Sistemas Flashcards
- What are some components of an anesthesia workstation?
Components of the anesthesia workstation include what was traditionally known as the anesthesia machine (with its pressure‐regulating and gas‐mixing components), vaporizers, the anesthesia breathing circuit, the ventilator, the scavenging system, and various monitoring systems (e.g., ECG, blood pressure, pulse oximetry, and gas analyzers). (220)
- What is the purpose of the fail-safe valve? What triggers the fail-safe valve on the anesthesia machine?
The fail-safe valve protects against the delivery of a hypoxic gas mixture; it is triggered when the oxygen supply pressure drops below 30 psi, causing it to shut off or proportionally decrease the flow of all gases. (221)
- Can a hypoxic mixture be delivered from the anesthesia machine with an intact fail-safe valve? Explain.
Yes – because the fail-safe valve is essentially a pressure sensor; if the oxygen flow is zero but the pressure is still sensed as adequate, a hypoxic mixture might still be delivered. This highlights the critical role of the oxygen analyzer and constant vigilance by the anesthesia provider. (221)
- How are oxygen, nitrous oxide, and air gases that are used in anesthesia typically delivered to the anesthesia machine? At what pressure must these gases be delivered for proper function of the anesthesia machine?
These gases are usually delivered from a central hospital supply via pipelines that use color-coded outlets and noninterchangeable fittings; they must be delivered at approximately 50 psi for the anesthesia machine to function properly. (221)
- How is the delivery of erroneous gases to the anesthesia machine minimized?
Erroneous gas delivery is minimized by the use of color-coded wall outlets and pressure hoses plus noninterchangeable fittings (using systems such as DISS or Quick Connects) that prevent misconnection. (221)
- What is the purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine?
They serve as backup supplies of oxygen and nitrous oxide in case the central gas supply fails. (222)
- How is an erroneous hookup of a gas cylinder to the anesthesia machine minimized?
Cylinders are color-coded and attached using a hanger yoke assembly that incorporates a pin index safety system (PISS), which ensures that only the correct gas cylinder can be connected to its designated inlet. (222)
- Please complete the following table illustrating the characteristics of compressed gases stored in E-sized cylinders:
Oxygen: Cylinder color – Green; Physical state – Gas; Contents – ~625 L; Full pressure – ~2000 psi. Nitrous Oxide: Blue; Physical state – Liquid and gas; Contents – ~1590 L; Full pressure – ~750 psi. Carbon Dioxide: Gray; Physical state – Liquid and gas; Contents – ~1590 L; Full pressure – ~838 psi. Air: Yellow; Physical state – Gas; Contents – ~625 L; Full pressure – ~1800 psi. (223)
- How is the pressure of oxygen related to the volume of oxygen in an oxygen gas cylinder? What does this mean with regard to calculating the volume of oxygen remaining in a used oxygen cylinder?
Pressure in an oxygen cylinder is directly proportional to the volume of oxygen remaining. For example, if a full oxygen cylinder reads approximately 2000 psi (625 L), a reading of 500 psi (one fourth of full pressure) indicates roughly 1/4 of the oxygen volume remains (~156 L). (223)
- How is the pressure of nitrous oxide related to the volume of nitrous oxide in a nitrous oxide gas cylinder?
Because nitrous oxide is stored as a liquid and gas, its pressure gauge remains constant at about 750 psi as long as liquid is present; only after the liquid is exhausted does the pressure begin to drop, indicating that roughly 75% of the gas has been used. (223)
- Why does atmospheric water vapor accumulate as frost on the outside surface of oxygen tanks and nitrous oxide tanks in use? Does internal icing occur?
The process of vaporization and expansion absorbs heat, cooling the exterior of the cylinders so that atmospheric water vapor condenses as frost; however, internal icing does not occur because the compressed gas inside is virtually free of water vapor. (223)
- What is the purpose of flowmeters on an anesthesia machine?
Flowmeters precisely control and measure the flow of gases to the common gas inlet of the anesthesia machine. (223)
- How do flowmeters on an anesthesia machine work?
Gases flow into a tapered, vertically oriented glass tube where they lift a bobbin or ball; the position of this float, determined by the balance between gas flow pressure and gravity, indicates the flow rate in mL or L per minute. (223)
- Are flowmeters for various gases interchangeable?
No; each flowmeter is calibrated for the specific density and viscosity of its designated gas, so they are not interchangeable. (223)
- Why is the oxygen flowmeter the last flowmeter in a series on the anesthesia machine with respect to the direction in which the gas flows?
Because oxygen is added last to the gas mixture, ensuring that any leaks upstream do not dilute the oxygen concentration, thereby maintaining a safe and predictable oxygen delivery. (223)
- What is the purpose of the oxygen flush valve?
The oxygen flush valve provides a high flow (bypassing the flowmeters and manifold) of oxygen directly to the patient, typically used in emergencies or to quickly fill the breathing circuit. (223-224)
- What is the flow of oxygen delivered to the patient when the oxygen flush valve is depressed?
The oxygen flush valve delivers approximately 35 to 75 L/min of oxygen. (224)
- What is the risk of activating the oxygen flush valve during a mechanically delivered inspiration?
Activation during inspiration can transmit very high airway pressures to the patient’s lungs, potentially causing barotrauma. (224)
- Why do volatile anesthetics require placement in a vaporizer for their inhaled delivery to patients via the anesthesia machine?
Volatile anesthetics are liquids at room temperature; vaporizers are necessary to convert them into a vapor in a controlled and predictable manner so that an accurate concentration can be delivered to the patient. (224)
- What is the heat of vaporization?
The heat of vaporization is the amount of heat (calories) required to convert 1 gram of a liquid into vapor at a specific temperature. (224)
- What is vapor pressure? What influence does temperature have on vapor pressure?
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid; it increases with temperature and decreases as the liquid cools. (224)
- Describe how contemporary vaporizers for volatile anesthetics are classified.
Contemporary vaporizers are classified as agent-specific, variable-bypass, flow-over, temperature-compensated, and out-of-circuit devices. (224)
- Why are contemporary vaporizers unsuitable for use with desflurane?
Desflurane has a very high vapor pressure (near 1 atm at room temperature) which makes it incompatible with conventional vaporizers; specialized heated vaporizers are required. (224)
- What does the term agent-specific refer to?
It means that a vaporizer is designed and calibrated for a single, specific volatile anesthetic agent. (224)
- What do the terms variable-bypass and flow-over refer to?
‘Variable-bypass’ refers to the splitting of fresh gas flow between the vaporizing chamber and a bypass chamber, while ‘flow-over’ describes the portion of gas that passes over the liquid anesthetic to become saturated with vapor. (224)
- What does the term temperature-compensated refer to? Between what temperatures is vaporizer output reliably constant?
Temperature-compensated vaporizers automatically adjust for changes in anesthetic vapor pressure due to temperature fluctuations; they maintain constant output between approximately 20°C and 35°C. (225)
- What does the term out-of-circuit refer to?
It means that the vaporizer is not part of the direct breathing circuit but is isolated from it, ensuring more accurate delivery of anesthetic vapor. (225)
- How does tipping of a vaporizer affect vaporizer output?
Tipping can cause liquid anesthetic to spill from the vaporizing chamber into the bypass chamber, which increases the vapor concentration delivered to the patient. (225)
- How is the delivery of two different volatile anesthetics to the same patient via the same anesthesia machine prevented?
A safety interlock mechanism ensures that only one vaporizer can be activated at a time, preventing the simultaneous delivery of two different agents. (225)
- How is the potential risk of filling the agent-specific vaporizer with the erroneous volatile anesthetic minimized?
The use of an anesthetic-specific keyed filler device prevents misfilling, which is especially critical for desflurane due to its high vapor pressure. (225)
- What is the function of anesthetic breathing systems?
Anesthetic breathing systems are designed to deliver oxygen and anesthetic gases to the patient while eliminating carbon dioxide. (225)
- How do anesthetic breathing systems impart resistance to the spontaneously ventilating patient?
They introduce resistance through components such as unidirectional valves and connectors, which may increase the work of breathing during spontaneous ventilation. (225)
- What are some features of anesthetic breathing systems that enable them to be classified as either open, semiopen, closed, or semiclosed?
They are classified based on the presence or absence of a reservoir bag, the extent of rebreathing, whether carbon dioxide is chemically absorbed, and the use of unidirectional valves. (226)
- What are the most commonly used anesthetic breathing systems?
The most commonly used systems include the Mapleson F (Jackson-Rees) system, the Bain circuit, and the circle system. (226)
- What characterizes the Mapleson systems?
Mapleson systems are characterized by their simplicity – they have no valves to direct gas flow and lack chemical CO2 absorption. (226)
- Describe the Mapleson F anesthetic breathing system. What is another name for this anesthetic breathing system?
The Mapleson F system is a T-piece arrangement with a reservoir bag and an adjustable pressure-limiting (APL) valve; it is also known as the Jackson-Rees circuit. (226)
- When is the Mapleson F system commonly used?
It is commonly used for controlled ventilation during patient transport, particularly for intubated patients. (226)
- What are some advantages of the Mapleson F anesthetic breathing system?
Advantages include minimal dead space, low resistance, low cost, light weight, and versatility (usable with either a face mask or an endotracheal tube), which makes it ideal for pediatric anesthesia. (226-227)
- What are some disadvantages of the Mapleson F anesthetic breathing system?
Disadvantages include the need for high fresh gas flow to prevent rebreathing, risk of high airway pressure and barotrauma if the overflow valve becomes occluded, and lack of humidification. (227)
- Describe the Bain circuit anesthetic breathing system.
The Bain circuit is a coaxial version of the Mapleson D system; it features an inner fresh gas delivery tube running inside the corrugated expiratory tubing, with exhaled gases vented via an overflow valve near the reservoir bag. (227)
- What are some advantages of the Bain circuit anesthetic breathing system?
Advantages include warming of the fresh gas by the surrounding exhaled gases, conservation of moisture, ease of scavenging waste anesthetic gases, light weight, ease of sterilization, and reusability. (227)
- What are some disadvantages of the Bain circuit anesthetic breathing system?
Disadvantages include the risk of unnoticed disconnection or kinking of the inner fresh gas tube; the outer tube should be transparent for inspection. (227)
- How does the circle anesthetic breathing system get its name?
It is named for its circular arrangement of components that allows exhaled gases to be recirculated after CO2 absorption. (227)
- How does the circle system prevent rebreathing of carbon dioxide?
Rebreathing is prevented by chemically neutralizing exhaled CO2 using a carbon dioxide absorbent in a canister. (227-228)
- What are the classifications of a circle system, and on what feature does this classification depend?
Circle systems are classified as semiopen, semiclosed, or closed based on the fresh gas flow relative to the patient’s minute ventilation and the degree of rebreathing present. (228)
- What is the most commonly used circle system approach?
The semiclosed circle system, in which fresh gas inflow is less than the patient’s minute ventilation leading to some rebreathing, is the most commonly used. (228)
- What are some advantages of the semiclosed and closed circle systems?
They offer maximal humidification and warming of gases, reduced environmental pollution by limiting waste anesthetic gases, and improved economy in anesthetic use. (229-230)
- What are some disadvantages of the circle anesthetic breathing system?
Disadvantages include increased resistance to breathing due to valves and absorbents, bulkiness, loss of portability, and increased complexity that may lead to malfunction. (228)
- What is the impact of the rebreathing of anesthetic gases in a semiclosed circle system?
Rebreathing can dilute the inhaled concentration of anesthetic gases, especially during high uptake phases, although this can be offset by increasing the delivered anesthetic concentration. (228)
- What are the components of a circle system?
A circle system typically includes a fresh gas inlet, inspiratory and expiratory unidirectional check valves, corrugated tubing, a Y-piece connector, an adjustable pressure-limiting (APL) valve, a reservoir bag, a carbon dioxide absorbent canister, a bag/vent selector switch, and a ventilator. (229)
- What is the purpose of unidirectional valves in the circle system? What would occur if one of the unidirectional valves becomes incompetent?
Unidirectional valves ensure one-way flow of gases; if they fail (either by remaining open or closed), it can lead to rebreathing with hypercapnia or to complete circuit occlusion with breath stacking and barotrauma. (229)
- Where is the dead space in the circle system?
The dead space is located between the Y-piece connector and the patient. (229)
- What is advantageous about the corrugated tubing in the circle system?
Its large bore minimizes resistance, and its corrugated design provides flexibility and prevents kinking while promoting turbulent flow for improved gas mixing. (229)
- What is disadvantageous about the corrugated tubing in the circle system?
During positive-pressure ventilation, some gas may be compressed within the tubing, leading to a lower effective tidal volume. (229)
- Describe the Y-piece connector in the circle system circuit.
The Y-piece connector, located at the patient end, typically has a curved elbow with an outer diameter of about 22 mm (to fit a face mask) and an inner diameter of about 15 mm (to fit an endotracheal tube connector). (229)
- What are other names for the adjustable pressure-limiting (APL) valve?
It is also known as the overflow or pop-off valve. (229)
- What is the function of the APL valve when the bag/vent selector switch is set to bag?
It allows excess gas to be vented from the breathing circuit (usually into the scavenging system) and facilitates manual ventilation by controlling circuit pressure. (229)
- What are the advantages of the reservoir bag on the circle system?
The reservoir bag provides a gas reserve that meets the patient’s inspiratory flow demands, serves as a safety device by limiting circuit pressure, and allows manual ventilation if needed. (229)
- Describe a closed anesthetic breathing system. What is the inflow volume of fresh gases in a closed system?
A closed system completely recycles exhaled gases after CO2 absorption; the fresh gas inflow is minimal (approximately 150–500 mL/min) – just enough to replace anesthetic losses and meet the patient’s metabolic oxygen requirements (around 150–250 mL/min). (229)
- What are some advantages to the closed circle anesthetic breathing system?
Advantages include maximal humidification and warming of inspired gases, reduced waste of anesthetic gases, and decreased environmental pollution. (229-230)
- What is a disadvantage to the closed circle anesthetic breathing system?
A disadvantage is the slow responsiveness to changes in anesthetic or oxygen concentrations due to the low fresh gas inflow. (230)
- What are the dangers of the closed circle anesthetic breathing system?
Dangers include the potential for delivering unpredictable and possibly insufficient oxygen or excessive anesthetic concentrations due to the closed nature of the system. (230)
- Are inspired concentrations of oxygen more or less predictable when nitrous oxide is also being delivered in a closed circle system? Why?
They may be less predictable because, as tissue uptake of nitrous oxide decreases while oxygen uptake remains constant, the rebreathing of exhaled gases can dilute the oxygen concentration. (230)
- How can the potential problem of the inadequate delivery of oxygen using a closed circle system be minimized?
By using an oxygen analyzer on the circuit to continuously monitor and adjust the oxygen concentration. (230)
- In a closed circle system, to what extent is the inhaled concentration of anesthetic dependent on the exhaled concentration? What is the potential problem with this? How can this problem be partially offset?
The inhaled anesthetic concentration is partly determined by the concentration in the exhaled gases, which reflects tissue uptake; high tissue uptake initially dilutes the inhaled concentration. This can be partially offset by increasing the fresh gas flow temporarily during induction. (230)
- What parts of a circle system are eliminated in anesthesia machine ventilators when the bag/vent selector switch is set to vent?
When set to vent, the reservoir bag and the APL valve are bypassed, and ventilation is delivered directly by the machine’s ventilator. (230)
- What are two different ways in which anesthesia machine ventilators are powered?
They may be powered by compressed gas (pneumatic) or by electricity (or a combination of both). (230)
- Describe the mechanics of a conventional anesthesia machine ventilator during inspiration.
During inspiration, pressurized gas (from bellows or a piston mechanism) is delivered through the inspiratory limb of the circuit to the patient’s lungs while a relief valve prevents gas loss. (230)
- Why is oxygen preferred over air as the ventilator driving gas?
Oxygen is preferred because if a leak occurs, the resulting inspired gas will have a higher oxygen concentration, which is safer for the patient. (230)
- Describe the mechanics of a conventional anesthesia machine ventilator during exhalation.
During exhalation, the patient’s exhaled gas is collected as the bellows refill; the gas is then vented out of the circuit either into the room or to a scavenging system. (230)
- Describe the mechanically driven piston-type of ventilators found on some newer anesthesia machines.
Piston-type ventilators use a mechanically driven piston (similar to a syringe plunger) to deliver a set tidal volume or maintain a specified airway pressure. (230)
- Why are standing or ascending bellows preferred over hanging or descending bellows?
Because standing or ascending bellows will not continue to fill if the circuit becomes disconnected, reducing the risk of unnoticed disconnection and subsequent patient hypoventilation. (230-231)
- How are inhaled gases normally humidified in awake patients breathing through their native airway?
The upper respiratory tract, especially the nose, functions as a heat and moisture exchanger that warms and humidifies inspired gases. (231)
- What effect does tracheal intubation or the use of a laryngeal mask airway have on airway humidification? What are the negative consequences of this?
Tracheal intubation bypasses the upper airway, resulting in less humidification and warming of inspired gases. This can lead to dehydration of the tracheobronchial mucosa, impaired ciliary function, thicker secretions, atelectasis, and increased alveolar-arterial oxygen gradients. (231)
- Describe anesthetic breathing system humidification. What effect does chemical neutralization of carbon dioxide have on this process?
Humidification is achieved by adding water vapor to inspired gases; the neutralization of CO2 by absorbents produces water and heat, which help humidify and warm the gases. (232)
- What are three types of humidifiers used for anesthesia and in the intensive care unit?
They include heat and moisture exchanger (HME) humidifiers, heated water vaporizers/humidifiers, and nebulizer humidifiers. (232)
- Describe heat and moisture exchanger (HME) humidifiers. What is the difference between an HME and an HMEF?
HME humidifiers trap exhaled moisture and heat to return it during inspiration; an HMEF includes an additional bacterial/viral filter. (232)
- What are the advantages of HME humidifiers over other types of humidifiers?
Advantages include simplicity, low cost, disposability, portability, and the fact that they require no external power. (232)
- What are the disadvantages of HME humidifiers?
Disadvantages include less effective warming compared to heated humidifiers, added resistance which may increase the work of breathing, potential clogging with secretions, and increased dead space. (232)
- What is the advantage of heated water vaporizers and humidifiers over HME humidifiers? When are they used most frequently?
Heated water vaporizers provide superior humidification and temperature control; they are most often used in pediatric anesthesia and in intensive care settings. (232)
- What are the risks of heated water vaporizers and humidifiers?
Risks include thermal injury, potential for nosocomial infections, increased work of breathing, and a higher chance of equipment malfunction due to complexity. (232)
- Describe nebulizer humidifiers used for anesthesia and in the intensive care unit.
Nebulizer humidifiers produce a fine mist of water droplets that humidify the inspired gas; they can also deliver medications and are not limited by the carrier gas temperature. (232)
- In the operating room, what are the OSHA recommendations for the maximum concentrations of nitrous oxide and volatile anesthetics in parts per million?
OSHA recommends that nitrous oxide exposure not exceed 25 ppm and that volatile anesthetics not exceed 2 ppm. (232)
- What is required to control pollution of the atmosphere with anesthetic gases?
Control requires effective scavenging of waste anesthetic gases, regular maintenance of anesthesia equipment, proper anesthetic techniques, and adequate operating room ventilation. (232)
- Describe operating room scavenging.
Scavenging involves collecting and removing waste anesthetic gases from the operating room via active (vacuum-based) or passive (ventilation-based) systems. (233)
- Describe the two types of scavenging systems used in the operating room.
There are active scavenging systems, which are connected to the hospital’s vacuum system, and passive systems, which rely on the operating room’s ventilation duct to disperse waste gases. (233)
- What are the advantages of active scavenging with a waste gas receiver mounted on the side of the anesthesia machine?
Advantages include the ability to adjust vacuum flow via a needle valve, maintain a slightly inflated reservoir bag, and operate without requiring a high vacuum. (233)
- What are the potential hazards of scavenging systems?
Potential hazards include obstruction of the scavenging pathway leading to positive pressure in the breathing circuit, or excessive vacuum causing negative pressures in the system. (233)
- What two features do scavenging systems have to minimize their potential hazards?
They incorporate both a positive-pressure relief valve (which opens if pressure exceeds a threshold) and a negative-pressure relief valve (which opens if excessive vacuum is applied). (233)
- Where might be the source of a high-pressure leak of nitrous oxide?
High-pressure leaks can originate from faulty yokes or poor connections between the central nitrous oxide supply and the anesthesia machine. (233)
- Where might be the source of a low-pressure leak of nitrous oxide?
Low-pressure leaks may occur within the anesthesia machine or at connections between the machine and the patient. (233)
- What anesthetic techniques can lead to operating room pollution?
Techniques such as poorly fitting face masks, flushing the circuit, filling vaporizers, use of uncuffed endotracheal tubes, failure to shut off gas flows at the end of a case, and the use of semiopen circuits like the Jackson-Rees system can lead to pollution. (233)
- How often should the air in the operating room be exchanged?
The operating room air should be exchanged at least 15 times per hour. (233)
- How is carbon dioxide eliminated in open and semiopen breathing systems?
In open and semiopen systems, exhaled gases are vented directly to the atmosphere, thereby eliminating CO2. (233)
- How is carbon dioxide eliminated in a semiclosed or closed anesthetic breathing system?
In semiclosed or closed systems, CO2 is eliminated by chemical neutralization using a CO2 absorbent canister. (233)
- What three components are common to all carbon dioxide absorbents?
All absorbents contain a neutralizing base (commonly calcium hydroxide), water, and catalysts. (233)
- What do all carbon dioxide absorbents use as the neutralizing base for carbon dioxide produced during respiration?
They all use calcium hydroxide (Ca(OH)2) as the neutralizing base. (233)
- Why is water a necessary component of carbon dioxide absorbents?
Water is required to facilitate the chemical reaction that converts CO2 into carbonic acid, which is then neutralized by the absorbent. (233)
- How does the type of catalyst contained in the carbon dioxide absorbent influence the differences between the absorbents?
The catalyst affects the efficiency and safety profile of the absorbent; it differentiates traditional soda lime from newer absorbents such as Amsorb Plus. (234)
- Name three individual carbon dioxide absorbents. Which are traditional and which are new generation?
Traditional absorbents include soda lime; new-generation absorbents include Amsorb Plus and Litholyme. (234)
- What do soda lime granules consist of?
Soda lime granules consist of calcium hydroxide, water, and small amounts of sodium hydroxide and potassium hydroxide, which act as catalysts. (234)
- Why is silica added to soda lime?
Silica is added to soda lime to provide hardness to the granules and to minimize the formation of alkaline dust. (234)
- Describe the neutralization of carbon dioxide by soda lime.
CO2 first reacts with water to form carbonic acid, which then reacts with the hydroxides in soda lime to form bicarbonates/carbonates, water, and heat. (234)
- Why is the water in the soda lime carbon dioxide absorbent canister hazardous?
The water, together with alkaline dust from the absorbent, can form a corrosive slurry that may cause skin irritation or damage. (234)
- Can soda lime lead to degradation of sevoflurane to compound A? What is responsible for this?
Yes; the strong bases (sodium hydroxide and potassium hydroxide) in soda lime can degrade sevoflurane to compound A. (234)
- Can soda lime lead to significant concentrations of carbon monoxide? What is responsible for this?
Yes; the same strong bases in soda lime can degrade inhaled anesthetics to produce carbon monoxide. (234)
- What are the compositional differences between the new generation carbon dioxide absorbents Amsorb Plus and Litholyme versus traditional soda lime?
Amsorb Plus and Litholyme consist mainly of calcium hydroxide and water, without the strong bases (NaOH, KOH) found in soda lime. (234)
- Can Amsorb Plus or Litholyme lead to degradation of sevoflurane to compound A? Why or why not?
No; they do not contain the strong bases that cause sevoflurane degradation. (234)
- Can Amsorb Plus or Litholyme lead to degradation of inhaled anesthetics to carbon monoxide? Why or why not?
No; without the strong bases, these new-generation absorbents do not degrade inhaled anesthetics to carbon monoxide. (234)
- Describe the neutralization of carbon dioxide by Amsorb Plus or Litholyme.
CO2 reacts with water and then with calcium hydroxide in the absorbent to form calcium carbonate, water, and heat. (234)
- Why is the water formed by the neutralization of carbon dioxide by all carbon dioxide absorbents useful? What if the carbon dioxide absorbent canister fails to become warm during use?
The water helps humidify the breathing gases and dissipate the heat generated; if the canister fails to warm, it may indicate that CO2 neutralization is not occurring properly. (234)
- What two factors influence the efficiency of carbon dioxide neutralization?
The size of the absorbent granules and the presence or absence of channeling within the canister. (234)
- How does the size of the carbon dioxide absorbent granules affect the efficiency of carbon dioxide neutralization?
Smaller granules increase the surface area for reaction, thus enhancing efficiency, but they also increase resistance to gas flow. (235)
- What is the optimal carbon dioxide absorbent granule size? How is this sizing system defined?
Granule size is defined by mesh size; in anesthesia practice, a mesh size between 4 and 10 is considered optimal, balancing absorptive efficiency with minimal resistance. (235)
- What does channeling in the carbon dioxide absorbent granule-containing canister refer to? How does channeling affect efficiency?
Channeling refers to the preferential passage of exhaled gases through low-resistance pathways that bypass most absorbent granules, thereby reducing CO2 neutralization efficiency. (235)
- What is the most frequent cause of channeling in the carbon dioxide absorbent granule-containing canister? How can it be minimized?
Channeling is most often caused by loose packing of the granules; it can be minimized by gently shaking the canister before use to ensure uniform packing. (235)
- Define carbon dioxide absorbent absorptive capacity. What can cause a decrease in absorptive capacity?
Absorptive capacity is the maximum amount of CO2 that can be absorbed by 100 g of absorbent; factors such as channeling and improper canister packing can reduce capacity. (235)
- Why do the carbon dioxide absorbent granules change color?
They contain a pH-sensitive indicator dye that changes color when the absorbent is exhausted (i.e., when the pH falls as CO2 is no longer being neutralized). (235)
- Contrast the color change of soda lime granules with those of Amsorb Plus and Litholyme.
Soda lime granules change from white to purple when exhausted but may revert back to white over time; Amsorb Plus and Litholyme change from white to purple and do not revert. (235)
- Contrast the degradation of inhaled anesthetics to toxic compounds by carbon dioxide absorbents. What is the impact of desiccation on the degradation process?
Desiccation (drying) of soda lime increases the production of compound A (with sevoflurane) and carbon monoxide (with other anesthetics) because the strong bases become more concentrated; new-generation absorbents do not show these degradative effects even when dry. (235)
- What factors lead to increased compound A production with carbon dioxide absorbents? What is the clinical effect of this?
High sevoflurane concentrations, low fresh gas flows, high absorbent temperatures, and desiccation of the absorbent increase compound A production; compound A is a dose- and time-dependent nephrotoxin, though clinical renal toxicity has not been definitively demonstrated. (235)
- Why is carbon monoxide (CO) poisonous?
CO binds with high affinity to hemoglobin, forming carboxyhemoglobin and thereby displacing oxygen, which leads to tissue hypoxia. (235)
- What factors lead to increased carbon monoxide production with carbon dioxide absorbents? Are the concentrations significant?
Factors include the use of desiccated soda lime, high anesthetic concentrations, high absorbent temperatures, and low fresh gas flows; these can lead to significant CO production with carboxyhemoglobin levels potentially reaching 30% or more. (235)
- Why do most instances of increased blood concentrations of carboxyhemoglobin occur in anesthetized patients on a Monday?
Because during the weekend, when the anesthesia machine is not in use, high fresh gas flows desiccate the soda lime absorbent, leading to increased CO production when anesthesia is resumed on Monday. (235)
- What causes the development of fire and extreme heat in the breathing system? How can this be avoided?
Desiccated Baralyme can react with sevoflurane to produce excessive heat and combustible products, potentially causing fire; this can be avoided by ensuring absorbents are not allowed to desiccate. (236)
- Complete the following table illustrating features of carbon dioxide absorbents: (See table in text)
For soda lime: Mesh size 4-8, generates compound A with sevoflurane, produces carbon monoxide, and carries a risk of exothermic reactions and fire; for Amsorb Plus: Mesh size 4-8, no compound A or CO generation, no exothermic reaction risk; for Litholyme: Mesh size 4-10, no compound A or CO generation, no exothermic reaction risk. (236)
- What are the current recommendations for pre-anesthesia checkout procedures? How do these apply to newer machines with automated checkout procedures?
The ASA recommends a complete pre-anesthesia checkout procedure before the first case each day, with an abbreviated checkout before subsequent cases; for newer machines with automated checkouts, supplemental manual checks for items not covered by automation are required. (236)
- How often should these checkout procedures be performed?
A full checkout should be performed daily before the first case, and an abbreviated check before each subsequent use on the same day. (236)
- What are the most important preoperative checks?
They include verifying the availability and function of an auxiliary oxygen cylinder and manual ventilation device (Ambu bag), performing a leak check of the low-pressure system, calibrating the oxygen monitor, and conducting a positive-pressure leak test of the breathing system. (236)
- Does the presence of a Jackson-Rees circuit along with a full oxygen E-cylinder mounted on the back of the anesthesia machine comply with current checkout recommendations?
No; the backup oxygen supply must be readily accessible and tested according to current guidelines, and the specific configuration mentioned may not fully meet these requirements. (236)
- What does a leak check of the machine’s low-pressure system evaluate? Why is this so important?
It evaluates the integrity of the low-pressure components (from the flowmeters to the common gas outlet); leaks here can result in hypoxia or intraoperative awareness, making this check critical for patient safety. (236)
- Why is calibration of the oxygen monitor so important?
Because the oxygen monitor is the only safety device that detects problems downstream of the flowmeters, ensuring accurate measurement of delivered oxygen concentrations. (237)
- Does a manual positive-pressure leak test check the integrity of the unidirectional valves?
No; a manual positive-pressure leak test does not evaluate the unidirectional valves, which may still be incompetent despite passing the leak test. (237)
