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Anesthesiology 398 and 466 > Lecture 6 Inhalational Anesthetic Agents > Flashcards

Lecture 6 Inhalational Anesthetic Agents Flashcards

1
Q

What was the first anesthetic?

A

Nitrous oxide

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2
Q

What are the 3 anesthetic agents we use today?

A
  1. Sevoflurane
  2. Desflurane
  3. Isoflurane
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3
Q

What are the different ways inhalation anesthetics are administered?

A
  1. Mask
  2. Induction chamber
  3. Endotracheal tubes
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4
Q
  1. Which anesthetics are liquiz at standard temperature and pressure (STP)?
  2. How are they delivered?
A
  1. Liquid:
    • Sevoflurane
    • Desflurane
    • Isoflurane
  2. Delivered via a vaporizer in gaseous state
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5
Q
  1. What anesthetic is gas at STP
  2. How is it delivered?
A
  1. Nitrous oxide
  2. Delivered via a flow meter in gaseous state
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6
Q
  1. What is partial pressure?
  2. Total pressure?
A
  1. Each gas exerts own pressure (partial pressure)
    • Dalton’s Law
  2. Total pressure = sum of partial pressures
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7
Q

What is Saturated Vapor Pressure (SVP)

A
  • Vapor pressure - exerted by molecules in gaseous phase in the container
  • Saturated – maximum achievable conc. of molecules in gaseous phase at a specific temperature
  • Equilibrium – dynamic exchange between molecules in liquid and gaseous phase
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8
Q
  1. Is saturated Vapor Pressure (SVP) dependent on atmospheric pressure?
  2. Temperature?
A
  1. Unaffected by altitude
  2. Is affected by temperature
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9
Q

Does the Saturated Vapor Pressure (SVP) change between agents

A

Yes, its Agent specific

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10
Q

What agent needs to be electricly heated?

A

Desflurane

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11
Q

Gas movement driven by:

A
  1. Partial pressure gradient across tissues
    • In mixtures each gas follows its gradient
  2. Chemical affinity for tissue e.g. lipid solubility
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12
Q

Movement stops at _____?

A
  • equilibrium
    • Same partial pressure, not same concentration!
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13
Q
  1. What is the Partition Coefficient
  2. What does a low or high number mean?
A
  1. Indicates gas affinity for adjacent tissue at equilibrium
    • Expressed with names of tissues followed by number
    • e.g. blood/gas p.c. = 0.5
    • blood/brain p.c. = 3
  2. low partition coefficient means less soluble
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14
Q

what is the purpose of Modern Vaporizers

A
  1. Dilute anesth. vapor to safe % for patient
  2. Deliver precisely the selected %
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15
Q
  1. Can you use different agents between vaporizers?
  2. Different concentrations?
  3. Is it temperature compensated?
A
  1. Agent specific
  2. Concentration calibrated
  3. Temperature compensated
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16
Q

What happens to the anesthetic agents if they are not temperature compensated?

A
  • Molecules evaporate –> liquid agent cools
  • SVP drops –> less molecules evaporate
  • Vaporizer % output becomes inaccurate
  • Less anesth. gas reaches the patient
  • Patient wakes up
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17
Q

14( need good notes)

How do the vaporizers do Temperature Compensation

A
  1. Made of copper or bronze
    • High thermal conductivity (heat sink)
  2. Device that alters carrier gas flow ratio
    • E.g. bimetallic strip
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18
Q

What affects the Kinetics of Inhalational Anesthetics from alveoli to blood?

A
  1. Gas delivery to alveoli
    • Gas % in alveoli
    • Alveolar ventilation
  2. Gas removal from alveoli
    • Solubility in blood
    • Alveolar-venous gradient
    • Cardiac output
      • High CO delays onset of anesthesia
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19
Q

What affects the Kinetics of Inhalational Anesthetics from blood to tissues?

A
  1. Blood supply to tissue/organ
  2. Solubility in tissue
  3. Tissue/organ size
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20
Q

What are the highly vascularized organs that recieve about 70% of cardiac output

A
  1. Brain
  2. Liver
  3. Kidney
  4. Heart
21
Q
  1. What affects how deep an animal gets in anesthesia (regarding kinetics)
  2. How does the animal recover?
A
  1. the uptake of anesthesia by the brain and spinal cord effects how deep the animal is
  2. reversing the gradient (turning off anesthetic) the anesthesia moves out from the tissues, into the blood, and is then exhaled out of the body- animal then recovers
22
Q
  1. What happens if an agent has a low blood/gas p.c?
  2. What about high?
A
  1. Will get to brain faster
  2. Will get to brain slower
23
Q
  1. What happens if an agent is least soluble?
  2. More soluble?
A

Rate of rise in the alveolar anesthetic concentration (FA) toward the inspired concentration (FI).

  1. The rise is most rapid with the least soluble agent and
  2. slowest with the most soluble agent.
24
Q

What is MAC?

A

Minimal Alveolar Concentration (MAC) of anesthetic that prevents purposeful movement in response to a standard noxious stimulus in 50% of a test population

25
Q
  1. How is MAC established?
  2. If you have a high MAC will you have a low or high potency?
A
  1. Established in experimental animals at STP
    • Anesthetized with anesthetic gas only
    • Stimulus = skin incision, tail or toe clamp
  2. High MAC = low potency
26
Q

What are the MAC values of isoflurane for

  1. Horse
  2. Dogs
  3. Cat
  4. Ranges
  5. Vaporizer scale
A
  1. Horse- 1.3
  2. Dog- 1.3
  3. Cat- 1.6
  4. Range- 1.3 - 1.6
  5. Vaporizer scale- 0-5
27
Q

What are the MAC values of sevoflurane for:

  1. Horse
  2. Dogs
  3. Cat
  4. Ranges
  5. Vaporizer scale
A
  1. Horse- 2.3
  2. Dog- 2.4
  3. Cat- 2.6
  4. Range- 2.3-2.5
  5. Vaporizer scale- 0-8
28
Q

What are the MAC values of desflurane for:

  1. Horse
  2. Dogs
  3. Cat
  4. Ranges
  5. Vaporizer scale
A
  1. Horse- 7
  2. Dog- 7-10
  3. Cat- 9-10
  4. Range- 7-10
  5. Vaporizer scale- 0-18
29
Q

What are factors that decrease MAC

A
  1. Sedatives, analgesic, N2O
    • MAC sparing effect
  2. Old age
  3. Hypothermia
  4. Hypotension
  5. Pregnancy (25-40% MAC reduction)
  6. Severe hypoxemia (PaO2 < 38 mm Hg)
  7. Severe hypercapnia (PaCO2 > 90 mm Hg)
30
Q

What are factors that increase MAC

A
  1. Hyperthermia
  2. Pediatric (human)
  3. Sympathoadrenal stimulation
31
Q
  1. How can you measure gas during anesthesia
  2. What do the numbers mean
A
  1. Gas analyzer: displays insp. & exp. %
  2. Exp. % (ET or alveolar) mirrors brain tension
    • Compare exp. % to MAC for clinical use
32
Q

What does the 1.5 mean?

A

Are giving to much

33
Q

What is the Mechanism of Action of anesthetic agents

A

interaction with proteins

  • Transmembrane proteins of ion channels
    • GABAA and glycine receptors
      • Enhancement of inhibitory post-synaptic channel activity
    • NMDA and serotonin receptors
      • Inhibit excitatory synaptic channel activity
34
Q

How is nitrous oxide administered

A
  • 50% nitrous oxide mixed with 50% O2
    • O2 must be at least 30% O2 in mixture
    • Risk of hypoxic gas mixture
35
Q

What are advantages to Nitrous Oxide (N2O)

A
  1. Analgesic properties
  2. MAC sparing effect on other gases
  3. Does not cause hypotension
36
Q

What is the Second Gas Effect of N2O

A
  • If push a lot of N20 to the blood and the concentration is higher than the inhalant, then there isnt a lot of inhalant so then the inhalent will diffuse to the blood
    • N2O enhances initial uptake of co-administered gas (2nd gas)
    • Due to initial high-volume N2O uptake
37
Q

N2O Diffuses in Gas-filled Cavities, when do you not use it because of this?

A
  1. Rumen-stomach-intestine
  2. Middle ear
  3. Closed pneumothorax
  4. Air bubbles/emboli
  5. ET tube cuff
38
Q

What can cause a Hypoxic Gas Mixture during Anesthesia

A
  • Risk with circle system at low fresh gas flows
    • N2O not metabolized & rapidly equilibrates with brain
      • % builds up in the breathing system
    • Reduces O2 % in system
39
Q

If no gas analyzer available, how do you prevent a Hypoxic Gas Mixture during Anesthesia

A
  • High fresh flow to prevent N2O build up
  • Avoid N2O
40
Q
  1. What is Diffusion Hypoxia at Recovery using N2O
  2. How can you prevent it?
A
  1. As soon as administration is discontinued N2O leaves body tissues and ‘floods’ alveoli
    • Reduced O2 % in alveoli
  2. Provide high O2 flow for several minutes after N2O off
41
Q

What are N2O Toxicities

A
  1. Chronic exposure (traces)
  2. Impairs vitamin B12 synthesis
    • Myelin formation
    • DNA synthesis
  3. Has been associated with: (long term exposure)
    • Miscarriage
    • Teratogenicity
    • Bone marrow depression
    • Peripheral neuropathies
    • Depressed leucocyte function
42
Q

What do all anesthetic agents do to arterial blood pressure

A

Decrease, hypotension

43
Q

What cardiovascular effects do all anesthetic agents cause?

A

Decreased arteriole blood pressure and hypotension

44
Q
  1. Why does carbon monoxide get produced from anesthetic agents?
  2. Which agents?
A
  1. Anesth gas reaction with soda lime
  2. Agents:
    • Des & Isoflurane (CHF2 moiety)
    • Sevoflurane (if high T° & dry soda lime)
45
Q
  1. What are predisposing factors of Carbon Monoxide Production
  2. What can you do to avoid buildup?
A
  1. Predisposing factors
    • Dry soda lime
    • High NaOH conc.
  2. To avoid build up:
    • Fresh soda lime
    • High fresh gas flow
46
Q
  1. What causes compound A?
  2. Why is it bad?
  3. How do you prevent?
A
  1. Product of sevoflourine degradation
    • Likely when hot or dry soda lime
  2. Nephrotoxic in rats at high conc.
  3. For safety at least 2 L/min O2 in circle system
    • Probably not a clinical concern in animals
47
Q
  1. What is Malignant Hyperthermia
  2. What causes it?
  3. Which agents can cause it?
A
  1. Life-threatening myopathy
    • animal becomes stiff and increased temperature
  2. Due to genetic defect
  3. Possible with all -fluranes
    • Not with N2O
48
Q
  1. Which animals can get malignant hyperthermia
  2. What is the treatment?
A
  1. Humans, pigs, dogs, horses
  2. Treatment
    • Dantrolene (muscle relaxant)
    • Symptomatic

Anesthesiology 398 and 466 (22 decks)

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