Local Anesthetics Flashcards
Neurons maintain a resting membrane potential of?
-60 to -70 mV
3 states of Na channels:
- Resting (non conducting)
- Open (conducting)
- Inactivated (non conducting)
Voltage-gated Na channels are membrane-associated proteins comprising of one large ___ subunit through which Na ions pass, and one or two smaller ____ subunits
Alpha; beta
Ester LA are predominately metabolized by?
Pseudocholinesterase
Amide LA are metabolized by?
P-450 metabolites in the liver
Binding of which subunit prevents channel activation?
Alpha
Local anesthetics have a greater affinity for Na channel when?
Open or inactivated state (not resting)
What is the basis of the classification of LA as either esters or amides?
The nature of the intermediate chain
LA consist of a _____ group separated from a _____ group by an intermediate chaine
Lipophilic; hydrophilic
Factors that affect the minimum concentration of LA that will block impulse conduction:
Fiber size, myelination, pH, stimulation frequency, electrolyte concentration
acid + acid & base + base =?
Non-ionized
Acid + base = ?
Ionized
Lipid solubility correlates with?
Potency of LA
M-gate closed
Resting or closed phase
M-gate and H-gate are open
Activated or open phase
H-gate is closed
Inactivated phase
LA interaction with which gate causes the effect? What charge is necessary?
H-gate; a positive charge
Lipid soluble. Acid form. Generally hydrophobic. Readilly penetrates BBB/placenta
Non-ionized
Water soluble. Charged form. Conjugate base form.
Ionized
What drug is the exception to the rule that the closer pKa is to physiologic pH, the faster the onset? Is it protein bound?
Chloroprocaine (pKa 9.1) No protein binding
What can be added to LA to prolong duration?
Epinephrine
What can be added to LA to gain a quicker onset?
Bicarbonate
What dose of bicarb is needed when using bupivacaine?
0.1 mEq per 20 ml of bupivacaine
What dose of bicarb is needed when using Lidocaine?
1 mEq bicarb per 10 ml of lidocaine
Which drugs will Epi not increase the duration? Why?
Bupivacaine, Etidocaine, & Ropivacaine. They have a long duration naturally
Why is speed of onset slower when LA is injected into area of infection?
It increases the extent of ionization which slows diffusion through lipid bilayers
The greater the amount of LA that exists in the _____ form, the faster the onset
Unionized
Short acting LA
Procaine & Chloroprocaine
Intermediate acting LA
Lidocaine, Mepivacaine, Prilocaine
Long acting LA
Bupivcavine, Etidocaine, Tetracaine
LA with high pKa:
Are highly ionized at physiologic pH
Has to have an open (activated) Na channel for effect
The nerves with frequent depolarization have greater susceptibility to LA with high pKa:
Sensory nerves & autonomic nerves
Sympathetic block is ___ dermatomes _____ than sensory block
2-6; higher
Motor block is ___ dermatomes ____ than sensory block
2; lower
How does the LA progress in a blockade?
Autonomic, Temperature, Pain (ATP)
Touch, Pressure (TP)
Motor, Vibratory, Proprioception (MVP)
_______ must be blocked to stop nerve conduction myelinated axons
2-3 nodes of Ranvier
Weak acids combine with ______ charged ions such as:
Positive; Na, Mg, Ca
Weak bases combine with ______ charged ions such as:
Negatively; chloride & sulfate
Should a weak acid be stored in a low or high pH solution? Why?
High (base). Ionized form should not precipitate
