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anesthesiology > Clinical use of inhalant anesthetics (Granone) > Flashcards

Clinical use of inhalant anesthetics (Granone) Flashcards

1
Q

inhaled anesthetics produce anesthesia by

A
  • unconsciousness
  • immobility
  • muscle relaxation
  • no inherent analgesia properties
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2
Q

inhalent anesthetics don’t depend on

A
  • hepatic or renal function
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3
Q

inhaled anesthetics allow

A
  • rapid and precise adjustment of anesthetic depth
  • rapid and complete recovery
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4
Q

Inhaled anesthetics exist as

A
  • liquids, administered as vapors
    • requires device for accurate conversion
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5
Q

Potency

A
  • dose expressed as minimum alveolar concentration (MAC)
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6
Q

MAC

A
  • minimum alveolar concentration of anesthetic which prevents gross, purposeful movement in 50% of patients exposed to a noxious stimulus
    • birds don’t have alveoli so it’s ‘minimal anesthetic concentration’
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7
Q

relationship between MAC and potency

A
  • inversely related
  • higher the MAC number, the less potent a drug is
  • MAC is additive
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8
Q

What we put in the alveoli mirrors the

A

partial pressure in the brain

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9
Q

MAC values

ISO/SEVO/DES

Dogs and cats

A
  • Dogs: 1.14-1.15 / 2.1-2.4 / 7.2-10.3
  • Cats: 1.28-1.6 / 2.6-3.1 / 9.8-10.3
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10
Q

two sites of action of inhalents

A
  • brain (amnesia)
  • Spinal cord (immobility)
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11
Q

MAC at induction

MAC during a nesthesia maintenance

A
  • need 2-3 times agent MAC to induce
  • need 1.5-2 times agent MAC

*Take into consideration simultaneous drug administration and procedure being performed

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12
Q

Factors that inc MAC

A
  • Hyperthermia
  • Hypernatremia
  • Drugs that cause CNS stimulation
  • Increased levels of excitatory NTs
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13
Q

Factors that dec MAC

A
  • Other anesthetics
  • Hyponatremia
  • Hypotension
    • MAP < 50 mmHg)
  • PaO2 below 40 mmHg
  • PaCO2 above 90 mmHg
  • Pregnancy
  • inc Age
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14
Q

Factors that don’t affect MAC

A
  • Gender
  • Normal resp gas concentrations
  • Duration of anesthesia
  • Metabolic acidosis/alkalosis
  • Mild to moderate anemia
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15
Q

Atropine is a CNS …..

A

stimulant

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16
Q

All inhalants are administered as vapors except

A

N2O

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17
Q

At ambient temp and pressure, inhalant anesthetics are

A

liquids

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18
Q

Saturated vapor pressure

A

pressure exerted by a vapor when it exists in equilibrium with its liquid

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19
Q

Inhalant concentration

A

(Vapor pressure/ barometric pressure) X 100 = vol %

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20
Q

Inspired concentration of anesthetic (FI)

A
  • Patient inspired concentration
  • Not the same with RB vs. NRB systems
21
Q

Expired anesthetic concentration

A
  • Anesthetic concentration expired gases
  • Reflects alveolar concentration
  • Measured by gas analyzer
22
Q

Avleolar concentration of anesthetic (FA)

A
  • reflects arterial anesthetic concentration delivered to brain
  • concentration in brain and spinal cord produce general anesthesia
23
Q

Vaporizer to Brain

A
  • Inspired anesthetic concentration
  • Solubility of anesthetic in blood
  • Cardiac output of patient
  • Ventilation
  • Alveolar to venous partial pressure difference of anesthetic
24
Q

Factors Affecting FI

A
  • Fresh gas flow rate
    • inc flow rate through vaporizer; faster concentration reached
    • anesthetic concentration change is proportional to fresh gas flow rate
  • Circuit volume
    • larger volume, longer equilibration time
  • machine absorption of inhalant
    • older inhalants; rubber parts
25
Q

Flow meter on anesthetic machine is like…..

A
  • the gas pedal in the car
26
Q

Time Constant

A
  • Amount of time to fill container with desired substance
    • Container: lungs, machine
    • Substance: inhalant
    • 3T = 95% concentration change to be achieved
27
Q

Solubility

A
  • total amount of solute dissolved within a solvent at equilibrium
  • inherent property of vapor/gas
    • influenced by ambient temperature
  • Expressed as partition coefficient
    • Blood:gas partition coefficient
      • how much something wants to stay in blood = bad
      • we want inhalent in alveoli, not blood
    • relative affinity of an anesthetic vapor for blood compared to alveolar gas
28
Q

Blood:gas partition coefficient

A
  • speed of onset
  • speed of recovery
  • change in anesthetic depth
29
Q

Higher the blood:gas partition coefficient

A
  • inhalant favor being in blood (more soluble)
  • greater uptake by tissues
  • lower FA/FI ratio
  • longer onset of action, recovery
30
Q

High partition coefficient means drug wants to stay in

A

blood

31
Q

low partition coefficient means drug wants to stay in

A

alveoli

32
Q

Inc CO and uptake

A
  • Inc CO = greater amount of blood carrying inhalant away from alveolit to tissue
    • slows anesthetic onset
    • slows rate of FA
33
Q

Dec CO and uptake

A
  • dec CO = less blood flow through lungs and less anesthetic removed
    • quicker onset of anesthesia
    • anesthetic overdose
34
Q

Inc alveolar ventilation …

A
  • Faster FA reaches FI
35
Q

Partial pressure in alveoli is a balance between

A
  • input to alveoli => delivery
  • loss from alveoli => uptake
36
Q

Alveolar ventilation is more important with….

A

highly soluble agents

37
Q

apnea at induction equals….

A

awakening

38
Q

PA - PV

A
  • Venous blood returning to lungs for re-oxygenation will retain some inhalant
  • PA - PV gradient must exist for uptake to occur
  • Difference related to amount of anesthetic taken up by tissues
    • highly perfused tissues equilibrate faster
  • As gradient dec, uptake dec
39
Q

Distribution depends on …..

A
  • blood flow and tissue capacity
  • inc flow and capacity; inc uptake
40
Q

Inhalant Metabolism

amount of metabolism from most to least

A
  • minimal role in removal of inhalant from body
  • most
    • methoxyflurane: 50-75%
    • Sevoflurane: 2-5%
    • Isoflurane: 0.2%
    • Desflurane: 0.02%
41
Q

Inhalent metabolism and toxic metabolites

A
  • sevoflurane => compound A
  • Isoflurane, desflurane, enflurane => carbon monoxide
42
Q

Cardiovascular effects

A
  • largely impacted by inhalant anesthetics
  • All inhalants reduce cardiac output
    • negative inotropic effect: decrease in stroke volume
    • Decrease peripheral vascular resistance: negative effect on BP
  • Dose dependent
  • Dysrhythmias => halothane, less with iso and sevo
43
Q

Things that enhance cardiovascular compromise (5)

A
  • mechanical ventilation
  • PaCO2 changes
  • Surgical stimulation
  • Length of inhalant administration
  • Concomitantly administered drugs
44
Q

Pulmonary system effects

A
  • Dose related decrease in ventilation
    • blunt the response to increased CO2
    • can act as a safety mechanism

*inc PBRAIN => dec ventilation => dec uptake => dec PBRAIN

*inhalant overdose => respiratory arrest => cardiac arrest

45
Q

Inhalent anesthetics not often administered….

A

alone

  • premeds
  • induction agents
  • CRIs
46
Q

When using inhalant anesthetics strive to use

A

lowerst possible concentration

  • decrease adverse effects
  • MAC sparing drugs
47
Q

When using inhalant anesthetics you should use a

A

balanced anesthetic technique

48
Q

Nirous Oxide

A
  • gas at room temp
  • MAC 188% (can only put something at 100%)
  • mild analgesia and anesthetic effects
  • minimal cardiopulmonary effects
  • admin at 2:1 ratio with O2
  • Diffuses rapidly into closed gas spaces
    • GDV, Colics, middle ear probs, pneumothorax
  • high abuse potential => death
49
Q

Summary of inhaled anesthetics

A
  • unique administration and elimination
  • allow for precise control and adjustment
  • clinical properties are determined by
    • physical and chemical characteristics
    • solubility of agent
  • MOA not fully known
  • All possess desirable and undesirable effects

*Maybe don’t use with sick patients

anesthesiology (14 decks)

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