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Inhalant Anesthetics Flashcards

1
Q

Why use inhalant anesthetics?

A
  1. Predictable effects
  2. Rapid adjustment of anesthetic depth
  3. Minimal metabolism
  4. Economical
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2
Q

Nitrous oxide

A
  • Low blood gas PC (0.47)
  • Mild analgesic
  • Accumulation in closed gas spaces
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3
Q

Xenon

A

Expensive, used mostly experimentally

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4
Q

Solubility

A

Anesthetic vapors dissolve in liquids and solids

Equilibrium is reached when the PP of the anesthetic is the same in each phase (pressure, not number of molecules)

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5
Q

Partition coefficient

A

Expression of solubility
Concentration ratio of an anesthetic in the solvent and gas phases, describes the capacity of a given solvent to dissolve an anesthetic

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6
Q

Blood-gas partition coefficient

A

Most clinically useful number

Describes amount of anesthetic in the blood vs. alveolar gas at equal partial pressure

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7
Q

What does the pressure of anesthetic in the alveolar gas represent?

A

Brain concentration- location of effect

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8
Q

T/F: Anesthetic in blood is pharmacologically active?

A

False

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9
Q

Most to least soluble anesthetics

A 
Halothane= 2.54
Isoflurane= 1.46
Sevoflurane= 0.68
Desflurane= 0.42
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10
Q

Low blood-gas PC

A
  1. Less anesthetic dissolved in the blood at an equal PP
  2. Shorter time required to attain PP in brain
  3. Shorter induction and recovery

Clinically more useful

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11
Q

High blood-gas PC

A
  1. More anesthetic dissolved in the blood at an equal PP
  2. Longer time required to attain PP in brain
  3. Longer induction and recovery

Not very clinically useful

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12
Q

Effect of solubility on recovers

A

The lower the solubility, the faster the recovery

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13
Q

Order of inhalant uptake

A

Vaporizer > breathing circuit > alveoli > arterial blood > brain

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14
Q

Partial pressure in the brain is roughly equal to…

A

Partial pressure in the alveoli

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15
Q

Ways to increase partial pressure in the alveoli

A
  1. Increase anesthetic delivery to alveoli

2. Decrease removal from the alveoli

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16
Q

Increased alveolar delivery

A
  1. Increase inspired anesthetic concentration

2. Increase alveolar ventilation

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17
Q

How do you increase inspired anesthetic concentration?

A
  1. Increase vaporizer setting
  2. Increase fresh gas flow
  3. Decrease breathing circuit volume
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18
Q

How do you increase alveolar ventilation?

A
  1. Increase minute respiration

2. Decrease dead space ventilation

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19
Q

Decrease removal from alveoli

A
  1. Decrease blood solubility of anesthetic
  2. Decrease cardiac output
  3. Decrease alveolar-venous anesthetic gradient
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20
Q

Concentration effect

A

The higher the inspired pressure the more rapidly alveolar pressure approachs inspired pressure

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21
Q

As uptake into blood decreases, inspired pressure can…

A

be decreased

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22
Q

A ____ inspired pressure is required at the beginning of gas anesthesia to quickly increase____

A

High, alveolar pressure

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23
Q

Anesthetic elimination

A

Requres decrease in alveolar concentraions

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24
Q

Anesthetic elimination is most effected by:

A
  1. Anesthetic solubility
  2. Alveolar ventilation

(same that effect alveolar concentration)

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25
Q

How do you quickly decrease alveolar concentration?

A
  1. Turn off vaporizer
  2. Disconnect patient and flush O2
  3. Turn up O2 rate- dilutes the circuit
  4. Increase ventilation (IPPV)- increase fresh gas to alveoli
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26
Q

Definition: Minimum Alveolar Concentration (MAC)

A

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

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27
Q

Relationship between MAC and potency of an anesthetic

A

Inversely proportional

High MAC = low potency

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28
Q

T/F: Alveolar concentration is NOT the same as the vaporizer setting

A

True

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29
Q

How is MAC measured?

A

Percent of agent in expired gas

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30
Q

MAC: Halothane

A

Dog- 0.9%
Cat- 1%
Horse- 1%

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31
Q

MAC: Iso

A

Dog- 1.3%
Cat- 1.3-1.6%
Horse- 1.3-1.6%

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32
Q

MAC: Sevo

A

Dog- 2.3%
Cat- 2.6%
Horse- 2.3-2.8%

33
Q

MAC: Desflurane

A

Dog- 7.2%
Cat- 9.8-10.3%
Horse- 7-8%

34
Q

MAC: N2O

A

Dog- 188%
Cat- 255%
Horse- 205%

35
Q

Increase in MAC

A

Hyperthermia
Hypernatremia
Drugs causing CNS stimulation

36
Q

Decrease in MAC

A 
Hypothermia
Hyponatremia
Drugs causing CNS depression
MAP 95mmHg
Pregnancy
Increasing adult age
37
Q

What is MAC multiples?

A

Used to describe dose of gas in relaiton to pharmacologic and physiologic effect

38
Q

What multiple of MAC ensure immobility in 95% of patients?

39
Q

Is MAC additive?

40
Q

Why is the additive effect of MAC important?

A
  1. Changing gasses in the middle of a case
  2. Using N2O
  3. Using partial intravenous anesthesia (PIVA)
41
Q

Cardiovascular effects of volatile anesthetics

A

Decrease: CO, BP, vasculara resistance, contractility

No change in HR

42
Q

Respiratory effects of volatile anesthetics

A

Decrease ventilation- depress chemoreceptors and response to CO2

Bronchodilation

Irritating odor

Respiratory arrest at 1.5-3MAC

43
Q

Neurologic effects of volatile anesthetics

A

Increase ICP @ >1MAP
Decrease cerebral metabolic rate
Acts on brain and spinal cord to produce immobility
Suppress seizure activity (except enflurane)

44
Q

Renal effects of volatile anesthetics

A

Decrease GFR- decreased CO

Renal failure- methoxyflurane

45
Q

What anesthetic produces compound A?

A

Sevoflurane

46
Q

What is compound A?

A

A compound produced from sevoflurane breakdown in CO2 absorbant

47
Q

What species is compound A nephrotoxic in?

48
Q

Higher concentrations of compound A are formed in:

A
  1. Prolonged anesthesia
  2. Low fresh gas flows
  3. Desiccated absorbent
49
Q

Hepatic effects of volatile anesthetics

A

Reduce liver blood flow and O2 delivery

Halothane- hepatotoxicity

50
Q

Halothane hepatitis

A

Immune mediated, often fatal

51
Q

Malignant hyperthermia

A

Myopathy occuring in genetically predisposed pigs, dogs cats, and horses with exposure to halothane especially

52
Q

Cllinical signs of malignant hyperthermia

A

Rapid increase in EtCO2

Uncontrolled muscle contraction, severe hyperthermia, death

53
Q

Treatment of malignant hyperthermia

A
  1. Discontinue volatile anesthetic, flush line, switch to a new anesthetic
  2. Provide 100% O2
  3. Administer dantrolene
  4. Fluids and active cooling

Usually still fatal

54
Q

Nitrous oxide

A

Mostly humans

max 75%, low solubility, minimal CV/resp depression, mild analgesia

55
Q

Diffusion hypoxia

A

When N2O is stopped, it diffuses quickly out of the blood and displaces O2 in the alveoli

Must continue 100% O2 after discontinuing N2O for 5-10min to prevent

56
Q

Reducing gas exposure

A
  1. Scavenging system
  2. Minimize leaks
  3. Avoid mask or chamber induction
  4. Keep patient attached to circuit after anesthetic gas is turned off
  5. Minimize exposure to exhaled gas from patient
  6. Maximize ventilation
  7. Monitor waste gas concentrations
57
Q

Anesthetic related complications

A

Hypotension
Hypoventilation
Hypothermia

58
Q

Machine related complications

A

Closed pop-off
Stuck inspiratory-expiratory valves
Exhausted soda lime
Inadequate O2 flow in non-rebreathing system

59
Q

Human error complications

A

Improper intubation

Anesthetic overdose

60
Q

Hypotension

61
Q

Evaluating hypotension

A

Turn down the vaporizer if patient is too deep (often resolves issue)

OR

Consider adding MAC sparing drug and then turn down the vaporizer if patient is appropriately deep

62
Q

MAC sparing drugs

A

Opiods, benzodiazapines, lidocaine, ketamine, etc.

63
Q

If still hypotensive after turning down vaporizer:

A

Evaluate underlying cause and treat

  1. Hypovolemia- crystalloid/colloid bolus
  2. Vasodilation- give vasopressor
  3. Decreased contractility- give inotrope
64
Q

Hypoventilation

A

PaCO2>40mmHg or EtCO2>45mmHg

Turn down the vaporizer and perform IPPV (manual or mechanical)

65
Q

T/F: Inhalant anesthesia abolishes the normal vascular compensatory mechanisms to conserve heat.

A

True.

Causes peripheral vasodilation which increases heat loss

66
Q

Treatment for hypothermia

A

Prevention easier

Heating blankets, warm water blankets, warm room, keep patient covered etc.

67
Q

What happens when the pop-off/APV valve is closed?

A

Resevoir bag fills, breathing system pressure increases, pressure transmitted to patient lungs/throracic cavity

Decreased CO and potential for pneumothorax

68
Q

Clinical signs of a closed pop-off

A

Apnea, bradycardia, fading doppler signal

69
Q

Treatment for closed pop-off

A
  1. Pull reservoir bag
  2. Start CPR is patient has arrested
  3. Evaluate for pulmonary injury
70
Q

Stuck inspiratory-expiratory valves

A

Signs: rebreathing capnograph and hypercarbia

Treatment: dry and clean valves and replace as needed

71
Q

Exhausted Soda lime

A

Signs: rebreathing capnograph and hypercarbia

Looks the same as stuck valves

72
Q

Rebreathing capnograph

A

Waveform does not return to baseline between breaths- build up of CO2

73
Q

Causes of rebreathing capnograph/hypercarbia

A
  1. Stuck insp/exp valves
  2. Exhausted soda lime
  3. Inadequate O2 flow in a non-rebreathing system
74
Q

Tracheal tears

A

Associated with over filling the cuff

Not uncommon in cats

75
Q

Signs of tracheal tears

A

Subcutaneous emphysema

Pneumomediastinum and pneumoretroperitoneum

76
Q

Treatment of tracheal tears

A

Supportive care

May need surgical repair

77
Q

Anesthetic overdoses

A

Very low therapeutic index- overdosing not uncommon and can happen very quickly

If there is any doubt in patient status, turn the inhalant down or off while evaluating

78
Q

Indications of anesthetic overdose

A

Very low BP (MAP

79
Q

Do sick patients often need more or less anesthetic?

A

Often less, usually the sicker the patient the less inhalant you will need

MAC sparing drugs should be used in these patients to offset inhalant needs

Anesthesiology (27 decks)

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