Anesthesia machines and volatiles Flashcards
[Miscellaneous] What determines anesthetic uptake into tissues?
Tissue blood flow, not solubility, as partition coefficients don’t vary much.
[Miscellaneous] Which tissues are in the vessel-rich group (VRG)?
Brain, heart, liver, splanchnic bed (<10% body weight, 75% CO, 4–8 min equilibration).
[Vaporizers & Volatile Agents] Which tissue group equilibrates slowest with volatile agents?
Fat group due to low perfusion but high affinity for anesthetics.
[Miscellaneous] What is the primary determinant of anesthetic effect?
Partial pressure in the brain = blood = alveoli at equilibrium.
[Miscellaneous] What factors increase alveolar concentration (FA)?
Increased ventilation, higher inspired concentration.
[Miscellaneous] What factors slow FA/FI rise? Name 3
High solubility, high CO, high Pa-Pv gradient.
[Miscellaneous] How does cardiac output affect induction?
High CO slows induction, especially with soluble agents.
[Miscellaneous] What is overpressurization?
Using higher inspired concentration briefly to speed FA rise.
[Gas Laws & Uptake] What is the ‘second gas effect’ of N2O?
Accelerates uptake of a co-administered volatile by concentrating remaining gases.
[Miscellaneous] How does a shunt affect induction speed?
Slows it, especially for less soluble agents.
[Machine Systems & Safety] What is vapor pressure?
Pressure exerted by a vapor in equilibrium with its liquid at a given temperature.
[Machine Systems & Safety] Why is vapor pressure important in anesthesia?
Determines how much anesthetic is delivered from the vaporizer.
[Vaporizers & Volatile Agents] What happens if you put isoflurane in a sevoflurane vaporizer?
Overdose due to higher vapor pressure of isoflurane.
[Vaporizers & Volatile Agents] How does altitude affect volatile agent delivery?
Delivered % may increase, but partial pressure remains similar due to Dalton’s Law.
[MAC, Solubility, and Pharmacology] What is MAC?
Minimum alveolar concentration preventing movement in 50% of patients.
[MAC, Solubility, and Pharmacology] What factors (6) do NOT affect MAC?
Thyroid status, hyper/hypocapnia, gender, metabolic alkalosis, Hyperkalemia, duration of anesthesia.
[Toxicity & Special Effects] What are signs of fluoride nephrotoxicity?
Polyuria, high Na, BUN, Cr, serum osmolality; unresponsive to vasopressin.
[Vaporizers & Volatile Agents] Which agent produces the most fluoride?
Methoxyflurane > Sevoflurane > Enflurane.
[Breathing Circuits & CO₂ Absorbers] How is CO produced in the circuit?
From dry absorbents degrading desflurane, enflurane, or isoflurane.
[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.
[Miscellaneous] What is the concentration effect?
High inspired N2O increases FA faster by concentrating other gases.
[Breathing Circuits & CO₂ Absorbers] Which circuits are best for spontaneous and controlled ventilation?
Mapleson A for spontaneous, Mapleson D (Bain) for controlled.
[Vaporizers & Volatile Agents] How does desflurane vaporizer work?
Heated to 39°C, delivers constant % concentration, not partial pressure.
[MAC, Solubility, and Pharmacology] How is O2 measured in anesthesia machines?
Paramagnetic, Galvanic, or Polarographic (Clark electrode) analyzers.
[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?
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 pressure can reverse the anesthetic effects on the lipid bilayer.
[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.
[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.
