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63 Cards in this Set
- Front
- Back
Pain awareness is mediated by nerve ending receptors in ________ tissues and transmitted to the CNS by _______ afferent fibers and relayed by __________ afferent fibers to the brain.
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Periphery
Primary Secondary |
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Drugs that effectively and reversibly block impulse conduction along nerve axons and other excitable membranes that use sodium channels as the primary means of action potential generation.
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Local anesthetics
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The first local anesthetic introduced into medical practice.
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Cocaine
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What are the 3 nociceptors that are recognized?
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Acid, Heat, and Injury
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What 2 receptors modulate the transmission process?
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Alpha2 adrenoceptors and opioid receptors.
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The axon bears ____ and ____ channels, which are essential for AP propagation.
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Sodium and Potassium
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Synaptic transmission involves release of _______ and ______ and activation of their receptors on the secondary neuron.
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Substance P and glutamate.
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What is the general physical properties of local anesthetics?
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Lipophilic group connected by an intermediate chain via an ester or amide to an ionizable group.
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Which local anesthetic would have a shorter half-life, one with ester or amide linkage?
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Ester
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True or False
Local anesthetics are weak acids and at physiolocial pH, are mostly in the charged cationic form (active). |
False
Weak bases |
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True or False
The uncharged form is important for rapid penetration of biologic membranes and producing a clinical effect, since the local anesthetic receptor is not readily accessible from the internal side of the cell membrane. |
False
External |
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Why is the cationic form the most active form at the receptor site?
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Because it cannot readily exit from closed channels.
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What is the configuration of the m and h gates at a resting membrane potential?
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M closed
H open |
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What is the configuration of the m and h gates at the activated state?
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M open
H open |
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What is the configuration of the m and h gates at the inactivated state?
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M open
H closed |
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What is the primary MOA of local anesthetics?
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Blockade of voltage-gated sodium channels.
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What happens to sodium and potassium channels following a depolarization?
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Sodium closes
Potassium opens and flows out which results in cellular repolarization. |
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How are transmembrane ionic gradients maintained?
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The sodium pump
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Why is the cationic form the most active form at the receptor site?
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Because it cannot readily exit from closed channels.
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Local anesthetics bind to receptors near the intracellular end of the sodium channel and block the channel in a _______- and _______-dependent manner.
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Time and voltage
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What is the primary MOA of local anesthetics?
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Blockade of voltage-gated sodium channels.
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What happens to sodium and potassium channels following a depolarization?
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Sodium closes
Potassium opens and flows out which results in cellular repolarization. |
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For myelinated nerves, what is the critical length of sodium channels required to be blocked in order to abolish the AP?
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2-3 nodes of Ranvier
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Channels in the rested state predominate at more _________ membrane potentials have a _______ affinity for local anesthetics.
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Negative
Lower |
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Elevated extracellular calcium partially ___________ the action of local anesthestics.
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Antagonizes
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Elevated extracellular potassium __________ the action of local anesthetics.
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Enhances
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At concentrations used in spinal anesthesia, local anesthetics can inhibit transmission via _______, ________, and ____________ receptors in the secondary afferent neurons.
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Substance P
NMDA AMPA |
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C.R. requires a long acting, potent local anesthetic for a surgical procedure. What local anesthetics would you recommend?
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Tetracaine
Bupivacaine Ropivacaine. |
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True or False
Local anesthetics can block all nerves, cause motor paralysis and residual autonomic block. |
True
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True or False
Larger fibers are blocked first relative to smaller fibers. |
False
smaller fibers are blocked first |
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True or False
Myelinated fibers are blocked before unmyelinated nerves of the same diameter. |
True
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True or False
Preganglionic B fibers are blocked before unmyelinated C fibers involved in pain transmission. |
True
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Why are type A delta and C fibers blocked earlier and with lower concentrations of local anesthetics?
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They are small and high-frequency pain transmission fibers.
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True or False
During infiltration block of a large nerve, sensory analgesia first develops distally and then spreads proximally as the drug penetrates deeper into the core of the nerve. |
False
Proximally then distally |
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How can we reduce systemic absorption of local anesthetics from the injection site?
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Give epinephrine to reduce blood flow to these areas.
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What alpha 2 agonist is used to prolong the local anesthetic affect by inhibition of the release of substance P and reduction of neuronal firing?
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Dexmedetomidine
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With local anesthetics, acidification of urine leads to ____ _____________.
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Rapid elimination.
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How are ester linkages hydrolyzed?
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Butyrylcholinesterase
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How are amide linkages hydrolyzed?
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Liver microsomal CYP450 isozymes.
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Toxicity from amide-type local anesthetics is more likely to occur in patients with ________ disease.
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Hepatic
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Which local anesthetic has a fast onset and an intermediate duration of action that makes it suitable for use in dental procedures?
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Articaine
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How can you accelerate the onset of a local anesthetic?
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Sodium bicarb
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True or False
Topical anesthetics are commonly used for ENT procedures and in chronic pain. |
True
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How can repeated injections of local anesthetics result in loss of effectiveness?
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Extracellular acidosis due to depletion of the buffering capacity of the local tissues. This increases extracellular cationic forms which results in tachyphylaxis.
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What are early signs of CNS toxicity?
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Tongue numbness, metallic taste
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How does pregnancy affect the susceptibility of local anesthetics?
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Increases it.
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When large doses of a local anesthetic are required, how can you protect against local anesthetic-induced CNS toxicity by raising the seizure threshold?
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Premedication with a parenteral benzodiazepine (diazepam or midazolam)
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True or False
Topical anesthetics are commonly used for ENT procedures and in chronic pain. |
True
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True or False
You can treat seizures by hyperventilating. |
True.
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What are early signs of CNS toxicity?
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Tongue numbness, metallic taste
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What are the most neurotoxic local anesthetics?
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Chloroprocaine and lidocaine
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What effects do local anesthetics have on the cardiac pacemaker activity, excitability, and conduction?
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Depression
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When large doses of a local anesthetic are required, how can you protect against local anesthetic-induced CNS toxicity by raising the seizure threshold?
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Premedication with a parenteral benzodiazepine (diazepam or midazolam)
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True or False
You can treat seizures by hyperventilating. |
True.
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What effects do local anesthetics have on the cardiac pacemaker activity, excitability, and conduction?
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Depression
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True or False
Except for cocaine, local anesthetic toxicity causes systemic hypertension. |
False
Depress myocardial contractility Induces arteriolar dilation Systemic hypotension. |
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Which long-acting local anesthetic is more cardiotoxic than any other?
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Bupivacaine
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What happens in bupivacaine cardiotoxicity?
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Idioventricular rhythm, broad QRS, and electromechanical dissociation.
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How do you resuscitate from bupivacaine cardiovascular toxicity?
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Propafol
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Which bupivacaine isomer is safer?
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S
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Large doses of prilocaine can lead to accumulation of what metabolite capable of converting hemoglobin to methemoglobin.
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O-toluidine
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C.R. is released from surgery. Nurses document "chocolate-colored blood". What local anesthetic has the patient been given? How can you treat her toxicity?
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Prilocaine.
Methylene blue or ascorbic acid. |
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Which group of local anesthetics are metabolized to p-aminobenzoic acid derivatives, which cause allergic reactions?
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Ester-type local anesthetics
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