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Pharmacology Exam 3 > Inhalant Anesthetics > Flashcards

Inhalant Anesthetics Flashcards

(46 cards)

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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

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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

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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

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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

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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:

Study These Flashcards
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

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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
venous blood and inhalant anesthetics
* **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
elimination of inhalant anesthesia
* **decrease alveolar partial pressure** in the **breathing circuit** * **decreasing inspired inhalant partial P** which r**everses gradient** from blood to alveoli * affected by: * **inhalant solubility** * **cardiac output** * **duration of anesthesia**
27
inhalant A is highly soluble in blood (high blood:gas partition coefficient), and inhalant B is not. This means that:
inhalant B will cause a faster induction (less soluble)
28
goal of inhalant anesthetics
* antinociception * muscle relaxation * unconsciousness
29
how does **duration of anesthesia** influence **elimination** of inhalant anesthesia?
* **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
volatile anesthetic agents _________ cerebral metabolic rate, which __________ the brain
**decrease** helps **protect**
31
Minimum Alveolar Concentration (MAC)
* 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
partial pressure in alveoli
* **balance** between **input into alveoli** (**delivery**) and **loss from the alveoli** (**uptake** by blood/body tissues)
33
inhalant metabolism
* **minimole role in removal** of inhalant from body * **toxic metabolites** can still be produced * can **affect metabolism of other drugs**
34
pharmacodynamics of inhalants
* **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
inhalants and electroencephalogric wave (EEG)
* 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
inhalants __________ cerebral blood flow
**increase** * **decrease ventilation** -\> increase CO2 -\> **vasodilation** * **decrease systemic vascular resistance** -\> **vasodilation** of intracranial vessels * related to inhalant **dose** * **detrimental if ICP is elevated**
37
inhalants _________ ICP
**increase** * parallels **increase in CBF** * **space** **within calvarium is fixed** * pre-existing intracranial disease or mass * cerebral damage * herniation of brain
38
inhalants and CV effects
* **largely impacted by inhalants** * **all inhalants reduce CO** * **negative inotropic** effect * **decrease peripheral vascular resistance** * **dose dependent** * enhanced **CV compromise**
39
inhalants and pulmonary system
* **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
apneic index
* ratio of the **end tidal concentration** of a drug at which **apnea occurs** to the **MAC value** * **sevoflurane is highest**
41
inhalants and liver
* **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
malignant hyperthermia
* 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
isoflurane
* **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
sevoflurane
* **inhalant general anesthesic** * **MAC: 2.3**% * may cause **seizures** * **high apneic index** * good for geriatric/debilitated patients
45
desflurane
* **inhalant general anesthesic** * **MAC: 7.2% (highest, least potent)** * **respiratory irritant**
46
nitrous oxide
* 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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