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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
How do you quickly decrease alveolar concentration?
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
26
Definition: Minimum Alveolar Concentration (MAC)
Minimum alveolar concentration of an anesthetic that prevents movement in 50% of patients exposed to noxious stimulus
27
Relationship between MAC and potency of an anesthetic
Inversely proportional High MAC = low potency
28
T/F: Alveolar concentration is NOT the same as the vaporizer setting
True
29
How is MAC measured?
Percent of agent in expired gas
30
MAC: Halothane
Dog- 0.9% Cat- 1% Horse- 1%
31
MAC: Iso
Dog- 1.3% Cat- 1.3-1.6% Horse- 1.3-1.6%
32
MAC: Sevo
Dog- 2.3% Cat- 2.6% Horse- 2.3-2.8%
33
MAC: Desflurane
Dog- 7.2% Cat- 9.8-10.3% Horse- 7-8%
34
MAC: N2O
Dog- 188% Cat- 255% Horse- 205%
35
Increase in MAC
Hyperthermia Hypernatremia Drugs causing CNS stimulation
36
Decrease in MAC
``` Hypothermia Hyponatremia Drugs causing CNS depression MAP 95mmHg Pregnancy Increasing adult age ```
37
What is MAC multiples?
Used to describe dose of gas in relaiton to pharmacologic and physiologic effect
38
What multiple of MAC ensure immobility in 95% of patients?
1.2-1.4x
39
Is MAC additive?
Yes
40
Why is the additive effect of MAC important?
1. Changing gasses in the middle of a case 2. Using N2O 3. Using partial intravenous anesthesia (PIVA)
41
Cardiovascular effects of volatile anesthetics
Decrease: CO, BP, vasculara resistance, contractility No change in HR
42
Respiratory effects of volatile anesthetics
Decrease ventilation- depress chemoreceptors and response to CO2 Bronchodilation Irritating odor Respiratory arrest at 1.5-3MAC
43
Neurologic effects of volatile anesthetics
Increase ICP @ >1MAP Decrease cerebral metabolic rate Acts on brain and spinal cord to produce immobility Suppress seizure activity (except enflurane)
44
Renal effects of volatile anesthetics
Decrease GFR- decreased CO Renal failure- methoxyflurane
45
What anesthetic produces compound A?
Sevoflurane
46
What is compound A?
A compound produced from sevoflurane breakdown in CO2 absorbant
47
What species is compound A nephrotoxic in?
Rats
48
Higher concentrations of compound A are formed in:
1. Prolonged anesthesia 2. Low fresh gas flows 3. Desiccated absorbent
49
Hepatic effects of volatile anesthetics
Reduce liver blood flow and O2 delivery Halothane- hepatotoxicity
50
Halothane hepatitis
Immune mediated, often fatal
51
Malignant hyperthermia
Myopathy occuring in genetically predisposed pigs, dogs cats, and horses with exposure to halothane especially
52
Cllinical signs of malignant hyperthermia
Rapid increase in EtCO2 | Uncontrolled muscle contraction, severe hyperthermia, death
53
Treatment of malignant hyperthermia
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
Nitrous oxide
Mostly humans max 75%, low solubility, minimal CV/resp depression, mild analgesia
55
Diffusion hypoxia
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
Reducing gas exposure
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
Anesthetic related complications
Hypotension Hypoventilation Hypothermia
58
Machine related complications
Closed pop-off Stuck inspiratory-expiratory valves Exhausted soda lime Inadequate O2 flow in non-rebreathing system
59
Human error complications
Improper intubation | Anesthetic overdose
60
Hypotension
MAP
61
Evaluating hypotension
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
MAC sparing drugs
Opiods, benzodiazapines, lidocaine, ketamine, etc.
63
If still hypotensive after turning down vaporizer:
Evaluate underlying cause and treat 1. Hypovolemia- crystalloid/colloid bolus 2. Vasodilation- give vasopressor 3. Decreased contractility- give inotrope
64
Hypoventilation
PaCO2>40mmHg or EtCO2>45mmHg Turn down the vaporizer and perform IPPV (manual or mechanical)
65
T/F: Inhalant anesthesia abolishes the normal vascular compensatory mechanisms to conserve heat.
True. Causes peripheral vasodilation which increases heat loss
66
Treatment for hypothermia
Prevention easier Heating blankets, warm water blankets, warm room, keep patient covered etc.
67
What happens when the pop-off/APV valve is closed?
Resevoir bag fills, breathing system pressure increases, pressure transmitted to patient lungs/throracic cavity Decreased CO and potential for pneumothorax
68
Clinical signs of a closed pop-off
Apnea, bradycardia, fading doppler signal
69
Treatment for closed pop-off
1. Pull reservoir bag 2. Start CPR is patient has arrested 3. Evaluate for pulmonary injury
70
Stuck inspiratory-expiratory valves
Signs: rebreathing capnograph and hypercarbia Treatment: dry and clean valves and replace as needed
71
Exhausted Soda lime
Signs: rebreathing capnograph and hypercarbia Looks the same as stuck valves
72
Rebreathing capnograph
Waveform does not return to baseline between breaths- build up of CO2
73
Causes of rebreathing capnograph/hypercarbia
1. Stuck insp/exp valves 2. Exhausted soda lime 3. Inadequate O2 flow in a non-rebreathing system
74
Tracheal tears
Associated with over filling the cuff Not uncommon in cats
75
Signs of tracheal tears
Subcutaneous emphysema | Pneumomediastinum and pneumoretroperitoneum
76
Treatment of tracheal tears
Supportive care May need surgical repair
77
Anesthetic overdoses
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
Indications of anesthetic overdose
Very low BP (MAP
79
Do sick patients often need more or less anesthetic?
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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