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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
Flow meter on anesthetic machine is like.....
* the gas pedal in the car
26
Time Constant
* Amount of time to fill container with desired substance * Container: lungs, machine * Substance: inhalant * 3T = 95% concentration change to be achieved
27
Solubility
* 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
Blood:gas partition coefficient
* speed of onset * speed of recovery * change in anesthetic depth
29
Higher the blood:gas partition coefficient
* inhalant favor being in blood (more soluble) * greater uptake by tissues * lower FA/FI ratio * longer onset of action, recovery
30
High partition coefficient means drug wants to stay in
blood
31
low partition coefficient means drug wants to stay in
alveoli
32
Inc CO and uptake
* Inc CO = greater amount of blood carrying inhalant away from alveolit to tissue * slows anesthetic onset * slows rate of FA
33
Dec CO and uptake
* dec CO = less blood flow through lungs and less anesthetic removed * quicker onset of anesthesia * anesthetic overdose
34
Inc alveolar ventilation ...
* Faster FA reaches FI
35
Partial pressure in alveoli is a balance between
* input to alveoli =\> delivery * loss from alveoli =\> uptake
36
Alveolar ventilation is more important with....
highly soluble agents
37
apnea at induction equals....
awakening
38
PA - PV
* 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
Distribution depends on .....
* blood flow and tissue capacity * inc flow and capacity; inc uptake
40
Inhalant Metabolism amount of metabolism from most to least
* minimal role in removal of inhalant from body * most * methoxyflurane: 50-75% * Sevoflurane: 2-5% * Isoflurane: 0.2% * Desflurane: 0.02%
41
Inhalent metabolism and toxic metabolites
* sevoflurane =\> compound A * Isoflurane, desflurane, enflurane =\> carbon monoxide
42
Cardiovascular effects
* 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
Things that enhance cardiovascular compromise (5)
* mechanical ventilation * PaCO2 changes * Surgical stimulation * Length of inhalant administration * Concomitantly administered drugs
44
Pulmonary system effects
* 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
Inhalent anesthetics not often administered....
alone * premeds * induction agents * CRIs
46
When using inhalant anesthetics strive to use
lowerst possible concentration * decrease adverse effects * MAC sparing drugs
47
When using inhalant anesthetics you should use a
balanced anesthetic technique
48
Nirous Oxide
* 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
Summary of inhaled anesthetics
* 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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