Anesthesia workstations, Anesthesia workstations,

Circle breathing systems,Circle breathing systems,

CO2 absorbents, CO2 absorbents,

Ventilators,Ventilators,

Scavenging systems, Scavenging systems,

Anesthesia Delivery System Checkout Anesthesia Delivery System Checkout Dr.M.Safavi Dr.M.Safavi

Associate Professor of AnesthesiaAssociate Professor of Anesthesia

Department of anesthesia and critical care medicine ,Isfahan University of Medical Science ,Isfahan ,IranDepartment of anesthesia and critical care medicine ,Isfahan University of Medical Science ,Isfahan ,Iran

بحث بحث سئواالت سئواالت؟ چیست بیهوشی ماشین اصلی ؟ عملکرد چیست بیهوشی ماشین اصلی عملکرد

چیست؟ بیهوشی دستگاه با مکانیکی تهویه حین چیست؟ عوارضوخیم بیهوشی دستگاه با مکانیکی تهویه حین عوارضوخیم

جدید و قدیم سیرکل سیستم و بیهوشی دستگاه عملکرد و اصلی جدید اجزا و قدیم سیرکل سیستم و بیهوشی دستگاه عملکرد و اصلی اجزا

؟ ؟ چیست چیست

است؟ نحو چه به کربن اکسید دی جاذبهای است؟ عملکرد نحو چه به کربن اکسید دی جاذبهای عملکرد

؟ ؟ چیست سیستمسیستم scavenging scavenging چیست

است؟ صورتی چه به عمل قبل بیهوشی دستگاه است؟ روشچک صورتی چه به عمل قبل بیهوشی دستگاه روشچک

bellow

Corrugated tube

Soda lime

APL valve

ventilator

Scavenging system

Dräger Narkomed 6000 anesthesia workstation Dräger Narkomed 6000 anesthesia workstation Series and Fabius GSSeries and Fabius GS

ventilator

Scavenging system

Corrugated tube

Components Anesthesia MachineComponents Anesthesia Machine

High Intermediate Low Pressure Circuit

Diagram of a generic two-gas anesthesia machineDiagram of a generic two-gas anesthesia machine    

Anesthetic Breathing CircuitsAnesthetic Breathing Circuits

As the prescribed mixture of gases from the flow meters and vaporizer exits the As the prescribed mixture of gases from the flow meters and vaporizer exits the anesthesia workstation at the anesthesia workstation at the common gas outletcommon gas outlet, it then enters an anesthetic , it then enters an anesthetic breathing circuit.breathing circuit.

The function of the anesthesia breathing circuit is not only to deliver oxygen The function of the anesthesia breathing circuit is not only to deliver oxygen and anesthetic gases to the patient but also to eliminate carbon dioxide. and anesthetic gases to the patient but also to eliminate carbon dioxide.

Carbon dioxide can be removed either by washout with adequate fresh gas Carbon dioxide can be removed either by washout with adequate fresh gas inflow or by the use of carbon dioxide absorbent media (e.g., soda lime inflow or by the use of carbon dioxide absorbent media (e.g., soda lime absorption).absorption).

Anesthetic Breathing CircuitsAnesthetic Breathing Circuits

Components of the circle systemComponents of the circle system (Breathing (Breathing

systems)systems)

The circle system consists of The circle system consists of sevenseven primary components, including primary components, including

1) a 1) a fresh gas inflow fresh gas inflow source, source,

2) inspiratory and expiratory 2) inspiratory and expiratory unidirectional valvesunidirectional valves, ,

3) inspiratory and expiratory 3) inspiratory and expiratory corrugated tubescorrugated tubes,,

4) a 4) a Y-pieceY-piece connector, connector,

5) an overflow or pop-off valve referred to as the 5) an overflow or pop-off valve referred to as the APLAPL valve, valve,

6) a reservoir bag,& 6) a reservoir bag,& ventilatorventilator

7) a canister containing a 7) a canister containing a carbon dioxide absorbentcarbon dioxide absorbent. .

250 Liters250 Liters

New Circle Breathing SystemsNew Circle Breathing Systems

For many years, the overall design of the circle breathing system has changed For many years, the overall design of the circle breathing system has changed very little from one anesthesia workstation manufacturer to the next. Both the very little from one anesthesia workstation manufacturer to the next. Both the individual components and the order in which they appeared in the circle individual components and the order in which they appeared in the circle system were consistent across major platforms.system were consistent across major platforms.

In recent yearsIn recent years, however, with the increasing technologic complexity of the , however, with the increasing technologic complexity of the anesthesia workstation, the circle system has undergone some major changes anesthesia workstation, the circle system has undergone some major changes as well. as well.

These changes have resulted in part from an effort to improve patient safety (as These changes have resulted in part from an effort to improve patient safety (as in the in the integration of fresh gas decoupling (FGD) integration of fresh gas decoupling (FGD) and and inspiratory pressure inspiratory pressure limiterslimiters) but have also allowed the deployment of new technologic advances..) but have also allowed the deployment of new technologic advances..

ContCont

Two such major new technologies Two such major new technologies used in some new workstations have been:used in some new workstations have been:

1) a return to the application of 1) a return to the application of single-circuit piston-type ventilatorssingle-circuit piston-type ventilators

2) the use of 2) the use of new spirometry devicesnew spirometry devices that are located at the Y-connector instead that are located at the Y-connector instead of at the traditional location on the expiratory circuit limb. of at the traditional location on the expiratory circuit limb.

The Traditional Circle Breathing SystemThe Traditional Circle Breathing System

The traditional circle system, referred to as either a “The traditional circle system, referred to as either a “universal Funiversal F” or a “” or a “single-limb single-limb circuitcircuit..

The circle system prevents rebreathing of carbon dioxide by use of carbon dioxide The circle system prevents rebreathing of carbon dioxide by use of carbon dioxide absorbents but allows partial rebreathing of other exhaled gases.absorbents but allows partial rebreathing of other exhaled gases.

The extent of rebreathing of the other exhaled gases depends on the arrangement The extent of rebreathing of the other exhaled gases depends on the arrangement of the breathing circuit components and the fresh gas flow rate. of the breathing circuit components and the fresh gas flow rate.

A circle system can be A circle system can be semiopen, semiclosed, or closedsemiopen, semiclosed, or closed, depending on the amount , depending on the amount of fresh gas inflow.of fresh gas inflow.

A semiopen system has no rebreathing and requires a very high flow of fresh gas. A semiopen system has no rebreathing and requires a very high flow of fresh gas.

A A semiclosed systemsemiclosed system is associated with some rebreathing of exhaled gases and is is associated with some rebreathing of exhaled gases and is the the most commonly used applicationmost commonly used application in anesthesia. in anesthesia.

ContContA closed system is one in which the inflow gas exactly matches that being taken up, or A closed system is one in which the inflow gas exactly matches that being taken up, or consumed, by the patient. consumed, by the patient.

In a In a closed systemclosed system there is there is complete rebreathingcomplete rebreathing of exhaled gases after absorption of carbon of exhaled gases after absorption of carbon dioxide, and the overflow (pop-off or APL) valve or ventilator relief valve remains closed.dioxide, and the overflow (pop-off or APL) valve or ventilator relief valve remains closed.

The The circle systemcircle system consists of seven primary components, including : consists of seven primary components, including :

1) a fresh gas inflow source, 1) a fresh gas inflow source,

2) inspiratory and expiratory unidirectional valves, 2) inspiratory and expiratory unidirectional valves,

3) inspiratory and expiratory corrugated tubes,3) inspiratory and expiratory corrugated tubes,

4) a Y-piece connector,4) a Y-piece connector,

5) an overflow or pop-off valve referred to as the APL valve,5) an overflow or pop-off valve referred to as the APL valve,

6) a reservoir bag, ventilator 6) a reservoir bag, ventilator

7) a canister containing a carbon dioxide absorbent. 7) a canister containing a carbon dioxide absorbent.

The inspiratory and expiratory valves are placed in the system to ensure that gas flow The inspiratory and expiratory valves are placed in the system to ensure that gas flow through the corrugated hoses remains unidirectional. The fresh gas inflow enters the circle through the corrugated hoses remains unidirectional. The fresh gas inflow enters the circle by a connection from the common gas outlet of the anesthesia machine.by a connection from the common gas outlet of the anesthesia machine.

Prevent Prevent rebreathing of carbon dioxide rebreathing of carbon dioxide in a traditional circle system, three in a traditional circle system, three rules rules must be followed:must be followed:

(1) a unidirectional valve must be located between the patient and the reservoir bag on (1) a unidirectional valve must be located between the patient and the reservoir bag on both the inspiratory and expiratory limbs of the circuit,both the inspiratory and expiratory limbs of the circuit,

(2) the fresh gas inflow cannot enter the circuit between the expiratory valve and the (2) the fresh gas inflow cannot enter the circuit between the expiratory valve and the patient, patient,

(3) the overflow (pop-off) valve cannot be located between the patient and the inspiratory (3) the overflow (pop-off) valve cannot be located between the patient and the inspiratory valve. valve.

If these rules are follwed, any arrangement of the other components will prevent If these rules are follwed, any arrangement of the other components will prevent rebreathing of carbon dioxide.rebreathing of carbon dioxide.

ContCont

The most efficient circle system The most efficient circle system arrangement with the highest conservation of arrangement with the highest conservation of fresh gases is one in which the unidirectional valves are near the patient and fresh gases is one in which the unidirectional valves are near the patient and the pop-off valve is located just downstream from the expiratory valve. the pop-off valve is located just downstream from the expiratory valve.

This arrangement This arrangement minimizes dead space gasminimizes dead space gas and preferentially and preferentially eliminates eliminates exhaled alveolar gasesexhaled alveolar gases. .

A more practical arrangement, the one used on most conventional anesthesia A more practical arrangement, the one used on most conventional anesthesia machines , is somewhat less efficient because it allows machines , is somewhat less efficient because it allows alveolar and dead alveolar and dead space gases to mix before they are ventedspace gases to mix before they are vented..

ContCont

The The main advantages of the circle systemmain advantages of the circle system over other breathing systems over other breathing systems include:include:

1) maintenance of relatively stable inspired gas concentrations, 1) maintenance of relatively stable inspired gas concentrations,

2) conservation of respiratory moisture and heat, 2) conservation of respiratory moisture and heat,

3) prevention of operating room pollution ,3) prevention of operating room pollution ,

4) the circle system can be used for closed-system anesthesia or semiclosed with very low 4) the circle system can be used for closed-system anesthesia or semiclosed with very low fresh gas flows.fresh gas flows.

The The major disadvantage of the circle systemmajor disadvantage of the circle system stems from its stems from its complex designcomplex design. . Commonly, the circle system may have Commonly, the circle system may have 1010 or more different connections. or more different connections.

These multiple connection sites set the stage for These multiple connection sites set the stage for misconnections, misconnections, disconnections, obstructions, and leaks.disconnections, obstructions, and leaks.

ContCont In a recent closed-claim analysis of adverse anesthetic outcomes arising from gas delivery In a recent closed-claim analysis of adverse anesthetic outcomes arising from gas delivery equipment, more than a third (25/72) of malpractice claims resulted from breathing circuit equipment, more than a third (25/72) of malpractice claims resulted from breathing circuit misconnections or disconnectionsmisconnections or disconnections..

Malfunction of the circle system's Malfunction of the circle system's unidirectional valvesunidirectional valves can result in life-threatening can result in life-threatening problems.problems.

RebreathingRebreathing can occur if the valves stick in the open position, and total occlusion of the can occur if the valves stick in the open position, and total occlusion of the circuit can occur if they are stuck shut.circuit can occur if they are stuck shut.

If the expiratory valve is stuck in the closed position, breath stacking and If the expiratory valve is stuck in the closed position, breath stacking and barotrauma or barotrauma or volutraumavolutrauma can result. can result.

Obstructed filters located in the expiratory limb Obstructed filters located in the expiratory limb of the circle breathing system have caused of the circle breathing system have caused increased airway pressure, hemodynamic collapse, and bilateral tension pneumothoraxincreased airway pressure, hemodynamic collapse, and bilateral tension pneumothorax ..

Causes of circle system obstruction and failure include manufacturing defects, debris, Causes of circle system obstruction and failure include manufacturing defects, debris, patient secretions, and particulate obstruction from other odd sources such as albuterol patient secretions, and particulate obstruction from other odd sources such as albuterol nebulization.nebulization.

Circle SystemCircle SystemAdvantagesAdvantages– Relative Relative stabilitystability of inspired concentration of inspired concentration

– Conservation of respiratory Conservation of respiratory moisture and heatmoisture and heat

– Prevention of operating room Prevention of operating room pollutionpollution

– PaCO2 depends only on ventilation, not fresh gas flowPaCO2 depends only on ventilation, not fresh gas flow

– Low fresh gas flows Low fresh gas flows can be usedcan be used

DisadvantagesDisadvantages– ComplexComplex design = potential for malfunction design = potential for malfunction

– High High resistanceresistance (multiple one-way valves) = higher work of (multiple one-way valves) = higher work of breathingbreathing

Carbon Dioxide AbsorbentsCarbon Dioxide AbsorbentsThe Absorber CanisterThe Absorber Canister

Chemistry of AbsorbentsChemistry of Absorbents

Absorptive CapacityAbsorptive Capacity

IndicatorsIndicators

Interactions of Inhaled Anesthetics with AbsorbentsInteractions of Inhaled Anesthetics with Absorbents

Typing CO2 absorbentsTyping CO2 absorbents

Carbon Dioxide AbsorbentsCarbon Dioxide AbsorbentsInhaled anesthetics can interact with carbon dioxide absorbents and Inhaled anesthetics can interact with carbon dioxide absorbents and produce toxic compounds. produce toxic compounds.

During During sevoflurane anesthesia, compound A sevoflurane anesthesia, compound A can be formed, particularly can be formed, particularly at low fresh gas flow rates, and during at low fresh gas flow rates, and during desflurane anesthesia, carbon desflurane anesthesia, carbon monoxide monoxide can be produced, particularly with desiccated absorbents.can be produced, particularly with desiccated absorbents.

Desiccated strong-base absorbents (particularly Desiccated strong-base absorbents (particularly BaralymeBaralyme) can react with ) can react with sevofluranesevoflurane and produce extremely high absorber and produce extremely high absorber temperatures and temperatures and combustible combustible decomposition products. decomposition products.

In combination with the oxygen- or nitrous oxide–enriched environment of In combination with the oxygen- or nitrous oxide–enriched environment of the circle system, these effects can produce fires within the breathing the circle system, these effects can produce fires within the breathing system.system.

Some of these undesirable interactions are quite dramatic, such as Some of these undesirable interactions are quite dramatic, such as sevoflurane interacting with desiccated Baralyme and resulting in fires sevoflurane interacting with desiccated Baralyme and resulting in fires within the breathing system and severe patient injury.within the breathing system and severe patient injury.

Although other sources of ignition and fire in the breathing system continue Although other sources of ignition and fire in the breathing system continue to be described, the to be described, the Baralyme-sevoflurane problem Baralyme-sevoflurane problem is somewhat unique is somewhat unique in that nothing “unusual” is added to or removed from the breathing system in that nothing “unusual” is added to or removed from the breathing system for this to occur.for this to occur.

Other reactions such as Other reactions such as desflurane or sevoflurane with desiccated desflurane or sevoflurane with desiccated strong-base absorbents strong-base absorbents can produce more insidious patient morbidity and can produce more insidious patient morbidity and even death from the release of by-products such as even death from the release of by-products such as carbon monoxide carbon monoxide (CO) or compound A.(CO) or compound A.

The The closed and semiclosed circle systems closed and semiclosed circle systems both both require that carbon require that carbon dioxide be dioxide be absorbed from the exhaled gases to absorbed from the exhaled gases to avoid hypercapniaavoid hypercapnia..

If one could design an ideal carbon dioxide absorbent, its characteristics If one could design an ideal carbon dioxide absorbent, its characteristics would include lack of reactivity with common anesthetics, absence of would include lack of reactivity with common anesthetics, absence of toxicity, low resistance to airflow, low cost, ease of handling, and efficiency toxicity, low resistance to airflow, low cost, ease of handling, and efficiency in carbon dioxide absorption.in carbon dioxide absorption.

1) The Absorber Canister1) The Absorber Canister

The canisters can be The canisters can be filledfilled either with loose bulk absorbent or with either with loose bulk absorbent or with absorbent supplied by the factory in prefilled plastic disposable cartridges absorbent supplied by the factory in prefilled plastic disposable cartridges called called prepacksprepacks..

Free granules from bulk absorbent can create a clinically significant lFree granules from bulk absorbent can create a clinically significant leakeak if if they lodge between the clear plastic canister and the O-ring gasket of the they lodge between the clear plastic canister and the O-ring gasket of the absorber.absorber.

LeaksLeaks have also been caused by defective have also been caused by defective prepacks prepacks that were larger than that were larger than factory specifications.factory specifications.

Prepacks can also cause Prepacks can also cause total obstruction total obstruction of the circle system if the clear of the circle system if the clear plastic shipping wrapper is not removed before useplastic shipping wrapper is not removed before use

2) Chemistry of Absorbents2) Chemistry of Absorbents

Two formulations of carbon dioxide absorbents are commonly available Two formulations of carbon dioxide absorbents are commonly available today: today: soda lime soda lime andand calcium hydroxide lime (Amsorb) calcium hydroxide lime (Amsorb). Of these agents, . Of these agents, the the most commonly used is soda lime.most commonly used is soda lime.

By weight, the approximate composition of “high-moisture” soda lime is 80% By weight, the approximate composition of “high-moisture” soda lime is 80% calcium hydroxide, 15% water, 4% sodium hydroxide, and 1% potassium calcium hydroxide, 15% water, 4% sodium hydroxide, and 1% potassium hydroxide (an activator). Small amounts of silica are added to produce hydroxide (an activator). Small amounts of silica are added to produce calcium and sodium silicate. This addition produces a harder, more stable calcium and sodium silicate. This addition produces a harder, more stable pellet and thereby reduces dust formation.pellet and thereby reduces dust formation.

Sodium hydroxide is the catalyst for the carbon dioxide absorptive Sodium hydroxide is the catalyst for the carbon dioxide absorptive properties of soda lime.properties of soda lime.

BaralymeBaralyme is a mixture of approximately 20% barium hydroxide and 80% is a mixture of approximately 20% barium hydroxide and 80% calcium hydroxide. It may also contain some potassium hydroxide.calcium hydroxide. It may also contain some potassium hydroxide.

BaralymeBaralyme is the primary carbon dioxide absorbent implicated as an agent that is the primary carbon dioxide absorbent implicated as an agent that may produce fires in the breathing system when used with may produce fires in the breathing system when used with sevofluranesevoflurane..

The most significant advantage of calcium hydroxide lime (The most significant advantage of calcium hydroxide lime (AmsorbAmsorb) over ) over other agents is its lack of the strong bases sodium and potassium other agents is its lack of the strong bases sodium and potassium hydroxide. hydroxide.

Absence of these chemicals eliminates the undesirable production of Absence of these chemicals eliminates the undesirable production of COCO and and the the nephrotoxic substance known as compound Anephrotoxic substance known as compound A, and it may reduce or , and it may reduce or eliminate the possibility of a eliminate the possibility of a firefire in the breathing circuit. in the breathing circuit.

The most significant disadvantages of calcium hydroxide lime are (1) less The most significant disadvantages of calcium hydroxide lime are (1) less absorptive capacity—absorptive capacity—about 50% less than absorbents about 50% less than absorbents containing strong containing strong bases—and (2) generally bases—and (2) generally higher cost per higher cost per unit than other absorbents.unit than other absorbents.

The smaller the granule size, the greater the surface area that is available for The smaller the granule size, the greater the surface area that is available for absorption. However, as particle size decreases, airflow resistance increases.absorption. However, as particle size decreases, airflow resistance increases.

The granular size of soda lime and Baralyme used in clinical practice is The granular size of soda lime and Baralyme used in clinical practice is between between 4 and 8 mesh4 and 8 mesh, a size at which absorptive surface area and , a size at which absorptive surface area and resistance to flow are optimized.resistance to flow are optimized.

3) Absorptive Capacity3) Absorptive Capacity

The maximum amount of carbon dioxide that can be absorbed by The maximum amount of carbon dioxide that can be absorbed by soda lime is soda lime is 26 L of CO2 per 100 g of absorbent. 26 L of CO2 per 100 g of absorbent.

The absorptive capacity of The absorptive capacity of calcium hydroxide lime is significantly less and calcium hydroxide lime is significantly less and has been reported to be 10.2 L per 100 g of absorbent.has been reported to be 10.2 L per 100 g of absorbent.

In practice, as a result of channeling, In practice, as a result of channeling, the efficiency of soda lime may be the efficiency of soda lime may be reduced such that only 10 to 20 L or less of carbon dioxide reduced such that only 10 to 20 L or less of carbon dioxide can actually be can actually be absorbed per 100 g of absorbent.absorbed per 100 g of absorbent.

As the absorbent granules stack up in the absorber canisters, small passageways As the absorbent granules stack up in the absorber canisters, small passageways inevitably form. These small passages channel gases preferentially through low-inevitably form. These small passages channel gases preferentially through low-resistance areas. resistance areas.

Because of this phenomenon, the functional absorptive capacity of either soda Because of this phenomenon, the functional absorptive capacity of either soda lime or calcium hydroxide lime may be substantially decreased.lime or calcium hydroxide lime may be substantially decreased.

Mesh sizeMesh size refers to the number of openings per linear inch in a sieve refers to the number of openings per linear inch in a sieve through which the granular particles can pass. A 4-mesh screen means that through which the granular particles can pass. A 4-mesh screen means that there are four quarter-inch openings per linear inch. Likewise, an 8-mesh there are four quarter-inch openings per linear inch. Likewise, an 8-mesh screen has eight per linear inch.screen has eight per linear inch.

4) Indicators4) Indicators

Ethyl violetEthyl violet is the pH indicator added to both soda lime and calcium is the pH indicator added to both soda lime and calcium hydroxide lime to help assess the functional integrity of the absorbent. This hydroxide lime to help assess the functional integrity of the absorbent. This compound is a substituted triphenylmethane dye with a compound is a substituted triphenylmethane dye with a critical pH of 10.3.critical pH of 10.3.

Ethyl violet changes from colorless to violet when the pH of the Ethyl violet changes from colorless to violet when the pH of the absorbent decreases as a result of carbon dioxide absorptionabsorbent decreases as a result of carbon dioxide absorption..

When the absorbent is fresh, the pH exceeds the critical pH of the When the absorbent is fresh, the pH exceeds the critical pH of the indicator dye, and it exists in its colorless form.indicator dye, and it exists in its colorless form.

However, as absorbent becomes exhausted, However, as absorbent becomes exhausted, the pH decreases below the pH decreases below 10.3, and ethyl violet changes to its violet form.10.3, and ethyl violet changes to its violet form.

This change in color indicates that the absorptive capacity of the material This change in color indicates that the absorptive capacity of the material has been consumed.has been consumed.

For example, prolonged For example, prolonged exposure of ethyl violet to fluorescent light exposure of ethyl violet to fluorescent light can can produce photodeactivation of this dye. When this occurs, the absorbent produce photodeactivation of this dye. When this occurs, the absorbent appears appears white white even though it may have a reduced pH and its absorptive even though it may have a reduced pH and its absorptive capacity has been exhausted.capacity has been exhausted.

5) Interactions of Inhaled Anesthetics with 5) Interactions of Inhaled Anesthetics with AbsorbentsAbsorbents

Trichloroethylene,Trichloroethylene, reacts with soda lime to produce toxic compounds. In reacts with soda lime to produce toxic compounds. In the presence of alkali and heat, trichloroethylene degrades into the the presence of alkali and heat, trichloroethylene degrades into the cerebral cerebral neurotoxinneurotoxin dichloroacetylene, which can cause dichloroacetylene, which can cause cranial nerve lesions and cranial nerve lesions and encephalitis. encephalitis.

PhosgenePhosgene, a potent , a potent pulmonary irritantpulmonary irritant, is also produced and can cause , is also produced and can cause adult respiratory distress syndrome.adult respiratory distress syndrome.

SevofluraneSevoflurane has been shown to produce degradation products upon has been shown to produce degradation products upon interaction with carbon dioxide absorbents. The major degradation product interaction with carbon dioxide absorbents. The major degradation product produced is an produced is an olefinolefin compound known as fluoromethyl-2,2-difluoro-1- compound known as fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether, or (trifluoromethyl)vinyl ether, or compound Acompound A..

During During sevoflurane anesthesiasevoflurane anesthesia,factors apparently leading to an increase in ,factors apparently leading to an increase in the concentration of the concentration of compound Acompound A include (1) low-flow or closed circuit include (1) low-flow or closed circuit anesthetic techniques, (2) use of Baralyme rather than soda lime, (3) higher anesthetic techniques, (2) use of Baralyme rather than soda lime, (3) higher concentrations ofsevoflurane in the anesthetic circuit, (4) higher absorbent concentrations ofsevoflurane in the anesthetic circuit, (4) higher absorbent temperatures, and (5) fresh absorbent.temperatures, and (5) fresh absorbent.

Interestingly, Interestingly, dehydration of Baralyme increases the concentration of dehydration of Baralyme increases the concentration of compound A, compound A, but dehydration of soda lime decreases the concentration of but dehydration of soda lime decreases the concentration of compound A.compound A.

Desiccated strong-base absorbents Desiccated strong-base absorbents can also degrade contemporary can also degrade contemporary inhaled anesthetics to clinically significant concentrations of inhaled anesthetics to clinically significant concentrations of COCO, as well as , as well as trifluoromethane,trifluoromethane, which can interfere with monitoring of anesthetic gases. which can interfere with monitoring of anesthetic gases.

Under certain conditions, this process can produce very high Under certain conditions, this process can produce very high carboxyhemoglobin concentrations that reach 35% or greater.carboxyhemoglobin concentrations that reach 35% or greater.

Higher levels of CO Higher levels of CO are more likely after are more likely after prolonged contact prolonged contact between absorbent between absorbent and anesthetics, as well as after and anesthetics, as well as after disusedisuse of an absorber for at least 2 days, especially of an absorber for at least 2 days, especially over a weekend. over a weekend.

Thus, case reports describing CO poisoning have been most common in patients Thus, case reports describing CO poisoning have been most common in patients anesthetized on anesthetized on Monday morningMonday morning, presumably because continuous flow from the , presumably because continuous flow from the anesthesia machine dehydrated the absorbents over the weekend.anesthesia machine dehydrated the absorbents over the weekend.

Fresh gas flow rates of 5 L/min or greater Fresh gas flow rates of 5 L/min or greater through the breathing system and through the breathing system and absorbent (without a patient connected) are sufficient to cause absorbent (without a patient connected) are sufficient to cause critical drying of the critical drying of the absorbent material.absorbent material.

The situation is even worse when the breathing bag is left off the breathing circuit.The situation is even worse when the breathing bag is left off the breathing circuit.

Absence of the reservoir bag facilitates retrograde flow through the circle Absence of the reservoir bag facilitates retrograde flow through the circle system system .Because the inspiratory valve leaflet produces some resistance to flow, fresh .Because the inspiratory valve leaflet produces some resistance to flow, fresh gas flow takes the retrograde path of least resistance through the absorbent and out gas flow takes the retrograde path of least resistance through the absorbent and out the 22-mm breathing bag mount.the 22-mm breathing bag mount.

Several factors appear to Several factors appear to increase the production of CO increase the production of CO and resultant and resultant elevated carboxyhemoglobin levels, including : elevated carboxyhemoglobin levels, including :

1.The inhaled anesthetic used (for a given MAC multiple, the magnitude of CO 1.The inhaled anesthetic used (for a given MAC multiple, the magnitude of CO production from greatest to least is production from greatest to least is desfluranedesflurane = enflurane > isoflurane » = enflurane > isoflurane » halothane = sevoflurane), halothane = sevoflurane),

2.2.drynessdryness of the absorbent (completely dry absorbent produces more CO than of the absorbent (completely dry absorbent produces more CO than hydrated absorbent does),hydrated absorbent does),

3. the type of absorbent (at a given water content, 3. the type of absorbent (at a given water content, BaralymeBaralyme produces more produces more CO than soda lime does), CO than soda lime does),

4. the 4. the temperaturetemperature(increased temperature increases CO production), (increased temperature increases CO production),

5. the 5. the anesthetic concentrationanesthetic concentration (more CO is produced with higher anesthetic (more CO is produced with higher anesthetic concentrations),concentrations),

6. 6. low fresh gas flow rates, low fresh gas flow rates,

7. reduced experimental animal(patient) size per 100 g of absorbent.7. reduced experimental animal(patient) size per 100 g of absorbent.

Elimination of sodium and potassium hydroxide from desiccated soda Elimination of sodium and potassium hydroxide from desiccated soda lime diminishes or eliminates degradation of desflurane to CO and lime diminishes or eliminates degradation of desflurane to CO and sevoflurane to compound Asevoflurane to compound A, but it does not compromise carbon dioxide , but it does not compromise carbon dioxide absorption.absorption.

Several interventions have been suggested to Several interventions have been suggested to reduce the incidence of CO reduce the incidence of CO exposure in humans undergoing general anesthesia.Such interventions exposure in humans undergoing general anesthesia.Such interventions include :include :

(1) educating anesthesia personnel regarding the cause of CO production; (1) educating anesthesia personnel regarding the cause of CO production;

(2) turning off the anesthesia machine at the conclusion of the last case of the day to eliminate (2) turning off the anesthesia machine at the conclusion of the last case of the day to eliminate fresh gas flow, which dries the absorbent; fresh gas flow, which dries the absorbent;

(3) changing the CO absorbent if fresh gas is found to be flowing during the morning machine (3) changing the CO absorbent if fresh gas is found to be flowing during the morning machine check; check;

(4) rehydrating desiccated absorbent by adding water to the absorbent; (4) rehydrating desiccated absorbent by adding water to the absorbent;

(5) changing the chemical composition of soda lime to reduce or eliminate potassium hydroxide (5) changing the chemical composition of soda lime to reduce or eliminate potassium hydroxide (such products now available include Dragersorb 800 Plus, Sofnolime, and Spherasorb), (such products now available include Dragersorb 800 Plus, Sofnolime, and Spherasorb),

(6) using absorbent material that is free of both sodium and potassium hydroxide, such as (6) using absorbent material that is free of both sodium and potassium hydroxide, such as calcium hydroxide lime.calcium hydroxide lime.

One extremely rare, but One extremely rare, but potentially life-threatening complication potentially life-threatening complication related related to the carbon dioxide absorbent used is the development of to the carbon dioxide absorbent used is the development of firesfires within the within the breathing system. Specifically, this can occur as a result of interactions breathing system. Specifically, this can occur as a result of interactions between the strong-base absorbents (between the strong-base absorbents (particularly Baralymeparticularly Baralyme) and the ) and the inhaled inhaled anesthetic sevoflurane.anesthetic sevoflurane.

It seems that when desiccated strong-base absorbents are exposed to It seems that when desiccated strong-base absorbents are exposed to sevoflurane, absorber temperatures of several hundred degrees may result sevoflurane, absorber temperatures of several hundred degrees may result from their interaction.from their interaction.

The buildup of very high temperatures, the formation of combustible The buildup of very high temperatures, the formation of combustible degradation by-products (degradation by-products (formaldehyde, methanol, and formic acidformaldehyde, methanol, and formic acid), and ), and the oxygen- or nitrous oxide–enriched environment provide all the the oxygen- or nitrous oxide–enriched environment provide all the substrates necessary for a fire to occur.substrates necessary for a fire to occur.

Avoidance of use of the combination of sevoflurane with strong-base Avoidance of use of the combination of sevoflurane with strong-base absorbents, particularly Baralyme and especially if it has become absorbents, particularly Baralyme and especially if it has become desiccated, is the best way to prevent this unusual, potentially desiccated, is the best way to prevent this unusual, potentially lifethreatening complication.lifethreatening complication.

Anesthesia VentilatorsAnesthesia VentilatorsThe ventilator on the modern anesthesia workstation serves as a mechanized The ventilator on the modern anesthesia workstation serves as a mechanized substitute for the substitute for the hand of the anesthesiahand of the anesthesia care provider in manipulating the care provider in manipulating the reservoir bag of the circle system, the Bain circuit, or another breathing system. reservoir bag of the circle system, the Bain circuit, or another breathing system.

As recently as the As recently as the late 1980slate 1980s, anesthesia ventilators were mere adjuncts to the , anesthesia ventilators were mere adjuncts to the anesthesia machine.anesthesia machine.

Today, they have attained a prominent Today, they have attained a prominent central role in newer anesthesia central role in newer anesthesia workstationsworkstations. In addition to the nearly ubiquitous role of the anesthesia ventilator . In addition to the nearly ubiquitous role of the anesthesia ventilator in today's anesthesia workstation, in today's anesthesia workstation, many advanced intensive care unit (ICU)-style many advanced intensive care unit (ICU)-style ventilation features have also been integrated into anesthesia ventilators ventilation features have also been integrated into anesthesia ventilators . .

Anesthesia care providers should be aware that even though Anesthesia care providers should be aware that even though more similarities more similarities exist between today's anesthesia ventilator and the ICU ventilator than ever exist between today's anesthesia ventilator and the ICU ventilator than ever beforebefore, some fundamental differences in ventilation parameters and control , some fundamental differences in ventilation parameters and control systems still remain. systems still remain.

Anesthesia VentilatorsAnesthesia Ventilators (central role in newer anesthesia workstations)(central role in newer anesthesia workstations)

ClassificationClassification

Operating Principles Operating Principles

HazardsHazards

Classification VentilatorsClassification Ventilators

VentilatorsVentilators can be classified according to their: can be classified according to their:

1) P1) Powerower source, source,

2) D2) Driverive mechanism, mechanism,

3) C3) Cyclingycling mechanism, mechanism,

4) Type of 4) Type of bellowsbellows

1) Power Source1) Power Source

Power sourcePower source– Pneumatic & Compressor Pneumatic & Compressor – electric electric – BothBoth

ContCont

The power source required to operate a mechanical ventilator is provided by The power source required to operate a mechanical ventilator is provided by compressed gas, electricitycompressed gas, electricity, or both., or both.

Older pneumatic ventilators required only a Older pneumatic ventilators required only a pneumatic powerpneumatic power source to source to function properly.function properly.

Contemporary electronic ventilators from Dräger Medical, Datex-Ohmeda, and Contemporary electronic ventilators from Dräger Medical, Datex-Ohmeda, and others require either an others require either an electrical-only or both an electrical and a pneumatic electrical-only or both an electrical and a pneumatic power sourcepower source..

2) Drive Mechanism and Circuit Designation2) Drive Mechanism and Circuit Designation

Drive mechanismDrive mechanism– double circuit driven (DCD)double circuit driven (DCD)– Single circuit driven (SCD)Single circuit driven (SCD)

ContContDouble-circuit ventilatorsDouble-circuit ventilators are most commonly used on modern anesthesia are most commonly used on modern anesthesia workstations.workstations.

Generally, these conventional ventilators are Generally, these conventional ventilators are pneumatically drivenpneumatically driven. .

In a double-circuit ventilator, a driving force such as pressurized gas compresses a In a double-circuit ventilator, a driving force such as pressurized gas compresses a component analogous to the reservoir bag known as the ventilator bellows. component analogous to the reservoir bag known as the ventilator bellows.

The bellows then in turn delivers ventilation to the patient. The bellows then in turn delivers ventilation to the patient.

The driving gas in the Datex-Ohmeda 7000, 7810, 7100, and 7900 is The driving gas in the Datex-Ohmeda 7000, 7810, 7100, and 7900 is 100% oxygen100% oxygen. .

In the North American Dräger AV-E and AV-2+, a venturi device In the North American Dräger AV-E and AV-2+, a venturi device mixes oxygen and airmixes oxygen and air. .

Some newer pneumatic anesthesia workstations enable the user to select whether Some newer pneumatic anesthesia workstations enable the user to select whether compressed air or oxygencompressed air or oxygen is used as the driving gas. is used as the driving gas.

In recent yearsIn recent years, with the introduction of circle breathing systems that integrate , with the introduction of circle breathing systems that integrate fresh gas decouplingfresh gas decoupling, a resurgence in the use of mechanically driven , a resurgence in the use of mechanically driven anesthesia ventilators has occurred. anesthesia ventilators has occurred.

These “These “piston”-type ventilatorspiston”-type ventilators use a computer-controlled stepper motor use a computer-controlled stepper motor instead of instead of compressed drive gascompressed drive gas to actuate gas movement in the breathing to actuate gas movement in the breathing system. system.

In these systems, rather than having dual circuits with patient gas in one and In these systems, rather than having dual circuits with patient gas in one and drive gas in another, drive gas in another, a single patient gas circuita single patient gas circuit is present. is present.

Thus, they are classified as Thus, they are classified as piston-driven single-circuit ventilatorspiston-driven single-circuit ventilators. .

The piston operates much like the The piston operates much like the plunger of a syringeplunger of a syringe to deliver the desired to deliver the desired tidal volume or airway pressure to the patient. tidal volume or airway pressure to the patient.