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APEX Pharmacology > PHARMACOLOGY-Inhaled anesthetics PD > Flashcards

PHARMACOLOGY-Inhaled anesthetics PD Flashcards

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1
Q

How does nitrous oxides solubility compare to nitrogen.

Why is this significant

A

N2O is 34 times more soluble than nitrogen

For every 1 N molecule that leaves a space, 34 N2O take it’s place

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2
Q

What effect does N2O have on a compliant air space

examples

A

It increases the volume of the space

ie blebs, bowel, air bubbles in blood

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3
Q

What effect does N2O have in a fixed airspace

examples

A

It increases pressure in the space

i.e. middle ear, eye during retinal detachment surgery, brain during intracranial surgery

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4
Q

What effect can N2O have on anesthesia equipment

A
  1. ETT cuff volume increasing pressure on trachea
  2. LMA cuff increased volume/pressure
  3. Balloon-tipped PA cath
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5
Q

What effect does N2O have on B12. Why is this significant

A

Irreversibly inhibits vitamin B12, which inhibits methionine synthase. This enzyme is required for folate metabolism and myelin production

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6
Q

What effect can nitrous oxide have on the middle ear

A
  1. Increases pressure which can damage tympanic membrane grafts
  2. Discontinuation can quickly decrease middle ear pressure leading to serous otitis
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7
Q

What effect does nitrous oxide have during retinal detachment surgery

A

N2O can expand the bubble that is being used as a retinal splint during detachment surgery

Retinal perfusion can become compromised causing permanent blindness

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8
Q

When should N2O be avoided with SF6 use in eye surgeries (Before vs after)

A

Before: d/d N2O at least 15 minutes prior to bubble placement

After: avoid N2O for 7-10 days

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9
Q

How long should N2O be avoided after injection of the following types of bubbles
Air=
Perfluoropropane=
Silicone oil=

A

Air= 5 days
Perfluoropropane= 30 days
Silicone oil= no CI

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10
Q

What is the significance of B12 inhibition by N2O and possible side effects

A

Significance:
Decreases methionine synthase which is needed for folate metabolism and myelin production

Side effects:

  1. Immunocompromised
  2. Decreased DNA synthesis
  3. Neuropathy
  4. Megaloblastic anemia from marrow suppression
  5. Homocysteine accumulation
  6. Possible teratogenicity
  7. Possible risk of SBA
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11
Q

What 4 factors increase risk of complications with B12 and N2O

A 
Prolonged exposure
Pts w/ pre-existing B12 deficiency
-pernicious anemia
-alcoholism
-strict vegan
-recreational N2O use
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12
Q

Fire risk with N2O use

A

It is not flammable but it does support combustion

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13
Q

Compare the potency of N2O, Des, Iso, and Sevo from greatest to least

A

Iso&raquo_space; Sevo&raquo_space;> Des > N2O

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14
Q

What does MAC measure

A

Potency

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15
Q

Define MAC

A

Minimum alveolar concentration is the concentration of inhalational anesthetic that prevents movement following painful stimulus in 50% of the population

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16
Q 
What percentage equals 1 MAC for each anesthetic
Iso=
Sevo=
Des=
N2O=
A 
Iso= 1.2%
Sevo= 2.0%
Des= 6.6%
N2O= 104%
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17
Q

What are 5 effects produced by general anesthetics

A
  1. amnesia
  2. loss of consciousness
  3. Immobility
  4. Modulation of autonomic function
  5. Some analgesia
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18
Q

Level for…
MAC-awake induction
MAC-awake on emergence
MAC-bar

A

MAC-awake induction = 0.4-0.5 MAC
MAC-awake on emergence = 0.15 MAC
MAC-bar = 1.5 MAC

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19
Q

Movement is prevented in 95% of the population at what MAC

A

1.3 MAC

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20
Q

Awareness and recall are prevented at what MAC

A

0.4 - 0.5 MAC

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21
Q

What is MAC compared to for systemic drugs

A

ED50

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22
Q

5 Factors that increase MAC

A
  1. Chronic etoh consumption
  2. Increased CNS neurotransmitter activity
  3. Hypernatremia
  4. Infants 1-6 months
  5. Hyperthermia
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23
Q

8 drugs that decrease MAC

A
  1. Acute etoh intoxication
  2. IV anesthetics
  3. N2O
  4. Opioids
  5. a-2 agonist
  6. Lithium
  7. Lidocaine
  8. Hydroxyzine
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24
Q

Does potassium level or gender affect MAC potency

A

No

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25
Electrolyte and other physiologic abnormalities that can decrease MAC
1. Hyponatremia 2. Older age (dec MAC 6% per decade after 40 yrs) 3. Extremes of age 4. Hypothermia 5. Metabolic acidosis 6. Pregnancy 7. HoTN 8. Hypoxia 9. Sever hypercarbia
26
6 drugs that increase MAC
1. Chronic ETOH 2. Acute meth intoxication 3. Acute cocaine intoxication 4. MAOIs 5. Ephedrine 6. Levodopa
27
What is the Meyer-Overton rule
That lipid solubility is directly proportional to the potency of an inhaled anesthetic
28
Define the unitary hypothesis
All anesthetics share similar mechanisms of action, but each may work at different sites
29
General anesthesia is produced by what mechanism at which sites
Mechanism=membrane-bound protein interactions Site=Brain and spinal cord
30
How do volatile anesthetics affect inhibitory vs stimulatory receptors
stimulate inhibitory receptors inhibit stimulatory receptors
31
What is the most important site of volatile anesthetic action in the brain
GABA-A receptors
32
What are the most important receptor sites of volatile anesthetic action in the spinal cord (3)
glycine receptor stimulation NMDA receptor inhibition Na+ channel inhibition
33
What 2 receptors do N2O and xenon target
NMDA receptor antagonism | K+ 2P-channel stimulation
34
How is immobility produced by volatile anesthetics
Action at receptor sites in the ventral horn of the spinal cord
35
Unconsciousness if produced by volatile anesthetics due to interacting with which 3 parts of the brain
1. Cerebral cortex 2. Thalamus 3. reticular activating system
36
Amnesia is produced via what location of the brain (2)
1. amygdala | 2. hippocampus
37
Autonomic effects are produced via which parts of the brain
1. Pons | 2. Medulla
38
Analgesia is produced via what tract
Spinothalamic tract
39
Immobility is due to anesthetic action at what location
Ventral horn of the spinal cord
40
The hippocampus and amygdala produce what effect with volatile anesthetic
Amnesia
41
The pons and medulla produce what effect with volatile anesthetics
Autonomic effects
42
The reticular activating system produces what effect with volatile anesthetics
loss of consciousness (arousal)
43
The ventral horn in the spinal cord produces what effect with volatile anesthetics
Immobility
44
The spinothalamic tract produces what effect with volatile anesthetics
Analgesia | Ascending nociceptive signals are inhibited
45
``` What effect do halogenated anesthetics have on MAP Contractility SVR HR ```
``` MAP = decrease Contractility = decrease SVR =decrease HR: -iso/des=increase -sevo=no effect ```
46
What effect does N2O have on MAP and SVR
It increases MAP and SVR by SNS activation
47
What physiologic effect do volatile anesthetics have on cardiac and vascular smooth muscle
- Reducing Ca++ influx in the sarcolemma - Decreasing Ca++ release from the SR - Modulate NO release - Inhibit Ach-induced vasodilation - Impair Na+/Ca++ pump
48
What is the mechanism of MAP decrease by volatile anesthetics
Decreased Ca++ in vascular smooth muscle causes vasodilation which decreases SVR and VR Myocardial depression d/t decreased Ca++ in the cardiac myocyte. This decreases inotropy
49
How do volatile anesthetics affect cardiac conduction
1. decreased SA node automaticity 2. Decreased conduction velocity via AV node, His-Purkinje system and ventricular conduction pathways 3. Increased duration of myocardial repolarization 4. Altered baroreceptor function
50
How is conduction affected by volatile anesthetics
It is decreased through the AV node, His-Purkinje system, and ventricular conduction pathways
51
How is cardiac repolarization affected by volatile anesthetics and why
Increased duration of repolarization due to impaired outward K+ current This increases the action potential duration and prolongs QT interval
52
Explain the increase in HR caused by Iso and Dex
SNS activation from respiratory irritation Pulmonary irritation leads to SNS activation. Increase norepi release and beta-1 stimulation
53
How can the increase in HR from Iso and Des be countered
Opioids Alpha-2 agonist Beta-1 antagonist
54
Which anesthetic agent reduces SVR the LEAST
Sevoflurane
55
What effect doe volatile agents have on coronary blood flow
INCREASE CBF in excess of myocardial O2 demand This dilates small cardiac vessels
56
Compare the potency of coronary artery vasodilation with volatile agents from greatest to least
Iso > des > sevo
57
How do volatile anesthetics affect PaCO2 (5)
1. Hypercapnia thru depressed central chemoreceptors and respiratory muscles 2. Decreased Vt and increased RR 3. Increased apneic threshold 4. Relaxed upper airway muscle tone causing obstruction 5. Bronchodilation
58
How much does minute ventilation change with increased PaCO2
For every 1 mmHg PaCO2 increase above baseline, Vm increases 3 L/min
59
How are respiratory mechanics altered by volatile anesthetics Effects on PaCO2
Dose-dependent depression of central chemoreceptors and respiratory muscle contribute to hypercarbia Impaired motor neuron output and muscle tone to upper airway and thoracic muscles
60
How is the respiratory pattern altered by volatile anesthetics Effects on PaCO2
Reduced Vt Compensates with increase RR Smaller, faster breaths increase dead space and PaCO2
61
How is dead space altered by volatile anesthetics
It's increased due to smaller Vt and increase in RR
62
What does the slope of the CO2 response curve represent
The sensitivity of the entire respiratory apparatus to PaCO2
63
What are causes of left shift in the CO2 response curve (7)
``` Anxiety Surgical stimulation Metabolic acidosis Increased ICP Salicylates Aminophylline Dozpram ```
64
What effect does a left shift of the CO2 curve have on ventilation
Stimulates ventilation | Breathe off CO2
65
What are causes of a right shift in the CO2 response curve (4)
General anesthetics Opioids Metabolic alkalosis Denervation of peripheral chemoreceptors
66
What effect does a right shift of the CO2 curve have on ventilation
Depresses ventilation | Retain CO2
67
What is the significance of a right shift in the CO2 response curve
1. Decrease response to CO2 | 2. Increased apneic threshold (PaCO2 level that stimulates respiration)
68
What upper airway muscles lose tone with anesthetic agents, causing upper airway obstruction
``` Genioglossus (oropharynx obstruction) Tensor palatine (nasopharyngeal obstruction) Geniohyoid? (hypopharynx obstruction) ```
69
How do anesthetic agents affect airway patency
Impairment of airway dilator muscles (genioglossus and tensor palatine)
70
How is FRC affected by anesthetic agents
FRC is decreased d/t impaired pulmonary muscles
71
What effect do halogenated agents have on airway diameter
Most volatiles are bronchodilators Des can cause bronchoconstriction in asthmatics
72
Where is hypoxemia monitored peripherally
In the peripheral chemoreceptors of the carotid bodies
73
What is the PaO2 threshold for hypoxic drive
<60 mmHg
74
What is the response to stimulation of the hypoxic ventilatory response
When PaO2<60 mmHg minute ventilation increases to restore arterial O2
75
How are afferent impulses from the carotid and aortic bodies.
Carotid bodies = glossopharyngeal nerve (CN 9) | Aortic bodies = vagus nerve (CN 10)
76
What changes stimulate the carotid bodies
Changes in arterial gas tension of PaO2, PaCO2, H+ concentration
77
What changes stimulate the aortic bodies
Changes in BP
78
How long can volatile agents impair peripheral chemoreceptors
Up to several hours after anesthesia
79
At what MAC can the response to acute hypoxia be impaired
0.1 MAC
80
What cells in the carotid bodies sense decreased PaO2 | How do anesthetics affect this cell
Glomus type 1 cells Anesthetics may create a reactive O2 species that impairs the glomus type 1 cells
81
Compare the ability to inhibit hypoxic drive for volatile agents, from greatest to least
Sevo > Iso > Des
82
Which anesthetic impairs the hypoxic drive the most and why
Halothane, because it undergoes the most biotransformation Sevo
83
Which anesthetic agent may be best for patients who rely on hypoxic drive to breathe
Desflurane
84
What effect do pain and surgical stimulation have on the hypoxic ventilatory drive
None | Unlike their ability to affect the ventilatory response of CO2
85
``` What neurophysiologic effects do volatile anesthetics have on the following CMRO2 ICP CBF Cerebral blood volume EEG ```
``` Dose-dependent effects CMRO2 = reduction ICP = increase CBF = increase Cerebral blood volume = increase EEG = isoelectric at 1.5-2.0 MAC ```
86
What 2 factors is CMRO2 dependent on
1. Electrical activity | 2. Cellular homeostasis
87
At what MAC is an isoelectric state induced
1.5 - 2.0 MAC
88
Which agent can induce seizures at high concentrations
Sevo | At >2.0 MAC
89
What effect do anesthetic agents have on cerebral vasculature
Vasodilation
90
How do anesthetic agents affect the coupling of CMRO2 and CBF
They are uncoupled by volatile anesthetics | CBF is increased while CMRO2 is decreased at concentrations >0.5 MAC
91
How can ICP be addressed in patients receiving volatile anesthetics
Mild hyperventilation to PaCO2<35 mmHg Concurrent use of propofol, opioids and barbiturates to decrease MAC needs
92
What effect does N2O have on CBF and CMRO2
Both CBF and CMRO2 are increased
93
What effect do volatile anesthetics have on cerebral autoregulation
It is attenuated, especially and moderate to high doses | The MAP changes based on CBF (whereas, normally, the MAP can be maintained with altered CBF within a range)
94
How do volatile agents impact CSF production Iso Des Sevo
``` Iso= no change Des= no change to possibly increased Sevo= decreased ```
95
How do volatile agents impact CSF absorption Iso Des Sevo
``` Iso= increased Des= no change Sevo= unknown ```
96
What does SSEP monitor
``` The integrity of the DORSAL column (medial lemniscus) SENSORY tract (posterior) ```
97
What arteries perfuse the areas monitored by SSEP
The posterior spinal arteries
98
What does MEP monitor
``` The integrity of the corticospinal tract MOTOR tract (anterior) ```
99
What arteries perfuse the areas monitored by MEP
The anterior spinal artery
100
When is nerve ischemia concerning in evokes
Amplitude DECREASED >50% Latency INCREASE >10%
101
What impact do volatile anesthetics have on evoke potential monitoring
Decrease amplitude | Increase latency
102
What is the best anesthetic technique to preserve evoke potential monitoring
TIVA without N2O | No NMBD
103
What are recommendations for volatile agent use when evoked potentials are being monitored
<0.5 MAC supplemented with IV agents | No N2O
104
What type of evoked potentials are most sensitive to the effects of volatile agents
Visual evoked potentials
105
Which type of evoked potential are most resistant to the effects of volatile anesthetics
Brain auditory evoked potentials
106
What is the purpose of evoked potential monitoring
To monitor the integrity of neural pathways
107
What are 4 types of evoked potentials that are monitored
Somatosensory (SSEP) Motor (MEP) Visual (VEP) Brainstem auditory (BAEP)
108
How are SSEP produced
Applying current to a peripheral nerve
109
In evoked potentials, what do amplitude and latency measure
``` Amplitude = strength of nerve response (voltage) Latency = speed of nerve conduction (time) ```
110
What are the guidelines for muscle relaxant use when evokes are monitored
They should not be used for maintenance Short-acting NMB use during induction but should metabolized ore reversed by the time potentials are monitored
111
What effect does ketamine have on evoked potentials
Enhances signal
112
What does loss of the evoked potential signal suggest
Ischemia to the neural pathway being monitored
113
What are 4 interventions anesthesia can perform to aid in the loss of evoked potential signal
1. Improve neural tissue perfusion by increasing BP 2. Volume expansion 3. Transfusion if anemic 4. Normalize gas tension (PaO2/PaCO2)
114
What physiologic alterations can impact evoke potential amplitude or latency
Hypoxia Hypercarbia Hypothermia

APEX Pharmacology (8 decks)

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