Block 15 Local Anesthetics MCQ's

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Block 15 Local Anesthetics MCQs - Quiz

William T. G Morton was the first person in the world to successfully demonstrate the use of ether anesthesia for surgery. Today anesthetics render a patient unresponsive and unconscious, most patients may have amnesia and feel no pain. Jog your memory on block 15 on local anesthetics by taking up the simple quiz below.


Questions and Answers
  • 1. 

    A 43-year-old patient underwent an emergency minor arm repair procedure after a car accident. A standard dose of lidocaine was administered near the brachial plexus for peripheral nerve block. Which of the following adverse effects would most likely occur after the administration?

    • A.

      Ventricular tachycardia

    • B.

      Abdominal colic

    • C.

      Drowsiness

    • D.

      Tonic-clonic convulsions

    • E.

      Nystagmus

    Correct Answer
    C. Drowsiness
    Explanation
    After the administration of lidocaine near the brachial plexus for peripheral nerve block, the most likely adverse effect to occur would be drowsiness. Lidocaine is a local anesthetic that can cause systemic effects when administered in larger doses or when it enters the bloodstream. Drowsiness is a common side effect of lidocaine and is typically a result of its central nervous system depressant properties. Ventricular tachycardia, abdominal colic, tonic-clonic convulsions, and nystagmus are less likely to occur as adverse effects of lidocaine administration in this scenario.

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  • 2. 

    The primary mechanism of action of local anesthetics involves the blockade of which of the following ion channels?

    • A.

      Inactivated, voltage-gated, Na+ channels

    • B.

      Inactivated, ligand-gated, K+ channels

    • C.

      Resting, voltage-gated, K+ channels

    • D.

      Resting, ligand-gated, Na+ channels

    • E.

      Activated, ligand-gated, Ca2+ channels

    • F.

      Activated, voltage-gated, Ca2+ channels

    Correct Answer
    A. Inactivated, voltage-gated, Na+ channels
    Explanation
    Local anesthetics primarily work by blocking inactivated, voltage-gated Na+ channels. When these channels are inactivated, they are unable to open and allow the influx of sodium ions, which is necessary for the propagation of action potentials. By blocking these channels, local anesthetics prevent the generation and conduction of nerve impulses, resulting in temporary loss of sensation in the localized area.

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  • 3. 

    Which of the following nerve fibers are most sensitive to the action of local anesthetics?

    • A.

      Resting fibers

    • B.

      Rapidly firing fibers

    • C.

      Fibers with high conduction velocity

    • D.

      Unmyelinated fibers

    • E.

      Fiber of large diameter

    Correct Answer
    B. Rapidly firing fibers
    Explanation
    Rapidly firing fibers are most sensitive to the action of local anesthetics because these fibers have a higher frequency of action potentials. Local anesthetics work by blocking sodium channels and preventing the generation and propagation of action potentials. Since rapidly firing fibers have a higher frequency of action potentials, they are more likely to be affected by the blocking action of local anesthetics compared to resting fibers, fibers with high conduction velocity, unmyelinated fibers, or fibers of large diameter.

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  • 4. 

    When a local anesthetic is applied to a nerve fiber, which of the following nerve properties will most likely increase?

    • A.

      Rate of rise of the action potential

    • B.

      Conduction velocity of the nerve

    • C.

      Amplitude of the action potential

    • D.

      Resting potential of nerve membrane

    • E.

      Refractory period of the nerve

    Correct Answer
    E. Refractory period of the nerve
    Explanation
    When a local anesthetic is applied to a nerve fiber, the refractory period of the nerve is most likely to increase. The refractory period is the time during which the nerve is unable to generate another action potential. By increasing the refractory period, the local anesthetic prolongs the time it takes for the nerve to recover and generate another action potential. This can help block pain signals and prevent the transmission of nerve impulses.

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  • 5. 

    Which of the following functions is blocked last when a local anesthetic is applied to a nerve?

    • A.

      Motor function

    • B.

      Pain sensation

    • C.

      Muscle tone

    • D.

      Temperature sensation

    • E.

      Sympathetic activity

    Correct Answer
    A. Motor function
    Explanation
    When a local anesthetic is applied to a nerve, it blocks the transmission of nerve signals. Motor function refers to the ability of muscles to contract and move. Since the local anesthetic blocks the nerve signals, it will affect the motor function last, as the other functions such as pain sensation, muscle tone, temperature sensation, and sympathetic activity will be blocked before the motor function.

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  • 6. 

    Which of the following molecular events makes the nerve membrane more sensitive to the action of local anesthetics?

    • A.

      Increased extracellular concentration of Ca2+

    • B.

      Increased extracellular concentration Na+

    • C.

      Decreased extracellular concentration of Cl-

    • D.

      Increased extracellular concentration of K+

    • E.

      Increased extracellular concentration of Mg2+

    Correct Answer
    D. Increased extracellular concentration of K+
    Explanation
    An increased extracellular concentration of K+ makes the nerve membrane more sensitive to the action of local anesthetics. Local anesthetics work by blocking sodium channels, preventing the generation and conduction of nerve impulses. Increasing the extracellular concentration of potassium ions (K+) depolarizes the nerve membrane, making it more likely for sodium channels to open and allowing local anesthetics to have a greater effect on blocking these channels. This increased sensitivity to local anesthetics can lead to a more potent and prolonged anesthetic effect.

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  • 7. 

    A main feature of the mechanism of action of local anesthetics is a voltage dependent blockade of Na+ channels. Which of the following statements best explains this voltage dependency?

    • A.

      The more negative the membrane potential, the lower the affinity for local anesthetics

    • B.

      The more negative the membrane potential, the higher the affinity for local anesthetics

    • C.

      The higher the frequency of firing of the fiber, the lower the affinity for local anesthetics

    • D.

      The lower the frequency of firing of the fiber, the higher the affinity for local anesthetics

    • E.

      The faster the conduction velocity of the fiber, the higher the affinity for local anesthetics

    Correct Answer
    A. The more negative the membrane potential, the lower the affinity for local anesthetics
    Explanation
    Local anesthetics work by blocking sodium channels, which are responsible for the conduction of nerve impulses. The voltage dependency of local anesthetics means that their affinity for binding to these channels is influenced by the membrane potential. In this case, the more negative the membrane potential (hyperpolarization), the lower the affinity for local anesthetics. This means that local anesthetics are less likely to bind to sodium channels and block nerve conduction when the membrane potential is more negative.

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  • 8. 

    The ionized form of local anesthetics is mainly responsible for which of the following properties of the drug?

    • A.

      Tissue redistribution

    • B.

      Liver biotransformation

    • C.

      Systemic toxicity

    • D.

      Receptor binding

    • E.

      Half-life

    Correct Answer
    D. Receptor binding
    Explanation
    The ionized form of local anesthetics is mainly responsible for receptor binding. When local anesthetics are ionized, they are able to bind to specific receptors in the body, blocking the transmission of nerve signals and producing their anesthetic effects. This binding to receptors is crucial for the local anesthetics to exert their desired pharmacological effects.

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  • 9. 

    Which of the following statements best explains why the onset of the therapeutic effect of a local anesthetic is usually slower in infected tissues?

    • A.

      They are very rich in drug-metabolizing enzymes

    • B.

      They are poorly vascularized, so that the drug slowly reaches the nerve terminals

    • C.

      They are rich in extracellular K+ which lowers the drug-receptor binding

    • D.

      They have a low extracelluar pH, which hinders drug diffusion into the cell

    • E.

      They have a high extracellular pH, which hinders drug diffusion into the cell

    Correct Answer
    D. They have a low extracelluar pH, which hinders drug diffusion into the cell
    Explanation
    In infected tissues, the presence of bacteria and inflammation causes a decrease in extracellular pH, making it more acidic. This acidic environment hinders the diffusion of the local anesthetic drug into the cell, slowing down its onset of action.

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  • 10. 

    The pKa of lidocaine is 7.9. Which fraction of the drug will be in the lipid soluble form in the extracellular fluids (pH = 7.4)?

    • A.

      10%

    • B.

      24%

    • C.

      50%

    • D.

      76%

    • E.

      90%

    Correct Answer
    B. 24%
    Explanation
    Lidocaine is a weak base with a pKa of 7.9. The pKa is the pH at which half of the drug is in its ionized form and half is in its non-ionized form. In extracellular fluids with a pH of 7.4, which is lower than the pKa, more of the drug will be in its non-ionized, lipid soluble form. Since the pH is closer to the pKa, we can expect that a significant fraction of the drug will be in its non-ionized form. The closest option is 24%, which suggests that approximately 24% of the drug will be in the lipid soluble form in extracellular fluids at pH 7.4.

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  • 11. 

    Which of the following local anesthetics is mainly metabolized by the liver?

    • A.

      Cocaine

    • B.

      Bupivacaine

    • C.

      Procaine

    • D.

      Tetracaine

    • E.

      Benzocaine

    Correct Answer
    B. Bupivacaine
    Explanation
    Bupivacaine is mainly metabolized by the liver. This is because it undergoes extensive hepatic metabolism, primarily through the process of ester hydrolysis. The liver enzymes break down bupivacaine into various metabolites, which are then eliminated from the body through urine. In contrast, cocaine is primarily metabolized by enzymes in the blood and other tissues, while procaine, tetracaine, and benzocaine are mainly metabolized in plasma and tissues other than the liver.

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  • 12. 

    Which of the following is the most cardiotoxic local anesthetics drug?

    • A.

      Benzocaine

    • B.

      Procaine

    • C.

      Tetracaine

    • D.

      Lidocaine

    • E.

      Bupivacaine

    Correct Answer
    E. Bupivacaine
    Explanation
    Bupivacaine is the most cardiotoxic local anesthetic drug. Cardiotoxicity refers to the potential of a drug to cause harmful effects on the heart. Bupivacaine has a higher affinity for sodium channels in cardiac tissues, which can lead to the inhibition of cardiac conduction and potentially result in arrhythmias, cardiac arrest, or other cardiovascular complications. This makes it more cardiotoxic compared to other local anesthetics such as benzocaine, procaine, tetracaine, and lidocaine.

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  • 13. 

    A 14-year-old boy complained of burning pain due to multiple superficial skin abrasions, after a motorcycle accident. Which of the following local anesthetics would be appropriate for this boy?

    • A.

      Benzocaine

    • B.

      Procaine

    • C.

      Cocaine

    • D.

      Prilocaine

    • E.

      Bupivacaine

    Correct Answer
    A. Benzocaine
    Explanation
    Benzocaine would be appropriate for this boy because it is a local anesthetic that is commonly used for topical application to relieve pain and itching caused by minor skin irritations, such as abrasions. It works by numbing the affected area and providing temporary relief from discomfort. Benzocaine is often used in over-the-counter products such as creams, ointments, and sprays for skin conditions. It is generally considered safe and effective for use in children and adolescents.

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  • 14. 

    Which of the following are the main purposes for adding a vasoconstrictor drug to a local anesthetic? (Check all that apply)

    • A.

      To speed up the onset of the anesthetic effect

    • B.

      To increase the duration of anesthetic effect

    • C.

      To decrease the risk of systemic overdose toxicity of the drug

    • D.

      To decrease the risk of allergic reactions of the drug

    • E.

      To increase the affinity of the drug for the Na+ channels

    Correct Answer(s)
    B. To increase the duration of anesthetic effect
    C. To decrease the risk of systemic overdose toxicity of the drug
    Explanation
    Adding a vasoconstrictor drug to a local anesthetic serves the purpose of increasing the duration of the anesthetic effect by constricting the blood vessels at the site of administration, thus reducing the systemic absorption and prolonging the local effect. It also helps decrease the risk of systemic overdose toxicity by limiting the amount of drug that enters the bloodstream.

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  • 15. 

    Which of the following systems are more likely involved when a toxic dose of a local anesthetic is inadvertently given IV? (Check all that apply)

    • A.

      Gastrointestinal system

    • B.

      Respiratory system

    • C.

      Urinary system

    • D.

      Immune system

    • E.

      Cardiovascular system

    • F.

      CNS

    Correct Answer(s)
    E. Cardiovascular system
    F. CNS
    Explanation
    When a toxic dose of a local anesthetic is given intravenously, it can have severe effects on the cardiovascular system and the central nervous system (CNS). The cardiovascular system is likely involved because the local anesthetic can cause changes in heart rate, blood pressure, and rhythm, leading to cardiovascular collapse. The CNS is also likely involved because the local anesthetic can cause seizures, respiratory depression, and central nervous system depression. The other systems listed (gastrointestinal, respiratory, urinary, and immune) are not directly involved in the immediate effects of a toxic dose of a local anesthetic given IV.

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  • 16. 

    A 25-year-old pregnant woman who is near term decides to have the delivery under spinal anesthesia. Past history of the patient include an anaphylactic reaction 3 years ago apparently due to a sun screen cream containing para-aminobenzoic acid. Which of the following local anesthetics would be appropriate for this patient?

    • A.

      Procaine

    • B.

      Tetracaine

    • C.

      Lidocaine

    • D.

      Benzocaine

    • E.

      Proparacaine

    Correct Answer
    C. Lidocaine
    Explanation
    Lidocaine would be appropriate for this patient because it is a local anesthetic that does not contain para-aminobenzoic acid, which the patient had an anaphylactic reaction to in the past. Therefore, using lidocaine for spinal anesthesia would minimize the risk of another allergic reaction in this patient.

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  • 17. 

    A 65-year-old man is scheduled for a lithotripsy to shatter a bladder stone. Lumbar epidural anesthesia is selected for the procedure. Since the anticipated duration of the procedure is about 30 minutes,  which of the following drugs should be used?

    • A.

      Cocaine

    • B.

      Procaine

    • C.

      Benzocaine

    • D.

      Tetracaine

    • E.

      Lidocaine

    Correct Answer
    E. Lidocaine
    Explanation
    Lidocaine is the most appropriate drug to use for lumbar epidural anesthesia during a lithotripsy procedure. Lidocaine is a local anesthetic that provides rapid onset and intermediate duration of action. It is commonly used for procedures of short to moderate duration, such as this 30-minute procedure. Cocaine, procaine, benzocaine, and tetracaine are also local anesthetics but are not typically used for epidural anesthesia.

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