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76 Cards in this Set
- Front
- Back
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What are the two classes of local anesthetics?
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Esters
Amides |
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What are the prototype ester local anesthetics?
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Procaine
Chloroprocaine Tetracaine Benzocaine Cocaine |
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What are the prototype amide local anesthetics?
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Lidocaine
Prilocaine Mepivacaine Ropivacaine Bupivacaine Dibucaine |
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What is the mechanism of local anesthetics?
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Block the inward Na current by blocking channels.
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What are the two theories of how local anesthetics block Na current?
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1. Direct block of channels
2. Increasing membrane fluidity and disorganization |
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What is the pKa of local anesthetics? Why?
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8-9 (weak bases), need to by uncharged to gain access to site of action.
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How is specificity obtained with local anesthetics?
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via route of administration
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Discuss the differential block of local anesthetics. Small vs large nerves. Myelinated vs unmyelinated.
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Local anesthetics preferentially block small diameter nerves first. Size the fibers is most important. Then myelinated fibers more than unmyelinated fibers.
SUM>SM>LM |
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What is the order of sensory loss with local anesthetics?
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Pain>Temp>Touch>Pressure
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What fibers carry pain and temperature?
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c-fibers (small unmyelinated)
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Why are local anesthetics often used with epinephrine?
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To cause vascular constriction
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When using a local anesthetic in the subarachnoid space, how can you keep the drug from spreading?
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Use a dense solution (10% glucose) or tilt the patient.
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Where is the action targeted with an epidural?
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at nerve roots as they leave the spinal cord
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How will an infect alter the effects as of local anesthetics?
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Infects make pH more acid. Because local anesthetics are weak bases, they need to be uncharged to access site of action. This will slow the onset of effects.
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What protein will metabolize ester local anesthetics? Where? How fast?
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pseudocholinesterase in the blood, and esterases in the liver, very rapid metabolism
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How are amide local anesthetics metabolized?
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Biotransformed in the liver by amidases
N-dealkylation then hydrolysis in the p450 system. |
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What is the effect of moderate dose local anesthetics on the CNS? High dose?
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Moderate: stimulation
High: depression |
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What are the cardiovascular effects of local anesthetics?
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Depressant: slow conduction, low contractility, long refractory
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What is the vascular effect of local anesthetics? What is the exception?
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Generally all vasodilators, except for cocaine
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Which anesthetics can cause hypersensitivity reactions?
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Esters
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What is the common cause for local anesthetic toxicity?
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systemic absorption
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What factors determine the amount of local anesthetic used for a pt?
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age, weight, health, carrier solution, vasoconstrictor adjunct
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What are common toxic effects of local anesthetics?
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Allergic reaction
light headed shivering seizures hypotension |
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Discuss lidocaine as a local anesthetic. (Type, duration, potency, use)
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An amide
Long duration 2-3 times more potent than procaine Versatile use |
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Why would you use prilocaine instead of lidocaine? What is a risk of prilocaine use?
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Both amides with comparable duration, but prilocaine is less toxic acutely.
Metabolite of prilocaine can cause methemoglobinemia. |
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Which local anesthetic is useful for elderly pts with CV disease?
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Mepivacaine
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Which local anesthetic is not used in obstetrics? Why?
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Mepivacaine because it has slow metabolism in the fetus increasing the risk of toxic effect.
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What is ropivacaine?
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Amide local anesthetic
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Compare bupivacaine and procaine?
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Bupivacaine is a amide that is 10 times for potent with long duration of action, procaine is an ester with potent CNS stimulant effects. Procaine has a metabolite that can cause methemoglobin.
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What local anesthetic is 15 times more potent than procaine, but has slow onset of action? What type is it?
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Dibucaine - an amide
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Which local anesthetic is a vasoconstrictor?
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Cocaine
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Discuss tetracaine as a local anesthetic. (Type, duration, potency)
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An ester
Duration longer than procaine, with slower onset 10 times more potent than procaine |
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What are the two types of general anesthetics?
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Volatiles and Injectables
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What are the prototype volatile anesthetics?
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NO
Ether Halothane Enflurane Isoflurane |
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What are the prototype injectable anesthetics?
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Thiopental
Ketamine Etomidate Propofol Midazolam |
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What are the essential features of general anesthesia?
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Hypnosis
Amnesia Analgesia Immobility |
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What modulated the depth of anesthesia with inhalant anesthetics?
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The partial pressure of the drug in the brain
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How does solubility effect inhalant anesthetics?
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The less soluble the anesthetic the lower the concentration needed to saturate the blood and get the necessary partial pressure in the brain. More soluble drugs take longer to concentrate and get action.
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What is the common structure of general anesthetics?
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Small symmetrical molecules
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What neuronal structures are targeted by general anesthetics?
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Ligand gated ion channels like GABAa Cl channel, nAChR, glutamate
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What is MAC for general anesthetics?
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minimum alveolar concentration = ED-50
Alveolar concentration in which 50% of pts will respond to a surgical incision. |
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What does a low or high MAC mean when using a general anesthetic?
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Low = High potency
High = Low potency Low MAC: lower concentration of drug needed to achieve ED-50. |
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What is the difference between MAC and blood/gas solubility (general anesthesia)?
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MAC is a measure of potency. Low = more potent.
B/G solubility is correlational to the speed of onset. |
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Describe the action of a general anesthetic with a high MAC and low solubility.
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Low potency with fact action.
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Describe the action of a general anesthetic with low MAC and high solubility.
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High potency with slow action.
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Describe Nitrous Oxide as a general anesthetic. MAC, solubility, effect, limitation, uses.
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Very high MAC (>100%)
Very low solubility (0.47) Causes amnesia and analgesia Limitations: no muscle relaxation, causes anoxia. Uses: Reduces the amount of secondary anesthetic that is used to achieve depth. |
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Describe Ether as a general anesthetic. MAC, solubility, effect, limitation, benefits.
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MAC is low (2%)
Solubility is very high (15) Profound muscle relaxant Limitations: low induction and recovery, flammable, irritating to breathe. (VERY SAFE). Benefits: Very little metabolism, nontoxic metabolite, maintains CV stability |
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What are the advantages to Halothane use?
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1. Nonflammable
2. Nonirritating 3. No hypoxia |
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What are the disadvantages to halothane use?
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1. Slow induction, slow recovery
2. Poor analgesia and relaxation 3. Hypotension and respiratory depression 4. Liver toxic |
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What is malignant hyperpyrexia?
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Rare reaction to anesthesia causing a fever above 106.7 due to hypermetabolic reaction in skeletal muscles.
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What drug combination is halothane typically used in?
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Halothane + NO + opiate + NMJ block
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What general anesthetic is at risk for causing seizures?
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Enflurane
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Which inhalant general anesthetic is a good muscle relaxant and potentiates the action of neuromuscular blocking agents?
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Isoflurane
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Which inhalant general anesthetic sensitizes the heart to catecholamines?
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Halothane
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What are inhalant anesthetics used for?
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Induction and maintenance of anesthesia
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Which barbiturate is used to induce anesthesia?
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Thiopental
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Which anesthetic is contraindicated in acute intermittent porphyria?
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Thiopental
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Discuss thiopental. Pros vs cons.
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Pros: No CV sensitization, little metabolism and excretion during anesthesia.
Cons: Profound respiratory depression, bronchospasms in asthmatics, no analgesia, CV output reduced, PR increased. |
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What is the mechanism of Ketamine? What is it used for?
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General injectable anesthetic that blocks glutamate NMDA receptors and may block nAChR
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What are the features of ketamine induced anesthesia?
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Catalepsy: increased muscle tone without convulsion
Catatonia: muscle rigidity with mental stupor Amnesia Analgesia No guaranteed hypnosis |
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Which general anesthetic has elevated CV fx?
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Ketamine
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What are the disadvantages of ketamine as a general anesthesia?
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psychosis: hallucinations, mood changes and altered body image following emergence from anesthesia.
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Which anesthetic is contraindicated for intracranial operations? Why?
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Ketamine, due to increased CV fx causing increased cerebral blood flow and CSF pressure.
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Which injectable nonbarbiturate is used to induce anesthesia?
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Etomidate
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What are the cons for etomidate use in general anesthesia?
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No analgesia
Myoclonic muscle movements common Post-op N/V |
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What are the advantages of etomidate?
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No CV or respirator effect
Decreases cerebral blood flow, ICP, and cerebral metabolism No hepatic, renal, or blood effects |
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What is the most significant adverse effect associated with propofol?
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Hypotension
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Why is propofol typically used with an opioid?
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Propofol does not have analgesic function, but does decrease the amount of opiate needed when used in combination
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Which general anesthetic is very fast acting with short recovery time?
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Propofol
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Propofol should be used with caution is which pts?
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Cardiac disease pts
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Which general anesthetic is used in the maintenance of anesthesia in short procedures?
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Midazolam
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Which benzodiazepine is used as a general anesthetic?
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Midazolam
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What drug combination is used to achieve neuroleptic anesthesia?
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Antipsychotic + fentanyl or sufentanil
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What drug combination is used to achieve a balanced anesthesia?
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Barbiturate + narcotic (opioid) + neuromuscular block + NO + one more potent inhalant
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Which general anesthetic has the highest MAC? Which as the lowest?
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Highest: Nitrous oxide
Lowest: Halothane |
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Which general anesthetic has the highest solubility? Which as the lowest?
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Highest: Ether
Lowest: Nitrous oxide |
