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Anesthesiology > Inhalants > Flashcards

Inhalants Flashcards

1
Q

Why use inhalants?

A

They cause unconsciousness, anti-nociception, and immobility

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2
Q

Disadvantages of inhalants

A
  • Requires specialized equipment
  • Requires airway access
  • Adversely affects mult organ systems
  • Occupational & environmental hazards
  • Horses: assoc w/ incr rate of complications
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3
Q

What are some unique properties of inhalants?

A
  • Administered & eliminated via lungs
  • Predictable & rapid titration
  • State of anesthesia = reversible
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4
Q

What considerations should be made when choosing an inhalant?

A
  • Know what equipment is available (each requires own vaporizer)
  • Desired speed of induction & recovery: diff solubilities
  • Overall costs (Desflurane $$$ > Sevo > Iso $)
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5
Q

Why do inhalants require vaporizers?

A

Isoflurane, sevoflurane, and desflurane are VAPORS!

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6
Q

Define saturated vapor pressure

A

Pressure molecules push against walls of a container when in equilibrium at standard temperature; dictates the max # of vapor molecules available for delivery to a patient

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7
Q

What is the saturated vapor pressure of sevoflurane? Isoflurane? Desflurane?

A
  • 20.7%
  • 31.3%
  • 88.0% - most volatile

*these concentrations will cause ANESTHETIC OVERDOSE! - why we need vaporizers

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8
Q

Why require a vaporizer?

A

Dilutes inhalants with a carrier gas to deliver a clinically safe concentration of inhalant to the patient

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9
Q

What to do if mixing occurs?

A

DON’T USE ON PATIENTS - send out vaporizer for servicing or drain and run a high flow of O2 through for several hours then check for trace vapor levels with a gas analyzer

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10
Q

What is the major goal of inhalant delivery?

A

Achieve an adequate partial pressure in the brain to create unconsciousness

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11
Q

The partial pressure of the brain should be the same as that of what other body part?

A

Alveolar

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12
Q

Why might it be difficult to keep patients anesthetized at high altitudes using equal concentration?

A

B/c there’s a lower atmospheric pressure at higher altitudes, so the partial pressure will be lower (% of inhalant x atm pressure)

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13
Q

A rapid increase in alveolar partial pressure leads to ________

A

A rapid increase in anesthetic depth

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14
Q

In order to rapidly increase anesthetic depth, you must do what 2 things?

A

Increase alveolar delivery and minimize uptake from alveoli

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15
Q

To increase alveolar delivery, you need to do what 2 things?

A

Increase fresh gas flow and minimize breathing circuit volume

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16
Q

Define time constant

A

Time it takes to make 50% change in a closed system (exponential equation)

Time constant = volume/flow

17
Q

When the time constant decreases, what 2 things happen?

A

Faster change in inhalant concentration in the system and faster anesthetic induction

18
Q

How many time constants are needed to make 98.5% change in the system?

A

Five (exponential increase)

19
Q

T or F: agents with low solubility in blood cause faster induction

A

True

20
Q

Higher solubility agent definition and example

A

Gas rapidly moves into blood, but concentration that reaches brain increases more SLOWLY; e.g. isoflurane

21
Q

What is an example of a low solubility agent?

A

Desflurane

22
Q

What are ways to minimize uptake from alveoli?

A

Using agents with low solubility and slowing cardiac output

23
Q

What are the steps for rapid induction or quickly making changes in anesthetic depth?

A
  • Increase inspired concentration of inhalant
  • increase fresh gas flow
  • ventilate patient
  • minimize dead space within circuit
  • premed to minimize pain/anxiety
  • utilize agents with low blood:gas partition coefficient
24
Q

What are the 6 steps to facilitate rapid recovery from inhalant anesthesia?

A

1) Minimize delivery of inhalant (turn off vape, remove excess inhalant from reservoir, remove P from machine)
2) Utilize agents w/ low blood solubility
3) Increase fresh gas flow
4) Assist ventilating the patient
5) Shorten duration of anesthesia
6) Increase cardiac output

25
Q

Define minimum alveolar concentration?

A

Minimum alveolar concentration of an anesthetic that prevents gross purposeful movement in 50% of patients exposed to a noxious stimulus

  • surgical procedures induce patients at 2-3 x MAC
  • anesthetic maintenance 1.2-1.5 x MAC
26
Q

Potency is inversely related to what?

A

Minimum alveolar concentration

27
Q

Rank these according to potency: Sevoflurane Desflurane Isoflurane

A

Isoflurane > Sevo > Desflurane

28
Q

What factors increase MAC?

A
  • Hyperthermia
  • Hypernatremia
  • Drugs that cause CNS stim
  • Incr levels of excitatory NTs
29
Q

What factors decrease MAC?

A
  • Other anesthetics
  • Hyponatremia
  • Hypotension (MAP<50 mmHg)
  • Hypothermia
  • PaO2 <40 mmHg
  • PaCO2 > 90 mmHg
  • Pregnancy
  • Incr age
30
Q

What factors have no effect on MAC?

A
  • Gender
  • Normal resp gas concentrations
  • Duration of anesthesia
  • Metabolic acidosis/alkalosis
  • Mild to moderate anemia
31
Q

What are the CV effects of inhalants?

A
  • CV depression - decr myocardial contraction/CO
  • Hypotension
    • decr CO, widespread vasodilation
  • Minimal direct effect on HR & Arrhythmogenicity
  • Dose dependent

Tx: fluid tx + inotrope/vasopressors

32
Q

What are the effects of inhalants on the respiratory system?

A
  • Resp depression: depressed alveolar ventilation —> hypoventilation
  • apnea possible
  • tolerance to elevated arterial CO2
  • Bronchodilation
    • Dose dependent

Tx: support ventilation

33
Q

What are the neurological effects of inhalants?

A
  • Cause unconsciousness and immobility
  • Elevations in ICP: doses > 1 MAC
  • cerebral vasodilation–> incr cerebral perfusion pressure
  • Decr cerebral metabolic rate
34
Q

What are the effects of inhalants on MS system?

A

Malignant hyperthermia - genetic mutation of ryanodine receptor

  • Inhalants cause massive Ca release from SR in mm —> elevated arterial CO2, tachycardia, hyperthermia, e- imbalances, acidosis—> circ shock & death

Tx: STOP inhalants! Actively cool patient, Dantrolene (impossible to find)

35
Q

Ways to limit occupational hazards of inhalants

A
  • Utilize scavenging systems
  • Limit use of mask & chamber inductions
  • Avoid unnecessary spillage
  • Turn off vaporizer & fresh gas flow when disconnecting patients
  • Pregnant women can wear charcoal facemask
  • Well-ventilated rooms
36
Q

What are the advantages of NO?

A
  • Speeds induction & Reduces inhalant dose
  • Minimal CV effects
37
Q

What are the disadvantages of NO?

A
  • Avoid use in animals with closed gas spaces (colic, GDV, pneumothorax, etc)
  • Diffusion hypoxia at end of anesthesia

Anesthesiology (12 decks)

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