circle system Flashcards
what is the benefit of rebreathing alveolar gas
conserves heat & humidity
what is the purpose of the carbon dioxide absorbent?
elimination of CO2 to prevent hypercarbia
CO2 absorbents contain hydroxide salts that are capable of neutralizing carbonic ac
Name one common absorbent material used for CO2 absorbers ?
soda lime
capable of absorbing up to 23 L of CO2/100 g of absorbent.
what acid is produced produced when CO2 combines with water?
carbonic acid
what are the end products of the neutralizing reaction provided by the CO2 absorber?
heat
water
calcium carbonate
In regards to soda lime, what minimizes the risk of inhalation of sodium hydroxide dust
adding silica to increase hardness
what prevents dust formation in the CO2 absorbers?
hardness of the lime agent
In regards to the CO2 absorber, how could it delay the induction or emergence?
Absorbent granules can absorb & later release significant amounts of volatile anesthetic. The drier the soda lime, the more likely it will absorb & degrade volatile anesthetics.
you’re checking your machine in the a.m., the CO2 absorbent looks to be a new canister, but after 2 hours into your first case you notice rebreathing on the monitor and notice the canister is now 75% puprle. what is this phenomenon
peaking or regeneration
seen with absorbents that contain strong bases, absorbent appears to be reactivated with rest
what are indications to change absorbent?
CO2 in inspired gases (FiCO2)
Color change
Heat in canisters
True or false. Double CO2 canisters lower gas flow resistance.
True
which canister goes on top when loading a new CO2 absorbent canister in a double canister system?
the new one goes on bottom, the older bottom canister is moved to the top
what should be done after changing out the CO2 canisters?
circuit leak check
what is the puprose of the unidirectional valves?
check valves that prevent flow in opposite directions, make the circle circuit possible
which valve is exposed to humidity of alveolar gas?
expiratory
discuss the valves at inspiration
Inhalation opens the inspiratory valve allowing the patient to breath a mixture of fresh & exhaled gas that has passed thru the CO2 absorber. Simultaneously, the expiratory valve closes to prevent rebreathing of exhaled gas that still contains CO2.
discuss the valves at expiration
exhalation opens the expiratory valve. This gas is vented thru the APL valve or rebreathed by the patient after passing thru the absorber. Closure of the inspiratory valve during exhalation prevents expiratory gas from mixing with fresh gas in the inspiratory limb.
What are some problems that could come about due to damaged valves?
rebreating CO2 – related to both
a stuck inspiratory valve- pressure build up in machine
a stuck expiratory valve - pressure build up in patient
what is true of deadspace in the breathing circuit.
- occurs where there is bi-directional flow
- occurs from y piece to patient
- The length of the tubes does not affect the amount of dead space
what is an advantage of concentric patient circuit? Disadvantage?
a. outer corrugated tube carrries exhaled gas that can moderately warm inspired tube gases
b. disadvantage - increased resistance, hypercapnea due to inner tube leak
what is true of the Y piece
- contains deadspace
- has (2) male ports at 22 mm
- has (1) female port at 15 mm
what size is the facemask orifice?
22 mm
what is function of APL (adjustable pressure limit) valve ?
Controls pressure in breathing system
Releases gases to scavenging system
what happens when the pressure has reached APL valve setting?
the valve opens & excess gas is vented to the scavenging system during inspiration.
what is function of reservoir bag?
- gas storage
- Method of generating positive-pressure ventilation
- Way to monitor spontaneous respiration
- Protects patient from excessive pressure in breathing system
what type of switch is the bag/ventilator selector switch?
3 way (stop cock like)
what is bypassed when switch is set to ventilator?
APL valve
where is drive gas in relation to the bellows?
inside the plastic canister, surrounding bellows (not actually in the bellows)
which gas makes the bellows go down?
drive gas — from pipeline (oxygen or air)
which gas makes the bellows go up?
with patient exhalation —- in the bellows is pt. exhaled gas, agent, and fresh gas flows
true or false. Drive gas can be delivered to the patient?
False. drive gas is never delivered to the patient. only to atmosphere
what is an indication via the bellows that the patient is fighting the vent?
bellows will dip down slightly with an inspiration when you expect an exhalation
what is the pressure gauge associated with the circle circuit?
displays the airway pressure
what is the respiratory gas monitor sensor?
Analyzes concentrations of gases in breathing system
what is the function of the airway Pressure Monitor Sensor
alarm that Warns clinicians of high or low-pressure conditions in breathing system
what Measures ventilatory volumes
Respirometer
ojectives of the circle system
Maximum inclusion of fresh gas in inspired mixture & maximum venting of alveolar gas Minimize absorbent dessication Minimal absorbent consumption Accurate respirometer readings Maximal inspired gas humidification Minimal dead space Low resistance Minimal pull on mask, ETT, or LMA Convenience
why is inclusion of fresh gas in inspired mixture important?
will result in faster inductions & emergences
what is the most common location of the fresh gas inlet?
upstream of the inspiratory valve and downstream of the absorber
what is the most common location of the APL valve?
near reservoir bag downstream of the expiratory valve & upstream of the absorber
what is most common location of reservoir bag?
between the expiratory valve & the absorber
what is most common location of ventilator?
upstream of the absorber, near APL valve
during spontaneous exhalation, where do exhaled gases go?
into the reservoir bag until it is full then excess gases are vented thru the APL valve
where does fresh gas flow enter in the datex-ohmeda circle system?
fresh gas enters the system between the inspiratory valve & the Y-piece
what is true of low flows of fresh gases in a circle circuit?
Require CO2 absorber
Vary O2 & anesthetic concentrations
Prolong induction & recovery
What is true of high flows of fresh gases in a circle circuit
> 5 L/min don’t require CO2 absorber
Accelerate induction & recovery
Compensate for circuit leaks
Decrease unanticipated gas mixture risk
what is Tidal volume that is not part of alveolar ventilation
dead space
what increases resistance in a circle system?
Unidirectional valves
CO2 absorber
Coaxial tubings
what are the advantages of a circle system?
Economy
Reduced operating room pollution
Reduced environmental pollution
Estimation of anesthetic agent uptake & oxygen consumption
Buffered changes in inspired concentrations
Heat & humidity conservation
Reduced barotrauma risk
what are the disadvantages of a circle system?
Larger overall size Less portability Increased complexity Increased resistance Difficult to predict inspired gas concentrations with low fresh gas flows Hypercarbia risk Faster absorbent exhaustion
