Local Anesthesia CH. 2 Pharmacology of Local Anesthesics PG. 27-38
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| What happens to local anesthetics when they are absorbed into the systemic circulation? | Cease to provide a clinical effect when absorbed from site of administration into the circulation.
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| T/F All local anesthetics possess a degree of vasoactivity, most producing vasodilation and some vasoconstriction. | True
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| Why would procaine be administered by an IA (intraarterial) injection? | attempt to break the arteriospasm and reestablish blood flow to the affected limb. This happens due to an irritating drug being accidental IA administrated.
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| What is the only local anesthetic consistently producing vasoconstriction? | Cocaine
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| What is a significant clinical effect of vasodilation? | Increase in rate of absorption of local anesthetic into blood, decreasing duration and depth of pain control and increasing anesthetic blood concentration and potential for overdose.
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| What is the hepatic first pass effect? | All drug dose absorbed from the gastrointestinal tract is first delivered to the liver by the portal vein. Fraction of it can then be metabolized into the liver before it reaches the systemic circulation.
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| The rate of uptake (absorption) of a local anesthetic after administration is related to what? | Vascularity of injection site and vasoactivity of the drug.
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| Once absorbed into the blood what happens to the local anesthetic? | Distributed throughout the body to all tissues.
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| What organs of the body have a higher blood level of the anesthetic than less highly perfused areas? | Head, liver, brain, kidneys, lungs, and spleen
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| What is the blood level of the local anesthetic influenced by? | Rate at which it is absorbed into the cardiovascular system, rate of distribution of the drug from vascular tissues, elimination of the drug through metabolic or excretory pathways.
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| T/F Rate of distribution is more rapid in the healthier adult than in those what are medically compromised (i.e. congestive heart failure) thus leading to lower blood levels in healthier patients. | True
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| Elimination half-life | Rate at which a local anesthetic is removed from the blood
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| T/F All local anesthetics readily cross the blood-brain barrier and the placenta and enter the circulatory system of the developing fetus. | True
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| Why is metabolism or biotransformation of local anesthetics important? | Toxicity depends on the balance of rate of absorption into the blood stream at the injection site and removal from the blood stream by uptake and metabolism.
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| Where are Ester local anesthetics hydrolyzed? | Plasma by the enzyme pseudocholinesterase
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| Procaine undergoes hydrolysis into what? | PABA, paraaminobenzoic acid
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| Why do Ester local anesthetic commonly have allergic reactions? | PABA, major metabolic product of ester local anesthetics.
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| Atypical pseudocholinesterase causes what? | Inability to hydrolyze ester local anesthetics
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| What does Atypical pseudocholinesterase lead to? | prolongation of higher local anesthetic blood levels and increase potential for toxicity.
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| What is a relative contraindication of Atypical pseudocholinesterase to the use of ester local anesthetics? | Any familial history of difficulty during general anesthesia
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| Absolute contraindication | under no circumstances should this drug be administered to a patient due to potentially toxic or lethal reaction is increased.
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| Relative contraindication | drug in question may be administered to the patient after weighing the risks of using the drug to its potential benefit and nothing else is available.
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| Where is the primary biotransformation of amides? | Liver
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| Prilocaine undergoes metabolism in the liver but also occurring where? | Lungs
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| What influences the rate of biotransformation of an amide local anesthetic? | liver function and hepatic perfusion
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| Who is unable to biotransform amide local anesthetics at a normal rate? | Patients with lower than usual hepatic blood flow (i.e. hypotension, congestive heart failure, poor liver function, cirrhosis)
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| What does slower than normal biotransformation rate lead to? | increased anesthetic blood levels and a potential increase in toxicity.
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| What represents as a relative contraindication to the administration of amide local anesthetic drugs? | Significant liver dysfunction (ASA IV or V) or heart failure
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| What local anesthetic has a shorter half-life due to a portion being biotransformed by the enzyme plasma cholinesterase? | Articaine (Septocaine)
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| The kidneys are primary excretory organ for what? | Local anesthetics and its metabolites
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| Significant renal impaired patients may be unable to eliminate what? | Parent local anesthetic compound or its major metabolites from the blood, resulting in slightly elevated blood levels and an increased potential for toxicity.
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| T/F Patients undergoing renal dialysis and those with chronic glomerulonephritis or pyelonephritis have a relative contraindication to local anesthetics. | True
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| Local anesthetics | chemicals that reversibly block action potentials in all excitable membranes.
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| When local anesthetics are absorbed from their site of administration into the circulatory system, what happens next? | Circulatory system dilutes it and carries it to all cells of the body.
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| What does the blood level of the anesthetic depend on? | Uptake from site of administration into the circulatory system resulting in increasing the blood level and rate of distribution in tissue and biotransformation in the liver which then removed from the blood level.
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| What is the pharmacologic action on the CNS from local anesthetics. | Depression
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| At higher (toxic overdose) levels the clinical manifestation is what? | Generalized tonic-clonic convulsions.
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| What local anesthetics have demonstrated anticonvulsant properties at a blood level below which some produce seizure activity? | Procaine, Lidocaine, Mepivacaine, Prilocaine, and Cocaine
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| How do local anesthetics action on CNS depression benefit anticonvulsant properties? | Raise threshold by decreasing the excitability of neurons preventing or terminating seizures.
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| Initial clinical signs and symptoms of CNS toxicity are usually what in nature? | Excitatory
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| Lidocaine and Procaine produce what? | Mild sedation or drowsiness
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| If sedation develops in place of excitatory signs 5-10 minutes after administration it should serve as what? | Warning of rising local anesthetic blood levels and a possible serious reaction as in generalized convulsive episode.
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| What increases during local anesthetic induced convulsions? | Cerebral blood flow and cerebral metabolism
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| What happens if there is an increase in blood flow to the brain? | Increase of blood volume of local anesthetic being delivered to the brain prolonging the seizure.
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| What happens if there is increased cerebral metabolism? | Leads to progression of metabolic acidosis as seizure continues prolonging seizure acitivy
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| It is known that local anesthetics exert a depressant action on excitable membranes but what is the primary clinical manifestation with high local anesthetic blood levels? | Stimulation
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| T/F Local anesthetics have a direct action on the myocardium and peripheral vasculature. | True
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| T/F Cardiovascular system is more resistant to the effects of local anesthetic that the CNS. | True
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| As a local anesthetic blood level increases, the rate of what is reduced? | rise of various phases of myocardial depolarization is reduced.
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| Direct cardiac actions of local anesthetics at the blood levels greater than the therapeutic level include what? | Decrease in myocardial contractility and decreased cardiac output, which can lead to circulatory collapse.
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| What is the common local anesthetic drug that consistently produces vasoconstriction? | Cocaine
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| How is peripheral vasodilation conducted? | Relaxation of the smooth muscles in the walls of blood vessels.
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| Increase in local blood flow increases what? | The rate of drug absorption, leading to decreased depth and duration of the local anesthetic action, increased bleeding in treatment area, and increased anesthetic blood levels.
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| What is the primary effect of local anesthetics on blood pressure? | Hypotension
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| What type of tissue is more sensitive to local irritant properties of local anesthetics? | Skeletal muscle
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| What type of local anesthetic causes more localized skeletal muscle damage? | Longer-acting compared to shorter-acting
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| T/F Local anesthetics exert dual effects on respiration. | True
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| Block Neuromuscular Blockade | inhibition of sodium diffusion through a blockade of sodium channels in the cell membrane
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| Malignant Hyperthermia | pharmacogenic disorder in which a genetic variant in the individual alters that persons response to certain drugs.
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