What is the primary site of local anesthetic action?
What is the sodium channel.
100
An action potential must be decreased by how much before measurable loss of function is observed.
What is 50%.
100
These are hydrolized by plasma cholinesterase.
What are esters.
100
Name three additives to local anesthetics.
What is epinephrine, opioids, bicarbonate.
100
What factor is tachyphylaxis most dependant on?
What is the dosing interval. If the dosing intervals are short enough, such that the pain doesn't occur, then tachyphylaxis doesn't occur. In contrast, the longer the patience is in discomfort, the faster it occurs.
200
Name two things that increase conduction velocity in a nerve.
Increased mylination and nerve diameter.
200
Even with close proximity of deposition, how much of the injected LA penetrates into the nerve?
What is 1 - 2%.
200
How are amide local anesthetics metabolized.
They are degraded by hepatic carboxylesterase.
200
What is the purpose of adding epinephrine to a LA.
Vasoconstriction of surrounding blood vessels to decrease reabsorption and prolong duration of action.
200
What are the signs/symptoms of TNS and how quickly do they occur.
What is moderate to severe pain in the lower back, buttocks, and posterior thighs. They appear within 6 to 36 hours after complete recovery of a spinal. Full recovery usually occurs in 1 to 7 days.
300
What is the resting potential of the neural membrane?
Averages between -60 to -70 mV with the cell interior being negative to the cell exterior.
300
Degree of nerve blockade depends on what two things.
What is LA concentration and volume.
300
A local anesthetic with a lower pKa (compared to other LA) will have this effect.
What is increase the potency and duration of action of the LA - the lower the pKa will increase the amount of LA in the lipid soluble form allowing for more penetration of the neural membrane.
300
What is the purpose of adding bicarbonate to LA?
To increase the pH of surrounding tissues (to be closer to LA pKa) to allow more of the local anesthetic to be in the lipid soluble form and cross through the nerve membrane.
300
What are the motor and sensory findings in patients with TNS?
Both normal!
400
How is the nerve's resting potential maintained?
Maintained by a potassium gradient with 10x greater concentration of potassium within the cell.
400
Different nerve types have a minimal concentration necessary to completely block the nerve. Which nerve type (comparing A and C fibers) requires the most and the least?
A fibres require the least (ie more susceptible to LA block) and C fibres the most.
400
Are esters or amides more associated with allergic reactions and why?
Esters produce metabolites related to paraaminobenzoic acid (PABA).
400
What is the effect if adding clonidine to LA.
Some studies suggest alpha agonist properties reduce reabsorption and other studies suggest direct analgesic effect.
400
Name, IN ORDER, 6 signs/symptoms you will find in LA toxicity.
Name two ways a local anesthetic affects the sodium channel.
Modification of the lipid membrane surrounding it or by direct interaction with its protein structure.
500
Differential blockade means that not all sensory and motor modalities are blocked equally. What is the normal sequence?
First to last: temp sensation -> proprioception -> motor function -> sharp pain -> light touch
500
Name 5 clinical uses for local anesthetics.
Neuraxial anesthesia, peripheral nerve blocks, topical application (airway, eye, skin), IV to blunt laryngoscopy, tx cardiac arrhythmia, lidocaine infusion for pain
500
What makes 2-chloroprocaine different from other LA agents in regards to additives?
2-chloroprocaine interferes with efficacy of morphine (mechanism remains unclear).
500
Certain drugs and chemicals cause oxidation of hemoglobin to methemoglobin (which cannot bind oxygen or carbon dioxide). Name 2 (of 4) topical LA that can cause this.
What is prilocaine, benzocaine, cetacaine, and lidocaine.