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Pharmacology Exam 3 > Inhalant Anesthetics > Flashcards

Inhalant Anesthetics Flashcards

1
Q

goal of inhalant anesthetics

A
  • antinociception
  • muscle relaxation
  • unconsciousness
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2
Q

modern inhalants

A
  • organic compounds
    • hydrocarbons
    • ethers (iso, sev, des)
  • inorganic compound (N2O)
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3
Q

halogenation

A
  • addition of Cl, Br, or F
    • decreases reactivity and increases potency
    • makes inhalants non-flammable
  • Br & Cl: increase potency
  • F: improves stability, but rreduces potency and solubility
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4
Q

physcial characteristics of inhalants

A
  • determine how inhalants are administered
    • vapor pressure
    • boiling point
    • liquid density/SG
  • determine how inhalants travel around body
    • solubility
    • blood:gas partition co-efficient
  • states of matter: gas, liquid, solid
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5
Q

gas

A
  • agent that exists in gaseous form at room temp and atmospheric pressure
  • nitrous oxide
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6
Q

vapor

A
  • gaseous state of an agent that exists as liquid at room temp and atmospheric pressure
  • isoflurance, sevoflurane, desflurane
  • still have same physical properties as gas when in gaseous form
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7
Q

vapor pressure

A
  • pressure vapor molecules exert when the liquid and vapor phases are in equilibrium
  • measure of a substance’s ability to evaporate
  • directly related to temperature of liquid
    • as temp increases, vaporization of liquid increases
    • as temp decreases, vaporization decreases
  • unaffected by surrounding atmospheric pressure
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8
Q

partial pressure

A
  • pressure an individual gas exterts on walls of a closed container
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9
Q

dalton’s law of partial pressure

A
  • total pressure of a mixture of gases is equal to sum of partial pressure of all gaseous substances present
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10
Q

three ways to quantify inhalants

A
  • pressure (mmHg)
  • concentration (%)
  • mass (g or mg)
  • most often reported as concentration
    • X% of agent A in relation to whole gas mixture
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11
Q

relationship of partial pressure of inhalant and atmospheric pressure

A

partial pressure of inhalant (mmHg) = fractional anesthetic concentration (%) x total ambient pressure (mmHg)

  • partial pressure will be the same, but volume percent will change with changes in ambient pressure
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12
Q

inhalant concentration (%)

A
  • changes relative to concentration of whole gas mixture
  • changes with changes in atmospheric pressure
  • may be different in various body compartments
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13
Q

saturated vapor pressure of liquid

A
  • maximum concentration of molecules in the vapor state that exists for a given liquid at a given temp
  • pressure exerted on sides of a container from escaped molecules from liquid
  • determines highest attainable anesthetic concentration
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14
Q

critical temperature

A

temperature above which the substance is in its gaseous form and cannot be liquefied by compression

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15
Q

boiling point

A
  • temperature at which vapor pressure = atmospheric temperature
  • decreases with increasing altitude
  • desflurane: boiling point close to room temp, requires heated vaporizer
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16
Q

solubility

A
  • total number of gas molecules dissolved into a solvent
  • amount of gas dissolved depends on
    • partial presure gradient between gas & solvent
    • chemical nature of gas (MW)
    • chemical nature of solvent
  • changes with temperature
  • expressed as partition coefficient
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17
Q

blood:gas partition coefficient

A
  • can help predict speed of anesthetic induction, recovery, and change in depth
  • lower: faster onset and recovery
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18
Q

which anesthetic agent has the fastest onset time at similar conditions?

A

nitrous oxide

blood: gas partition coefficent = 0.41

iso-1.4, sevo-0.68, des-0.45

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19
Q

MOA of inhalants

A
  • not fully known
  • several theories
    • protein receptor hypothesis
    • neurotransmitter availability
    • Meyer-Overton theory
  • principal sites of action: brain, spinal cord
  • partial pressure of anesthetic in brain/spinal cord produces anesthesia
20
Q

oil:gas partition coefficient

A
  • solubility characteristic
  • describes ratio of concentration of anesthetic in olive oil vs. gas phase at equilibrium
  • inversely related to MAC & proportional to potency
21
Q

uptake of inhalant

A
  • removed from alveoli by pulmonary blood
  • influenced by:
    • solubility of anesthetic
    • patient’s CO
    • alveolar-venous anesthetic partial pressure difference
  • increase in any of these will increase uptake
22
Q

solubility of anesthetic agent in body

A
  • whether or not agent will remain in blood
    • less soluble: readily leaves blood to reach equilibrium with gas and tissues
    • more soluble: more “reluctant” to leave blood
23
Q

inhalants with low solubility or low blood:gas partition coefficient are associated with:

A
  • more rapid induction of anesthesia
  • more precise control of anesthetic depth
  • more rapid elimination of anesthetic and recovery
24
Q

inhalant anesthetics and CO

A
  • amount of blood flow to lungs and tissues influences uptake
  • increased CO: greater amount of blood carrying inhalant away from alveoli to tissue
  • decreased CO: less blood flow through lungs with less anesthetic removed
25
Q

venous blood and inhalant anesthetics

A
  • venous blood returning to lungs for reoxygenation will retain some inhalant
  • PA-PV: partial pressrue difference between alveolar and venous blood
  • PA-PV gradient must exist for uptake to occur
  • highly perfused tissues equilibrate faster with PA
26
Q

elimination of inhalant anesthesia

A
  • decrease alveolar partial pressure in the breathing circuit
    • decreasing inspired inhalant partial P which reverses gradient from blood to alveoli
  • affected by:
    • inhalant solubility
    • cardiac output
    • duration of anesthesia
27
Q

inhalant A is highly soluble in blood (high blood:gas partition coefficient), and inhalant B is not.

This means that:

A

inhalant B will cause a faster induction (less soluble)

28
Q

goal of inhalant anesthetics

A
  • antinociception
  • muscle relaxation
  • unconsciousness
29
Q

how does duration of anesthesia influence elimination of inhalant anesthesia?

A
  • elimination of highly soluble agents is slower
    • more time for agent to diffuse into tissues (acts as stored deposits)
  • during recovery, large amount of agent must be removed from these deposits and delivered to alveoli
  • high O2 flow rates and emptying reservoir bag can help hasten recovery
30
Q

volatile anesthetic agents _________ cerebral metabolic rate, which __________ the brain

A

decrease

helps protect

31
Q

Minimum Alveolar Concentration (MAC)

A
  • minimum alveolar concentration of anesthetic which prevents gross, purposeful mov’t in 50% of patients exposed to noxious stimuli
  • inversely proportional to potency of inhalant anesthetics
    • low potency: high MAC value
  • MAC is additive among multiple inhalants
  • can be influence by several factors
    • hyperthermia-increase, pre-meds-decrease
32
Q

partial pressure in alveoli

A
  • balance between input into alveoli (delivery) and loss from the alveoli (uptake by blood/body tissues)
33
Q

inhalant metabolism

A
  • minimole role in removal of inhalant from body
  • toxic metabolites can still be produced
    • can affect metabolism of other drugs
34
Q

pharmacodynamics of inhalants

A
  • effect of a drug on the body
  • desirable and undesirable effects
  • desirable:
    • reversible, dose dependent general anesthesia
    • non-addictive
    • decrease cerebral metabolic rate
    • not dependent on hepatic and renal function
35
Q

inhalants and electroencephalogric wave (EEG)

A
  • EEG gives info about brain electrical activity
  • as depth of anesthesia becomes greater, EEG becomes desynchronized
  • can provide info about abnormal brain function (seizures)
36
Q

inhalants __________ cerebral blood flow

A

increase

  • decrease ventilation -> increase CO2 -> vasodilation
  • decrease systemic vascular resistance -> vasodilation of intracranial vessels
  • related to inhalant dose
  • detrimental if ICP is elevated
37
Q

inhalants _________ ICP

A

increase

  • parallels increase in CBF
  • space within calvarium is fixed
  • pre-existing intracranial disease or mass
    • cerebral damage
    • herniation of brain
38
Q

inhalants and CV effects

A
  • largely impacted by inhalants
  • all inhalants reduce CO
    • negative inotropic effect
    • decrease peripheral vascular resistance
    • dose dependent
  • enhanced CV compromise
39
Q

inhalants and pulmonary system

A
  • dose related decrease in ventilation
    • blunt response to increased CO2
    • can acty as a safety mechanism
  • as inhalant dose increases
    • depressed spontaneous ventilation and tidal volume followed by resp. frequency
    • increased arterial CO2
    • medullary stimulation of respiration due to hypercapnea is reduced
  • respiratory arrest occurs at 1.5-3 MAC
40
Q

apneic index

A
  • ratio of the end tidal concentration of a drug at which apnea occurs to the MAC value
  • sevoflurane is highest
41
Q

inhalants and liver

A
  • minimal hepatic metabolism of inhalants
  • prolongation of drug metabolism
    • decreased CO -> decreased hepatic BF
    • isofluorance most likely to maintain hepatic BF
  • can impact hepatic metabolism of co-administered drugs
42
Q

malignant hyperthermia

A
  • most commonly seen in swine
  • myopathy secondary to inhalant exposure
  • increase in core body temp, secondary to muscle contracture
    • decreased O2 supply and increased CO2
    • circulatory collapse and death
  • tx
    • discontinue inhalants
    • dantrolene sodium (skeletal muscle relaxant)
43
Q

isoflurane

A
  • inhalant general anesthetic
  • rapid induction and recovery
  • minimal cardiac depression
  • low solubility
  • MAC 1.5% (lowest, most potent)
  • best for maintaining hepatic BF
  • precise vaporizer needed
44
Q

sevoflurane

A
  • inhalant general anesthesic
  • MAC: 2.3%
  • may cause seizures
  • high apneic index
  • good for geriatric/debilitated patients
45
Q

desflurane

A
  • inhalant general anesthesic
  • MAC: 7.2% (highest, least potent)
  • respiratory irritant
46
Q

nitrous oxide

A
  • cannot be used along to provide anesthesia due to high MAC (200%)
  • usually give concurrently to lower MAC of other agents

Pharmacology Exam 3 (9 decks)

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