Podcast
Questions and Answers
Which of the following is a potential CNS effect of local anesthetics?
Which of the following is a potential CNS effect of local anesthetics?
- Thirst
- Nystagmus (correct)
- Muscle weakness
- Nausea
What is a possible cardiovascular effect of bupivacaine?
What is a possible cardiovascular effect of bupivacaine?
- Increased cardiac output
- Arrhythmias (correct)
- Tachycardia
- Hypertension
How might repeated epidural injections in anesthetic doses affect the individual?
How might repeated epidural injections in anesthetic doses affect the individual?
- Increased heart rate
- Improved coordination
- Tachyphylaxis (correct)
- Enhanced pain relief
Which local anesthetic is known to be less cardiotoxic compared to bupivacaine?
Which local anesthetic is known to be less cardiotoxic compared to bupivacaine?
What type of anesthesia involves slow infusion at low concentrations for postoperative pain relief?
What type of anesthesia involves slow infusion at low concentrations for postoperative pain relief?
Besides cardiovascular effects, what other toxic effects can local anesthetics produce?
Besides cardiovascular effects, what other toxic effects can local anesthetics produce?
What determines the differential sensitivity of various types of nerve fibers to local anesthetics?
What determines the differential sensitivity of various types of nerve fibers to local anesthetics?
Why are smaller fibers blocked more easily by local anesthetics compared to larger fibers?
Why are smaller fibers blocked more easily by local anesthetics compared to larger fibers?
What will be the sequence of sensory block occurrence from proximal to distal when anesthetic is placed outside a nerve bundle?
What will be the sequence of sensory block occurrence from proximal to distal when anesthetic is placed outside a nerve bundle?
How does local anesthetic affect pain sensation in relation to activated pain fibers?
How does local anesthetic affect pain sensation in relation to activated pain fibers?
Which fibers located within a thick nerve bundle are blocked sooner by local anesthetics?
Which fibers located within a thick nerve bundle are blocked sooner by local anesthetics?
What effect does local anesthetic have on the upstroke of sodium-dependent action potentials in the heart?
What effect does local anesthetic have on the upstroke of sodium-dependent action potentials in the heart?
What is the primary mechanism of action of local anesthetics?
What is the primary mechanism of action of local anesthetics?
How can the duration of action of shorter-acting local anesthetics be extended?
How can the duration of action of shorter-acting local anesthetics be extended?
Which local anesthetic is considered an exception due to its intrinsic sympathomimetic action?
Which local anesthetic is considered an exception due to its intrinsic sympathomimetic action?
How do longer-acting local anesthetics differ from shorter-acting ones in terms of vasoconstrictor dependency?
How do longer-acting local anesthetics differ from shorter-acting ones in terms of vasoconstrictor dependency?
What effect does cocaine have on norepinephrine reuptake into nerve terminals?
What effect does cocaine have on norepinephrine reuptake into nerve terminals?
How do local anesthetics restrict their effect to a localized area?
How do local anesthetics restrict their effect to a localized area?
What is the primary goal of sustained-release formulations in local anesthesia?
What is the primary goal of sustained-release formulations in local anesthesia?
Why are less toxic and more selective agents explored in the development of local anesthesia formulations?
Why are less toxic and more selective agents explored in the development of local anesthesia formulations?
What is Neosaxitoxin primarily known for in the context of local anesthesia?
What is Neosaxitoxin primarily known for in the context of local anesthesia?
What does sustained-release delivery have as an added advantage compared to catheter administration?
What does sustained-release delivery have as an added advantage compared to catheter administration?
Why does anesthetic neurotoxicity not result from blockade of the voltage-gated sodium channel?
Why does anesthetic neurotoxicity not result from blockade of the voltage-gated sodium channel?
What is the primary advantage of drug delivery systems that slowly release anesthetic?
What is the primary advantage of drug delivery systems that slowly release anesthetic?
Which of the following is a cardiovascular toxicity associated with the use of cocaine?
Which of the following is a cardiovascular toxicity associated with the use of cocaine?
Why has the popularity of cocaine as a topical anesthesia diminished recently?
Why has the popularity of cocaine as a topical anesthesia diminished recently?
Why is bupivacaine often avoided for techniques that require high concentrations of concentrated anesthetic?
Why is bupivacaine often avoided for techniques that require high concentrations of concentrated anesthetic?
What is a reason why spinal bupivacaine is not well suited for outpatient or ambulatory surgery?
What is a reason why spinal bupivacaine is not well suited for outpatient or ambulatory surgery?
Why are relatively low concentrations of bupivacaine (≤ 0.25%) used for prolonged peripheral anesthesia and analgesia?
Why are relatively low concentrations of bupivacaine (≤ 0.25%) used for prolonged peripheral anesthesia and analgesia?
Why is there no specific antidote for local anesthetic (LA) toxicity mentioned in the text?
Why is there no specific antidote for local anesthetic (LA) toxicity mentioned in the text?
Study Notes
Local Anesthetics
- Block sensory transmission from a local area of the body to the CNS
- Accomplished by disrupting afferent neural traffic via inhibition of impulse generation or propagation
- Chemically similar agents (esters and amides) that block sodium channels of excitable membranes
Mechanism of Action
- Injection or topical application restricts effect to localized area
- Inhibit impulse generation or propagation in afferent neural traffic
- Block sodium channels of excitable membranes
Pharmacokinetics
- Most shorter-acting local anesthetics are readily absorbed into the blood from the site of administration
- Duration of action is limited unless blood flow to the area is reduced
- Vasoconstrictors can be used to reduce blood flow and increase duration of action
- Cocaine is an exception due to its intrinsic sympathomimetic action (inhibition of norepinephrine reuptake into nerve terminals)
Pharmacologic Effects
- Differential sensitivity of various types of nerve fibers to local anesthetics depends on:
- Fiber diameter
- Myelination
- Physiologic firing rate
- Anatomic location
- Smaller fibers are blocked more easily than larger fibers
- Myelinated fibers are blocked more easily than unmyelinated fibers
- Activated pain fibers fire rapidly, and pain sensation appears to be selectively blocked by local anesthetics
- Fibers located in the periphery of a thick nerve bundle are blocked sooner than those in the core
Cardiovascular Toxicity
- Cocaine:
- Contributes to cardiovascular toxicity due to its vasoconstricting actions and ability to block norepinephrine reuptake
- Can cause severe hypertension, arrhythmias, and myocardial infarction
- Bupivacaine:
- Can produce severe cardiovascular toxicity including arrhythmias and hypotension
- Levobupivacaine is less cardiotoxic
- Ropivacaine:
- Can produce cardiotoxicity when used for peripheral nerve block
Commonly Used Local Anesthetics
- Bupivacaine:
- Agent of choice for epidural infusions used for postoperative pain control and labor analgesia
- Has a relatively unblemished record as a spinal anesthetic
- Chloroprocaine:
- Used for postoperative pain control and labor analgesia
- Articaine:
- Used for dental anesthesia
Toxicity
- CNS:
- Can produce a spectrum of central effects, including light-headedness, sedation, restlessness, nystagmus, and tonic-clonic convulsions
- Severe convulsions may be followed by coma with respiratory and cardiovascular depression
- Cardiovascular:
- All local anesthetics are capable of producing cardiovascular toxicity, with the exception of cocaine
- Patients with pre-existing cardiovascular disease may develop heart block and other disturbances of cardiac electrical function at high plasma levels of anesthetics
Future Developments
- Sustained Release Formulations:
- Can provide prolonged analgesia or anesthesia without the drawbacks of a catheter
- Reduced risk of systemic toxicity
- Less Toxic Agents:
- Developing compounds with considerably better therapeutic indexes
- Neosaxitoxin:
- A site 1 Na⁺ channel biotoxin explored as a method to provide prolonged block, with the goal of obviating the need for catheter placement and continuous anesthetic infusion
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Description
Test your knowledge on the uses and administration of local anesthetics in medical practice, including spinal anesthesia, autonomic blockade, postoperative analgesia, and pain management in neuropathic states.
