Local Anesthetics Flashcards
What is the general MOA for local anesthetics?
They bind reversibly to sodium channels in nerves and block ion movement through the channel pore, blocking the action potentials responsible for nerve conduction. It can act on any part of the nervous system and on every type of nerve fiber
Which of the following is an amide and have the longest duration of action? A. Procaine B. Tetracaine C. Bupivacaine D. Lidocaine E. Medpivacaine
C. Bupivacaine.
In general which groups of local anesthetics (esters or amides) have shorter duration of action?
Esters are more prone to hydrolysis than those with amide links and thus generally have a shorter duration of action. Procaine has the shortest!
Why might one administer a vasoconstrictor with a local anesthetic?
It will reduce systemic absorption of agents and are useful for drugs with intermediate or short duration of actions.
Where are ester and amide anesthetics metabolized?
Ester types are metabolized in the plasma; amide agents are metabolized in the liver; and both then excreted in the urine as charged substances.
True or false. The smaller and more lipophilic the local anesthetic, the faster the rate of interaction with the Na channel and the more potent the agent’s action.
True
Tetracaine, Bupivacaine, and ropicaine are _ (more or less)_ lipophilic than lidocaine, procaine, and mepivacaine, and therefore are (more or less) potent and have have longer duration of action
More and more
What size and nerve types, and frequency of firing do local anesthetics prefer?
Local anesthetics preferentially block bundled smaller myelinated fibers that fire at a higher frequency.
Rank the following in the order of greatest sensitivity to block by local anesthetics A. Type C sympathetic fibers B. Type C, dorsal root C. Type B, preganglionic autonomic D. Type A, Delta fibers E. Type A, Gamma fibers F. Type A, Alpha fibers
Of the ones listed, Type B is lightly myelinated, and type C are not myelinated. But, their diameters are significantly smaller than Type A fibers. Therefore type B and C will be more sensitive to block.
A > B > C > D > E > F
If you wanted to use a local anesthetics for a simple surgery distal to the knee, where would you inject the anesthetic?
You’d inject it in the nerve trunk that supplies that region. Usually injecting at the trunk anesthetizes the area distal to that trunk. For a surgery distal do the knee, the femoral nerve trunk is injected.
What is a Bier Block?
Its a type of anesthetic that is used for short surgical procedure (less than 60min) involving the upper and lower extremities. An IV is injected in a distal vein while circulation of the limb is isolated with a proximal placed tourniquet.
application of vasoconstrictors can prolong local anesthetics. In which anatomical areas, are application of vasoconstrictor contraindicated?
Tissues supplied by end arteries (fingers, toes, ears, penis)
What effects can low concentration of local anesthetics have on the CNS?
produce sleepiness, light-headedness, visual and auditory disturbances, and restlessness.
What effects can high concentration of local anesthetics have on the CNS? administration of what other agent can help with these.
nystagmus, muscular twitching, and convulsions. Premedication with a parenteral benzodiazepines (diazepam or midazolam) can provide prophyalxis against CNS tox by raising the seizure threshold.
What effects does local anesthetics have on the CV system and which agent is the most cardiotoxic?
Blocks cardiac sodium channels, and decrease electrical excitability, conduction rate, force of contraction, and arteriolar dilation, leading to systemic hypotension.
- Bupivacine may be most cardiotoxic due to it’s long duration of action.
