Local anesthetics Flashcards
Mech of Local anesthetics
Bind reversibly to a site within the pore of Na+ channels in nerves thus blocking ion movement through the pore
locally, act on any part of the nervous system and any nerve fiber ____________action potential responsible for nerve conduction
reversibly blocking
Topical application of anesthetic
for skin, mucous, ulcerated surface or opthalmic to produce anesthesia of cornea and conjunctiva
Local infiltration of anesthesia
local injection of an agent into tissues irrespective of the course of cutaneous nerves
`provides regional anesthesia around sites of injection
injection of a local anesthetic around indi nerves or nerve plexuses that lead to operative site
Nerve block anesthetics
injection into the cerebrospinal fluid in the lumbar space
spinal anesthesia
local injection into the epidural space in the sacral, thoracic, lumbar, or cervical regions
Epidural anesthesia
Locals work directly on nerve cells to block their ability to
conducnt impulses
What fiber types do locals work on?
every type
Locals work by blocking action potential propagation on
______ neurons, eliminate pain sensation
- completely reversible; no nerve damage
nociceptic
Local anesthetics bind directly to voltage-dependent ______channels
sodium
Locals bind to a site on the _____ side of the Na channel (segment 6 in domain IV)
intracellular
What form do local anesthetics bind in?
bind in the cationic form, but must reach their site of action by penetrating the nerve
sheath and axonal membrane in the unionized species
All local anesthetics are
all weak bases
–uncharged in its protonated form so it can diffuse through epineurium and travel thorugh membrane
Locals will inhibit voltage gated Na channels
effect on rate of depolarization?
On height of AP?
On rise of AP?
slow depolarization
reduces height of AP
reduces size of AP
Locals will inhibit voltage gated Na channels
effect on axonal condution
on propagation of AP
on threshold potential
slow axonal conduction
prevents propagation
increaes threshold potential
What happens to the RMP d/t local anesthetics
NO CHANGE!!! voltage gated Na play no role in RMP
When do local anesthetics get into channel?
get into channel when its opened
what state do local anesthetics prefer to bind in?
higher affinity in the inactive channel over the unopened channel
degree of block by local anesthetic depends on
the frequency of nerve stimulation and the resting membrane potential
______nerves much less sensitive to block compared to one that is repetitively stimulated
resting
nerves with more positive membrane potential more sensitive to block… occurs because:
1) gain access to the channel binding site more easily when the channel is open
2) have higher affinity for the inactivated channel than for resting channels
When channel is in resting state it is
inactive and open
______form binds to the channel but________ form penetrates into the nerve; thus, alterations in the extracellular pH can influence efficiency
charged
uncharged
sites of inflammation or infection have lower pH; local anesthetic is in the _______ form and therefore less diffusion across membranes producing less effective block
ionized
Why are vasoconstrictors given with local anesthetics?
decreases rate of vascular absorption, increases the depth of anesthesia
less systemic absorption so less toxicity and increases the maximal dose that can be given
in general, autonomic fibers, small non-myelinated C fibers (pain sensation), and small myelinated Aδ fibers (pain and temp) are blocked before
larger myelinated Aδ, Aβ, and Aα fibers (mediating postural, touch, pressure, and motor information)
Order of pain block
recovery is in reverse
pain cold warmth touch deep pressure motor
Toxicity of locals:
interfere with the function of organs that:
have conduction or transmission of impulses (CNS or muscles)
Systemic toxic rnx are related to high conc of local anesthetic in:
circulation
what type of injection can result in irreversible damage
intraneuronal
What enantiomer is the least toxic
S-enatiomer
We see CNS _____ first then at higher doses we see _____
CNS stimulation
then depression
Why do we see CNS depression in local anesthetics
depression of cortical inhibitor neurons: see restlessness, tremors and convulsions
At higher doses of anesthetics we see
drowsiness, general depression, respiratory depression, potential respiratory arrest
Death from local anesthetics is related to
severe toxicity caused by respiratory depression
