Anesthetics II Flashcards
What are the major disadvantages of local anesthesia?
Potential for systemic toxicity if use large enough amounts
Poor minute-minute control
Procaine = ?
Novocain
What is perineural infiltration of anesthetics?
Nonspecific injection of the agent at one or more sites around specific area
What is regional nerve blocks?
Inject around a specific nerve to block sensory and motor fibers distal to the block
What is the major advantage and major disadvantage to nerve blocks?
Advantage = less drug required
Disadvantage = Require more skill and anatomical knowledge
What is the MOA of a spinal block?
Injection of an agent into the lumbar subarachnoid space to read the roots of the spinal nerves that supply a specific region
True or false: once in the spinal canal, there are no barriers to keep a drug from reaching the brain
true
What are the two main advantages of spinal blocks?
More reliable; return of CSF indicates correct placement
Pt is conscious with minimal disruption of heart/lungs
What are the major disadvantages of spinal blocks?
Not reversible
No titration
Why can spinal blocks lead to hypotension?
Blockage of sympathetic innervation to the distal regions of the block
What is an epidural block?
Inject into the extradural space and block the root as it passes through the space
What is the major advantage to epidurals?
Not time limited
Can be titrated
What is the major disadvantage to an epidural?
Less reliable than spinal block
What is the way to inject IV anesthesia locally?
Inject with tourniquet, but will eventually go through circulation, so not used often
For the ideal local anesthetic, do you want it to be short or long lasting?
Short
What is the MOA of brain signalling of pain? What signalling pathway is utilized? Where does this cross?
Local release of bradykinin, substance P causes activation of local spinothalamic fibers, which crosses at and above the level, and ascends to the sensory cortex
What is the MOA of local anesthetics?
Block the transient increase in Na channel permeability, thereby raising the threshold for excitability
Is the resting permeability of K affected by local anesthetics?
Yes
What happens to local anesthetics when they enter the body? How do they get into a cell?
Deprotonated, which allows them to cross the lipid bilayer
Which side of the Na channels do local anesthetics work on: intracellular or extracellular side?
Intracellular
What are the local anesthetics that bind to the outside of the Na channel?
Biotoxins
What is the MOA of lidocaine?
Binds to the intracellular side of the Na channel, preventing its opening
What is the MOA of benzocaine?
Gets into the lipid bilayer, and changes the conformation of the Na channel (membrane expansion theory)
What is the MOA of most locally used anesthetics?
Binds to the intracellular Na channel binding site
Interrupts the geometry of lipid bilayer
What is the MOA of tetrodotoxin? Where does this come from?
Pufferfish toxin that binds to the outside of the local Na channels, and prevents opening of the channel
What are the two chemical structural parts of all local anesthetics? Why is each important?
Aromatic ring for lipophilicity to pass through membrane
Tertiary amine (polar) for binding
What are the two general classification of local anesthetics (based on chemical structure)? What differentiates each agent within each of these groups?
Amides
Esters
The intermediate chain (between the amide/ester and the tertiary amine group)
What is the suffix associated with local anesthetics?
“-caine”
What is the rule for differentiating amides from esters?
Generally, amides have two “i”s in their name, while esters have one
Amide or ester: lidocaine
Amide
Amide or ester: cocain
Ester
Amide or ester: articaine
Amide
Amide or ester: mepivacaine
Amide
Amide or ester: procaine
Ester
Amide or ester: etidocaine
Amide
Amide or ester: benzocaine
Ester
Amide or ester: tetracaine
Ester
Amide or ester: Prilocaine
Amide
Amide or ester: Bupivacaine
Amide
Amide or ester: chloroprocaine
Ester
Amide or ester: ropivacaine
Amide
Amide or ester: levobupivacaine
Amide
What type of chemical are all local anesthetics: weak bases, weak acids, strong bases, or strong acids?
Weak bases
What is the uncharged form of local anesthetics important for?
Lipid penetration of membranes
What is the charged forms of local anesthetics useful for?
Active form at Na receptor
How are amides metabolized? Esters? Which, therefore, is impaired with hepatic problems
Amides = p450s **hepatic Esters = butyryl cholinesterases
What is the relative half life of amides? Esters?
Amides = Long Esters = short (
What is the minimum anesthetic concentration (Cm)?
Minimum concentration of drug for standard block (relative standard of potency)
How does the size of the neuronal fiber that is being blocked relate to the Cm needed to block it?
increased fiber size = increase Cm needed
What is order of fibers that are blocked, from first to last? (hint: same order as smallest to largest)
B fibers C fibers A-delta A-gamma A-beta A-alpha
Are C fibers myelinated? What information do they carry?
No
Slow pain and temp
What are A-alpha fibers used for?
motor/proprioception
What are A-beta fibers used for?
Discriminative touch
What are A-delta fibers used for?
Fast pain, temp, crude touch
What are B fibers used for?
Preganglionic fibers
What is the standard of potency for local anesthetics?
Cm
Which are affected first: myelinated or unmyelinated fibers?
Myelinated
What is the relationship between pH and local anesthetic Cm?
Increased pH means lower Cm needed
What is the relationship between [Ca] and Cm?
Increased [Ca] = Increased Cm
What is the relationship between nerve stimulation rate and Cm?
Higher frequency nerves are most sensitive to LA
Why are vasoconstrictors added to LA preparations?
Stays local longer
Increases duration of action
What is the vasoconstrictor commonly used with LAs?
Epi
What are the areas that should never be injected with LA that have epi? (5) Why?
Digits Toes ear Lobes Nose Penis
All have arterioles, and have the potential to develop sloughing off of tissue
What are the four factors that affect reversal of LAs?
- Dilution by ECF
- Absorption into circulation
- Redistribution to other areas
- use of vasoconstrictors
What is the most important factor that affects the reversal of LAs?
Absorption into circulation
What are the two factors that are involved in redistribution of LAs?
Organ blood flow and plasma protein binding
Where are amides/esters metabolized
Amide = liver Esters = plasma by BChE
What is the metabolite that is produced by metabolism of esters? Why is this concerning?
Para-Aminobenzoic acid (PABA)
May cause allergic reaction
True or false: there is cross reactivity between esters and amides. Thus if a pt is allergic to one group, they are likely allergic to the other
False
Why are esters less likely to have systemic toxic effects?
Rapid metabolism in the blood
Most of the allergic reaction in LA are actually due to what preservative?
Methylparaben
Systemic toxicity of what LA can cause Cardiac collapse and death d/t its selectivity
Bupivacaine
What is the treatment for local anesthetic systemic toxicity (LAST)? MOA?
IV lipid emulsion (intralipid)
Forms a sink for the LA
What is the reference standard for amide LAs?
Lidocaine
What is the LAs that can be used both topically and via injection?
Lidocaine
If attempting to give an epidural for a c-section, what LA would you use?
Lidocaine
What is the toxic effect of lidocaine?
Transient neurologic symptoms (with spinal administration
What is the clinical use of bupivacaine?
Agent of choice for epidural infusion for labor analgesia and post-op pain
True or false: bupivacaine is an excellent spinal anesthetic?
True
What are the toxic effects of bupivacaine?
CNS excitation and cardiac collapse
What is the less toxic form of bupivacaine?
Levobupivacaine
What is the clinical use of articaine?
Dental anesthetic
What is the clinical use of cocaine?
Topical anesthetic for HENT procedures
What is the clinical uses for benzocaine?
Topical only anesthetic,
What is the clinical use of chloroprocaine
epidural agent for labor
What is exparel-liposome?
Encased bupivacaine in a liposome, that is given post op for pain
What is EMLA? Clinical use?
Eutectic mixture of Local Anesthetics (lidocaine + prilocaine)
Topical anesthetic
What is TAC? Clinical use?
Tetracaine
Adrenalin
Cocaine
Topical used in pediatric emergencies
What are neurolytics?
Agents that are not reversible, and achieve a permanent local anesthesia
What are the two prototypical neurolytics?
Ethyl alcohol
Phenol
