quiz 5 Flashcards
Agents with a _____ pKa value will have a _____ onset because a ______ fraction of the molecules will exist in the uncharged form and thus will more easily diffuse across nerve membranes.
lower
faster
greater
range of LA pKa’s? lowest and highest drug?
7.6 - 9.1
- mepivicaine
- Chloroprocaine
the lower the pKa = ?
faster onset
weak base + acid becomes?
more ionized
weak base + base becomes?
more non-ionized
More non-ionized the ______ the drug b/c ?
quicker
-non-ionized gets into cell
MOA of LA’:
- Block nerve conduction by impairing propagation of the action potential in axons.*
- Decrease the rate of rise of the action potential such that the threshold potential is not reached.
- Interact directly with specific receptors on the Na+ channel, inhibiting Na+ ion influx
lipid solubility effects?
increases potency (some increase in DOA too)
protein binding effects?
higher protein binding = longer DOA
_______ fibers are more easily blocked than _____ ones.
Thin
thick
_______ fibers are more readily blocked than ______ ones. Why?
Myelinated
unmyelinated
-produce block only at Node of Ranvier
Fibers for Sharp/fast pain, temp, touch (fine sensation)
C fibers
Fibers for pressure touch
A beta
Fibers for proprioception
A alpha
A beta
Fibers for motor control?
A alpha
A gamma
which fiber unmyelinated?
C fibers
Sequence of blockade in order?
-ATP TP MVP
ATP - autonomic, touch, pain
TP - Temp and pain
MVP - motor, Vibration, pressure (deep)
Esters:
- Broken down by?
- metabolite?
- half-life?
plasma cholinesterase
PABA (p-aminobenzoic acid)
1 minute in circulation
Amides:
- Broken down by?
- concerns?
- half-life?
- Through N-dyalkylation followed by hydrolysis
- severe hepatic disease
- 2-3 hours
CSF has a specific gravity of ?
1.003–1.009
difference b/w hyper/hypo/isobaric
hyper - floats downward
hypo - floats upward
iso - stays put
what does epi do for LAs?
- Prolong duration of anesthesia
- Decrease systemic toxicity by decreasing the rate of absorption
- Increases intensity of block.
- Decreases surgical bleeding.
- Assist in evaluation of test dose. To assure correct location
when not to add epi:
- Peripheral nerve blocks in areas with poor collateral circulation (e.g. finger, toes).
- IV regional technique (bier block).
- History of severe uncontrolled HTN, CAD, arrhythmia, hyperthyroid, utero-placental insufficiency.
adding Bicarb:
- Raises the pH and increases the concentration of non-ionized (free) base.
- Increases the rate of diffusion across the nerve membrane and speeds onset of neural blockade.
- 1mEq added to each 10ml of lidocaine or mepivacaine.*
- 0.1mEq added to each 10ml of bupivicaine (to avoid ppt of the drug).*
adding an opioid:
- Addition of 50-100ug of fentanyl to the local anesthetic shortens the onset, increases the level and prolongs the duration of a regional block.
- A selective action at the dorsal horn of the spinal cord modulates pain transmission.*
- Action is synergistic with the action of the local anesthetic
when can an Amide cause an allergic reaction?
If a methyl-paraben preservative is used, it may produce allergic reaction in someone allergic to PABA
when can an Ester cause an allergic reaction?
- may cause allergic reaction due to metabolite similar in structure to PABA.
- Also may produce allergic reaction in persons sensitive to sulfonamides or thiazide diuretics.
Result of accidental intravascular injection or overdose of local anesthetic. Can be minimized by :
- Aspiration prior to injection
- Use of epi-containing solutions for test dose
- Use of small incremental volumes to establish the block
- Use of proper technique during IV regional (bier block)
CNS Toxicity:
Lightheadedness
Tinnitus
Metallic taste
Visual disturbance
Numbness of tongue and lip
May progress to:
- Muscle twitching
- Loss of consciousness
- Grand mal seizure
- Coma
- death
what to do if pt starts to seize?
blow of co2 (convusive threshold higher in lower pt co2)
treatment of CNS toxicity?
-Administer o2
- Midazolam 1-2 mg
- Thiopental 50-200mg
- Propofol
CV toxicity:
Decreased contractility
Decreased conduction
Loss of peripheral vasomotor tone