Term
| Local anesthesia is the reversible ___ in a ___ |
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Definition
Depression of CNS/PNS conduction = loss of sensation
Circumscribed area of the body |
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Term
| Local anesthetics shouldn't be in the general circulation because of ___ |
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Definition
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Term
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Definition
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Term
| ___, ___, and ___ are dense blocks becuase they're cutting off the signal at the start |
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Definition
Epidural
Caudal
Spinal/subarachnoid |
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Term
| Procaine is an ___, metabolized by ___ to ___, which are eliminated by ___ |
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Definition
Ester
Pseudocholinesterases
Water soluble metabolites
Kidney |
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Term
| Lidocaine is an ___, metabolized by ___ to ___, which are eliminated by ___ |
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Definition
Amide
P450
Water soluble metabolites
Kidney |
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Term
| Structural components of all local anesthetics (3) |
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Definition
Aromatic ring = lipophilic
Amine = hydrophilic
Intermediate hydrocarbon chain with ester/amide |
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Term
| The ___ structure is essential for anesthetic activity |
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Definition
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Term
| Anesthetics come in salts to confer solubility and stability: ___ and ___ |
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Definition
Unionized = free base = lipid soluble
Ionized = conjugate acid = water soluble |
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Term
| Most anesthetics are ___. So to increase stability, they're stored at ___ |
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Definition
Weak bases = unstable
Acidic pH (keeps the base unionized) |
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Term
The ___ form is responsible for ___.
Then ___ occurs in the ___ to the ___ form, which ___ |
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Definition
Unionized/free base/lipid soluble
Penetrating the nerve sheath
Re-equilibration occurs in the interior of the nerve
Ionized/conjugate acid/water soluble form
Binds to the active site in the nerve membrane |
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Term
| Factors that influence onset and density of block (7) |
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Definition
Dose
Volume
Rate
Duration
Potency
Site
Local pH (more acidic conditions = decreased efficacy because it's primarily in the ionized form and can't get through the membrane to do its business) |
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Term
| Duration of local anesthetic depends primarily on ___ and secondarily on ___ |
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Definition
Diffusion away from the application site
Metabolism |
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Term
| ___ increases duration of the block |
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Definition
| Reducing local blood flow = VC |
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Term
| Lidocaine is more ___, ___, and ___ than procaine |
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Definition
Potent
Lipid soluble
Durable (long-lasting) |
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Term
| Amide anesthetic metabolization depends on (3) |
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Definition
Hepatic blood flow
Liver disease (decreased metab = increased blood levels and toxicity)
Competition by other drugs ( = delay elimination) |
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Term
| Local anesthetics: MOA, more effective in... |
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Definition
Bind to and block voltage-gated Na channels in the inactivated-closed state
Prevents the channel's change to rested-closed and then activated-open
Decreased rate of electrical depol = failure to achieve threshold potential and make an AP
Increased refractory period
Progressive! More absorption of anesthetic = more channels blocked
RMP
More effective in smaller/rapidly firing nerves |
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Term
| Local anesthetics preferentially block fibers that are... (3) |
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Definition
Unmyelinated
Small
High frequency of firing, low conduction velocity |
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Term
| Toxicity is directly rated to... (3) |
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Definition
Blood levels of local anesthetic
-Increased lipid solubility
-Vascularity of block (intercostal > caudal, administration of EPI)
-Unavailability of plasma proteins to act as a sink (binding up free anesthetic) |
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Term
| Local anesthetic toxicity: S/E including epidural/subarachnoid S/E |
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Definition
CNS
-Apprehension
-Salivation
-Tremor
-Excitation and convulsions with increasing concentrations
Cardiovascular: direct effects on cardiac and smooth muscle, indirect on autonomic nerves
-Altered pacemaker activity = increased HR
-Cardiovascular collapse
Epidural or subarachnoid: transient numbness, radicular irritation of lumbosacral nerves, myotomal weakness |
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Term
| Local anesthetic toxicity: tx (2) |
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Definition
Restore normal ventilation and circulatoin
BZs for seizures |
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Term
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Definition
CV disease, drugs that inhibit cardiac impulse propagation (B-blockers, digitalis, Ca-channel blockers): lower threshold for cardiac toxicity
Allergies (esters): bronchospasm, anaphylaxis |
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Term
| Lidocaine: some other stuff you should know (4) |
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Definition
Metab via oxidative dalkylation
Effective topically
Effective orally as antiarrhythmic
Intrinsic VD |
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