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Questions and Answers
Which of the following local anesthetics has the fastest onset of action?
Which of the following local anesthetics has the fastest onset of action?
Local anesthetics can produce unconsciousness in patients.
Local anesthetics can produce unconsciousness in patients.
False
What is the primary site of action for local anesthetics?
What is the primary site of action for local anesthetics?
Cell membrane
Lidocaine is the most frequently employed local anesthetic of ______ duration.
Lidocaine is the most frequently employed local anesthetic of ______ duration.
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Match the local anesthetic with its characteristic:
Match the local anesthetic with its characteristic:
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Which characteristic increases the potency and duration of action of local anesthetics?
Which characteristic increases the potency and duration of action of local anesthetics?
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Cocaine is one of the most widely used local anesthetics available today.
Cocaine is one of the most widely used local anesthetics available today.
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Name one route of administration for local anesthetics.
Name one route of administration for local anesthetics.
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Local anesthetics block the ______ movement through the Na+ channels.
Local anesthetics block the ______ movement through the Na+ channels.
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Which local anesthetic is known for low solubility?
Which local anesthetic is known for low solubility?
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What characteristic of nerve fibers affects their sensitivity to local anesthetics?
What characteristic of nerve fibers affects their sensitivity to local anesthetics?
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Larger, myelinated fibers are blocked more easily by local anesthetics.
Larger, myelinated fibers are blocked more easily by local anesthetics.
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What is the dual service provided by vasoconstrictors when added to local anesthetics?
What is the dual service provided by vasoconstrictors when added to local anesthetics?
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The onset of action of local anesthetics can be accelerated by the addition of __________.
The onset of action of local anesthetics can be accelerated by the addition of __________.
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Match the following local anesthetics to their undesired effects:
Match the following local anesthetics to their undesired effects:
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Which local anesthetic is known for causing cardiotoxicity?
Which local anesthetic is known for causing cardiotoxicity?
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Adding epinephrine to a local anesthetic increases the rate of anesthetic absorption.
Adding epinephrine to a local anesthetic increases the rate of anesthetic absorption.
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What type of pain can oral and parenteral forms of local anesthetics be used to treat?
What type of pain can oral and parenteral forms of local anesthetics be used to treat?
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Adverse effects from local anesthetics can lead to __________ and cardiovascular collapse.
Adverse effects from local anesthetics can lead to __________ and cardiovascular collapse.
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Which of the following increases the duration of action of a local anesthetic?
Which of the following increases the duration of action of a local anesthetic?
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Why should mepivacaine not be used in obstetric anesthesia?
Why should mepivacaine not be used in obstetric anesthesia?
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Procaine is associated with frequent allergic reactions.
Procaine is associated with frequent allergic reactions.
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What is one undesired effect of spinal and epidural anesthesia?
What is one undesired effect of spinal and epidural anesthesia?
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Local anesthetics can cause _____ contractions in the intact bowel.
Local anesthetics can cause _____ contractions in the intact bowel.
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Match the type of local anesthetic with its characteristic effect:
Match the type of local anesthetic with its characteristic effect:
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Which of the following is a common use for local anesthetics?
Which of the following is a common use for local anesthetics?
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Local anesthetics have no effect on vascular and bronchial smooth muscle.
Local anesthetics have no effect on vascular and bronchial smooth muscle.
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What factor significantly affects the safety of local anesthetics?
What factor significantly affects the safety of local anesthetics?
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Binding of the anesthetic to proteins in the serum reduces the concentration of the _____ free drug.
Binding of the anesthetic to proteins in the serum reduces the concentration of the _____ free drug.
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Why is the metabolic fate of local anesthetics important?
Why is the metabolic fate of local anesthetics important?
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Study Notes
Local Anesthetics
- Block nerve conduction of sensory impulses from the periphery to the CNS.
- Abolish sensation and, in higher concentrations, motor activity in a limited area of the body without producing unconsciousness
- Inhibit the function of Na+ channels by interacting with their protein receptors
- Most frequently employed local anesthetic is Lidocaine
- Action site: cell membrane
Local Anesthetic Mechanisms
- Prevent the generation and conduction of the nerve impulse
- Bind to specific receptor sites within the pore of the Na+ channels and block the ion movement through the pore
- Prevent depolarisation of the membrane and blocking conduction of the action potential
Local Anesthetic Administration
- Topical, infiltration, field/nerve block, intravenous regional, spinal, epidural.
Factors Influencing Local Anesthetic Sensitivity
- Small, unmyelinated nerve fibres that conduct impulses for pain, temperature, and autonomic activity are most sensitive
- Fibers in the periphery if a thick nerve bundle are blocked sooner than those in the core
- Weak blocking effects on skeletal muscle neuromuscular transmission
Most Widely Used Local Anesthetics
- Bupivacaine
- lidocaine – the most widely used local anesthetic
- mepivacaine
- Procaine – first synthetic local anaesthetic
- Benzocaine – low solubility
- ropivacaine
- Tetracaine - ophthalmic use
- Cocaine
- Articane – fastest onset of action
Local Anesthetic Structure and Hydrophobicity
- Contain hydrophilic and hydrophobic moieties
- Hydrophobicity increases both potency and duration of action
- Receptor site for these drugs on Na+ channels is hydrophobic
- Hydrophobicity also increases toxicity
Pharmacologic Effects of Local Anesthetics
- Nerves: differential sensitivity of various types of nerve fibers depends on fiber diameter, myelination, physiologic firing and anatomic location.
- Smaller, myelinated fibers are blocked more easily.
- Pain sensation appears to be selectively blocked by local anesthetics.
Duration of Action and Vasoconstrictors
- Duration of action is proportional to the time the drug is in contact with the nerve.
- Vasoconstrictors (e.g., epinephrine) are added to keep the drug at the nerve and prolong the period of anaesthesia.
- Vasoconstrictors decrease the rate of anesthetic absorption, minimizing systemic toxicity and increasing the duration of action.
Local Anesthetic Action: Onset and Other Considerations
- Onset of action may be accelerated by addition of sodium bicarbonate which enhances intracellular access.
- Used in spinal anesthesia and to produce autonomic blockade in ischemic conditions.
- Slow epidural infusion at low concentration has been used successfully for post-operative analgesia or IV forms can be used for reducing pain post-op.
- Oral and parenteral forms – used adjunctly in neuropathic pain states.
Local Anesthetic Undesired Effects
- Adverse effects result from systemic absorption of toxic amounts of the locally applied anesthetic.
- Seizures and cardiovascular collapse are the most significant systemic effects.
- Restlessness and tremor proceeding to clonic convulsions.
- All are vasodilators – patients with existing CV disease may develop heart block and other disturbances of cardiac electrical function
- Bupivacaine - cardiotoxicity: decreases in electrical excitability, conduction rate and force of contraction leading to ventricular tachycardia and fibrillation; hypotension.
- Mepivacaine should not be used in obstetric anesthesia due to its increased toxicity to the neonate.
- Allergic reactions may be encountered with procaine, which is metabolized to p-aminobenzoic acid.
- Spinal and epidural anesthesia and instillation of local anesthetics into the peritoneal cavity causes sympathetic nervous system paralysis, which can result in an increased tone of GI musculature.
Local Anesthetic Undesired Effects: Effects on Smooth Muscle
- Depress contractions in the intact bowel
- Relax vascular and bronchial smooth muscle
- Affects transmission at the neuromuscular junction
- Hypersensitivity reactions (rare)
Metabolism of Local Anesthetics
- Metabolic fate is of great practical importance
- The rate of degradation of local anesthetics varies greatly, and this is a major factor in determining its safety
- Because toxicity is related to the concentration of the free drug, binding of the anaesthetic to proteins in the serum and to tissues reduces the concentration of the free drug in the systemic circulation and consequently reduces toxicity.
Local Anesthetic Uses
- Topical anaesthetic agents on the skin and/or mucus membrane
- Preparations are effective in the symptomatic relief of anal and genital pruritus, poison ivy rashes, acute and chronic dermatoses.
- Combined with glucocorticoids or antihistamines
- Used for minor surgical procedures
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Description
Explore the mechanisms, administration, and effects of local anesthetics. Understand how these agents block nerve conduction and affect sensation in targeted areas of the body. Delve into factors influencing their sensitivity and the role of sodium channels.
