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Pharm II > test 5 inhalation anesthetics > Flashcards

test 5 inhalation anesthetics Flashcards

1
Q

Inhalation Anesthetics

A
  • Maintenance AFTER administration of an IV agent
  • Depth of anesthesia rapidly altered by changing concentration
  • Very narrow therapeutic indices
    * Difference between surgical anesthesia and severe cardiac and respiratory depression is small
  • No antagonists exist
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2
Q

Inhalation Anesthetics Mechanism of Action

A
  • NO SPECIFIC RECEPTOR IDENTIFIED for how they work
  • Variety of molecular mechanisms may contribute
    * Increase sensitivity (affinity for GABA) of GABA receptors to inhibitory neurotransmitter GABA
    * CNS activity diminished
    * Block excitatory postsynaptic currents of nicotinic receptors
    * Increased activity of inhibitory glycine receptors in spinal motor neurons
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3
Q

Inhalation Anesthetics- Common Features

A
  • Nonflammable
  • Nonexpolosive
  • Volatile (Except nitrous oxide, which is gaseous)
  • Decrease cerebral vascular resistance= increased brain perfusion
  • Bronchodilation with decreased spontaneous respiration
  • Depress normal cardiac contractility
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4
Q

Volatile Anesthetics

A
  • require a precision vaporizer for inhalation

• Often incorporated into CPB circuits!

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5
Q

MAC- Minimal Alveolar Concentration

A
  • Median effective dose (ED50) = concentration of the anesthetic at which 50% of the patients will have no movement upon an incision being made
  • Effective dose: elimination of movement during a standard incision
  • Expressed as percentage of gas in a mixture
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6
Q

Low MAC

A
  • More potent = need a lower percentage of it to reach that ED50
  • More lipid soluble
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7
Q

High MAC

A
  • Less potent
  • Less lipid soluble
  • Nitrous oxide
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8
Q

Factors that increase MAC

A
  • Hyperthermia
  • Drugs that ↑ CNS catecholamines
  • Chronic ethanol abuse
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9
Q

Factors that decrease MAC

A
  • Hypothermia
  • ↑ age
  • Acute intoxication
  • Pregnancy
  • Sepsis
  • Concurrent IV anesthetics
  • α2 anesthetics
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10
Q

Inhalation Anesthetic Uptake

A

• GOAL: constant and optimal brain partial pressure of inhaled anesthetic
• MECHANISM: partial pressure drives anesthetic to move => ALVEOLI → BLOOD → BRAIN
• RESULT: partial pressure between alveoli and brain equilibrate and reach a steady state
Palv = Pbld = Pbr

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11
Q

Rate at which equilibration is reached is dependent upo

A
  1. Ventilation
  2. Solubility
  3. Cardiac output
  4. Blood flow distribution
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12
Q

Inhalation Anesthetic Uptake: Ventilation

A
  • Replacement of the normal lung gases with the anesthetic mixture
  • Controlled by:
    * Inspired concentration
    * Ventilation rate
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13
Q

Inhalation Anesthetic Uptake: Solubility

A

• Blood/Gas partition coefficient
• Physical property of the gas
• Low Solubility → little dissolves into blood → few more molecules necessary to increase partial pressure → arterial tension rises rapidly
- small changes can change the anesthetic depth
• High Solubility → dissolves more completely into blood → more molecules dissolve before partial pressure changes significantly → arterial tension increases less rapidly
• Greater amount of anesthetic and longer time required to increase partial pressure in the blood
• Increased time of induction and recovery
• Slower changes in anesthetic depth with increasing concentration

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14
Q

Inhalation Anesthetic Uptake: Cardiac Output

A

• Higher pulmonary blood flow removes anesthetic from alveoli and slows the rate of rise of alveolar gas concentration
• Longer time for Palv = Pbld = Pbr
• Slower induction
- Blood flowing through the lungs pulls away the anesthetics so it’s hard to reach a high partial pressure

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15
Q

Inhalation Anesthetic Uptake: Blood Flow Distribution

A

• Alveolar-venous partial
pressure difference
• Driving force of anesthetic delivery
• Dependent on uptake of anesthesia by tissues
• The greater the A-V difference, the longer the time it will take to achieve equilibrium with the brain
- Palv = Pa = Pbr

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16
Q

Recovery From Inhalation Anesthetics

A

• Same principals in reverse
- blood travels back to your lungs and into the alveoli -> is ventillated -> then out of your body
• Eliminated via ventilation (only metabolized to small extent) (increase ventillation rate to eliminate it faster)
• Less soluble anesthetics eliminated faster than more soluble anesthetics
• Inspired concentration reduced to 0%
• Alveolar ventilation can speed rate of elimination

17
Q

Inhalation Anesthetics: Halothane

A
  • Prototype (co-administered)
  • Mostly replaced due to adverse effects
  • Therapeutic uses:
    * Potent anesthetic/weak analgesic
    * Potent bronchodilator
    * Relaxes skeletal and uterine muscle
18
Q

Halothane Adverse Effects

A
  • Cardiac
    * Vagomimetic- bradycardia (atropine sensitive)
    * Arrhythmias
    * Hypotension
  • Malignant hyperthermia
19
Q

Malignant Hyperthermia (MH)

A 
 Life threatening hyper-metabolism involving the skeletal muscle
 Abnormal receptor interferes with calcium regulation
 Increased CO2 production
 Heat production
 Activation of SNS
 Hyperkalemia
 DIC
 Multiple organ dysfunction
 Death
20
Q

Isoflurane (Forane)

A
  • Does not induce cardiac arrhythmias
  • Pungent odor
  • Stimulates respiratory reflexes so not used for induction
  • Higher solubility than others- used when cost is a factor
  • Dose-dependent vasodilation
    * USEFUL FOR PRESSURE CONTROL ON CPB
21
Q

Sevoflurane (Ultane)

A
  • Low pungency
  • Rapid induction without irritation of airways
  • Rapid onset and recovery
  • Dose-dependent vasodilation
    * USEFUL FOR PRESSURE CONTROL ON CPB
22
Q

Desflurane (Suprane)

A
  • Low solubility= rapid onset and recovery
  • Popular for outpatient procedures
  • Decreases vascular resistance
  • Stimulates respiratory reflexes- no induction
  • Relatively expensive so not used during lengthy procedures
23
Q

Isoflurane (Forane) dosing

A
  • Bottle must be used with appropriate adaptor to fill forane vaporizer on your pump
    * Spillage can cause structural degradation of plastic
  • Set vaporizer at 0.5% to 2% after initiation of gas flow
  • Can be temporarily increased for blood pressure control
  • Concentrations reduced before termination of CPB to minimize myocardial depressant effects
  • Scavenge oxygenator gas outflow when using anesthetic gas (recommended by Prof Gaspar and most people with a conscience)
24
Q

AMSECT standard about anesthetic gas scavenge

A
  • An anesthetic gas scavenge line shall be employed whenever inhalation agents are introduced into the circuit during CPB procedures
25
Q

Short term exposure to Isoflurane (Forane)

A
  • Liver and kidney disease
  • Headache
  • Irritability
  • Fatigue
  • Nausea
  • Drowsiness
  • Compromised performance
    * Decreased vigilance
    * Slow reaction time
26
Q

Long term exposure to Isoflurane (Forane)

A
  • Miscarriage
  • Genetic damage
  • Cancer
  • Miscarriage and birth defects in the SPOUSES of exposed workers
27
Q

Approaches for Scavenging (2)

A
  1. Gas Deactivation: activated charcoal

2. Gas removal: active gas scavenger system connected to anesthesia machine vents to outside hospital

28
Q

Perfusion Relevant Approaches

A

Gas removal:

  1. Ventilate to the outside
  2. Ventilate to vacuum source
29
Q

Perfusion Concerns

A
  • Generation of back pressure into the oxygenator
  • Insufficient oxygenation
  • Cracks in polycarbonate components due to spilled agent
30
Q

Nitrous Oxide

A
  • LAUGHING GAS
    * Concentration of 30-50% with oxygen
  • Potent analgesic
  • Weak anesthetic
    * Commonly combined with other more potent anesthetics
  • May cause diffusion hypoxia during recovery
    * Poor solubility allows rapid movement
    * Fills alveoli upon discontinuation (down concentration gradient)
    * O2 and CO2 are diluted, PO2 decreases and leads to hypoxia
    * Prevention: Ventilate patient with high FiO2

Pharm II (37 decks)

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