Anesthetics

Question 1

Minimal Alveolar Concentration (MAC)

Answer 1

Measurement of anesthetic potency
is the minimal alveolar concentration that prevents movement in response to pain for 50% of subjects
Advantage: continuously monitored by measuring end-tidal anesthetic concentration, provides a direct correlate to anesthetic concentration at site of action, simple to measure end point ( lack of movement)

Question 2

Mechanism of Anesthesia

Answer 2

Membrane hyperpolarization and effects on synaptic function (inhibitor neurotransmission increased and excitatory reduced)
Molecular Targets:
GABA receptors (chloride channel enhanced)
NMDA receptors- glutamate regulated cation channels (anesthetics that don't interact with GABA inhibit NMDA)

Question 3

Sodium Thiopental

Answer 3

Barbiturate and parenterally administered
Duration of action= 10 minutes
Long half life of 12 hours so residual effects (hangover)
Dose should be reduced if premeditated with other CNS depressants like opiates, Benzodiazapemes, and alpha 2 agonists
Intra-arterial injection= severe inflammation and necrotic
Administered rectally in pediatrics
Side effects:
CNS- reduced cerebral oxygen utilization so reduced cerebral blood flow and intracranial pressure
CV- vasodilation on venous side and severe drops in BP if unable to compensate for venodilation
Respiratory depression

Question 4

Propofol

Answer 4

Onset and duration is same as barbiturates and is used to maintain and induce anesthesia
Antiemetic and advantage for nausea post surgery
Shorter half life than thiopental so used in out patient surgery
Rapidly metabolized in liver and lungs to inactive (excrete in urine)
Side effects:
Elicit pain on injection (given with lidocaine or into larger veins or give prodrug which is water soluble)
Produce excitation during induction
CNS: reduce cerebral oxygen utilization so reduce cerebral blood flow and intracranial pressure
CV: more severe decrease in bp than thiopental (vasodilation and depression of myocardial contractility, blunt baroreceptors reflexes)
More respiratory depression

Question 5

Etomidate

Answer 5

Induce anesthesia if high risk for hypotension
High incidence of pain on injection and myoclonus (spasm of groups of muscles)–> use lidocaine for pain and benzodiazepines or opiates for myoclonus
Side Effects:
CNS- Reduce cerebral oxygen utilization so reduced cerebral blood flow and intracranial pressure
CV- less than thipental and Propofol (small increase in HR with little change in BP)
Less respiratory depression than thiopental
More nausea and vomiting than thiopental
Increase post surgical mortality because suppression of adenocortical stress response

Question 6

Ketamine

Answer 6

Dissociative anesthesia–> profound analgesia, unresponsive to commands (eyes can be open), amnesia (incomplete unless benzodiazapemes administered) , spontaneous respiration
Typically given IV
Advantage: bronchodilator, profound analgesic with less respiratory depression
Side Effects:
Nystagmus, salivation, lacrimation, spont limb movement and increased muscle tone
Increase in ICP
Emergence delirium: hallucinations, vivid dreams, and illusions (reduced with benzodiazepines)
Increased Blood pressures becuase of sympathomimetic activity
Usefulness: used with bronchospasm and children with short painful procedures

Question 7

Midazolam

Answer 7

Short acting benzodiazepine (1-5 hours)–> GABAa activators, used for conscious sedation
Induction agent and as an adjunct for regional anesthesia and anti-anxiety
SLower induction and lower duration than thiopental and Propofol
Metabolized by hydroxylation to active metabolite
Side Effects:
Respiratory depression and respiratory arrest (with conscious sedation)
Cardiovascular- vasodilation on venous side
Effects can be reversed by flumazenil

Question 8

Flumazenil

Answer 8

Reversal of effects caused by Midazolam

Question 9

Components of Anesthetic State

Answer 9

1. Amnesia
2. Unconsciousness
3. Analgesia (inability to interpret, respond or remember pain)
4. immobility in response to noxious stimuli
5. Attenuation of autonomic response to noxious stimuli

Question 10

Isoflurane

Answer 10

Moderate blood: glass partition coefficient
99% excreted from lungs
Uses: common inhaled anesthetic, induce and maintain anesthesia, co-admin with NO to allow for reduction in dose of Isoflurane
Side effects:
Respiratory- bronchodilation, airway irritant, decrease tidal volume and increase respiratory rate, respiratory depressant
CV- vasodilation and decrease in preload and after load so decrease bp, increase heart rate via activation of baroreflex, arrhythmia so, dilates cerebral blood vessel increasing intracranial pressure

Question 11

Desflurane

Answer 11

Liquid that is very volatile at room temp and need special equipment
Very low blood: gas partition coefficient so very rapid induction and recovery
Excreted unchanged
Clinical use: outpatient surgeries, given intravenously, direct skeletal muscle relaxation
Side effects:
CV- similar to Isoflurane and can also trigger activation of sympathetic nervous system to increase HR abd BP
Respiratory- same as Isoflurane and is an irritant

Question 12

Sevoflurane

Answer 12

Ver low blood: gas partition coefficient
About 5% of dose is metabolized to fluoride ion in the liver
Clinical use: inpatient and outpatient for induction and maintenance not a respiratory irritant
Side effects:
CV- similar to Isoflurane except not as much increase in HR because dampen baroreflex
Respiratory: similar to Isoflurane but less respiratory depression

Question 13

Nitrous Oxide

Answer 13

Very insoluble in blood so get rapid equilibration and rapid induction and recovery
Rapid uptake so increase “concentration” of other gasses administered at same time
Need to place patients on 100% oxygen
Use: weak anesthetic and used to produce sedation and analgesia in outpatient dentistry and used in adjunct with other inhalation anesthetics, allows for reduction in their doses
Side effects: can exchange with nitrogen in air containing cavity (pneumothorax), depressed myocardial function but also sympathostimulatn, respiratory effect are minimal, abuse liability

Question 14

Cocaine

Answer 14

Ester local anesthetic
Coal anesthetic activity and blocks NE uptake into presynaptic adrenergic nerves
Potent vasoconstrictor properties
Toxicity and potential for abuse have decreased it’s clinical use
Topical anesthesia of upper respiratory tract where its actions as both vasoconstrictor and local anesthetic provide anesthesia and shrinking of mucosa to limit bleeding

Question 15

Procaine

Answer 15

Short acting local anesthetic
First synthetic local anesthetic
Supplanted by newer agents but still used for infiltration anesthesia
Lower potency, slow onset and short duration of action

Question 16

Tetracaine

Answer 16

Long acting ester local anesthetic
More potent and longer duration of action than procaine
Widely used in spinal anesthesia and in topical and opthalmic preparation
Rarely used for peripheral nerve block because large doses are necessary increasing potential for toxicity

Question 17

Benzocaine

Answer 17

Anesthetic with low solubility in water and too slowly absorbed when applied topically
Applied to wounds and ulcerated surfaces to provide relief for long periods

Question 18

Lidocaine

Answer 18

Amide local anesthetics - intermediate duration of action
Faster, more intense, longer lasting, and more extensive anesthesia than procaine
Use with epinephrine to decrease rate of absorption and toxicity
Metabolized in liver
Clinical uses: any application when local anesthetic of intermediate duration is needed

Question 19

Bupivacaine

Answer 19

Long acting Amide local anesthetic
Long prolonged anesthesia and more sensory than motor block
More cardiotoxic than lidocaine- ventricular arrhythmia and myocardial depression
Dissociates from Na channel slowly resulting in increased potency for blocking cardiac conduction
S- enantiomer available that is less cardiotoxic

Question 20

Ropivacaine

Answer 20

Long acting Amide local anesthetic
S-enantiomer
Similar action to Bupivacaine with less cardio toxicity
Suitable for epidural and regional anesthesia
Even more motor- sparing