Anesthesia Systems Flashcards
3 Essential Components of a Breathing Circuit
Low resistance conduit for gas flow
Reservoir for Gas that meets inspiratory flow demand
Expiratory port or valve to vent excess gas
Requirements of a Breathing System (5)
- Deliver the gases from the machine or device to the alveoli in the same concentration as set and in the shortest possible time
- Effectively eliminate carbon dioxide
- Minimal apparatus dead space
- Low resistance to gas flow
- Allow rapid adjustment in gas concentration and flow rate
Effects of hypercarbia
Right shift on oxygen-hemoglobin dissociation curve
- Acidosis
- Vasodilation -> hypotension
- tachycardia
- increased ICP
The anatomic dead space in the circle system begins at
The Y Piece
Desirable Features in a Breathing System (8)
- Economy of fresh gas
- conservation of heat
- adequate humidification
- light weight
- convenience during use
- efficiency during spontaneous and controlled ventilation
- adaptability for adults, children, and mechanical ventilators
- proviso to reduce environmental pollution - safe disposal of waste gas
Higher FGF is associated with
less rebreathing in any circuit
Dead space increases
The chance of rebreathing CO2
Apparatus Dead space ends where
The inspiratory and expiratory gas streams diverge (Y-piece)
Apparatus dead space can be minimized by
separating the inspiratory and expiratory streams as close to the patient as possible (hence Y piece)
The concentration of inspired gas most closely resembles that delivered from the common gas outlet when
rebreathing is minimal or absent
Open classification =
no reservoir, no rebreathing (NO VALVES)
ex. sufflation, blow by, tenting, bronchoscopy port, nasal canula
Semi-Open classification =
Reservoir, no breathing
ex. some Maplesons, FGF dependent.
circle systems if FGF > MV (i.e. no rebreathing)
Semi-Closed classification =
Reservoir, partial rebreathing
Circle systems, FGF < MV
Closed classification =
Reservoir, complete rebreathing
FGF is minimal, APL closed.
Advantages of open systems
(i.e. blow-by, insufflation) - 7
Simple! Avoids direct patient contact No rebreathing of CO2 No reservoir bag No valves so less resistance and no chance of disconnection Good for peds Good for facial surgery
Disadvantages of Open Systems (blow-by, insufflation) - 5
No ability to assist or control ventilation
Requires high FGF to eliminate CO2 (especially with drapes/tenting)
No control of anesthetic depth/Fio2
Environmental pollution
Increased Fire Risk
Mapleson Components (4)
Connection point to a facemask or ETT
Reservoir Tubing
Fresh Gas inflow tubing
Expiratory pop-off valve / port
Best Measure of optimal FGF to prevent re-breathing
End tidal CO2
Fundamental ways that maplesons differ from circle systems
Bidirectional flow
Lack of CO2 absorber, elimination is dependent on FGF
Instances when maplesons are used - 5
Pediatrics
Transportation of patients
Procedural sedation
Weaning tracheal intubation
pre oxygenation during out of OR management
Three distinct functional groups of maplesons
A
BC
DEF
Structure of Mapleson A (Magill)
FGF is after reservoir bag,
Pop off valve is near face mask/ETT
FGF and pop valve are opposite each other
Best mapleson for Spontaneous Ventilation
All > Dogs > Can > Bite
With Mapleson A during Spontaneous Ventilation:
FGF = 1x MV then
there is no rebreathing
How to achieve no rebreathing with mapleson A during spontaneous ventilation
FGF. = 1 x MV
Steps of Spontaneous Ventilation with Mapleson A
- Pt takes a breath from reservoir (FGF) inhaling mostly FGF, emptying reservoir bag
- Pt expires alveolar gas/dead space gas into tubing. EXPIRATORY PAUSE
- During expiratory pause, FGF continues to flow, pressure in system is enough to open APL/pop off valve, gas escapes via valve, because this valve is closest to pt, the gas escaping is EXPIRED GAS.
Gas filling reservoir tubing is FGF.
Best Mapleson for Controlled Ventilation
Dog > Bites > Can > Ache
Steps of Controlled Ventilation with Mapleson A
With the APL valve closed, the anesthetist squeezes the reservoir bag to deliver a breath.
FGF is behind reservoir bag, gas is pushed towards pt.
Pt expires, alveolar gas/dead space gas mixes with FGF in reservoir bag.
Another breath given = not only FGF, but mixed gas. There will be rebreathing, extra pressure will allow mixed gas to leave via pop off valve.
To prevent rebreathing in Mapleson A with controlled ventilation
Much larger FGF, up to 20L/min
Disadvantages of Mapleson A (5)
- Inefficient for controlled ventilation (requires up to 20L/min to flush out mixed gas)
- Impractical design for operating room
- Proximal location of pop off valve makes scavenging difficult
- Difficult to adjust in head/neck surgery
- Heavy valve can dislodge small ETT
Structure of Mapleson B/C
FGF and pop off valve are located near each other and right near patient.
Mapleson C is used
For resuscitation and in patient transfer
Disadvantages of Mapleson B/C
FGF and pop off are so close to each other so mixing will always occur, requires huge FGF to wash out CO2.
Structure of Mapleson D
FGF is near patient,
pop off valve is closest to reservoir bag, they are far from each other as in A but D is the opposite of A.
Most efficient Mapleson for both spontaneous and controlled
Mapleson D
All Dogs Can Bite
Dog Bites Can Ache
Dogs are friends *
Steps of Spontaneous Ventilation with Mapleson D
- FGF is flowing closet to patient, so patient inhales mostly FGF,
- Pt exhales, expired gas mixes with FGF, goes down tube to reservoir bag.
EXPIRATORY PAUSE allows FGF to flush tubing, pop off valve opens when pressure is high enough, mixed gas escapes via pop off valve.
A higher FGF is still required to prevent rebreathing (2-3 x MV)
FGF required to prevent rebreathing in spontaneous ventilation with Mapleson D
2-3 x MV
Steps of Controlled Ventilation with Mapleson D
- FGF is flowing close to patient,
when reservoir is compressed to deliver a breath, pt receives breath that is mostly FGF. - Pt exhales, reservoir bag is mixed gas. No expiratory pause to flush gas, but when reservivr bag is compressed it pushes DISTAL FGF into pt, so less FGF overall is needed.
FGF for no rebreathing in controlled ventilation of Mapleson D
1 -2 x MV
Critical Difference between Spontaneous and Controlled Ventilation =
Expiratory Pause
Faster rate = shorter
expiratory pause, less ability for FGF to flush out expired air, greater risk for rebreathing
Conditions that increase CO2 production
fever, catabolic state, malignant hyperthermia
How to decreased CO2 with mapleson
Must increase rate and also FGF
Advantages of Bain Circuit
- warming of FGF by inflow of exhaled gas in corrugated tubing
- Conservation of moisture as a result of partial rebreathing
- Ease of scavenging waste anesthetic gases from overflow valve
- Light weight, easily sterilized reusable, useful for limited access to pt as in during head/neck surgery
Disadvantages of Bain Circuit:
unrecognized disconnect of inner FGF tubing
Pethick Test:
Used to assess integrity of Bain circuit, assure that inner FGF tube isn’t disconnected.
Occlude patient end of circuit, flow in high flow oxygen until reservoir is filled.
Let go of patient side, if the inner tube is intact, the the bag will deflate.
If the inner tube is not intact, gas escapes from FGF line to corrugated tubing and the reservoir remains inflated.
Only mapleson without a reservoir
Mapleson E
Structure of Mapelson E
No reservoir!
Expiratory limb functions as reservoir.
No Pop off valve.
FGF is near patient.
Mapleson E functions most like
Maplseon D
A, BC, !!DEF!!
Ventilation with Mapelson E
During expiration, the tubing fills with dead space and alveolar gas which is then flushed out by FGF
Rebreathing is dependent on amount of FGF,
In a mapleson E, If FGF is not equal to the inspiratory flow rate then
room air will be entrained through open end
Recommended FGF in Mapleson E to prevent rebreathing
2-3 x MV
Mapleson F (Jackson-Rees) is a modification of
Mapleson E
- Mapleson E + reservoir bag = Mapleson F
/DEF/
FGF to prevent rebreathing in Mapleson F =
2- 3 x MV
Mapleson F is commonly used for
controlled ventilation and transportation of intubated patients
Mapleson F is ideal for
Pediatric anesthesia
In Mapleson F there are no
moving parts except the pop valve at the end of the reservoir bag, therefor circuit dead space is minimal
Mapleson F during spontaneous ventilation
Pt inhales from FGF and reservoir bag, exhales into tubing, EXPIRATORY PAUSE, FGF helps flush expired air towards reservoir bag
Advantages of Mapleson F - 4
Used for both spontaneous and controlled ventilation
Inexpensive, can be used with face mask or ETT
Is light weight, can be repositioned easily
Pollution of the atmosphere with anesthetic gases while using this system can be decreased by adapting it to scavenging system.
Disadvantages of Mapleson F
Requires high FGF to prevent rebreathing
Possibility of high airway pressure and barotrauma should the pop off valve become occluded
Lack of humidificaiton
-can add a humidifier
If you’re using a volatile ambu bag with a volatile anesthetic
The spring in the ambu bag can break r/t the anesthetic gases
Jackson-Rees allows you to see
lung compliance with inflation of bag
Difficulty of transporting with Jackson-Rees
its flow inflating, so you need to carry oxygen
CO2 rebreathing depends on (5)
FGF
MV of patient
Mode of ventilation (spontaneous vs controlled)
CO2 Production of individual patient
Respiratory wave form characteristics (insp. flow, I:E times, expiratory pause)
7 components of a circle system
- FGF source
- Inspiratory / expiratory unidirectional valves
- Insp./ Exp limbs
- Y piece
- APL valve
- Reservoir bag
- CO2 absorber
More cost effective to save on
anesthetic gases rather than CO2 absorbents
Opposite of patient lung in circle system is
reservoir bag / counter lung
The carbon dioxide absorber in a circle system is most often placed on
The inspiratory limb on the bag side.
Preferred location for FGF inlet in circle system
Between CO2 absorber and inspiratory valve
- in case there is a problem with CO2, fresh gas comes after it
Essential characteristics of unidirectional valves in circle system
low resistance, high competence
Unidirectional valves must be placed
On exp and insp limb. Between the reservoir bag and the patient
properly positioned and functioning unidirectional valves prevent:
any part of the circle system from contributing to the apparatus dead space
Primary sources for resistance is an anesthesia machine
ETT, valves, Co2 absorber
Unidirectional valves will exert significantly more resistance when
When they are moist from water vapor
3 functions of reservoir bags
- Serve as a reservoir for anesthetic gases or oxygen
- Visual assessment of spontaneous ventilation & rough estimate of the volume
- Means for manual ventilation
A reservoir function is necessary because:
Anesthesia machines cannot provide the peak inspiratory gas flow needed during normal spontaneous inspiration
Optimally sized reservoir bag :
Can hold a volume that exceeds the patients inspiratory capacity (3L most common)
Spontaneous Respiration means APL valve is
Valve fully open
Assisted ventilation means APL valve is
partially open/partially closed
in a circle system, the pop-off/APL valve is usually located
between the exp valve and the bag mount
Any circuit should be tested before use by determining the O2
O2 flow required to maintain 30 cm h2o of pressure in the circuit
Advantages of the circle system - 8
Relative stability of concentration of inspired gases
conservation of moisture and heat
Low resistance (but not as low as mapleson)
can be used for closed-system anesthesia
Can be used with fairly low flows with no rebreathing of co2
economy of anesthetics and gases
can scavenge waste gases
prevention of OR pollution
Disadvantages of circle system - 6
complex design
has at least 10 connections
potential of malfunctioning valves
increased resistance to breathing (Compared to mapleson)
less portable and convenient than mapleson system due to its bulkiness
increased dead space BUT dead space ends at Y piece
Unidirectional valve stuck open
rebreathing will occur
unidirectional valve stuck closed
airway obstruction will occur
Leak test in circle system
Set all gas flows to zero, occlude the Y-piece, close the APL valve, pressurize the circuit to 30 cm of water pressure using the O2 flush valve, ensure pressure holds for 10 seconds, listen for sustained pressure alarm,
Leak test does not assess for
integrity of unidirectional valves
Flow test in circle system
Attach breathing back to Y -piece, turn on ventilator, assess integrity of system
ASSESS INTEGRITY OF UNIDIRECTIONAL VALVES
Potential Problems in Circuit (Circle) System: (5)
misconnections or disconnections
leaks
valve failure
carbon dioxide absorber defect
bacterial filter occlusion
slide 54
Basic function of a breathing circuit
interface between patient and anesthesia machine, to delivery oxygen and other gases , eliminates carbon dioxide
has 3 essential components
- low resistance conduit for gas flow
- pop off valve / port
- reservoir for gas that meets inspiratory demand
“Things to consider” with breathing systems (6)
Low resistance Rebreathing Dead space Dry gases/humidification manipulation of inspired content bacterial colonization
– slides 7&8
Recommended bacterial filter
One with an efficiency rating of more 95% for particles sizes 0.3 micrometers, protects the machine from colonization of airborne infectious disease.
Pros of Maplesons (4)
Simplicity of design
Ability to change the depth of anesthesia rapidly
Portability
Lack of rebreathing of exhaled gases (only if FGF is adequate)
Disadvantages of Maplesons (3)
lack of conservation of heat and moisture
limited ability to scavenge waste gas
high requirements for FGF
With mapleson E, the sole determinant of wether rebreathing will occur is
The FGF (and the pt’s MV)
for spontaneous breathing the FGF must be 2-3 x the MV
Steps of steal induction
Child is usually already sleeping (from versed or anti-anxiolytic)
Mask is primed with O2 and N2O, mask is brought near child, insufflation, when child is further anesthetized, mask is placed on childs face (now a semi-open system r/t reservoir of mask)
Advantages of Mapleson (4)
simplicity of design
ability to change the depth of anesthesia rapidly (because FGF is usually higher than in circle system)
portability
lack of breathing of exhaled gases (as long as FGF is high enough)
Disadvantages of Mapleson
lack of conservation of heat/humidity (unless Bain)
limited ability to scavenge waste gas (r/t where the aPL is)
high requirements for FGF
FGF and common gas inflow site:
is usually between CO2 absorber and inspiratory valve
can be incorporated in housing of CO2 absorber housing or with the unidirectional inspiratory valve
APL valve purposes (4)
Purpose: permits PEEP during SV or allows for pressure- limited controlled respiration
Releases gases to scavenge or to atmosphere
User-adjustable, pressure required to open it changed by user
Provides control of pressure in system
slide 40
Semi-Open Circle system
No rebreathing occurs (as it is a semi-open system)
therefore, requires HIGH gas flows. High = FGF > MV
10-15 L/min
No conservation of waste gas/ heat
APL valve is all the way open or ventilator is in use with. high gas flow so CO2 absorber is doing nothing.
Gas flow needed for a semi-open CIRCLE system
10-15 L/min
slide 46
Most commonly used circle system is
Semi-closed circle system, partial rebreathing. Low gas flows, but not minimal.
Semi-Closed Circle System:
Allows for some re-breathing of agents and exhaled gases (minus CO2 due to CO2 absorption)
Uses relatively low flow rates (about 1-3L/min)
FGF
Gas flows for semi-closed circle system
1-3 L /min
slide 47
Closed Circle system
Used often in long surgical cases and third world countries
Inflow gas exactly matches metabolic needs/ O2 consumption of the patient using very low flows (O2 flow rate ~ @ 250 mL/min)
Total re-breathing of all exhaled gases after absorption of CO2
APL is closed
Change in gas concentrations is VERY slow
Closed circle systems are used most in
Very long surgeries or third world countries.
Minimal gas flows.
In closed circle systems, the FGF flow =
Inflow gas exactly matches metabolic needs/ O2 consumption of the patient using very low flows (O2 flow rate ~ @ 250 mL/min)
