Exam 3 - Inhaled Anesthetics Flashcards
(96 cards)
1
Q
What are the four functions of the anesthesia circuit?
A
- Delivers O2
- Delivers inhaled drugs
- Maintain temperature/ humidity
- Removes CO2 and exhale drugs
2
Q
What three types of circuits?
A
- Rebreathing (Bain)
- Non-rebreathing (Self-inflating Bag Valve Mask - Ambu Bag)
- Circle System
3
Q
Why is a Bain circuit good to transport intubated patients?
A
- Has APL valve
- Supplemental O2 source
- Long tubing, making it easier to bag
4
Q
When fresh gas enters the circle system from the fresh gas inlet and goes towards the inspiratory limb. Why can’t gas flow backward?
A
There is an inspiratory unidirectional valve that prevents the backward flow of gas.
5
Q
From the inspiratory limb, where will gas flow next?
A
Gas will flow into the Y-piece and towards the paient
6
Q
Where will gas go after leaving the expiratory unidirectional valve?
A
- Gas will either go back into the bag or bellows
- CO2 will go into the absorbent canister
7
Q
What is high-flow inhalation anesthesia? Uses?
What are some downsides to high-flow anesthesia?
A
- Fresh gas flow (FGF) exceeds minute ventilation.
- High flow allows providers to make rapid changes in anesthetics (induction) and prevents rebreathing (washes out gases in the circuit).
- Used for preoxygenation/denitrogenation during induction
- Wasteful (not all gas is inhaled, some washed downstream) and cools/dries delivered volume.
8
Q
What is low-flow inhalation anesthesia? Benefits?
What are some downsides to low-flow anesthesia?
A
- Fresh gas flow (FGF) less than minute ventilation.
- Low cost, conserves gas, less/cooling and drying.
- A very slow change in anesthestic depth - may be good for slow emergence
- Compound A production (not clinically relevant)
9
Q
Factors that contribute to the price/cost of anesthesia?
A
- Cost of liquid/ml
- Vol % of anesthetic delivered - Potency (desflurane more expensive d/t having to use more volume)
- Fresh gas flow rate
10
Q
How do volatile anesthetics cause bronchodilation?
A
- Relax airway smooth muscle by blocking VG Ca2+ channels.
- For bronchodilation to occur, there needs to be an intact epithelium. Inflammatory processes and epithelial damage will alter responses.
11
Q
A patient without a history of bronchospasm will not see baseline pulmonary resistance change with ____ to ____ MAC of volatile anesthetics.
A
1 to 2 MAC
Bronchodilation seen more with active bronchospasm
12
Q
Risk factors for bronchospasm?
A
- Coughing from ETT
- Age < 10
- URI
13
Q
For a patient with bronchospasm which volatile gas will be most beneficial for bronchodilation?
Which gas will worsen bronchospasm for smokers?
A
Sevoflurane (best bronchodilator)
Desflurane
14
Q
What are the 3 best anesthetic gases to use if you do not want to encounter respiratory resistance?
A
- Sevoflurane
- Halothane
- Isoflurane
15
Q
What are the neuromuscular effects of volatile anesthetics?
A
- Dose-dependent skeletal muscle relaxation, not paralysis.
- Potentiate depolarizing and non-depolarizing NMBD (nAch receptors at NMJ) and enhance glycine in the spinal cord
16
Q
What gas has no effect on skeletal muscles?
A
Nitrous Oxide
17
Q
What is ischemic preconditioning?
A
Brief periods of ischemia and exposure to volatile anesthetics can enhance tolerance to subsequent ischemia, enhance cardiac function, and reduce infarction size.
Stoelting p. 2744
18
Q
How does ischemic preconditioning work physiologically?
A
Mediated by adenosine:
* Increases PKC activity
* ATP sensitive K+ channels are phosphorylated
* Reactive oxygen species are produced
* Vascular tone is better regulated
19
Q
Ischemic preconditioning can occur with __________ MAC.
A
0.25
20
Q
What are the benefits of ischemic preconditioning?
Clinically, when can ischemic preconditioning be useful?
A
Prevents “reperfusion injury”
Do not see as many cardiac dysrhythmias.
Less contractile dysfunction.
Clinically apparent in delaying MI for PTCA or CABG.
21
Q
How will volatile anesthetics affect CNS activity?
A
Dose-dependent decrease in CMRO2 and cerebral activity.
22
Q
At ______ MAC, wakefulness changes to unconsciousness.
What MAC will there be burst suppression?
What MAC will there be electrical silence?
A
0.4
1.5
2.0
23
Q
Rank the 3 volatiles in relation to decreasing CMRO2 and cerebral activity.
A
Isoflurane, sevoflurane, and desflurane all have equal effects on CNS activity.
24
Q
Which volatiles have anticonvulsant activity?
Which volatiles have pro-convulsant activity?
A
- Des, Iso, and Sevo (at high concentrations and with hypocarbia)
- Enflurane (no longer used) - especially above 2 MAC or PaCO2< 30 mmHg
25
How will volatile anesthetics affect somatosensory evoked potentials (SSEP) or motor evoked potentials (MEP)?
How is this a problem?
* A dose-related decrease in amplitude and increase in latency (*waves further apart*) with a 0.5 to 1.5 MAC.
* Harder to discern whether or not there is damage to the spinal cord.
26
What is SSEP?
There will be a stimulation to the periphery, and response will be measured in the brain to ensure adequate neurotransmission up the spinal cord.
27
What is MEP?
There will be a stimulation of the brain and response will be measured in the periphery (muscle) to ensure adequate transmission down the spinal cord.
28
How do you prevent the negative effects on SSEP and MEP monitoring when using volatiles?
* Do not use more than 0.5 MAC if you are monitoring SSEP or MEP for spinal cases.
* Instead, use 0.5 MAC of volatile with 60% of N2O or IV anesthetic/opioid.
29
How do volatile anesthetics affect CBF?
Increase CBF d/t decrease cerebral vascular resistance. This can result in an increase in ICP.
30
At what MAC will there be an onset of CBF increase?
* Above 0.6 MAC
* Can occur within minutes despite the lack of BP change.
31
What is the best volatile anesthetic to use for a patient with a known increased ICP?
Which volatile will have the greatest vasodilatory effect?
* Sevoflurane has the least vasodilatory effect. (*not shown in graph*)
* Halothane will have the greatest increase in CBF.
* Nitrous is okay at less than 1 MAC
32
Autoregulation maintains cerebral blood flow relatively constant between ____ and ____ mm Hg mean arterial pressure
50 to 150 mmHg
33
Autoregulation will be lost by what MAC with Halothane, Sevoflurane, Isoflurane, and Desflurane?
Halothane: 0.5 MAC
Sevo: 1 MAC (**Best at preserving autoregulation**)
Iso and Des: 0.5-1.5 MAC
34
Which patients are at the most risk of increased ICP from volatiles?
Patients with space-occupying lesions
35
How does hyperventilation decrease ICP?
Inducing hypocapnia via hyperventilation reduces PaCO2, which will cause vasoconstriction in the cerebral arterioles decreasing ICP
36
At what MAC will there be an increase ICP?
How much will ICP increase?
0.8 MAC
Increase by 7 mmHg.
37
How do volatile anesthetics affect respiration?
A dose-dependent increase in rate and decrease in tidal volume.
38
How do volatile anesthetics cause respiratory depression?
Direct depression of medullary ventilatory center.
Interference with intercostal muscles.
*Rate change insufficient to maintain minute ventilation or PaCO2*
39
At what MAC will there be apnea?
1.5 to 2.0 MAC
40
Hypoxic responses are mediated by the ____ .
How do volatile anesthetics affect hypoxic responses?
Carotid bodies
Blunt hypoxic response
41
There will be a 50-70% depression in hypoxic response with ____ MAC.
100% depression at ____ MAC
0.1 MAC
1.1 MAC
42
Which gasses will blunt the hypoxic response? How long will the effects?
* All volatiles including nitrous
* Several hours post-op
43
What are the effects of volatiles on hypercarbic response?
Do all volatiles cause this?
* Dose-dependent blunting of hypercarbic response.
* Nitrous does not increase PaCO2.. can be used as a part of MAC to decrease depression
44
How do volatile anesthetics affect HPV?
A 50% depression occurs at what MAC?
* A dose-dependent decrease in HPV response.
* 2 MAC (we never keep patients at this level)
45
How do volatile anesthetics cause myocardial depression?
* Inhibits calcium entry, and alters SR function.
* ↓ in contractility, SV, and CO (*Halothane the most*).
* ↓ MAP d/t ↓ SVR
## Footnote
Worsened in already diseased/dysfunctional hearts
46
What gas will not cause cardiac depression?
Nitrous
47
How do volatile anesthetics affect heart rate?
A dose-dependent **increase** in HR.
48
Sevoflurane will see a HR increase at a MAC greater than ____ .
What about Iso and Des?
1.5 MAC
*Iso and Des at lower concentrations*
49
What happens to HR with desflurane overpressurization?
* A significant increase in HR (60 bpm to 140 bpm)
* Can be catastophic in pts with aortic stenosis or bad hearts
## Footnote
Per the Eger vidoes this response is very transient (couple of mins)
50
What variables may obscure the increase in HR seen with volatiles?
- Anxiety (may ↑ HR further)
- Opioids
- BB
- Vagolytic administration
51
What is the effect of the volatile anesthetic on cardiac output?
What drug is the exception?
* A dose-dependent decrease in CO (offset by a mild increase in HR for most volatiles).
* Nitrous - mild ↑ in CO
52
Which volatile anesthetic will have the largest decrease in the cardiac index?
Least decrease?
* Halothane
* Desflurane
53
Which gas is least proarrhythmic?
Nitrous
54
How can volatiles potentially increase the risk of Torsade's?
Inhibition of K+ channels caues prolonged QT interval
55
Which volatile anesthetic will be used in an ablation case?
Sevoflurane does not increase the refractoriness of accessory pathways, where as Iso does. This will be the best gas to use if you want to evaluate if the ablation was successful.
*In clinical settings, volatile anesthetics will not be used in ablation cases. MAC cases.*
56
Volatiles effect the neuroendocrine stress response. What is activated/increased and what is suppressed?
Activated: HPA (Hypothalamic-Pituitary-Adrenal) and ANS
Increased: Catecholamines, ACTH, cortisol
Supressed: monocytes, macrophages, and T-cells
57
Some studies suggest GA compared to neuraxial have increase ____ and increase ____ .
metastasis
mortality
58
How do volatile anesthetics affect hepatic blood flow?
Which volatiles effect it the most?
Total hepatic blood flow and hepatic artery flow are maintained.
Volatiles dilate the portal vein which will increase blood flow at 1-1.5 MAC.
*Iso, Des, and Sevo have the same effects*
**Halothane decreases hepatic flow**
59
At what MAC will the portal vein flow increase?
1 to 1.5 MAC
60
Which gas will decrease hepatic flow and decrease oxygen delivery?
Halothane
## Footnote
*Halothane Hepatitis*
61
Hepatotoxicity occurs when there is inadequate ____ of hepatocytes.
oxygenation
*Decrease blood flow, will lead to enzyme induction, increasing O2 demand.*
62
Type I Hepatotoxicity related to volatile gas:
Occurs in ____ % of patients.
________ (length) after exposure.
Symptoms:
Type I Hepatotoxicity related to volatile gas:
Occurs in **20%** of patients.
**1-2 weeks** after exposure.
Symptoms: **Nausea, lethargy, fever**
63
Type II Hepatotoxicity related to volatile gas:
Less common
____ (length) after exposure.
High mortality rate d/t ________ and ________
Immune-mediated response against hepatocytes will present with ______ and _______.
Type II Hepatotoxicity related to volatile gas:
Less common
**1 month** after exposure.
High mortality rate d/t **acute hepatitis** and **hepatic necrosis**
Immune-mediated response against hepatocytes will present with **fever** and **eosinophilia**.
64
Some anesthetics are metabolized through P450 to ____ metabolites.
What gases are metabolized the most?
When could this potentially cause an antibody reaction?
Acetyl Halide
Enflurane > Isoflurane > Desflurane
If previously sensitized to halothane or enflurane
65
Which anesthetic is not capable of stimulating hepatic antibodies?
Sevoflurane
Metabolized to vinyl halide, not acetyl halide
66
What are the renal effects of volatile anesthetics?
Prevention?
* A dose-dependent decrease in RBF, GFR, and U/O d/t ↓ CO
* Can be prevented by preoperative hydration
67
Nephrotoxicity is caused by ?
Fluoride metabolites.
*Volatile anesthetics have fluoride in them*
68
How do fluoride metabolites cause nephrotoxicity?
- Hyperosmolarity
- Hypernatremia
- Increased Cr
69
Which volatile anesthetic causes the worst nephrotoxicity?
Methoxyflurane
*70% metabolized, removed from the market*
70
Why is it presumed that the newer volatiles do not cause nephrotoxicity?
They have lower solubility and are exhaled prior to renal metabolism and excretion
71
What is compound A?
How is it formed?
- Fluromethyl-2,2-difluro-1-vinylether
- Nephrotoxin formed from reactions between sevoflurane and CO2 absorbents ( KOH and NaOH) *at low flow rates*
72
Why is compound A not considered a problem today?
- Most absorbents are composed of CaOH
- Levels of compound A formation at low flow rates are well below the level that causes ATN
73
How can sevo spontaneously combust?
How is this mitigated?
- A dried (dessicated) absorbent can produce methanol and formaldehyde when reacted with sevo
- The reaction leads to increasing heat and eventually spontaneous combustion
- Additional water has been added to sevo
- Check to make sure absorbent cannister is not getting warm
74
How is MH diagnosed?
Caffeine contracture test
75
What are the triggers of MH?
All volatile anesthetics and succinylcholine
76
MH produces a hypermetabolic state of skeletal muscles that leads to ____ , ____ , and ____ .
Excessive release of calcium
Muscle ridgidity
Rhabdomyolysis
77
Sx of MH
* Increase body temp
* Increase CO2 production
* Increase O2 consumption
78
How does dantrolene treat MH?
Blocks intracellular Ca++ release
79
These volatiles cause PONV?
All of them
80
Nitrous above what level is very proemetic?
> 0.5 MAC
81
What metabolic deficiency can be caused by N2O?
Who is most at risk?
B12 deficiency
Developing fetus at risk (inhibits DNA synthesis by inhibiting methionine synthase)
*Make sure to use a scavenging system with pregnant mothers (first trimester) and avoid giving N2O*
82
Why would we avoid giving volatiles to immunosupressed patients?
Can cause megaloblastic bone marrow suppression
83
How can volatiles potentially increase perioperative myocardial events?
Increased levels of plasma homocysteine → atherosclerosis
84
What are the effects of volatile anesthetics on obstetrics?
* A dose-dependent decrease in uterine smooth muscle contractility (0.5-1.0 MAC)
* This can be useful for a retained placenta stuck in the patient.
* Worsen blood loss in uterine atony (need uternine contraction to decrease bleeding)
85
Which gas has no effect on uterine contractility but can increase analgesia without opioids/BZD?
Nitrous
86
What is the structure of halothane?
Why can it be used as an induction agent?
* Halogenated alkane
* Swet smelling, non-pungent, high potency
87
Concerns with halothane?
* Catecholamine induced arrythmias
* Hepatitis
* Pediatric bradyarrhythmias
* Decomposes to HCl
88
Isoflurane is an isomer of ____ .
Isoflurane is highly ____ and highly ____ .
Isoflurane is not good for ____ .
* Enflurane
* Highly pungent and highly potent
* Inhalation induction
89
Pros of Isoflurane:
Cons of Isoflurane:
Pros: Resistant to metabolism = unlikely to cause organ toxicity. Very stable (no deterioration after 5 years).
Cons: Distillation is complex and expensive to purify
90
Desfluranes structure?
- Fluorinated methyl ethyl ether
- Identical to isoflurane except F substituted for Cl
91
Which volatile anesthetic is the most pungent?
Desflurane (Suprane)
It will cause coughing, salivation, breath-holding, and laryngospasm at concentrations > 6% (close to 1 MAC)
92
Over-pressurizing desflurane will cause ____ stimulation.
SNS
93
List the volatiles from most to least likely to degrade to CO if the absorbent is dehydrated?
Desflurane > Enflurane > Isoflurane > Sevoflurane
94
Sevoflurane structure?
Fluorinated methyl isopropyl ether
95
What volatile is least irritating to airways and is used as an induction agent?
Sevoflurane
96
When is nitrous used and not used?
- Not used as a sole anesthetic; cannot achieve 1 MAC; does not produce skeletal muscle relaxaxation
- Not used in neonates - ↑ PVR and can increase R → L shunt
- Has good analgesic properties - can be used if spinal is wearing thin
