General and Local Anesthetics Flashcards by Sarah Gillen

What drugs are considered inhaled general anesthetics

Desflurane
Enflurane
Halothane
Isoflurane
Nitrous oxide
Sevoflurane

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What drugs are considered IV general anesthetics?

Dexmedetomidine
Diazepam
Etomidate
Fentanyl
Fospropofol
Ketamine
Lorazepam
Methohexital
Midazolam
Propofol
Thiopental

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What are the 5 component changes that make up what is known as the “anesthetic state”

Unconsciousness
Amnesia
Analgesia
Attenuation of autonomic reflexes to noxious stimulation
Immobility in response to noxious stimulation (skeletal muscle relaxation)

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Define monitored anesthesia care and what drugs are typically used

A sedation-based anesthetic technique used for diagnostic and/or minor therapeutic surgical procedures

Typically involves use of midazolam for premedication (anxiolysis, amnesia, mild sedation) followed by titrated propofol infusion (moderate to deep sedation)

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Define conscious sedation and what drugs are typically used

Used primarily by nonanesthesiologists (e.g., dentists) where the patient retains the ability to maintain a patent airway and is responsive to verbal commands

Benzodiazepines and opioid analgesics (e.g., fentanyl) are useful because they are reversible by receptor antagonists

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Benzodiazepines and opioid analgesics (e.g., fentanyl) are useful for conscious sedation because they are reversible by receptor antagonists

______ is used to reverse the effects of benzodiazepines

______ is used to reverse the effects of opioid analgesics like fentanyl

Flumazenil

Naloxone

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Define deep sedation and what drugs are typically used

Similar to light state of general anesthesia involving decreased consciousness from which the patient is not easily aroused; accompanied by a loss of protective reflexes, an inability to maintain a patent airway, and lack of verbal responsiveness to surgical stimuli

Propofol and midazolam are often used, sometimes in combination with potent opioid analgesics or ketamine, depending on level of pain associated with the surgery or procedure

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What is the common mechanism of general anesthetic action?

Most general anesthetics cause CNS depression by facilitating Cl- channel activation (GABA and glycine receptors)

Some reduce activity of excitatory ion channels (nAChRs and mAChRs), AMPA receptors, kainite receptors, and NMDA receptors

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Both volatile and gaseous anesthetics are administered by inhalation. What is the difference between volatile and gaseous anesthetics?

Volatile (halothane, enflurane, isoflurane, desflurane, sevoflurane) have LOW vapor pressure and thus HIGH boiling points so they are LIQUID at room temp

Gaseous (Nitric oxide) have HIGH vapor pressure and LOW boiling points and are in GAS form at room temp

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Inhaled anesthetics are absorbed through gas exchange in the alveoli into the blood where the anesthetic is distributed throughout the body. The rate at which this absorption occurs is dependent upon what 3 factors?

Concentration of anesthetic in inspired air
Ventilation rate
Drug solubility in air, blood, and CNS

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What is the blood:gas partition coefficient

Defines the relative affinity of an anesthetic for the blood compared with that of inspired gas (i.e., blood solubility)

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What is the relationship of blood:gas partition coefficient and rate of anesthesia onset?

Inverse relationship — the lower the blood:gas partition coefficient, the more rapid the rate of anesthesia onset

[agents with low blood solubility reach high arterial pressure rapidly, which in turn results in rapid equilibration with the brain and fast onset of action]

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T/F: the brain:blood partition coefficient values for inhaled anesthetics are relatively similar and indicate that all agents are more soluble in the brain than in the blood

True

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What 3 inhaled anesthetics are known for their medium rate of onset and recovery?

Isoflurane
Enflurane
Halothane

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What 2 inhaled anesthetics are known for their rapid onset and recovery?

Nitrous oxide (incomplete anesthetic)

Sevoflurane

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What inhaled anesthetic has a low volatility, is a poor induction agent, and a rapid recovery?

Desflurane

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What areas of the body are highly perfused (over 75% of resting cardiac output) and as a result have higher immediate concentrations of anesthetic?

Brain, heart, liver, kidneys, splanchnic bed

[muscle and skin accumulate anesthetic much more slowly]

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Clearance of inhaled anesthetics via the _____ is the major route of elimination from the body, although some agents are metabolized by the ____ to varying degrees

Lungs; liver

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What is the MAC?

Describes the potency of an anesthetic

The concentration of inhalation anesthetic that prevents movement in response to surgical stimulation in 50% of subjects

[A dose of 1 MAC of any anesthetic prevents movement in response to surgical incision in 50% of patients]

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What would a MAC value of greater than 100% indicate?

If 100% of inspired air is the anesthetic, the MAC value would still be less than 1 and other agents must be supplemented to achieve full surgical anesthesia (example: nitrous oxide)

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Effects of inhaled anesthetics on cardiovascular system

Decrease mean arterial pressure in direct proportion to their alveolar concentration

All inhaled anesthetics can increase right atrial pressure in dose-related manner

Effects on heart rate are mixed — Halothane can cause bradycardia; desflurane and isoflurane can increase HR

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Effects of inhaled anesthetic on respiratory system

Volatile anesthetics are respiratory depressants (the body has a reduced response to increased levels of CO2)

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_____ is an inhaled anesthetic that may cause hepatitis with or without previous exposure (symptoms include anorexia, nausea, myalgias, arthralgias, rash, eosinophilia, hepatomegaly, and jaundice); develops 2 days to 3 weeks after exposure

Halothane

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_____ and ____ are inhaled anesthetics that can cause renal toxicity due to fluorinated metabolites

Enflurane; sevoflurane

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In combination with succinylcholine, inhaled volatile anesthetics may cause what life-threatening condition?

Malignant hyperthermia, consisting of rapid onset tachycardia and HTN, severe muscle rigidity, rhabdomyolysis, hyperthermia, hyperkalemia, and acid-base imbalance acidosis

What is the antidote given to reverse malignant hyperthermia?

Dantrolene (blocks ryanodine receptors)

IV anesthetic characterized by: Rapid onset and moderately fast recovery Provides CV stability; causes decreased steroidogenesis and involuntary muscle movements

Etomidate

IV anesthetic characterized by: Moderately rapid onset and recovery CV stimulation, increased cerebral blood flow, and emergence reactions that impair recovery

Ketamine

IV anesthetic characterized by: Rapid onset and recovery Preferred over thiopental for short ambulatory procedures

Methohexital

IV anesthetic characterized by: Slow onset and recovery Used in balanced anesthesia and conscious sedation; provides CV stability and marked amnesia

Midazolam

IV anesthetic characterized by: Rapid onset and recovery Used in induction and for maintenance; can cause hypotension; has useful antiemetic action

Propofol

IV anesthetic characterized by: Rapid onset and recovery (bolus dose) - slow recovery following infusion Standard induction agent; causes CV depression; avoid in porphyrias

Thiopental

IV anesthetic characterized by: Slow onset and recovery Opioid used in balanced anesthesia and conscious sedation; produces marked analgesia

Fentanyl

MOA of propofol

Most likely targets GABA-A receptors as an agonist and potentiates the Cl- current

Metabolism of propofol

Rapidly metabolized in the liver (phase I and II reactions — glucuronide and sulfate conjugates) with extensive extrahepatic metabolism (lung tissue may account for elimination of up to 30% of bolus dose)

What is the context-sensitive half-life phenomenon that affects IV anesthetics?

After prolonged infusions, drug half-lives and durations of action are dependent on factors such as the rate of redistribution of the drug, the amount of drug accumulated in fat, and the drug’s metabolic rate

The half-lives of _____, _______, and ______ increase only modestly with prolonged infusions The half-lives of _____ and ______ increase dramatically with prolonged infusions

Etomidate; propofol; ketamine Diazepam; thiopental

CNS effects of propofol

General suppression of CNS No analgesic properties Decreases cerebral blood flow and cerebral metabolic rate for oxygen, which decreases intracranial pressure and intraocular pressure

What IV anesthetic, when compared to other induction agents, producs the most pronounced decrease in systemic blood pressure?

Propofol This is due to a profound vasodilation in both arterial and venous circulation leading to reductions in preload and afterload; hypotensive effects are augmented by inhibition of the normal baroreflex response

What is the water-soluble prodrug of propofol that is rapidly metabolized by alkaline phosphatase? What are common adverse effects?

Fospropofol Paresthesias (including perineal discomfort or burning) Pruritis (genital, perineal, generalized)

What IV anesthetic causes minimal cardiovascular and respiratory depression, so it is useful in pts with impaired CV and respiratory systems?

Etomidate

MOA of etomidate

Enhances the actions of GABA on GABA-A receptors

Etomidate has hypnotic but not analgesic effects. It is extensively metabolized by the _____ and in the _____

Liver; plasma

CNS and endocrine effects of etomidate

CNS: potent cerebral vasoconstrictor; decreases cerebral blood flow and intracranial pressure Endocrine: adrenocortical suppression by producing a dose dependent inhibition of 11B-hydroxylase (necessary for conversion of cholesterol to cortisol); thus it has limited use as continuous infusion

MOA of ketamine and general effects

NMDA receptor antagonist Dissociative anesthetic state characterized by catatonia, amnesia, and analgesia with or without LOC (eyes remain open with slow nystagmic gaze); note that lacrimation and salivation may be increased, necessitating pretreatment with an anticholinergic

Main factor limiting ketamine’s use

Unpleasant emergence reactions (vivid dreams, hallucinations, out-of-body experiences, increased and distorted visual, tactile, and auditory sensitivity); may induce euphoric state (potential for abuse)

Only IV anesthetic to produce profound analgesia, stimulation of the sympathetic nervous system, bronchodilation, and minimal respiratory depression

Ketamine

CNS and cardiovascular effects of ketamine

Increases cerebral blood flow (increases ICP) CV: increases systemic BP, HR, and CO

IV anesthetic principally used for short-term sedation of intubated or ventilated patients in an ICU setting or as an adjunct to general anesthesia

Dexmedetomidine

MOA of dexmedetomidine

Alpha2-adrenergic agonist that produces hypnosis presumably from stimulation of alpha-2 receptors in the locus ceruleous and analgesic effects at the level of the SC

Infusion of dexmedetomidine results in moderate _______ in HR, systemic vascular resistance, and systemic BP

Decreases [bradycardia may require tx]

Common IV opioid analgesic agents used as anesthetic adjuncts and their MOA

Fentanyl Sufentanil Remifentanil Morphine MOA: agonists at opioid receptors

Barbiturates commonly used as anesthetic adjuncts, and their MOA

Thiopental Methohexital MOA: acts on GABA-A receptor to increase duration of channel opening (agonist) and enhances inhibitory neurotransmission

T/F: barbiturates induce CYP450 enzymes

True

Benzodiazepines used as common adjuncts to other anesthetic agents, and their MOA

Diazepam, lorazepam, midazolam MOA: acts on GABA-A receptor to increase receptor sensitivity to GABA (agonist) and enhances inhibitory neurotransmission

Which of the benzodiazepines is water-soluble, and thus is considered the drug of choice for parenteral administration?

Midazolam — this is also the drug of choice for patients entering the OR because it has a more rapid onset, shorter elimination half-life, and steeper dose-response curve than the other benzodiazepines

Which of the local anesthetics is surface-use only?

Benzocaine

Which of the local anesthetics are known for having medium duration of action?

Lidocaine Mepivacaine Articaine Cocaine

Which of the local anesthetics are known for having long duration of action?

Bupivacaine Ropivacaine Tetracaine

Which of the local anesthetics are known for having short duration of action?

Procaine (has ester linkages so is more prone to hydrolysis)

_____ is considered a unique local anesthetic due to its intrinsic sympathomimmetic vasoconstrictive properties

Cocaine

Differentiate metabolism of ester-type local anesthetic agents vs. amide-type

Ester-type: metabolized in the plasma Amide-type: metabolized by the liver then excreted in the urine as charged substances (CYP450)

MOA of local anesthetics

Blocks voltage-gated Na+ channel currents and stops the spread of action potentials across nerve axons (receptor site is at inner vestibule of Na+ channel); blocks nerve conduction be decreasing or preventing the large transient increase in the permeability of excitable membranes to sodium that normally is produced by a depolarization of the membrane

The smaller and more lipophilic the local anesthetic, the ______ the rate of interaction with the Na+ channel

Faster; also contributes to potency and longer duration of action

Define infiltration anesthesia

Injection directly into tissue in the vicinity of peripheral nerve endings without taking into consideration the course of cutaneous nerves

Define block anesthesia

Injection into major nerve trunks to anesthetize a region distal to the site of injection

Define spinal anesthesia

Injection into the CSF in the lumbar space; produces anesthesia over a considerable fraction of the body

Define epidural anesthesia

Injection into the epidural space; can be performed in the sacral hiatus or in the lumbar, thoracic, or cervical regions of the spine

Describe IV regional anesthesia (Bier block)

Used for short surgical procedures (<60 mins) involving upper and lower extremities An IV injection of the agent is placed in a distal vein while circulation of the limb is isolated with a proximally-placed tourniquet

Why should you use caution when injecting epinephrine-local anesthetic combinations into muscle tissue?

Epinephrine can activate beta2-adrenergic receptors in skeletal muscle vascular beds and cause dilation —> increased potential for systemic toxicity

Undesired CNS effects of local anesthetics at low doses vs. high doses

Low doses: sleepiness, light-headedness, visual and auditory disturbance, and restlessness (early signs of toxicity = circumoral and tongue numbness + metallic taste) High doses: nystagmus, muscle twitching, convulsions (can premedicate with benzodiazepine when high doses will be used)

Undesired effects of local anesthetic agents on CV system Note the exception!

Local anesthetics block cardiac sodium channels and decrease electrical excitability, conduction rate, force of contraction, and cause arteriolar dilation, leading to systemic hypotension Exception is cocaine, which inhibits NE reuptake and results in vasoconstriction - which can lead to local ischemia, HTN, and cardiac arrhythmias

Which local anesthetic may be the most cardiotoxic due to its long duration of action?

Bupivacaine

Which of the local anesthetics is a class Ib antiarrhythmic? How does it work?

Lidocaine — suppresses automaticity of conduction tissue by increasing electrical stim threshold of ventricle, His-Purkinje system, and spontaneous depolarization of the ventricles during diastole by a direct action on the tissues [blocks initiation and conduction of nerve impulses by decreasing the neuronal membrane’s permeability to sodium ions, which results in inhibition of depolarization with resultant blockade of conduction]

Most common adverse effect associated with lidocaine

CNS toxicity — typically mild, dose-dependent, and always resolves upon discontinuation

Allergies to which type of local anesthetic are more common?

Ester-type [amide-type allergies are extremely rare]

What local anesthetic is described below: Poor solubility in water, used only as a topical agent; used topically for dermatologic conditions, hemorrhoids, premature ejaculation, and as an anesthetic lubricant (e.g., nasogastric and endoscopic tubes and catheters)

Benzocaine

What local anesthetic is described below: Long duration of action capable of producing prolonged anesthesia; has a tendency to provide more sensory block than motor block

Bupivacaine

What local anesthetic is described below: Clinically desired properties are the blockade of nerve impulses and local vasoconstricting actions; primarily used as a topical anesthetic of the upper respiratory tract

Cocaine

What local anesthetic is described below: Due to toxicity associated with injections, now used only as a topical cream for use on the skin

Dibucaine

What local anesthetic is described below: Alternative choice for individuals sensitive to ester-type local anesthetics; produces faster, more intense, longer-lasting, and more extensive anesthesia than an equal dose of procaine; used as antiarrhythmic agent

Lidocaine

What local anesthetic is described below: Compared to newer agents, generally has lower potency, slower onset, and shorter duration of action; used only for infiltration anesthesia; metabolized by para-aminobenzoic acid, which inhibits action of sulfonamide abx

Procaine

The chemical with which blood:gas partition coefficient will reach the highest concentration in the brain the fastest? ``` A. 0.42 B. 0.47 C. 0.69 D. 1.4 E. 1.8 ```

A. 0.42

Two inhaled general anesthetics have the following MAC values: ``` X = 2% Y = 100% ``` Based on this info, which statement is true? A. Drug X has a longer duration of action than drug Y B. Drug X is more soluble in the blood than drug Y C. Drug Y causes greater general analgesia and skeletal muscle relaxation than drug X D. The concentration of drug in inspired air that is needed to cause adequate anesthesia is higher for drug Y than for drug X E. The concentration of drug in inspired air that is needed to cause adequate anesthesia is higher for drug X than for drug Y

D. The concentration of drug in inspired air that is needed to cause adequate anesthesia is higher for drug Y than for drug X

A 27 y/o female undergoes a minor suture procedure for a skin cut on her right leg. A local anesthetic is injected around the wound to provide regional anesthesia. Blockade of which of the following ion channels most likely mediates the pharmacologic effects of the drug? ``` A. Activated, ligand-gated Ca2+ channel B. Activated, voltage-gated Ca2+ channel C. Inactivated, ligand-gated K+ channel D. Inactivated, voltage-gated Na+ channel E. Resting, ligand-gated Na+ channel F. Resting, voltage-gated K+ channel ```

D. Inactivated, voltage-gated Na+ channel

A 42 y/o male presents to the ED following an MVA. He undergoes a minor arm repair procedure requiring a standard dose of lidocaine administered near the brachial plexus for peripheral nerve block. Fifteen minutes later, the anesthesia is still incomplete, and another dose of lidocaine is administered. What adverse effects may occur? ``` A. Drowsiness B. Nystagmus C. Convulsions D. Tachycardia E. Muscle twitching ```

A. Drowsiness

A 2 y/o female presents to the ED after cutting herself with a kitchen knife. The fingers are bleeding. Exam reveals 2 clean wounds on the middle and ring fingers of the right hand. Lidocaine without epinephrine is administered prior to suturing the wounds closed. Why was epinephrine avoided in this situation?

Epinephrine-containing solutions should not be injected into tissues supplied by end arteries (fingers, toes, ears, nose, penis, etc.) because the resulting vasoconstriction can lead to ischemic gangrene

A 60 y/o male is scheduled for lithotripsy to shatter a bladder stone. Lumbar epidural anesthesia is selected for the procedure. The anticipated duration of the procedure is about 20 minutes. Which local anesthetic is most appropriate for this patient? ``` A. Benzocaine B. Bupivacaine C. Cocaine D. Lidocaine E. Tetracaine ```

D. Lidocaine

A 56 y/o female presents to the ED after accidental self-injury with a box cutter. She is visibly agitated and firmly refuses any injection procedure. Exam of the wound shows a long superficial cut of the skin with extensive bleeding. The anesthesiologist applies a solution of a topical anesthetic that also causes local vasoconstriction. Which of the following was most likely administered? ``` A. Bupivacaine B. Cocaine C. Lidocaine D. Prilocaine E. Tetracaine ```

B. Cocaine

Nitrous oxide is a common component in the technique of balanced anesthesia. It is used in conjunction with such other drugs as a halogenated hydrocarbon volatile liquid anesthetic, and usually included as 80% of the total inspired gas mixture. Why isn’t nitrous oxide utilized as a singular agent for general anesthesia? A. Almost total lack of analgesic activity, regardless of concentration B. Inspired concentrations greater than 10% or so tend to have profound cardiac negative ionotropic effects C. MAC is greater than 100% D. Such great solubility in blood that its effects take an extraordinarily long time to dvelop E. Very high frequency of bronchospasm

C. MAC is greater than 100%