Apex- Volatile Anesthetics- Pharmacodynamics Flashcards
(113 cards)
1
Q
What is the blood:gas partition coefficient of Nitrogen?
A
0.014
- you know that nitrous oxide is 34x more soluble than nitrogen
- You know the blood:gas coefficient for N20 is 0.46
- 0.46 / 34 = 0.014
And that somehow = the blood:gas coefficient of nitrogen ::shrugs::
2
Q
For every 1 molecule of nitrogen that leaves a closed space, ____ molecules of nitrous oxide enter to take it’s place
A
34
3
Q
Is nitrous oxide flammable?
A
No, but it supports combustion
4
Q
Nitrous oxide irreversibly inhibits what? Why is this an issue
A
Vitamin B12
Issue bc vitamin b12 promotes methionine synthase (the enzyme required for folate metabolism and myelin production) so your also inhibiting this
5
Q
What is the gas bubble called they use for retinal detachment surgery that gets placed over the retinal break as a “splint” to hold the retina in place while healing occurs.
Why can’t you use N20?
A
Sulfur hexafluoride (SF6)
-Nitrous oxide is to be avoided bc it can diffuse into the bubble faster than the other gasses in the bubble can diffuse out > bubble expands > compromised rental perfusion > permanent blindness
6
Q
When to avoid N20 with a SF6 bubble (2)
A
Before SF6 is placed > discontinue N20 at least 15 mins before placement
After SF6 is placed > avoid N20 for 7-10 days
7
Q
When to avoid N20 in retinal bubbles other than SF6: Air, perfluropropane , silicone oil
A
Air - 5 days
Perfluopropane- 30 days (propane bill comes q30 days)
Silicone oil - no contraindication
8
Q
Populations to avoid n20 in due to the risk of complications associated with inhibition of vitamin B12 (4)
A
- Pernicious anemia
- ETOHism
- Strict vegan diet
- Recreational use of N20
9
Q
Example of when N2O can pose a fire risk
A
During laparoscopy with pneumoperitoneum if electrocautery is used
10
Q
7 potential side effects of prolonged expose to N20 secondary to vitamin B12 inhibition
A
- Megaloblastic anemia
- Neuropathy (mylin destruction)
- Immunocompromise
- Impaired DNA synthesis
- Possible teratogenicity (data lacking)
- Risk of spontaneous abortion (avoid in first 2 trimesters)
- Homocysteine accumulation (data lacking)
11
Q
MAC values of ISO, sevo, des, nitrous
A
ISO- 1.15%
SEVO- 2%
DES- 6.6%
N20- 104%
12
Q
General anesthetic produce what 5 effects
A
LIMAS
Loss of consciousness Immobility Modulation of autonomic function Amnesia Some analgesia
13
Q
T/F: MAC is additive
A
True
14
Q
MAC “awake” during induction/emergence
A
Induction ~ 0.4-0.5 MAC awake
Emergence ~ 0.15 MAC awake
15
Q
MAC BAR
A
1.5 MAC
16
Q
1.3 MAC: movement is prevented in ____% of the population
A
95%
17
Q
Awareness and recall are prevented at ___ - _____ MAC
A
0.4-0.5 MAC
18
Q
The essential triad of anesthetic action includes what 3 things:
A
Amnesia
Loss of consciousness
Immobility
19
Q
Define MAC BAR
A
The alveolar concentration required to block autonomic response following a supra-maximal painful stimulus (1.5 MAC)
20
Q
What is MAC a measure of? (1 term)
A
Potency
21
Q
Arrange inhalational agents from most to least potent
A
ISO > Sevo > DES > N20
22
Q
If volatile anesthetic potency is decreased by something, does that increase or decrease MAC
A
Increase
Ie) volatile anesthetic potency is decreased by chronic ETOH consumption and red hair (you need more, so your MAC increases)
23
Q
Drugs that increase MAC (6)
A
- Chronic ETOH consumption
[increased CNS neurotransmitters]
- Acute amphetamine intoxication
- Acute Cocaine intoxication
- MAOi’s (MAO helps break down catecholamines so if you inhibit their break down, they will be circulating)
- Ephedrine (increase NT- NE)
- Levodopa
24
Q
Drugs that decrease MAC (8)
A
- Acute ETOH intoxication
- IV anesthetic
- N20
- Opioids
- Lidocaine
- Alpha-2 Agonists (precedex, clonidine)
- Lithium
- Hydroxyzine
25
Does Lithium increase or decrease MAC
Decrease
26
How do sodium levels affect MAC? Potassium? Mag?
```
HYPERnatremia = INCREASES Mac
Hyponatremia = decreases Mac
```
K and MAG levels do NOT affect MAC
27
Premise: increased or decreased MAC
Decreased
28
What age group has increased MAC requirements?
Infants 1-6 months (sevo same for infants and neonates)
29
How much does MAC decrease after 40?
6% every decade after 40
30
How does temperature effect MAC?
```
HYPERTHERMIA = increased MAC
Hypothermia = decreased Mac (cold, holding onto blankets/that anesthetic/doesn’t want to give it up)
```
31
how much does red hair increase MAC requirements?
By 20%
32
Why do pts with red hair have increased Mac requirements?
Due to mutations in the melanocytes stimulating hormone receptor and an increase production of phenomelanin
33
Increased or decreased MAC: CPB
Decreased
34
Increased or decreased Mac or no change:
Hypotension
Hypoxia
Anemia
Hypotension - decrease
Hypoxia- decrease
Anemia- decrease
35
Increased or decreased Mac or no change:
| Metabolic acidosis
Decreased MAC
36
Increased or decreased Mac or no change:
Hypo-osmolarity (SIADH)
Decreased MAC
37
Increased or decreased Mac or no change:
Pregnancy
Postpartum
Decreased pregnancy > postpartum 24-72 hrs
38
Increased or decreased Mac or no change:
PaCO2 > 95
Decreased MAC
39
Increased or decreased Mac or no change:
Hyper/Hypothyroidism
NO DIRECT CHANGE; however changes in CO can affect MAC
40
Increased or decreased Mac or no change:
HTN
No change
41
Increased or decreased Mac or no change:
Gender
No change
42
MAC is unchanged with a PaCO2 between what?
15-95mmHg
43
What rule states that lipid solubility is directly proportional to potency
The Meyer-Overton rule
44
What theory suggest that a inhalational anesthetic interact with stereo selective receptors
Modern anesthetic theory
45
What states that all anesthetic share a similar MOA but each may work at a different site
Unitary hypothesis
46
The Meyer-Overton rule states that lipid solubility is (directly/inversely) proportional to the potency and (directly/inversely) proportional to MAC of an inhaled anesthetic
Directly proportional to potency (increased lipid solubility = increased potency)
Inversely proportional to MAC (increased lipid solubility = decreased MAC)
47
Do volatile anesthetic most likely exert their effects by stimulating and inhibiting a variety of stereoselective receptors or disrupting the integrity of the phospholipid bilayers
By inhibiting a variety of steroselective receptors
48
What are the primary targets of volatile anesthetic in the spinal cord? (2)
Stimulating glycine channels (inhibitory)
| & inhibiting NMDA receptors and sodium channels (stimulatory)
49
Where do volatile anesthetic produce immobility?
In the ventral horn of the spinal cord
50
Where do upper and lower MOTOR neurons synapse?
In the VENTRAL horn of the spinal cord
51
What is the primary target of halogenated agents in the brain?
The GABA-A receptor
52
T/F: volatile anesthetic produce immobility by the GABA-A receptor in the spinal cord
FALSE
53
Does nitrous oxide stimulate the GABA-A receptor?
No- it antagonizes the NMDA receptor and stimulates potassium 2P channels
54
Where do volatile anesthetics produce unconsciousness (3) places
1. Reticular activating system (RAS- in brain stem - responsible for consciousness and arousal)
2. Thalamus - relay station of sensory and motor input into the cortex
3. Cerebral cortex - Higher order cerebral functions
55
Where do volatile anesthetics produce amnesia (2)?
1. Hippocampus (temporal lobe: learning and memory)
| 2. Amygdala (emotional, response to pain, formation of stress response)
56
Where do volatile anesthetics produce analgesia?
Spinothalmic tract (nociceptive signals along the ascending pathway are inhibited)
57
Where do volatile anesthetics produce autonomic modulation? (2)
Pons & Medulla (control center for autonomic reflexes)
58
What are the most important sites of VA action in the spinal cord (3)?
1. Glycine receptor stimulation
2. NMDA receptor inhibition
3. Sodium channel inhibition
59
How do VA effect cardiac conduction cycle?
Prolong the QT
- they increase the duration of myocardial depolarization by impairing an outward K+ current, which prolonged the QT interval
60
How is the HR effected by Iso, Des, Sevo, N20
Iso, Des, and N20- HR increases
| SEVO- no change
61
By what mechanism does N20 increase MAP and SVR?
By SNS activation
62
Which VA decreases SVR the least?
Sevo
63
What is the primary and secondary methods by which halogenated agents decrease MAP
Primary: decreased intracellular calcium in VSM > vasodilation > decreased SVR & venous return
Secondary: decreased intracellular calcium in the cardiac monocytes > myocardial depression > decreased inotropy
64
What are the effects on HR by ISO and DES and why?
Increases HR 5-10% from baseline - likely do to SNS activation from respiratory irritation
SNS activation > increased NE release > beta 1 stimulation
65
Of the volatile agents, which one reduces SVR the least?
Sevo
66
Potency of coronary artery vasodilation from most potent to least
Iso > Des > Sevo
| Why they use Iso in heart rooms I’m assuming
67
Hearts extraction ratio of O2
75%
68
How do halogenated agents affect minute ventilation?
Decrease tidal volume and increase RR > increase in dead space ventilation
69
What maintains tight control of PaCO2?
The central chemoreceptors in the medulla
70
For every 1mmHg increase in PaCO2 above baseline, minute ventilation will increase by ________L/min
3L/min
71
How do halogenated agents affect the CO2 response curve?
Shifts down and right
72
A (left/right) shift in the CO2 response curve results in a minute ventilation that is greater than predicted, causing a respiratory (acidosis/alkalosis)
Left - Alkalosis
73
Causes of right shifts in the CO2 response curve (4) What does this imply
GA’s, opioids, metabolic alkalosis, denervation of peripheral chemoreceptors
*implies that for a given PaCO2, the minute ventilation is less than predicted, creating a resp acidosis
74
How do volatile anesthetics lead to upper airway obstruction?
By impairing the airway dilator muscles such as the genioglossus or tensor palatine muscles
75
Which volatile agent can induce bronchoconstriction in asthmatics?
Desflurane
76
The carotid bodies relay afferent input to the respiratory center via which cranial nerve?
IX - Glossopharyngeal
CG - Cover Girl - Carotid bodies, Glossopharyngeal
77
The aortic bodies relay afferent input via which cranial nerve?
X - vagus
| AV - AV node - Aortic bodies - Vagus
78
Halogenated agents decrease tidal volume and increase RR leading to what?
Increased deadspace ventilation
79
What receptors maintains tight control of PaCO2? Where are they located?
Central chemo receptors in the medulla
80
Every 1mmHg increase in PaCO2 above baseline will increase minute ventilation by ____L/min
3L/min
81
What does a left shift in the CO2 response curve imply?
That for a given PaCO2, the minute ventilation would me MORE than predicted
>creating a resp alkalosis
82
Causes of left shift in PaCO2 response curve (7)
1. Anxiety
2. Surgical stimulation
3. Metabolic acidosis
4. ICP (body trying to blow off CO2 to decrease it)
5. Salicylate
6. Doxapram
7. Aminophylline
(think what would make someone breathe faster)
83
What does a right shift of the PaCO2 response curve imply?
That for a given PaCO2, the minute ventilation would be LESS than predicted
>results in a resp acidosis
84
Things that cause right shift of the PaCO2 response curve (depresses ventilation) (4)
1. Volatile anesthetics
2. Opioids
3. Metabolic alkalosis
4. Denervation of peripheral chemoreceptors
85
What kind of receptors monitor for hypoxemia? Where are they located?
Peripheral chemoreceptors in the Carotid bodies
86
PaO2 < ________mmHg is a stimulus to increase minute ventilation in an effort to restore arterial oxygenation
60mmHg
87
What are carotid bodies vs aortic bodies more sensitive to?
Carotid bodies - change in arterial gas tensions (PaO2, PaCO2) & H+ concentration
Aortic bodies- change in BP
88
How long do volatile anesthetics impair the peripheral chemoreceptors for?
Several hours after surgery
89
Which cells in the carotid bodies provide the sensory arm of the hypoxia drive?
Globules type 1 cells
90
Reactive oxygen species impair glomulus type 1 cells (provide sensory arm for hypoxic drive)
- anesesthetic metabolism is a source of reactive oxygen species
- list the volatile agents that inhibit the hypoxic drive from most to least
*What patient population is this a consideration for?
Halothane > Sevo > Iso > Des
20% metabolism > 2% > 0.2% > 0.02%
*Important for pts who rely on hypoxic drive to breathe > emphysema/COPD > Des is best for these pts then iso then sevo
91
Mechanism by which volatile anesthetics increase cerebral blood flow
VA’s uncouple metabolism from cerebral blood flow > meaning they supply the brain with more blood flow than it actually needs —> since more blood is delivered to the brain per minute, cerebral blood volume increases
92
What is CMRO2 dependent on (2)?
1. Electrical activity (60%)
| 2. Cellular hemostasis (40%)
93
Do volatile anesthetics decrease CRMO2?
Yes, but only to the extent that they decrease electrical activity — once the brain is iso-electric, VA’s cannot reduce CMRO2 any further
94
What MAC is required to produce an isoelectric state?
MAC 1.5-2
95
Which VA, in high concentrations (2 MAC) can produce seizure activity?
What is this exacerbated by and in when is it more commonly seen?
Sevo
—exacerbated by hypocapnea
— more common is pediatric inhalational induction
96
The cerebral vascular use continuously adjusts vessel diameter to maintain a constant cerebral perfusion pressure of what?
50-150mmHg
97
When metabolic demand increases, blood vessels (constrict/dilate) and cerebral vascular resistance (increases, decreases)
Vessels dilate and CVR decreases
98
When metabolic demand decreases, blood vessels (constrict/dilate) and resistance (increases/decreases)
Vessels Constrict, resistance increases
99
Volatile anesthetics result in vasoconstriction from reduction in CRMO2 + vasodilation from the anesthetic agent . What is the net effect of this? (3)
How is nitrous oxide different?
Increased CBF, increased CBV, increased ICP
Nitrous oxide increases both CMRO2 and CBF
100
Which agents have what effects on CSF production and CSF absorption? Iso, Des, Sevo
Iso - increased CSF absorption (no production so it just increases absorption instead)
Des- increased/no change CSF production (no effect on absorption)
Sevo- DECREASED CSF production, ?effect on absorption
101
What are evoked potentials used to monitor?
Integrity of a neural pathway
102
What do SSEPs monitor the integrity of?
What perfuses this region of the spinal cord?
The dorsal medial lemniscus column
-the posterior spinal arteries
103
What do MEPs monitor the integrity of?
What perfuses this region of the spinal cord?
The corticospinal tract
-The anterior spinal artery
104
What is the best technique to preserve evoked potentials?
TIVA w/o N20
105
If you use a volatile agent during evoked potential monitors, what should you keep MAC below?
0.5 MAC
106
What drug enhances evoked potential signals?
Ketamine
107
What type of evoked potentials are the most resistant to anesthetics and any technique can be used?
Brain auditory evoked potentials
108
Which evoked potentials are most sensitive to anesthetics and are rarely used?
Visual EPS
109
Evoked potentials: What is amplitude vs latency?
Amplitude: The strength of the nerve response
Latency: The speed of nerve conduction
110
Evoked potentials: As a general rule, you should be concerned about nerve ischemia when amplitude decreases by ____ % or latency increases by _______%
Amplitude decreases by 50% or more
| Latency increases by 10% or more
111
What do volatile anesthetics due to amplitude and latency on evoked potentials?
What factors exaggerate this? (4)
Decrease amplitude and increase latency
>addition of N20
> hypoxia
> hypercarbia
> hypothermia
112
What should happen if EPS diminish or go away?
The surgeon should investigate a mechanical cause. Anesthetic goals are directed towards improving neural tissue perfusion by:
Increasing BP, volume expansion, transfusion if anemic, normalizing gas tensions
113
At what MAC is the response to hypoxia impaired? Is the CO2 response impaired at this level?
0.1 MAC; no
