Anesthesia machines and volatiles Flashcards by A. Ozumba

[Miscellaneous] What determines anesthetic uptake into tissues?

Tissue blood flow, not solubility, as partition coefficients don’t vary much.

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[Miscellaneous] Which tissues are in the vessel-rich group (VRG)?

Brain, heart, liver, splanchnic bed (<10% body weight, 75% CO, 4–8 min equilibration).

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[Vaporizers & Volatile Agents] Which tissue group equilibrates slowest with volatile agents?

Fat group due to low perfusion but high affinity for anesthetics.

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[Miscellaneous] What is the primary determinant of anesthetic effect?

Partial pressure in the brain = blood = alveoli at equilibrium.

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[Miscellaneous] What factors increase alveolar concentration (FA)?

Increased ventilation, higher inspired concentration.

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[Miscellaneous] What factors slow FA/FI rise? Name 3

High solubility, high CO, high Pa-Pv gradient.

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[Miscellaneous] How does cardiac output affect induction?

High CO slows induction, especially with soluble agents.

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[Miscellaneous] What is overpressurization?

Using higher inspired concentration briefly to speed FA rise.

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[Gas Laws & Uptake] What is the ‘second gas effect’ of N2O?

Accelerates uptake of a co-administered volatile by concentrating remaining gases.

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[Miscellaneous] How does a shunt affect induction speed?

Slows it, especially for less soluble agents.

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[Machine Systems & Safety] What is vapor pressure?

Pressure exerted by a vapor in equilibrium with its liquid at a given temperature.

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[Machine Systems & Safety] Why is vapor pressure important in anesthesia?

Determines how much anesthetic is delivered from the vaporizer.

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[Vaporizers & Volatile Agents] What happens if you put isoflurane in a sevoflurane vaporizer?

Overdose due to higher vapor pressure of isoflurane.

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[Vaporizers & Volatile Agents] How does altitude affect volatile agent delivery?

Delivered % may increase, but partial pressure remains similar due to Dalton’s Law.

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[MAC, Solubility, and Pharmacology] What is MAC?

Minimum alveolar concentration preventing movement in 50% of patients.

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[MAC, Solubility, and Pharmacology] What factors (6) do NOT affect MAC?

Thyroid status, hyper/hypocapnia, gender, metabolic alkalosis, Hyperkalemia, duration of anesthesia.

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[Toxicity & Special Effects] What are signs of fluoride nephrotoxicity?

Polyuria, high Na, BUN, Cr, serum osmolality; unresponsive to vasopressin.

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[Vaporizers & Volatile Agents] Which agent produces the most fluoride?

Methoxyflurane > Sevoflurane > Enflurane.

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[Breathing Circuits & CO₂ Absorbers] How is CO produced in the circuit?

From dry absorbents degrading desflurane, enflurane, or isoflurane.

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[Toxicity & Special Effects] What is the mechanism of N2O-induced megaloblastic anemia?

B12 deficiency: N2O oxidizes cobalt atom within vitamin B12 -> inhibiting vitamin B12 dependent enzymes such as methionine synthetase -> impairing DNA/myelin synthesis.

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[Miscellaneous] What is the concentration effect?

High inspired N2O increases FA faster by concentrating other gases.

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[Breathing Circuits & CO₂ Absorbers] Which circuits are best for spontaneous and controlled ventilation?

Mapleson A for spontaneous, Mapleson D (Bain) for controlled.

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[Vaporizers & Volatile Agents] How does desflurane vaporizer work?

Heated to 39°C, delivers constant % concentration, not partial pressure.

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[MAC, Solubility, and Pharmacology] How is O2 measured in anesthesia machines?

Paramagnetic, Galvanic, or Polarographic (Clark electrode) analyzers.

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[Breathing Circuits & CO₂ Absorbers] What are the benefits of closed-circuit anesthesia? (3)

Less agent use, better humidity/heat retention, less microatelectasis.

[Machine Systems & Safety] What are the three major pressure systems in the anesthesia machine?

High-pressure, Intermediate-pressure, Low-pressure systems.

[Machine Systems & Safety] What does the high-pressure system include?

Cylinders, pressure regulators, pressure gauges.

[Machine Systems & Safety] What is the pressure and volume of an O2 E-cylinder?

2000 psi, ~625 L.

[Miscellaneous] How can you determine the amount of N2O left in the tank?

By weighing the tank.

[Machine Systems & Safety] What components are in the intermediate-pressure system? (4)

Pipeline gas (50 psi), O2 flush valve, fail-safe valves, flowmeters.

[Machine Systems & Safety] What is the function of the O2 pressure failure alarm?

Alarms if O2 pressure drops below 30 psi.

[Machine Systems & Safety] What does the fail-safe valve do?

Prevents flow of other gases if O2 supply fails.

[Machine Systems & Safety] What is the danger of the O2 flush valve?

Delivers 35–75 L/min and can cause barotrauma.

[Machine Systems & Safety] What components are in the low-pressure system? (3)

Flowmeters, vaporizers, common gas outlet.

[Machine Systems & Safety] What is the risk of leaks in the low-pressure system?

Not detected by automated machine checks.

[Vaporizers & Volatile Agents] What are key features of vaporizers? (3)

Agent-specific, temperature-compensated, keyed fillers.

[Vaporizers & Volatile Agents] How is desflurane's vaporizer different?

It is electrically heated to 39°C and pressure-regulated.

[Vaporizers & Volatile Agents] What happens if isoflurane is added to a sevoflurane vaporizer?

Overdose due to higher vapor pressure of isoflurane.

[Machine Systems & Safety] What does the O2/N2O proportioning system (Link-25) do?

Prevents delivering less than 25% oxygen.

[Machine Systems & Safety] What is the function of the vaporizer interlock system?

Allows only one vaporizer to be used at a time.

[Gas Laws & Uptake] What monitor is essential to detect a hypoxic gas mixture?

The O2 analyzer.

[Machine Systems & Safety] What are the components of the circle system? (5)

Inspiratory/expiratory limbs, unidirectional valves, CO2 absorbent, reservoir bag, APL valve.

[Breathing Circuits & CO₂ Absorbers] What is a common cause of bellows not rising?

Circuit leak or patient disconnection.

[Breathing Circuits & CO₂ Absorbers] What substances are used in CO2 absorbents?

Soda lime or Amsorb Plus.

[Breathing Circuits & CO₂ Absorbers] What indicates exhausted CO2 absorbent?

Color change due to ethyl violet (pH <10.3).

[Breathing Circuits & CO₂ Absorbers] What toxic compounds can be produced by dry absorbents?

Compound A (sevo) and CO (desflurane, enflurane).

[Gas Laws & Uptake] What is the mnemonic for gas laws?

Prince Charles is under constant pressure. Water Boyle’s at constant temperature.

[Gas Laws & Uptake] Which gas law explains cuff expansion in the trachea?

Gay-Lussac’s Law (P1/T1 = P2/T2).

[Gas Laws & Uptake] What is the Ideal Gas Law and its relevance to anesthesia?

PV = nRT; explains how pressure, volume, and temperature affect anesthetic gas delivery.

[Gas Laws & Uptake] What does Dalton’s Law state about volatile anesthetics at altitude?

Px = (Pb – Ph2O) * F; at high altitude, a higher volume % of gas is needed to maintain the same partial pressure.

[Gas Laws & Uptake] What does Charles’ Law explain in clinical anesthesia?

V1/T1 = V2/T2; relates gas volume changes with temperature—relevant in warming of gases.

[Gas Laws & Uptake] What clinical scenario illustrates Gay-Lussac’s Law?

ETT cuff expands as injected gas warms from room to body temperature.

[Gas Laws & Uptake] How does Henry’s Law relate to anesthetic uptake?

Gas solubility is proportional to its partial pressure; explains gas exchange in blood.

[Gas Laws & Uptake] What is the mnemonic for gas laws?

“Prince Charles is under constant pressure. Water Boyle’s at constant temperature.”

[Miscellaneous] What is the Meyer-Overton correlation?

Anesthetic potency correlates with lipid solubility (higher oil:gas = lower MAC).

[Miscellaneous] What is the Critical Volume Hypothesis?

Anesthetics distort lipid bilayer structure, altering ion channel function.

[Machine Systems & Safety] What is the Pressure Reversal Effect?

Increased atmospheric pressure can reverse the anesthetic effects on the lipid bilayer. | Part of critical volume effect

[Miscellaneous] What do protein-based theories propose about anesthesia?

Volatile agents interact with hydrophobic sites on proteins, not just lipid bilayers.

[Miscellaneous] Which brain areas are associated with specific anesthetic effects?

Amnesia: hippocampus; Sedation: hypothalamus; Akinesia: spinal cord.

[Gas Laws & Uptake] What does the Ideal Gas Law state?

PV = nRT; explains the relationship between pressure, volume, and temperature of gases.

[Gas Laws & Uptake] How does Dalton’s Law apply to anesthetic gases at altitude?

Lower barometric pressure at altitude means higher delivered gas volume % is needed to maintain the same anesthetic partial pressure.

[Miscellaneous] What is the Meyer-Overton correlation?

Anesthetic potency is linearly correlated with lipid solubility (oil:gas partition coefficient).

[Miscellaneous] What is the site of action for volatile anesthetics causing amnesia?

Higher brain structures, including the hippocampus.

[Miscellaneous] Which tissue group has the fastest equilibration with volatile anesthetics?

Vessel-rich group (VRG) equilibrates in 4–8 minutes. ## Footnote brain, heart, splanchnic bed and liver

[Vaporizers & Volatile Agents] What determines the pharmacologic effect of an inhaled agent?

Partial pressure in the brain, which equals that in alveoli and blood at equilibrium.

[MAC, Solubility, and Pharmacology] How does blood solubility affect the rise of FA/FI?

High solubility slows the rise of FA/FI due to increased uptake into blood.

[Miscellaneous] What is overpressurization in volatile anesthetic delivery?

Brief use of higher vaporizer settings to reach target FA faster.

[Miscellaneous] How does cardiac output affect induction with volatile anesthetics?

Higher CO slows induction, especially with soluble agents.

[Miscellaneous] What factors increase FA/FI ratio?

Increased MV, decreased CO, low blood solubility, low Pa-Pv.

[Gas Laws & Uptake] What is the second gas effect with nitrous oxide?

N2O increases the FA/FI of a co-administered volatile anesthetic by accelerating uptake.

[Vaporizers & Volatile Agents] What happens if sevoflurane vaporizer is filled with isoflurane?

Overdose occurs because isoflurane has higher vapor pressure.

[MAC, Solubility, and Pharmacology] What is MAC and what does 1.3 MAC prevent?

Minimum alveolar concentration; 1.3 MAC prevents movement in 99% of patients.

[Vaporizers & Volatile Agents] What volatile agent causes coronary steal?

Isoflurane via coronary vasodilation.

[Vaporizers & Volatile Agents] Which volatile agent is most pungent and causes airway irritation?

Desflurane.

[Miscellaneous] What causes Halothane hepatitis?

Immune-mediated hepatotoxicity from reactive metabolites; risk factors include obesity, multiple exposures.

[Vaporizers & Volatile Agents] What is fluoride-induced nephrotoxicity and which agents cause it?

High-output renal failure from fluoride ions; methoxyflurane > sevoflurane > enflurane.

[Miscellaneous] What does the PANDA trial say about anesthesia in young children?

No difference in neurodevelopmental outcomes at age 2 or 5 for brief single exposure.

[Breathing Circuits & CO₂ Absorbers] Which volatile anesthetics degrade to carbon monoxide in dry CO2 absorbents?

Desflurane, enflurane, isoflurane.

[Miscellaneous] How does nitrous oxide cause megaloblastic anemia?

Oxidizes B12, inhibiting methionine synthase, disrupting DNA synthesis.

[Gas Laws & Uptake] What are contraindications to N2O due to gas expansion?

Bowel obstruction, pneumothorax, intracranial air, intraocular air, tympanoplasty.

[Vaporizers & Volatile Agents] How does desflurane vaporizer differ from others?

It’s electrically heated to 39°C and delivers constant vapor pressure, not fixed % concentration.

[Machine Systems & Safety] What does the oxygen flush valve bypass?

Flowmeters and vaporizers.

[Breathing Circuits & CO₂ Absorbers] What is the function of ethyl violet in CO2 absorbents?

Color indicator that turns purple when absorbent is exhausted (pH <10.3).

[Breathing Circuits & CO₂ Absorbers] Which Mapleson circuit is best for spontaneous ventilation?

Mapleson A.

[Breathing Circuits & CO₂ Absorbers] What are benefits of closed circuit anesthesia?

Reduced agent use, better humidity, less heat loss, less microatelectasis.

Anesthesia machines and volatiles Flashcards

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