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Inhalant Anesthetics Flashcards

1
Q

purpose of inhalant anesthetics

A
  • produce general anesthesia by:
    • rendering patient unconscious
    • providing some degree of muscle relaxation
  • do not have any inherent analgesic properties
  • suitable for wide variety of species
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2
Q

main difference with inhalant anesthetics

A

administered and in large part removed from the body via the lungs

do not rely on hepatic metabolism and renal elimination

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3
Q

how inhalants are administered

A

liquid anesthetics are first vaporized and then administered in an enriched concentration of oxygen via a breathing circuit to the patient

requires specialty equipment (heavy, bulky)

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4
Q

equipment needed for inhalants

A
  • vaporizer
  • source of oxygen
  • anesthetic machine
  • breathing circuits
  • scavenging equipment
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5
Q

scavenging equipment is essential to:

A

help minimize occupational hazards involving waste gases

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6
Q

potency of inhalants

A

is an expression of the relationship between the administered dose of an inhalant and the anesthetic effect that is obtained

MAC is the most commonly used expression of potency of inhalants

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7
Q

MAC

A

minimum alveolar concentration of anesthetic which prevents gross, purposeful movement in 50% of patients exposed to a noxious stimulus

similar to ED50

determined in young healthy animals without use of additional CNS depressant drugs

mirrors the brain partial pressure of the inhalant

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8
Q

MAC of isoflurane

A

Dog: 1.14-1.5%

Cat: 1.28-1.6%

Horse 1.3-1.6%

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9
Q

MAC of sevoflurane

A

Dog: 2.1-2.4%

Cat: 2.6-3.1%

Horse: 2.3-2.8%

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10
Q

MAC of desflurane

A

Dog: 7.2-10.3%

Cat: 9.8-10.3%

Horse: 7.0-8.0%

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11
Q

general guideline for MAC during surgery

A

anesthesia is begun at 2-3 times MAC for the particular agent and anesthesia can be maintained at 1.5-2 times agent’s MAC value

will depend on individual patient, other drugs used and type of surgery

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12
Q

factors that can increase MAC

A
  • hyperthermia
  • hypernatremia
  • drugs that cause CNS stimulation (ephedrine)
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13
Q

variables that decrease MAC

A
  • drugs such as premedications and induction agents
  • use of local anesthetics
  • mean BP below 50 mmHg
  • hyponatremia
  • hypothermia
  • substantial alterations in respiratory gases
  • severe anemia
  • age of patient
  • pregnancy
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14
Q

factors that do not alter MAC

A
  • gender
  • normal respiratory gas concentrations
  • duration of anesthesia
  • metabolic acidosis or alkalosis
  • moderate anemia
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15
Q

vapors

A

administered as a vapor mixed in a gas (usually oxygen) but at ambient temperature and pressure exist as liquids

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16
Q

saturated vapor pressure of a liquid

A

escaping gas molecules from a liquid exert pressure on the sides of the container

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17
Q

highest anesthetic concentration that can be achieved is determined by:

A

saturated vapor pressure of the agent

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18
Q

equation for maximum percentage of inhalant that can be achieved

A

anesthetic vapor pressure

————————————– x 100

atmospheric pressure

atmopsheric pressure at sea level = 760 mmHg

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19
Q

delivered concentration of anesthetic

A

percent setting that is on the vaporizer dial

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20
Q

inspired or inspiratory concentration (FI) of an anesthetic

A

concentration of inhalant that the patient inspires

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21
Q

What should Fi be if patient is apneic?

A

inspired concentration of anesthetic is 0

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22
Q

What is the Fi if the patient is on a non-rebreather?

A

the inspired concentration of anesthetic should be equal to that set on the vaporizer

23
Q

What is the FI if the patient is on a circle rebreathing system?

A

the inspired concentration of anesthetic will be less than that set on the vaporizer as the concentration in the circle breathing system is diluted out by expired gases

24
Q

expired anesthetic concentration

A

the concentration of inhalant anesthetic that is contained in the expiratory gases of the patient

reflection of the alveolar concentration of inhalant

25
alveolar concentration (Fa) of anesthetic
concentration of anesthetic that is in the **arterial blood and delivered to the brain** the anesthetic concentration in the **brain and spinal cord produce unconsiousness and immobility** during inhalant general anesthesia
26
factors that affect getting the inhalant administered from the vaporizer to the brain:
* **inspired anesthetic concentration** * **solubility** of the anesthetic in the blood * patient's **CO** * **ventilation** * the **alveolar to venous partial pressure difference** of anesthetic
27
factors that affect inspired concentration of inhalant delivered to patient:
* **rate** at which **fresh gas** is flowing into the system * **volume** of breathing circuit * if inhalant is **absorbed by the anesthetic machine or breathing circuit** (rubber) * not very common anymore with newer inhalants
28
higher the carrier gas flow rate is through the vaporizer =
the **more rapid the circuit concentration** will **approach the concentration exiting the vaporizer** therefore, rate at which the circuit in a circle rebreathing system and inspired anesthetic concentration can be increased is **directly proportional to rate of fresh gas flow going through vaporizer and entering breathing circuit**
29
effect of the volume of the breathing circuit
a circuit with a **larger volume** will **take longer to equilibrate** and **reach the desired concentration** of anesthetic being delivered to patient
30
time constant
**amount of time** it takes to **fill a 'container'** with desired substance **time constant** (T) (min) = **volume** (L) / **flow** (L/min) **3 time constants** to reach **95%** of desired concentration container = lungs and anesthetic machine
31
factors that affect concentration of inhalant in alveoli
* **solubility** of anesthetic in the blood * patient's **CO** * alveolar **ventilation** * alveolar to venous **PP difference** of anesthetic Fa reflects amount of anesthetic in brain
32
anesthetic solubility
* **inherent property** of gas and is influenced by **ambient temperature** * major factor in **uptake and distribution** of anesthetic agents * expressed as **partition coefficient**
33
partition coefficient of an anesthetic gas
**measure of its solubility** in a specific solvent at a **specific temperature** defined as the **ratio of gas concentrations in the two phases at equilibrium**
34
blood:gas partition coefficient
**blood and inspired gas** provides information about **speed of onset, recovery** and change in **anesthetic depth** the higher the blood:gas partition coefficient, the more inhalant agent will **favor being in the blood** (greater solubility)
35
an inhalant with a **higher blood:gas partition** coefficient:
will have **greater uptake by the tissues** and will have a **lower Fa/Fi ratio** longer onset of action
36
greater the cardiac output =
the greater amount of blood **carrying inhalant away** from the **alveoli and to the tissues** this will **decrease the alveolar (Fa) anesthetic concentration** and slow down the rate at which the Fa reaches the inspired anesthetic concentration (Fi)
37
a decrease in cardiac output =
causes **less blood to flow through the lungs** and therefore **less anesthetic is removed** from them rendering the **onset of general anesthesia more quickly** anesthetic overdose
38
delivery of agent to alveoli depends on the:
**inspired anesthetic concentration** and **alveolar ventilation**
39
higher the alveolar ventilation =
the **faster** the **alveolar anesthetic concentration** will reach the **inspired anesthetic concentration** anesthetics that **decrease ventilation** will d**ecrease rate of rise of alveolar concentration** of inhalant anesthetics --\>support ventilation
40
(Pa-Pv)
partial pressure difference **between alveolar and venous blood** venous blood will **retain some inhalant** when it returns to the lungs for re-oxygenation **highly perfused tissues** (brain...) **equilibrate rapidly** with Pa of anesthetic compared to less well perfused tissues
41
role of metabolism in inhalant removal
**minimal** but **toxic metabolites** can still be produced!
42
inhalants and cardiovascular system
inhalants have a **large impact on CV** **all reduce CO** in a dose dependent fasion **type**, **dose**, and **concurrent drug administration** during anesthesia all affect CV system detrimental due to **effects on oxygen delivery (perfusion)**
43
oxygen delivery
product of oxygen content of blood and CO
44
equations: CO (Q) = BP =
**SV x HR** **Q x systemic vascular resistance (SVR)**
45
inhalants have a **_positive or negative_** inotropic effect?
**negative** results in a **decreased stroke volume**
46
inhalants cause an **_increase or decrease_** in peripheral vascular resistance?
**decrease** which in combo with reduction in CO will causes a **decrease in arterial BP**
47
what factors enhance CV compromise due to inhalants?
* **mechanical ventilation** * changes in **PaCO2** * **surgical** stimulation * **length of exposure** to the inhalant * **other drugs** administered with inhalant
48
ventilation
**arterial concentration of CO2** **tidal volume and respiratory frequency** play an important part inhalants cause a **dose related decrease in ventilation**
49
an increase in PaCO2 will __________________ in a conscious animal? what do inhalants do to this response?
**stimulate respiration** **blunt** the response "safety" mechanism
50
mechanical ventilation's effect on the "safety mechanism"
as **inhalant concentration increases** in the brain, **ventilation** becomes **reduced or absent**, and thus inhalant uptake will be reduce **mechanical ventilation** causes the safety mechanism to be **lost** **= respiratory arrest, then cardiac arrest can occur**
51
use of a balanced anesthetic technique
will allow for a **suitable plane of anesthesia** with **decreased cardiorespiratory compromise** as long as the drugs themselves **do not further exacerbate unwanted side effects** **MAC sparing drugs**: benzos, sedatives (Ace and alpha2s), opioids, and local anesthetics
52
nitrous oxide use
can be used to **supplement inhalants** **gas at room temp**, not a volatile anesthetic agent **MAC** in animals is **~188%** (can't be used alone) **mild analgesic and anesthetic effects**, **few CV side effects** and **minimal respiratory depression**
53
detrimental consequences of nitrous oxide
if administered at **greater than 70% of total gas flow**, **severe hypoxemia** can occur **very insoluble gas** which **readily diffuses out of blood** and into closed gas spaces-will cause **rapid expansion of closed gas spaces** (pneumothroax, sinuses) causing volume and pressure in cavity to increase can cause **bone marrow supppression and anemia** fairly **high abuse potential** which can be fatal

Anesthesia (14 decks)

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