Flashcards in Local Anesthetic Agents Deck (74):
The reversible block of the generation and propagation of the action potential in neural tissue is known as what?
Transient loss of what 3 functions can be seen with local anesthetics?
Local anesthetics target what?
Axons of A and C fibers (sensory nerves)
Which are more prone to hydrolysis, amide or ester links?
Which have a shorter duration of action, anesthetics with amide or ester links?
What are 4 examples of local anesthetics with esters?
What are 6 examples of local anesthetics with amides?
Where do local anesthetics act?
Site of injection.
Slow absorption into systemic circulation is usually desired with what?
What are 3 factors increasing systemic absorption?
- High dosage
- Increased blood flow at site of injection
Which remains at the receptor site longer, the cationic or non-charged form?
Which is able to rapidly penetrate membranes, the cationic or non-charged form?
What effect does pka have on onset?
- High pka has slow onset.
- Low pka has fast onset
Which has a faster onset, procaine or lidocaine?
Which has a faster onset, lidocaine or mepivacaine?
Which local anesthetic has the slowest onset?
Which has a faster onset, mepivacaine or bupivacaine?
An infection can have what effect on the internal environment?
Make it acidic.
Increased protein binding has what effect on duration of action?
Which has a higher percentage of protein binding, procaine or lidocaine?
Which has a higher percentage of protein binding, lidocaine or mepivacaine?
Which has a higher percentage of protein binding, mepivacaine or bupivacaine?
How is lipid solubility related to potency?
What effect does lipid solubility have on onset and duration?
Slower onset and longer duration
How does perfusion affect systemic absorption?
Highly perfused area leads to faster systemic absorption.
What are 2 examples of highly perfused areas?
- Mucus membranes
- Intercostal muscles
What are 3 examples of poorly perfused areas?
What are 2 examples of vasoconstrictors?
What can lead to reduced blood perfusion?
By how much?
T/F: Vasoconstrictors enhance the concentration of available drug in the premises of neuronal tissue.
What effect do vasoconstrictors have on duration of action?
What effect do vasoconstrictors have on analgesia?
Prolonged analgesic effects.
What are 2 advantages of epinephrine?
- Reduces systemic absorption of local anesthetics
- Reduces risks of systemic toxicity induced by local anesthetics
What is a disadvantage of epinephrine?
Potential for life-threatening arrhythmias
Where are amides metabolized?
- In the liver by cytocrome P450
Where might amides accumulate?
Where are esters metabolized?
- In plasma by pseudocholinesterase
What effect do local anesthetics have on nerve conduction?
Prevent sodium channels opening in neuronal axons, thus maintaining fully polarized state and blocking nerve propagation.
Action potentials are conducted along what part of the axon?
Where do local anesthetics act on the axon?
How many nodes of Ranvier need to be blocked in order for a local anesthetic to be effective?
2-3 nodes of Ranvier
T/F: Local anesthetics are only capable of blocking sensory nerves.
False - They are capable of blocking all nerves, not only sensory nerves.
Local anesthetics may cause what due to the blockade of motor neurons?
Local anesthetics may cause what 2 things due to the blockade of autonomic nerves?
Which type of fibers are more susceptible to local anesthesia?
Smaller non-myelinized fibers
Which type of fibers are less susceptible to local anesthesia?
Larger myelinized fibers
Is a blockade by local anesthetics more or less marked at higher frequencies of depolarization?
What type of nerves have a higher firing rate?
- Sensory nerves
- More susceptible
What effects does firing rate have on susceptibility?
- Higher firing rate means more susceptible
- Slower firing rate means less susceptible
Which have a higher firing rate, small or large diameter fibers?
Which fibers get blocked earlier or with low concentrations of local anesthetics?
Small diameter sensory nerves
Some local anesthetics can be used as what?
What are 2 examples of these?
- Antiarrhythmic agents
- Lidocaine and procaine
Some local anesthetics can cause what at high doses?
what are 2 examples of these?
- Lethal arrhythmias
- Bupivacaine and ropivacaine
What are 3 effects local anesthetics can have on cardiac cells?
- Suppress re-entrant ventricular arrhythmia
- Increase ventricular fibrillation threshold
- Decrease automaticity
What is the progression of toxicity for local anesthetics seen in the CNS?
First sedation, followed by tonic-clonic seizures, coma
What effect do local anesthetics have on the respiratory system?
What are 3 effects local anesthetics have on the CV system?
What are 4 possible toxic effects that can be seen with local anesthetics?
- Tissue irritation
- Allergic reactions
In which species can methemoglobinemia be more of a problem with local anesthetics?
What is the order of presentation for most amide type of local anesthetic toxicity?
- CNS signs
- Respiratory system depression
- Cardiovascular system depression
Which drug is the exception to the normal order of presentation of local anesthetic toxicity?
What is the difference?
- Causes cardiovascular depression first
What are 2 examples of isomers of bupivacaine that have less cardiac toxicity?
A toxic dose of local anesthetic can cause side effects when injected how?
What is considered to be a toxic dose of lidocaine?
Do not inject more than what dose of lidocaine in a dog?
- 4 mg/kg
- 2 mg/kg
What is considered to be a toxic dose of bupivacaine?
Do not inject more than what dose of bupivacaine in a dog?
- 2 mg/kg
- 1 mg/kg
T/F: Dogs are more sensitive to local anesthetics than cats.
False - Cats more more sensitive than dogs.
Always do what before injecting a local anesthetic?
Aspirate to check for accidental IV needle placement. Look for blood.
Allergic reactions are mainly seen with what type of local anesthetic?
What is a possible sign of methemoglobinemia?
Pulseox will be about 85% due to significant hypoxia
Cats are more prone to develop methemoglobinemia with which 2 local anesthetics?
What are 3 forms of supportive care that can be used for local anesthetic toxicity?
- CV and/or respiratory support
- Steroid for allergies
- Anti-epileptic drugs