important?

amino terminus, allows drugs to be dissolved in aqueous solution and prevents it from precipitating in interstitial fluids

pH and charge of LA lipophilic region

7.4; uncharged

pH and charge of LA hydrophilic region

4.5-6; cation

LA are ____ ____ occurring in equilibrium between the nonionized and ionized forms

weak bases

what is the pKa of an LA?

pH at which non-ionized and ionized forms of LA are equal

ionized form = ___ form

salt

pKa of LA can be affected by ____ of tissue

pH

Inflamed tissue can be more ____ - this could ____ the LA and ____ absorption into the nerve

acidic; ionize; prevent

2 vasoconstrictors used with local anesthetics in dental procedures

epinephrine or levonordefrin

what must require careful attention with addition of vasocontrictors

patients with uncontrolled cardiac history

3 things selections of vasoconstrictors depends on

1 - length of the dental procedure

2 - requirement for post operative pain control

3 - medical status of the patient

some things that addition of epinephrine is contraindicated with

BP over 200 syst. or 115 diast

severe cardiovascular disease

daily episodes of angina

medication with a B blocker, MOAIs, TCAs, general anesthesia with halothanes

___ _____ dictates the potency,

duration of action strongly depends on ____ ____. increasing protein binding ____ risk of toxicity

lipid solubility; protein binding; decreases

2 things that affect elimination

metabolism and excretion

2 ester type LA

procaine (novocaine)

benzocaine

major adverse reaction of benzocaine

methemoglobinemia, contraindicated in children under 2

pKa of lidocaine and what this means

7.8; rapid onset

lidocaine with epinephrine is good for ____ ____ ____

almost all dentistry

to avoid vasocontrictors, one should use mepivacaine _____

plain

ortho-toluidine can induce _______

methemoglobinemia

why does bupivacaine have a long duration of action? What is it? How could this potentially be a problem

it binds will to proteins; 340-440 minutes it could bind to Na+ channels necessary for other systems and lead to toxicity, try not to give in cardio conditions

Articaine is metabolized by what?

AChE

maximum safe doses are generally _____ in cardiovascular patients than in healthy patients

lower

some psychogenic reactions to LA administration

vasogagal

hyperventilation

anaphylactoid reaction

allergic reactions to LA are _____, but can range from ____ to ____ ____. Most common true allergic reactions occur in the _____ group due to production of ______

rare; rash; anaphylactic shock; ester; PABA

local anesthetic toxicity is directly related to the rate of LA ____ and _____.

absorption; elimination

two main systems affected by LA

CNS and cardiovascular system

some symptoms of methemoglobinemia

shortness of breath, cyanosis, headache, fatigue, seizures

reversed by IV methylene blue

draw the cycle of methemoglobinemia

3 ways to prevent LA toxicity

1 - give the lowest dose required for anesthesia

2 - use proper injection techniques (always aspirate)

3 - use a vasoconstrictor containing agent if not contraindicated

mechanism of reversal of local anesthetics

administration of phentolamine to shorten the duration of action of LA containing a vasoconstrictor and produces alpha-adrenergic blockade of vascular smooth muscle causing vasodilation

things that can cause failure of local anesthetics

1 - inflamed tissue (lower pH, increased blood flow, alteration in Na+ channel numbers)

2 - incorrect needle selection

3 - starting procedure prior to maximum LA effect