LA1 Flashcards
LA ———-(continue/cease) to provide their clinical effect when they are absorbed into the circulation.
LA cease to provide their clinical effect when they are absorbed into the circulation.
Classification of Local Anesthetics
- Esters
- Amides
- Quinolines
Esters:
Butacaine Cocaine Benzocaine Hexilcaine Piperocaine Tetracaine Chloroprocaine Procaine Propoxicaine
Amides
Articaine ●Bupivacaine ●Dibucaine ●Etidocaine ●Lidocaine ●Mepivacaine ●Prilocaine
Quinoline
Centbucridine
———- is the most potent vasodilator
Procaine
———— is the only LA that produces vasoconstriction
Cocaine is the only LA that produces vasoconstriction
All local anesthetics posses a degree of vasoactivity, most producing ———— (vasodilatation/vasoconstriction)
vasodilatation
With the exception of ———-, local anesthetic drugs are absorbed poorly from the ———- following oral administration.
cocaine, gastrointestinal tract
First Pass Effect of LA
50 to 90% of the absorbed drug is metabolized on the first pass through the liver
———-, uptake of LA is almost as rapid as IV administration.
Tracheal mucosa
when applied to intact skin, they ——(have/do not have) an anesthetic action
intact skin, they do NOT have an anesthetic action
———has been developed to provide surface anesthesia for intact skin
Eutectic mixture of local anesthetics(EMLA)
The rate of absorption after parenteral administration is related to both the ———- of the injection site and the ——- of the drug
vascularity and the vasoactivity
——-administration provides the most rapid elevation of blood levels of LA
IV
IV administration of LA is used in the primary treatment of ventricular dysrhythmias.Why.
IV administration provides the most rapid elevation of blood levels
All LA cross the blood brain barrier and the placenta. T/F
T.
All LA cross the blood brain barrier and the placenta
Blood level of LA depends on:
–rate of absorption into CVS
–rate of distribution
–elimination of the drug
Ester local anesthetics are hydrolyzed in the ——- by the enzyme ————.
plasma, enzyme pseudocholinesterase.
————- Causes an inability to hydrolyze ester local anesthetics
Atypical Pseudocholinesterase
Incidence: 1 out of every 2800 persons
Toxicity depends on:
rate of absorption into the bloodstream at the site of injection
–rate of removal from the blood through the processes of tissue uptake and metabolism
The primary site of biotransformation of amide drugs is the liver.
liver
During bio transformation, ——- (Amides/ Esters) are usually present as the parent compound in greater percentage than ——- (Amides/ Esters).
Amides are usually present as the parent compound in greater percentage than esters.
Slower than normal biotransformation rate leads to _______anesthetic blood levels and potentially ___ toxicity
increased and potentially increases toxicity
Slower than normal biotransformation rate effects on systems:
-Hypotension
-Congestive heart failure (CHF)
-Poor liver function:
Cirrhosis
It usually takes____ half lives to eliminate a drug from the system
6
One half-life =
50% reduction
Two half-lives =
75% reduction
Three half-lives =
87.5% reduction
Four half-lives =
94% reduction
Five half-lives =
97% reduction
Six half-lives =
98.5% reduction
The ____ are the primary excretory organ for both the local anesthetics and its metabolites.
kidneys
T/F:
A percentage of a given dose of local anesthetic drug will be excreted unchanged in the urine
T
Pure localanesthetics are basic compounds that are__(soluble/poorly soluble) in water
poorly soluble
pKa values of pure LA where they have no clinical value
Pure LA: pKa values range
7.5 to10
Why are local anesthetics used for injection are dispensed as acid salts
- localanesthetics are basic compounds that arepoorly soluble in water
- because they are weakly basic, they combine readily with acids to form local anesthetic salts, in which form they are quite soluble in water and comparatively stable.
Most common salt in which LAs are dispensed
hydrochloride salt (e.g., lidocaine HCl, articaine HCl), dissolved in sterile water or saline.
The local anesthetic salt, (both water soluble and stable,)is dissolved in ____
sterile water or saline
Local anesthetic salt, exists simultaneously as uncharged molecules (RN), also called the __,and positively charged molecules(RNH+), called the____.
Unchanged: base
+ : cation
The relative proportion of eachionic form of LA salt in the solution varies with _____
the pHof the solution or surrounding tissues.
In the presence of a highconcentration of hydrogen ions (low pH), the equilibrium shifts to the left, and most of the anesthetic solution exists in ___ form
cationic
As hydrogen ion concentration decreases (higher pH), the equilibrium shifts toward the ___ form
free base
_____is a measure of the affinity of amolecule for hydrogen ions (H+).
pKa
The relative proportion of ionic forms also depends on the _____ of the specific local anesthetic.
pKa, or dissociation constant,
When the__of the solution has the same value as the ____of the local anesthetic, exactly50% of the drug exists in the RNH+form and 50% in the RN form
pH, pKa
The percentage of drug existing in either form can be determined from the _____ equation
Henderson-Hasselbalch equation
pHof a ____ , as well as thepH of ____ greatly influences its nerve-blocking action
local anesthetic solution
pH of the tissue injected
_____ of tissue decreaseslocal anesthetic effectiveness
Acidification
Inadequate anesthesia results when local anesthetics areinjected into _____ or ____ areas
inflamed or infected areas
Most systemic reactions are related to the ____ level of the local anesthetic
plasma level
Systemic Actions of LA on CNS
- Anticonvulsant properties (0.5-4 µg/ml).: raise the seizure threshold
- Preconvulsive Phase (4.5-7µg/ml): Direct depressant action of the local anesthetic on the CNS
- Convulsive Phase (>7.5 µg/ml): Further elevation of the local anesthetic blood level produces clinical signs and symptoms consistent with a generalized tonic-clonic convulsive episode (>7.5 µg/ml)
- Final Stage:
Both inhibitory and facilitory impulses are totally depressed, producing general CNS depression
Preconvulsive Phase due to LA
- 5-7µg/ml).
- Slurred speech
- shivering
- muscular twitching
- tremor in muscle of face and distal extremities
Systemic Actions of LA on CVS
Cardiovascular System
Local anesthetic drug action
-decreases electrical excitability of the myocardium,
- decreases conduction rate, and
- decreases the force of contraction.
Sequence of LA – Induced Actions on the CVS
- At nonoverdose levels, a slight increase to no change in BP
- At levels approaching yet still below overdose, a mild degree of hypotension is noted;
- At overdose levels, profound hypotension is caused by decreased myocardial contractility, cardiac output, and peripheral resistance
- At lethal levels, cardiovascular collapse is noted.
At nonoverdose levels, why does a slight increase to no change in BP occur?
because of increased CO and HR as a result of enhanced sympathetic activity: direct vasoconstriction of certain peripheral vascular beds is noted
At levels approaching yet still below overdose, why is a mild degree of hypotension is noted?
direct relaxant action on the vascular smooth muscle
At overdose levels, why is there profound hypotension ?
due to decreased myocardial contractility, cardiac output, and peripheral resistance
Certain local anesthetics such as _____ may precipitate potentially fatal ventricular fibrillation
bupivacaine (and to a lesser degree ropivacaine and etiodocaine)
_____ muscles are more sensitive to the local irritant properties of local anesthetics
Skeletal muscle
_____ (longer-acting/shorter-acting) local anesthetics cause more localized skeletal muscle damage than (longer-acting/shorter-acting) LAs
longer-acting local anesthetics»_space; more skeletal muscle damage
than shorter-acting drugs
The skeletal muscle LA changes are reversible, with muscle regeneration being complete within __ (time)
2 weeks
Effect of LA at non-overdose levels, on respiratory system
direct relaxant action on bronchial smooth muscle
Effect of LA at overdose levels, on respiratory system
respiratory arrest as a result of generalized CNS depression.
T/F: In general, respiratory function is unaffected by local anesthetics until near-overdose levels are achieved
T
CNS depressants (e.g., opioids, antianxietydrugs, phenothiazines, barbiturates), when administered in conjunction with local anesthetics, lead to___of the CNS-depressant actions of the local anesthetic
CNS depressants»_space;>potentiation»_space;>more depression
Both ester local anesthetics and the depolarizing muscle relaxant succinylcholine require plasma _____ for hydrolysis.
pseudocholinesterase
Prolonged _____may result from concomitant use of CNS depressants
apnea
Drugs that induce the production ofhepatic microsomal enzymes (e.g., barbiturates) may alter therate at which ____ (amide/ester) local anesthetics are metabolized.
Amide
Increased/Decreased)_____ hepatic microsomal enzyme induction increases the rate of metabolism of the local anesthetic
Increased
Malignant Hyperthermia: Acute clinical manifestations include:
tachycardia, tachypnea, unstable bloodpressure, cyanosis, respiratory and metabolic acidosis, fever (as high as 42° C [108° F] ormore), muscle rigidity, and death
Factors in Selection of Local Anesthetic
- Length of time that pain control is required
- Potential for discomfort in the post- treatment period
- Requirement for hemostasis during treatment
- Medical status of the patient
Duration of Anesthesia
- Individual patient variation
- Accuracy in administration
- Anatomical variation
- Type of injection administered
