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51 Cards in this Set
- Front
- Back
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What path does a pain signal travel? (neuron to cortex)
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Nocireceptor -> Synapse in Dorsal Horn -> Cross midline -> Anterolateral Tract -> Terminate in Thalamus -> Synapse with Relay Cells -> Project to Cerebral Cortex
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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 |
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Local Anesthetics act by inhibiting, what?
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Inhibiting the activity of channels in the cell membrane that allow the entry of SODIUM IONS into the neuron. Blockade prevents initiation of AP.
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Example of Extracellular and Intracellular block
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TTX: extra
Local Anesth: intra |
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What is a "use-dependent" blockade?
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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.
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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. |
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What are the 3 distinct moieties of a local anesthetic?
Understand their classification |
Aromatic portion
Intermediate chain (ester or amide) Amine group (protonates +) |
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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. |
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Cocaine, Procaine, Tetracaine, Benzocaine
are examples of Esters or Amides? |
Esters
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Lidocain, Mepivacaine, Bupivacaine, Etidocaine, Prilocaine, Ropivacaine
are examples of Esters or Amides? |
Amides
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Which (Esters or Amides) have shorter duration, due to being prone to hydrolysis?
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Esters
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Which (Esters or Amides) rapidly metabolized (1 minute half-life) through enzymatic cleavage by pseudocholinesterase in the plasma?
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Esters
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Which (Esters or Amides) have the metabolite PABA, which is excreted in the urine?
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Esters
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Which (Esters or Amides) are more likely to give allergic reaction and why?
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Esters; PABA is a metabolite and an allergen.
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Which (Esters or Amides) can occur systemic toxicity when dose overwhelms pseudocholinesterase?
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Ester
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Which (Esters or Amides) have a half-life of 2-3 hours?
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Amides
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Which (Esters or Amides) could lead to systemic toxicity in a person with liver disease or who is elderly?
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Amides
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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.
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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?
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Because they are often administered by injection into the area to be blocked. But duration and likelihood of toxicity is important.
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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 |
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Why is Epinephrine used to reduce the systemic absorption of local anesthetics?
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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) |
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In spinal anesthesia epinephrine has what useful mechanism?
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Activates alpha2 receptors, reducing substance P release and dorsal horn neuron firing.
Prolongs action by as much as 50% |
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What are distinguishing properties of Cocaine?
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Ester. Systemic toxicity and high abuse potential.
It is unusual in that it causes VASOCONSTRICTION. |
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What are distinguishing properties of Procaine?
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Slow onset.
Short duration. Weak potency. Low systemic toxicity. High allergy potential due to PABA. EFFECTIVE: anesthesia or nerve block |
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What are distinguishing properties of Lidocaine?
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Amide (Xylocaine)
Rapid onset. Intermediate duration. Causes VASODILATION and therefore formulations include epinephrine. EFFECTIVE: most anesthetic blocks |
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What are distinguishing properties of Ropivacaine?
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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. |
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Which of:
Procaine Lidocaine Cocaine Ropivacaine Is used primarily by route of Mucous Membranes? |
Cocaine
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Which of:
Procaine Lidocaine Cocaine Ropivacaine Can be used topically on the skin surface? |
Lidocaine
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Which of:
Procaine Lidocaine Cocaine Ropivacaine Has the most rapid onset? |
Lidocaine
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Which of:
Procaine Lidocaine Cocaine Ropivacaine Has the shortest duration? |
Procaine
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What are the routes for Procaine use?
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Infiltration
Nerve block Epidural Spinal |
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What are the routes for Cocaine use?
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Mucous Membrane
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What are the routes for Lidocaine use?
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Infiltration
Nerve block Epidural Spinal Skin Mucous Membrane |
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What are the routes for Ropivacaine use?
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Infiltration
Nerve block Epidural Spinal |
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Which local anestetics are used by route of Infiltration?
Procaine Lidocaine Cocaine Ropivacaine |
Procaine
Lidocaine Ropivacaine |
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Which local anestetics are used by route of Nerve Block?
Procaine Lidocaine Cocaine Ropivacaine |
Procaine
Lidocaine Ropivacaine |
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Which local anestetics are used by route of Epidural?
Procaine Lidocaine Cocaine Ropivacaine |
Procaine
Lidocaine Ropivacaine |
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Which local anestetics are used by route of Spinal?
Procaine Lidocaine Cocaine Ropivacaine |
Procaine
Lidocaine Ropivacaine |
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Which local anestetics are used by route of Mucous Membrane?
Procaine Lidocaine Cocaine Ropivacaine |
Cocaine
Lidocaine |
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Which local anestetics are used by route of Skin?
Procaine Lidocaine Cocaine Ropivacaine |
Lidocaine
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Major adverse reaction to:
Procaine |
Allergy (PABA)
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Major adverse reaction to:
Cocaine |
Systemic toxicity
High abuse potential |
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which agent is most effective for infiltration anesthesia or nerve block?
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procaine
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what is the most commonly used LA?
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lidocaine
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which drug causes arrhythmia at high doses?
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lidocaine
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which drug has lower cardiac toxicity and why?
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ropivacaine
- S isomer form -> contributes to lower cardiac toxicity (rather than usual racemic combo) |
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which drug causes vasoconstriction contributing to reduced toxicity?
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epinephrine
ropivacaine |
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what are some local reactions to LAs?
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pain (low pH)
ecchymosis hematoma absecess nerve laceration tissue necrosis (vasonc.) |
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what does direct injection of LAs result in?
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blindness
aphasia hemiparesis convulsions resp. depression coma cardiac arrest |
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what side effect can occur at low concentrations?
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sensory perception is slightly affected
behavior disruption |
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discuss the reason for potentail convulsions to result from LA use.
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convulsions - due to block of GABA blockade
tx= diazepam (IV) |
