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51 Cards in this Set

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What path does a pain signal travel? (neuron to cortex)
Nocireceptor -> Synapse in Dorsal Horn -> Cross midline -> Anterolateral Tract -> Terminate in Thalamus -> Synapse with Relay Cells -> Project to Cerebral Cortex
Nocireceptors are found where?

Respond to?

Arise from?
Found: dermis, epidermis

Respond to: mechanical stimuli, temp, noxius stimuli (chili pepper)

Arise from: myelinated Adelta (15-80m/s), unmyelinated C (0.5-1m/s) fibers
Local Anesthetics act by inhibiting, what?
Inhibiting the activity of channels in the cell membrane that allow the entry of SODIUM IONS into the neuron. Blockade prevents initiation of AP.
Example of Extracellular and Intracellular block
TTX: extra
Local Anesth: intra
What is a "use-dependent" blockade?
Their site of action on the channel can be accessed when the ion channel is activated (being used). This can be seen as a systematic reduction in inward Na+ current during voltage-clamp experiments.
What dictates POTENCY of a LA?

What dictates ONSET of a LA?

and DURATION?
Primarily its lipid solubility (partition coefficient)

Low pHa anesthetics generally have a more rapid onset of action.

Duration relates to affinity of anesthetic for ion channel.
What are the 3 distinct moieties of a local anesthetic?

Understand their classification
Aromatic portion

Intermediate chain (ester or amide)

Amine group (protonates +)
Are local anesthetics weak base or weak acid?

In what species do they exist in the body?
Weak bases (PKa 8-9)

Uncharged base or Cation species (charged species most effective in channel blocking)

**Infected tissue is acidic and requires more anesthetic for uncharged species to become available for diffusion.
Cocaine, Procaine, Tetracaine, Benzocaine

are examples of Esters or Amides?
Esters
Lidocain, Mepivacaine, Bupivacaine, Etidocaine, Prilocaine, Ropivacaine

are examples of Esters or Amides?
Amides
Which (Esters or Amides) have shorter duration, due to being prone to hydrolysis?
Esters
Which (Esters or Amides) rapidly metabolized (1 minute half-life) through enzymatic cleavage by pseudocholinesterase in the plasma?
Esters
Which (Esters or Amides) have the metabolite PABA, which is excreted in the urine?
Esters
Which (Esters or Amides) are more likely to give allergic reaction and why?
Esters; PABA is a metabolite and an allergen.
Which (Esters or Amides) can occur systemic toxicity when dose overwhelms pseudocholinesterase?
Ester
Which (Esters or Amides) have a half-life of 2-3 hours?
Amides
Which (Esters or Amides) could lead to systemic toxicity in a person with liver disease or who is elderly?
Amides
In general, which nerves are more sensitive to block?
Smaller or Larger diameters
Myelinated or Unmyelinated
SMALL fibers are blocked easily and MYELINATED fibers are more easily blocked than unmyelinated fiber of the same size.
Why are the absorption and distribution of local anesthetics not as important in controlling onset, as is the duration and likelihood of central and cardiac toxicity?
Because they are often administered by injection into the area to be blocked. But duration and likelihood of toxicity is important.
What risk follows this trend?
intercostal > caudal > epidural > brachial plexus > sciatic nerve

Why?
Systemic toxicity increases in likelihood when LAs are administered, due to high vasculature in certain areas.

#1: intercostal
#2: caudal
#3: epidural
#4: brachial plexux
#5: sciatic nerve
Why is Epinephrine used to reduce the systemic absorption of local anesthetics?
Used to constrict local vessels, preventing local concentrations from being dispersed from site of action. This decreases systemic toxic effects. It also increases local concentrations.

(vasoconstriction at end organs can lead to tissue death)
In spinal anesthesia epinephrine has what useful mechanism?
Activates alpha2 receptors, reducing substance P release and dorsal horn neuron firing.

Prolongs action by as much as 50%
What are distinguishing properties of Cocaine?
Ester. Systemic toxicity and high abuse potential.

It is unusual in that it causes VASOCONSTRICTION.
What are distinguishing properties of Procaine?
Slow onset.
Short duration.
Weak potency.
Low systemic toxicity.
High allergy potential due to PABA.

EFFECTIVE: anesthesia or nerve block
What are distinguishing properties of Lidocaine?
Amide (Xylocaine)
Rapid onset.
Intermediate duration.
Causes VASODILATION and therefore formulations include epinephrine.

EFFECTIVE: most anesthetic blocks
What are distinguishing properties of Ropivacaine?
Amide.
New in '96 with lower cardiac toxicity.
Chirality: R is most efficacious as cardiac Na+ channel blocker, so S-isomer alone reduces cardiac toxicity.

Vasoconstriction reduces spread of drug and toxicity.
Which of:
Procaine
Lidocaine
Cocaine
Ropivacaine

Is used primarily by route of Mucous Membranes?
Cocaine
Which of:
Procaine
Lidocaine
Cocaine
Ropivacaine

Can be used topically on the skin surface?
Lidocaine
Which of:
Procaine
Lidocaine
Cocaine
Ropivacaine

Has the most rapid onset?
Lidocaine
Which of:
Procaine
Lidocaine
Cocaine
Ropivacaine

Has the shortest duration?
Procaine
What are the routes for Procaine use?
Infiltration
Nerve block
Epidural
Spinal
What are the routes for Cocaine use?
Mucous Membrane
What are the routes for Lidocaine use?
Infiltration
Nerve block
Epidural
Spinal
Skin
Mucous Membrane
What are the routes for Ropivacaine use?
Infiltration
Nerve block
Epidural
Spinal
Which local anestetics are used by route of Infiltration?

Procaine
Lidocaine
Cocaine
Ropivacaine
Procaine
Lidocaine
Ropivacaine
Which local anestetics are used by route of Nerve Block?

Procaine
Lidocaine
Cocaine
Ropivacaine
Procaine
Lidocaine
Ropivacaine
Which local anestetics are used by route of Epidural?

Procaine
Lidocaine
Cocaine
Ropivacaine
Procaine
Lidocaine
Ropivacaine
Which local anestetics are used by route of Spinal?

Procaine
Lidocaine
Cocaine
Ropivacaine
Procaine
Lidocaine
Ropivacaine
Which local anestetics are used by route of Mucous Membrane?

Procaine
Lidocaine
Cocaine
Ropivacaine
Cocaine
Lidocaine
Which local anestetics are used by route of Skin?

Procaine
Lidocaine
Cocaine
Ropivacaine
Lidocaine
Major adverse reaction to:
Procaine
Allergy (PABA)
Major adverse reaction to:
Cocaine
Systemic toxicity
High abuse potential
which agent is most effective for infiltration anesthesia or nerve block?
procaine
what is the most commonly used LA?
lidocaine
which drug causes arrhythmia at high doses?
lidocaine
which drug has lower cardiac toxicity and why?
ropivacaine
- S isomer form -> contributes to lower cardiac toxicity (rather than usual racemic combo)
which drug causes vasoconstriction contributing to reduced toxicity?
epinephrine
ropivacaine
what are some local reactions to LAs?
pain (low pH)
ecchymosis
hematoma
absecess
nerve laceration
tissue necrosis (vasonc.)
what does direct injection of LAs result in?
blindness
aphasia
hemiparesis
convulsions
resp. depression
coma
cardiac arrest
what side effect can occur at low concentrations?
sensory perception is slightly affected
behavior disruption
discuss the reason for potentail convulsions to result from LA use.
convulsions - due to block of GABA blockade
tx= diazepam (IV)