Inhaled anesthetics II Exam 3 Flashcards
What are the purposes of the anesthesia circuit? (3)
Delivery of O₂ and inhaled anesthetics
Maintenance of temperature & humidity
Removal of CO₂ and exhaled drugs
What types of gas delivery systems are there?
Rebreathing (Bain system)
Non-rebreathing (BVM system)
Circle systems (Anesthesia machine)
What type of system is depicted below? Where is the aPL valve located on this system?
Bain Circuit
Blue circle depicts aPL below.
In the figure below, what portion of the anesthesia circle system is indicated by 1?
Inspiratory Unidirectional Valve
In the figure below, what portion of the anesthesia circle system is indicated by pink arrow?
Fresh Gas Inlet (O₂ & medical air)
In the figure below, what portion of the anesthesia circle system is indicated by 2?
CO₂ Absorber
In the figure below, what portion of the anesthesia circle system is indicated by 3?
Bag/Ventilator Selector Switch
In the figure below, what portion of the anesthesia circle system is indicated by 4?
APL Valve
In the figure below, what portion of the anesthesia circle system is indicated by 5?
Expiratory Unidirectional Valve
In the figure below, what portion of the anesthesia circle system is indicated by 6? 8?
6 = Expiratory Limb
8 = Inspiratory Limb
In the figure below, what portion of the anesthesia circle system is indicated by 7?
Y-Piece
When fresh gas flow (FGF) exceeds V̇T then you have _________________.
High Flow Anesthesia
When V̇T exceeds fresh gas flow (FGF) then you have _________________.
Low Flow Anesthesia
When would one see lack of rebreathing, wasteful volatile use, and cool dried air?
High flow anesthesia
When would one see lower volatile use, less cooling/drying of air, and slow changes in anesthetics?
Low flow anesthesia
Do volatiles cause bronchoconstriction or bronchodilation?
Bronchodilation
How do volatiles cause bronchodilation?
Blockage of VG Ca⁺⁺ channels
Depletion of SR Ca⁺⁺
Is the bronchodilatory effect of volatiles still present in someone with reactive airway disease?
No (or very little effect). Bronchodilatory effects of volatiles require an intact epithelium, normal inflammatory processes, etc.
Will volatiles cause bronchospasm on their own (in a patient with no history of bronchospasm)?
No
Histamine release or vagal afferent stimulation needed to cause spasm.
In a patient without history of bronchospasm, how much would you anticipate PVR to change with 1-2 MAC?
PVR would be unchanged in patient with no history of bronchospasm.
What risk factors increase risk of bronchospasm? (4)
COPD
Coughing w/ ETT in place
<10 years old
URI
What anesthetic is generally the best at bronchodilating?
Sevoflurane
Which anesthetic can function as a pulmonary irritant (especially in smokers)?
Desflurane
Which volatile anesthetic in the graph below caused the greatest increase in airway resistance? Lowest?
Desflurane = ↑ airway resistance
Sevoflurane = ↓ airway resistance
Inhaled anesthetics provide a dose-dependent skeletal muscle relaxation. T/F?
True
Which volatile gas has no effect on the relaxation of skeletal muscles?
N₂O
Will volatiles potentiate or inhibit NMBD’s? How?
Potentiate via sensitization of nACh receptors at NMJ.
How do volatile anesthetics cause skeletal muscle relaxation as a solo agent?
Volatiles cause skeletal muscle relaxation via enhancement of glycine at the spinal cord.
What is ischemic preconditioning?
Brief periods of ischemia preparing the heart for longer periods of ischemia.
Ischemic preconditioning with volatile anesthetics can occur as low as ______ MAC.
0.25
Why does ischemic preconditioning happen?
↑ PKC activity
Phosphorylation of ATP sensitive K⁺ channels
Production of ROS (Reactive Oxygen Species)
Better regulation of vascular tone.
What molecule mediates ischemic preconditioning?
Adenosine
What does ischemic preconditioning prevent? (4)
Reperfusion injuries
Cardiac dysrhythmias
Contractile dysfunction
Delays MI’s in CAD patients.
At what MAC does volatile depression of CMRO₂ begin?
0.4 MAC
At what MAC would we see EEG burst suppression? What about total electrical silence?
1.5 MAC = burst suppression
2 MAC = EEG silence
Which volatile causes the most EEG suppression?
Trick question. They all affect EEG’s the same.
Which volatiles have anticonvulsant activity?
Des, Sevo, & Iso at high concentrations & with hypocarbia.
Which volatile is a proconvulsant?
Enflurane
Give an example of a somato-sensory evoked potential (SSEP).
Stimulation of the foot evoking an electrical response in the CNS.
Give an example of a motor-evoke potential (MEP).
Direct stimulation of the brain eliciting a twitch response in the hand.
You have a case where SSEPs and MEPs need to be monitored, what general anesthetics options do you have?
TIVA
N₂O 60% and 0.5 MAC volatile.
What specific effects will volatile agents have on SSEPs and MEPs? At what MAC?
Dose-dependent (0.5 - 1.5MAC):
↓ amplitude
↑ latency (delayed frequency)
What occurs with cerebral blood flow with volatile administration?
Dose dependent:
↑ CBF due to vasodilation ⇒ ↑ ICP
At what MAC would you expect to start to see an increase in CBF due to volatile administration?
At > 0.6 MAC
Which volatile has less cerebral vasodilatory effects?
Sevoflurane
Which volatiles have the greatest effect on increasing CBF? (and thus ICP)
Halothane and N₂O
Which volatile is the best for neuro cases? Why?
Sevoflurane
Preserves autoregulation mechanism up to 1 MAC & minimal cerebral vasodilation.
What patient population is most at risk due to the ICP increasing effects of volatile agents?
Patients with CNS occupying tumor/lesion.
What average ICP increase is seen with volatile use?
7mmHg
At what volatile dosage does ICP increase?
> 0.8 MAC
What do volatiles do to the respiratory system?
Dose dependent:
Tachypnea
↓ VT
How do volatiles cause their respiratory effects?
Direct depression of medullary ventilatory center.
Interference with intercostal muscles.
At what volatile dosage would apnea be seen?
1.5 - 2 MAC
All volatiles will blunt the hypercarbic response. T/F?
False. N₂O does not blunt the hypercarbic response.
All volatiles will blunt the hypoxic response. T/F?
True
How can the hypercarbic response be preserved whilst using volatile anesthetic gasses?
Use N₂O and volatile together.
What effect is seen in the graph below?
Volatile effects on CO₂
minimal effects with N₂O
What is hypoxic pulmonary vasoconstriction?
Contraction of pulmonary arteries to shunt blood away from poorly ventilated portions of the lung.
When is the blunting of HPV most concerning?
When one lung ventilation is being utilized.
How fast is the HPV response?
Fast: within 5 minutes regional blood flow is ½ of normal.
50% depression of HPV occurs at ___ MAC.
2
Which volatile(s) does not cause cardiac depression?
N₂O
How do volatiles cause hypotension?
Direct myocardial depression by altering Ca⁺⁺ entry and SR function.
Volatiles will cause a dose-dependent decrease in ______ , ______ , and CO.
contractility ; SV
When is volatile depression of cardiac function most concerning?
With pathologic hearts (particularly pathologies of ↓ contractility)
What volatile can cause significant tachycardia with overpressurization?
Desflurane
When will sevoflurane begin to cause increases in heart rate?
Only at > 1.5 MAC
What variables confound the tachycardic effect of volatiles? (↑ and ↓)
Increase tachycardia:
Anxiety
Vagolytics
Might help reduce Tachycardia:
Concurrent opioids
β blockade
What volatile is slightly sympathomimetic, causing a slight increase in CO?
N₂O
Is the coronary steal effect of volatiles clinically significant?
Nope
What electrocardiac effect do volatiles have?
QT prolongation via inhibition of K⁺ currents ⇒ risk of Torsade’s
Which volatile has minimal pro-arrhythmic activity?
N₂O
What volatile is the gas of choice for EP ablations? Why?
Sevoflurane
Other volatiles increase refractoriness of accessory pathways making identification of arrhythmia location difficult.
Volatile neuroendocrine modulation will cause a perioperative surge in _______, _______, and _______.
catecholamines; ACTH; & cortisol
Volatiles will suppress what important immune system components?
Volatiles suppress monocytes, macrophages, and T-cells.
What does the total neuroendocrine profile of volatile anesthetics suggest for cancer patients undergoing surgery?
Neuraxial anesthesia is likely better than GA for cancer patients.
What hepatic blood flow changes are seen with volatile administration? At what MAC might you see these changes?
Portal vein dilation = ↑ portal vein flow (at 1-1.5 MAC).
Maintained total hepatic flow.
Which volatile is the only one that decreases hepatic flow?
Halothane (likely contributes to halothane hepatitis)
What causes volatile hepatotoxicity? When is it a concern?
Inadequate oxygenation of liver cells via ↓ blood flow and ↑ O₂ demand.
Concern for patients with preexisting liver disease.
What is Type 1 Volatile hepatotoxicity?
Direct toxicity or free radical effect 1-2 weeks post surgically with N/V & fever in 20% of patients.
What is Type 2 Volatile Toxicity?
Immune-mediated response caused with previous exposure to volatile with eosinophilia, fever, and higher mortality rate from hepatitis and necrosis.
Which volatile is the choice anesthetic for severe liver disease? Why?
Sevoflurane
Broken down to vinyl halide and won’t stimulate antibody production causing a Type II reaction.
What volatiles are metabolized into acetyl halides? What is the significance of this?
Enflurane > Iso > Des
Acetyl halides can cause antibody reactions especially with previous exposure to halothane or enflurane.
What are the renal effects of volatile anesthetics?
Dose dependent decrease in RBF, GFR, and UO from CO depression.
How can the renal effects of volatile anesthetics be counteracted?
Hydration (both pre-operative and intra-operative).
What other organ (besides the heart) undergoes protective ischemic preconditioning from volatile anesthetics?
Kidneys
What toxic metabolites of volatiles can cause nephrotoxicity? Why is this not an issue typically?
Fluoride metabolites
Newer volatiles are exhaled prior to being metabolized and eliminated renally.
What volatile is 70% metabolized and can cause fluoride metabolite nephrotoxicity more than any of the other volatiles?
Methoxyflurane
What measure is utilized in CO₂ absorbents today to help prevent the formation of compound A?
75% or greater concentrations of calcium hydroxide.
What volatile is predisposed to starting fires? Why?
Sevoflurane
Reacts with dried absorbent to produce methanol and formaldehyde causing a heat reaction and eventual combustion.
How is sevoflurane fire avoided?
Addition of H₂O to Sevo
Check temp of absorbent cannister
Exchange exhausted absorbents
Which volatile anesthetics are emetogenic?
All
What rate of PONV is seen with two triggering agents? (ex. desflurane and fentanyl)
25 - 30% PONV
When is N₂O emetogenic?
At greater than 50% or 0.5 MAC
Why is N₂O administration in a pregnant patient with B12 deficiency dangerous?
N₂O will oxidize the cobalt ion in B12 thus inhibiting methionine synthase = inhibition of DNA synthesis.
Which volatile anesthetic can cause bone marrow suppression?
N₂O
What is the result from increases in plasma homocysteine levels from N₂O administration?
If the patient also has low B vitamins and atherosclerosis, then N₂O increases risk of myocardial events.
What is/are the obstetric effects of volatile anesthetics? And at what MAC?
Dose-dependent (0.5 - 1.0 MAC) decrease in uterine smooth muscle contractility. (relaxation)
When would a decrease in uterine muscle tone be useful?
With retained placenta
What is a downside to decreased uterine muscle contractility with volatile use?
Uterine atony (worsen blood loss)
Why is N₂O useful in mom’s post delivery?
Swiftly increases analgesia without opioid/benzo’s (use as the spinal starts to wear off).
Which volatiles have a sweeter smell?
Halothane
Sevoflurane
What is the only real benefit of halothane?
↓ N/V
What are the four major concerns of halothane?
Catecholamine-induced arrhythmias
Hepatic necrosis
Pediatric bradycardia
Decomposing into HCL acid.
Which two volatiles can’t be used for induction due to their pungency?
Isoflurane
Desflurane
Which volatile does not degrade, even after 5 years of storage?
Isoflurane
If a vaporizer has a heating element, then the gas for that vaporizer can be assumed to be ____________.
Desflurane
List the order in which volatiles will degrade into carbon monoxide if the absorbent becomes dehydrated.
Desflurane (worst) > Enflurane > Isoflurane > Sevoflurane (trivial)
Which volatile anesthetic would be the choice for inhalation induction? Why?
Sevoflurane
Least airway irritation & not pungent.
Which volatile causes the least increase in ICP?
Sevoflurane
How does N₂O produce skeletal muscle relaxation?
Trick question. It does not.
What are the benefits of N₂O? (2)
Good analgesia
2nd gas effect
What are the major cons of N₂O ? (3)
Significant N/V @ 0.5 MAC
↑ PVR
No surgeries with air filled spaces
At what MAC would cerebral autoregulation be lost with halothane? Sevo? Iso/Des?
Halothane lost by 0.5 MAC
Sevo lost by 1 MAC
Iso/Des lost by 0.5-1.5 MAC
Why is hypercarbia seen with volatiles?
↓VT, increased rate insufficient to maintain PaCO₂
At what MAC would you see 100% depression of hypoxic response? 50-70% depression?
1.1 MAC ⇒ 100%
0.1 MAC ⇒ 50-70%
What effect do volatiles have on CO?
dose dependent ↓CO but offset by mild ↑HR
Halothane has significant ↓CO
N₂O can cause mild ↑CO
How do you prepare for an expected Malignant Hyperthermia case?
Remove Vaporizers
Do case first in the day
Run machine cycle according to instructions
Replace components
