Local Anesthetics Flashcards
Where are afferrent and efferent neurons
Afferrent- dorsal roots, sensory. Efferent- ventral roots, motor
Myelinated nerve fiber
Schwan cell around axon several times
Unmyelinated nerve fiber
Single Schwann cell around several axons
Lytes in and out of cell
Extracellular: high na, low k. Intracellular: high k, low na
A alpha fiber function
Motor and proprioception
A beta fiber function
Motor, touch, pressure
A gamma fiber function
Motor/muscle tone, muscle spindle
A delta fiber function
Pain, temp touch
B fiber
Pre ganglionic autonomic
C fiber function
Dull pain, temp, touch. Postganglionic autonomic, no myelin
Size of fibers large to small
A alpha, a beta, a gamma, a delta, b fibers, C fibers
Large fibers have the highest what and lowest what
Highest conduction velocity lowest threshold for excitability
Sequence of anesthesia: 1 to 5
Sympathetic (vasodilation, warm). Loss of pain and temp. Loss of proprioception. Loss of touch and pressure. Motor block
Polarized state of neuron
Intracellular space is negative compared to extracellular
Movement of what maintains rmp
Potassium
Receptor for LA
Voltage gated na channels in inactivated closed state
What kind of nerve is more sensitive
Repetitively stimulated > resting
LA structure
Lipophilic head (aromatic ring), intermediate chain (amide nh or ester coo-) and hydrophilic tail (tertiary amine)
Which LAs are amides
I before the Caine. Lidocaine, bupivicaine, etidocaine
Amide link metabolism
Liver
Ester linkage metabolism
Hydrolyzed by non specific esterases in plasma and tissues (mostly liver)
What increases potency and toxicity of LA
Inc in length of intermediate chain w carbons. Length of terminal groups on tail and aromatic ring
Which LAs more potent and longer DOA
Lipid soluble > water soluble
Max dose exparel, dose depends on what
266 mg or 20 ml. Depends on surgical site
What contributes to differential nerve block
Distance d/w nodes of ranvier
An impulse can make it through how many blocked nodes
2
Blockade of __ nodes eliminated conduction along myelinated nerve fiber, __ fiber
- A.
Which agent can do sensory block w incomplete motor block
Bupivicaine. A delta and C fibers blocked. A alpha, beta, and gamma not completely blocked
Physiochemical factors for la absorption
PKA, ph, lipid solubility
Physiologic conditions for LA absorption
PH of tissue, pco2, temp, pt characteristics
High to low absorption of block
IV, tracheal, intercostal, caudal, paracervical, epidural, brachial plexus, subarachnoid, SQ
Ionization of LAs
Unionized diffuses across nerve membrane, once inside unionized and ionized equilibrate, ionized binds receptor inside na channel= blockade
Ionized form favored in which environment
Acidic drug in basic enviro. Basic drug in acidic enviro
Non ionized form favored when
Acidic drug in acidic enviro
LAs are __ in body and __ in bottle. PKA range
Basic, acidic. 7.5-9
___ drug penetrates nerve sheath and axon membrane to reach site of action
Non ionized
___ drug binds and blocks na channel
Ionized
In high/normal ph the rate and amt of absorption is ___
Higher
PKA high to low
Procaine (8.9), tetracaine (8.5), bupivicaine, chlorprocaine, lidocaine, etidocaine, mepivacaine
What bicarb does to block
Inc onset, enhances depth, and inc spread of block
What temp does to absorption
Decreasing temp reduces drug absorption across nerve membrane
Hasselbach eqn
Ph-pka= log nonionized/ionized
Most imp[ortant factor in potency. 3 most potent
Lipid solubility. Most lipid soluble: etidocaine, bupivicaine, tetracaine
DOA proportional to what
Amt of time LA in contact w nerve fiber
Most imp factor DOA
Protein binding
Purpose of using vasoconstrictor w LA
Inhibiting systemic absorption, prolonging effect, detecting IV injection
3 long acting
Tetracaine, etidocaine, bupivicaine
2 moderate acting
Lidocaine, mepivicaine
2 short acting
Procaine and chloroprocaine
What determines LA conc in blood
Concentration LA, tissue blood flow
LA metabolism
Hydrolyzed by pseudocholinesterase enzymes in plasma, less extent in liver
LA metabolite, exception to metab
PABA. Cocaine metab in liver mainly
Metabolism of amides
Liver, microsomal enzymes. More complex and slower than metab of esters. Aromatic hydroxylation, n dealkylation, amide hydrolysis
Onset most influenced by
PKA
Max dose: bupivicaine
2.5 mg/kg
Max dose: ropivicaine
3 mg/kg. 3.5 mg/kg w epi
Max dose: etidocaine
4 mg/kg
Max dose: lidocaine
4 mg/kg. 7 mg/kg w epi
Max dose: mepivicaine
4 mg/kg. 7 mg/kg w epi
Max dose: chlorprocaine
12 mg/kg
Max dose: cocaine
3 mg/kg
Max dose: tetracaine
3 mg/kg
Most cardiac toxic
Bupivicaine, cardiac arrest at low toxic levels
Inc risk of cv toxicity
Pregnancy, hypoxia, ph abn, cv modulating drugs
Dose of intralipid
20% 1.5 ml/kg rapid bolus. Gtt 0.25 ml/kg/min for 10 min
Allergic rxns: which more common, preservative rxn
Esters d.t paba. Methylparaben
Analgesia promoted by adding what to LA
Opioids, clonidine, epi
What prolongs DOA of ester anesthetics
Pseudocholinesterase inhibitors
Which drugs dec hepatic bf and dec clearance Of amide LA and cocaine
Cimetidine and propranolol
Procaine: what it is, use
Ester prototype, spinal anesthesia
Procaine: why not ideal
PKA 8.9, slow onset, 97% ionized. Short DOA. Nausea, cns SE, metabolite interferes w efficacy of sulfonamide abx
Tetracaine: use, DOA
Spinal and corneal anesthesia. Long, 6 hrs w epi
Tetracaine: implic w epidural
Not popular, slow onset and profound motor block. Toxicity risk w large doses
Chloroprocaine: use
OB epidural anesthesia, fast hydrolysis in serum reduces toxicity risk. Short duration
Lidocaine: % for topical, regional, PNB
4, 0.25-0.5, 1-2
Lidocaine: % for spinal and epidural
1.5-5%, 1.5-2%
Lidocaine metabolites
Monoethylglycinexylide 80% activity, xylidide 10%
Lidocaine linked to what w spinal use
Cauda equina syndrome
Mepivicaine: similarities
Structurally- bupivicaine. Clinically- lidocaine.
Mepivicaine: onset, DOA, e 1/2
Rapid, less vasodilation= longer DOA, 2 hrs
Mepivicaine: toxicity, not effective where
More cns toxicity than lidocaine. Topically
Prilocaine: metabolite, avoid in what
Ortho toluidine, toxic, avoid in OB
Prilocaine: max dose and what can happen
> 600mg leads to conversion of hgb to methemoglobin.
Prilocaine: tx for methemoglobinemia
Methylene blue 1-2 mg/kg iv over 5 min
Etidocaine: % for Pnb, epidural
0.5-1%. 1-1.5%
Etidocaine: about solubility and duration
Lipid soluble, long acting, rapid onset. PKA 7.7
Bupivicaine: comparison to lido, good choice for what
Longer DOA and onset than lido. Good for differential nerve block (sensory > motor) and for labor or post op pain
Bupivicaine: concentrations for spinal, epidural, PNB
Spinal: .5-.75. Epidural: .0625-.5, PNB: .25-.5
Bupivicaine: ___ bound to what. SE pro
Protein, alpha 1 glycoprotein. Low incidence of neuro complic w spinal.
Bupivicaine SE con
Cardio toxic (0.5% or lower conc for epidural and PNB), serum e 1/2 3.5 hrs, lasts super long
Ropivicaine: structure, good for what
S or levo enantiomer of homolog of bupivicaine w propyl tail on pipe riding ring. Differential block
Ropivicaine: less ___, more ___. Use when ___ __ needed
Cardiotoxic, vasoconstriction. Larger doses
Ropivicaine: how its different from bupivicaine
2 active metabolites, shorter 1/2t (2 hrs) than bupiv
Levo bupivicaine: structure, less what
S- enantiomer of bupiv. Less cardiotoxic
Levo bupivicaine: 1/2t, use when
2.6 hrs, large local doses needed
PNB dosing dictated by what
Volume by type of block. Conc based on limitations of max dose balanced w density of block desired
Epidural: vol dictated by what
Level of block, 1.25-1.6 ml/segment. Conc based on block density desired (labor v surgical epidural)
