Dr. Beevers - March 28, 2012 Semester 4, Mini 3
Terms in this set (38)
Which are the ester-type local anesthetics?
Which are the amide-type local anesthetics?
Why do the ester containing local anesthetics have a shorter duration of action?
esters are more prone to hydrolysis
Because local anesthetics are mostly basic, what form do they take at physiological pH?
On what side of the membrane do local anesthetics bind the Na+ channel receptor?
Why are local anesthetics less effective in infected tissues?
infected tissues are usually more acidic
→ ↓ unionized form → ↓ diffusion into cells
For regional anesthesia involving the block of large nerves, maximum blood levels of the drug decrease according to the site of administration in what order?
Intercostal (highest) > caudal > epidural > brachial plexus > sciatic nerve (lowest)
What can be given concomitantly with local anesthetics to reduce the systemic blood concentrations by 30%?
How does epinephrine act on the spinal cord to both enhance and prolong local anesthetic-induced spinal anesthesia by up to 50%?
α₂ receptor block → ↓ substance P release → ↓ sensory neuron firing
What enzymes break down ester-type local anesthetics in the blood?
What group of local anesthetics is more likely to occur in pts with hepatic disease or decreased hepatic blood flow?
What channel state do local anesthetics have a higher affinity for?
active or inactivated
What is the critical length of nodes of Ranvier to be blocked to the propagation of an action potential?
An increased concentration of what extracellular ion antagonizes the action of local anesthetics?
→ ↑ surface potential
→ low-affinity rested state of Na⁺ channel
An increased concentration of what extracellular ion enhances the action of local anesthetics?
→ ↓ surface potential
→ high-affinity inactivated state of Na⁺ channel
What nerve type is blocked first? second? third? fourth?
1. small, myelinated
2. small, unmyelinated
3. large, myelinated
4. large unmyelinated
Why are sensory fibers blocked before motor fibers?
sensory fibers have a high firing rate and a relatively long action potential duration;
motor fibers fire at a slower rate and have a
shorter action potential duration
During infiltration block of a large nerve, sensory analgesia first starts proximally or distally?
(proximal nerves on the periphery of nerve bundles)
Why aren't local anesthetics injected directly into a nerve?
painful and could cause nerve damage
What is the most commonly used drug for injected local anesthetics?
What are commonly used local anesthetics in epidural anesthesia?
also bupivacaine and ropivicaine
In spinal anesthesia, in relation to the sensory anesthesia, at what level is the sympathetic nerve block?
sympathetic block 2 spinal levels above sensory block
In spinal anesthesia, in relation to the sensory anesthesia, at what level is the motor nerve block?
motor block 2 spinal levels below sensory block
What type of operations is spinal anesthesia best reserved for?
operations below the umbilicus, gynecological and
urological operations, and operations on the
perineum or genitalia
What are the most commonly used local anesthetics in spinal anesthesia?
tetracaine, lidocaine, and bupivacaine
What is the Bier block?
IV regional anesthesia used for short surgical procedures (<60 min) involving the upper or lower extremities
→ IV injection of local anesthetic agent into a
distal vein while the circulation of the limb is isolated with a proximally placed tourniquet
What are the short-acting local anesthetics?
What are the intermediate-acting local anesthetics?
lidocaine, mepivacaine, prilocaine
What are the longer acting local anesthetics?
bupivacaine, ropivacaine, tetracaine, levobupivacaine
→ more lipophilic
What can be added to a mixture of local anesthetic to accelerate its onset?
→ ↑ unionized form
What complication associated with local anesthetics increases with repeated injections? Why?
→ extracellular acidosis due to ↓ buffering capacity
What is the preferred anesthetic in dental procedures?
(fast and intermediate duration)
What local anesthetic is commonly used by ENTs for topical anesthesia for mucous membranes?
What are some early symptoms of local anesthetic CNS toxicity?
circumoral and tongue numbness
When large doses of local anesthetics are required, what can be pre-administered perenterally to provide significant prophylaxis?
Pt complains of pain in the buttocks, and thigh following surgery where caudal epidural block was performed. Why can this occur?
transient radicular (dermatome) irritation results from
pooling of high concentrations
of the drug in the
region of the spinal cord leading to interference with axonal transport and disruption of Ca²⁺ homeostasis
How do local anesthetics cause cardiovascular toxicity?
direct effects of the drugs on cardiac and smooth muscle membranes and from indirect effects on autonomic nervous system function
Pt presents cyanotic with chocolate-coloured blood following surgery. High doses of which local anesthetic can cause these side effects? Tx?
→ tx: methylene blue or ascorbic acid
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