| Term | Definition |
|---|
| The first local anesthetic discovered was | Cocaine (1884, Koller) |
| The most widely used local anesthetic today is | Lidocaine (1943) |
| Properties of the ideal LA include | Reversible, no side effects, fast acting, predictable in duration, potent |
| LA's work by | Blocking voltage-gated Na+ channels along the axon |
| Equilibrium potential of Na+ is | +40 |
| Equilibrium potential of K+ is | -95 |
| Normal resting potential of an axonal membrane is | -60 to -90 |
| The LA can only work when Na+ channels are | Open (active nerve) |
| LA's bind to the ______ of the membrane | Inside |
| LA's can produce an incomplete or a complete block. With an incomplete block, action potentials can still be generated. T/F? | True, but 85% of unblocked Na+ channels must be opened. (In normal conduction, 75% must be opened) |
| In a myelinated nerve, the LA exerts its effect on the | Nodes of Ranvier |
| LA's must be both: | Water-soluble and lipid-soluble |
| Lipophilic and hydrophilic regions are bound by | Either an ester or amide linkage |
| Esters are | Procaine, cocaine, tetracaine |
| Amides are | Lidocaine, mepivacaine, bupivacaine |
| Allergic response to esters is caused by | PABA, a byproduct of their metabolism |
| Lipophilic region affects the LA's ability to | Diffuse through membranes and last longer in the body |
| Hydrophilic region affects LA's ability to | Diffuse through tissues and bind to the sodium channel |
| LA's that are more lipophilic have a faster onset of action. T/F? | True |
| The hydrophilic region must be ______ for the LA to pass through the membrane | Un-ionized |
| The hydrophilic region must be ______ for the LA to bind to the Na+ channel | Ionized |
| Esters are ______ metabolized by _______ in the ________. | Rapidly; Esterases; Bloodstream |
| Amides are ______ metabolized in the _______. | Slowly; Liver |
| LA's are _______ | Uncharged, weak bases |
| When a base (B), is ionized by H+, it forms its ________ | Conjugate acid (BH+) |
| The higher the pKa of the LA, the more likely it is to be found in its _________ form | Ionized |
| The higher the pKa of the LA, the _______ the rate of onset | Slower (because it's harder for it to diffuse through the membrane) |
| LA's with a pKa very near the body's pH are dangerous to a developing fetus because | A large # are in base form which cross readily into the fetus. Fetal pH is lower than maternal pH, and the LA will ionize and get trapped in fetal circulation. |
| Which will have a slower onset of action: Lidocaine with pKa=7.9 or Procaine with pKa=9.1? | pKa=9.1 |
| Infection increases _____ and makes LA's ______ effective | Acidity; less |
| Sodium bicarbonate can: | Hasten the onset of action and decrease the stinging sensation of injection |
| Normally rapidly-hydrolyzed esters persist in the spinal fluid because | Spinal fluid has little to no esterase |
| A(n) ______ in plasma protein binding _______ the toxicity of a LA. | Increase; lowers |
| LA's with _______ linkages tend to be more extensively bound to plasma proteins | Amide |
| Levels of esterases are low during ________ | Pregnancy |
| Use-dependent inhibition means | Active nerves are blocked first |
| A _____ dose of LA can be effective if administered along a ______ length of nerve | Lower; longer |
| Routes of administration of LA's include | Topical, infiltration, regional nerve block, spinal, epidural |
| Factors affecting clinical effectiveness of LAs are | Nerve fiber type and diameter |
| Most affected A-subtype | A-delta (carry pain and temperature information |
| LA's affect these nerve fibers | A-delta, B and C |
| A LA must block at least ________ in order to be effective | At least 3-4 successive nodes |
| The _______ fibers are affectect most readily by LA's | Smallest |
| Motor neurons are _______ and are relatively ________ by LA's. | Large; unaffected |
| In a nerve bundle, the outermost nerves are affected _______, and the innermost nerves are affected _______. | First; longest |
| In a nerve bundle, the innermost nerves travel most ________. | Distally (nerves to extremities) |
| An enzyme that can be given with LA's that allows easier penetration and longer duration is | Hyaluronidase (Breaks apart CT and increases penetration, decreases washout) |
| Most LA's ______ blood vessels, EXCEPT ________. | Dilate; cocaine |
| LA's promote their own ______ by _______. | Washout; dilating blood vessels |
| _______ can be used in conjunction with LA's to increase their duration of action. | Vasoconstrictors |
| Vasocontrictors should never be used with LA's in these regions: | Digits, ears, nose, penis |
| LA's more readily affect _________ of the CNS | Inhibitory neurons |
| The "glutamate reaction" is | An inhibition of inhibitory CNS neurons, causing excitation (restlessness, tinnitus, paraesthesias, tremors, seizures) |
| Drugs that are more _________ are more toxic. | Lipid soluble |
| LA's can lead to cardiovascular _________ | Depression (but at higher levels than CNS effects) |
| Duration of action of LA's range from | 20 minutes to 4 hours |
| Don't use ______ in patients with cardiac or respiratory disease | Prilocaine |
| Most cardiotoxic of the LA's | Bupivacaine |
| Newest LA similar to Lidocaine but absorbed much more quickly | Articaine |
| Used primarily for spinal anaesthesia, long duration in CSF, high lipid solubility and toxicity | Tetracaine |
| Used mostly topically to treat burns and pruritis | Benzocaine |
| Most arrhythmogenic of the LAs | Cocaine |
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