Anesthesia Delivery System Flashcards
What is the function of the anesthesia breathing system?
deliver oxygen and anesthetic gases to patient and remove CO2
What 2 ways can CO2 be removed from the breathing circuit?
washout with FGF or by use of CO2 absorber
What are the essential requirements of a breathing system?
deliver the gases from the machine or device to alveoli in the same concentration as set and in the shortest possible time
effectively eliminate CO2
have minimal apparatus dead space
low resistance
What are some desirable requirements of the breathing system?
economy of fresh gas
conservation of heat
adequate humidification of inspired gas
light weight
convenient to use
efficiency during spontaneous and controlled ventilation
adaptability for adults, children & mechanical vents
provision to reduce environmental pollution
You want low resistance in the breathing circuit, what are some ways this can be achieved?
short tubing, large diameter tubing, avoid sharp bends, caution with valves, minimize connections
Rebreathing may be beneficial, why?
cost reduction and adds humidification and heat to gas
What dont you want the patient rebreathing? How can this be prevented?
CO2; higher FGF is associated w/ less rebreathing in ANY type of circuit
What increases the chance of rebreathing CO2?
deadspace
Deadspace ends where the ___________&_____________gas streams diverge?
inspiratory and expiratory
How can apparatus dead space be minimized?
separating the inspiratory and expiratory streams as close to the patient as possible
T/F: The concentration inspired is closest to what is delivered from the common gas outlet when rebreathing is minimal or absent.
true
What are the 4 classifications of anesthesia delivery systems?
- open
- semi-open
- semi-closed
- closed
What are the characteristics of an open system?
no gas reservoir bag; no valves; no rebreathing of exhaled gases
What are the 2 types of open systems?
insufflation/blow by & open drop
What are some examples of insufflation?
blow by; tent; bronchoscopy port; nasal cannula; steal induction
What are some advantages to insufflation?
avoids direct patient contact; no rebreathing of CO2; no reservoir bag or valves
What are some disadvantages to insufflation?
no ability to assist or control ventilation; may have CO2/O2 accumulation under drapes; no control over anesthetic depths/FiO2; environmental pollution
Schimmelbusch mask was considered a true “open” circuit because it consisted of what?
piece of cloth saturated w/ ether, chloroform, or halathane and held over a patient’s face
The Schimmelbusch mask is an example of what type of open circuit?
open drop method
What are some advantages of the open drop method?
simplicity; low cost apparatus; portable
What are some disadvantages of the open drop method?
poor control of inspired concentration of anesthetic; accumulation of CO2 under mask; predisposes hypoxia risk; spontaneous ventilation only; OR pollution/healthcare provider risk
The semi-open system is characterized by what 5 components?
face mask pop valve reservoir tubing FGF inlet reservoir bag
What are some examples of a semi open system?
Mapleson A-F; Bain; circle
How many functional groups are there of the Mapleson systems?
3
Group 1 of mapleson is characterized as:
Mapleson A: pop off valve is located near face mask; FGF at opposite end
Group 2 of mapleson is characterized as:
Mapleson B & C: pop off valve and FGF both located near facemask
Group 3 of mapleson is characterized as:
Mapleson D-F: FGF located near facemask and popoff valve at opposite end opposite of Mapleson A
CO2 rebreathing depends on what 3 things?
- FGF rate
- MV of patient
- type of ventilation (controlled, spontaneous)
T/F: Mapleson D can be used for both spontaneous and controlled ventilation?
True
With the Mapleson D and spontaneous ventilation the FGF should equal what?
FGF=2-3xMV
With the Mapleson D and controlled ventilation, the FGF should equal what?
FGF=1-2xMV
Mapleson E has no __________and _________.
reservoir bag and popoff valve
For a Mapleson E, what is considered the reservoir?
expiratory limb
When using the Mapleson E for spontaneous ventilation, FGF should equal what?
FGF=2-3xMV
T/F: Modification of Ayre’s T-piece is commonly used to administer O2 in the ICU/ PACU?
true
Mapleson E is also known as _________
T piece
Mapleson F is a modification of what?
Mapleson E (Ayer’s T piece)
What feature does Mapleson F have that the E didnt?
adjustable pop off valve at the end of the reservoir
The Mapleson F (aka Jackson-Rees) is very popular in what patient population?
peds
A coaxial modification of Mapleson D is called __________
Bain circuit
Explain the coaxial design
FGF tube is within the corrugated tubing; this allows for the exhaled gas to warm the FGF or inspired gas. This also preserves heat and humidity
T/F: The Bain circuit can only be used for spontaneous ventilation.
false; can be used for controlled or spontaneous
What are the FGF requirements for Bain?
FGF=2-3xMV
What are some disadvantages to the Bain circuit?
potential for inner tube leaks, kinking, disconnection
Ambu bag is a modification of which Mapleson?
A
The Ambu bag contains a ________valve.
non-rebreathing
What are some characteristics of the ambu bag?
contains non-rebreathing valves capable of delivering high FiO2; reservoir is self filling; requires high FGF; depends on minute ventilation
What are some advantages of the Mapleson systems as a whole?
simple components; light weight; can provide positive pressure; portable; if using an inhaled anesthetic: more predictable anesthetic concentration; decreased room pollution
What are the disadvantages of the Mapleson system as a whole?
requires calculation of FGF which varies from both types of circuit and mode of ventilation
control of anesthetic depth is variable
if FGF is not maintained, there is an increase in CO2 and rebreathing is present
poor heat and humidity
FGF is costly
requires special assembly and function is complex
In the standard circle system, what are the available lengths?
40in, 60in, 72in
The circle system can be ___________, ___________ or ____________
semi open, semi closed; closed
depends on the adjustment of APL and FGF rates
The circle system prevents rebreathing of ______by chemical of neutralization but allows rebreathing of ___________
CO2; other exhaled gases
The circle system is characterized by what 7 components?
- FGF source
- Insp/Exp unidirectional valves
- Insp/Exp limbs and corrugated tubing
- Y piece connector
- APL valve
- reservoir bag
- CO2 absorber
Trace the flow of FGF through the circle system. 9 steps
- FGF enters through common gas outlet
- flows through insp unidirectional valve
- flows through insp breathing tube
- flows through y piece to patient
- from patient to exp breathing tube
- through exp one way vavlve
- in and out reservoir bag ( excess gas is vented out through APL valve to scavanging system)
- through CO2 absorber
- gas goes back to patient
How do the unidirectional valves function?
gas flowing into the valve raises the disk off its seat and then pass through the valve; reversing the gas flow causes the disk to contact its seat stopping further retrograde flow
The guide (cage) prevents _________ or ___________displacement of the disk in the unidirectional valve.
lateral or vertical
What are the characteristics of a reservoir bag?
made of neoprene or rubber; neck-22mm female fitting to a male; tail end opposite of neck
What are the functions of the reservoir bag?
accumulation of gas during exhalation; assist/control ventilation; visual/tactile monitor to observe spontaneous respirations; protects against excessive pressure
what are some characteristics of the breathing tube?
large bore non rigid corrugated tubing; plastic or rubber; 22mm female fitting w/ machine;
Patient end: 22mm male, 15mm female coaxial fitting
What are the other characteristics of the breathing tube?
flexible; low resistance; light weight connection, reservoir
What are some other common names for the APL valve?
pop off valve; pressure relief valve; safety relief valve
What is the function of the APL valve?
releases gases to the scavanging system
Turning the APL valve__________ will increase pressure within the system?
clock wise
During spontaneous ventilation the APL valve should be __________
fully open (close partially if reservoir bag collapses)
During assisted ventilation the APL valve should be ________
partially open
during mechanical ventilation the APL valve should be ___________
fully closed (if machine is not equipped w/ a switch)
If the unidirectional valves are working properly, the only dead space in the circle system is between the ___________ and _____________
y piece and patient
What are 3 rules regarding the circle system arrangemtn that must be followed?
- unidirectional valves must be located btw patient and reservoir bag between the insp and exp limbs
- FGF can not enter btw the pt and the exp valve
- APL valve cannot be located btw the pt and the insp valve
Explain the semi open circle system
not used often: occassionally for sedation
no rebreathing occurs
requires high FGF (10-15L/min) to eliminate rebreathing
no conservation; wastes gas and heat
APL valve open all the way
Explain the semi closed circle system
most commonly used breathing system in US
requires relatively low FGF (1-3L/min)
conserves some heat and gas
some rebreathing of agents and exhaled gas (not CO2)
APL valve is partially closed and adjusted as needed
Explain the closed system
often used in 3rd world countries
inflow of gas exactly meets metabolic needs/ O2 consumption of the patient using very low flows (200ml/min)
total rebreathing of all gases after absorption of CO2
total conservation of all exhaled gases
APL valve fully closed
How do you calculate O2 consumption needs
10xkg^(3/4)
i.e. 70kg pt
10x70^3/4
10x24.2= 242ml O2/min
What are the advantages of the circle system?
relative stability of inspired gas conservation of moisture and heat prevention of OR pollution can be used for closed system anesthesia can be used w/ very low flows with no rebreathing of CO2 economy of anesthetics and gases can scavenge waste gases
What are the disadvantages of circle system
complex design
many connections; possibility of leaks
1/3 of malpractice claims resulted from disconnections or misconnections
potential malfunction of valves
increased resistance for breathing
less portable and convenient compared to mapleson
what are the 2 circle system checks?
leak test and flow test
How do you perform leak test?
set all gas flows to zero, occlude y piece; close APL valve, pressurized circuit to 30cmH20 using O2 flush valve, ensure pressure hold for 10 second; listen for sustained pressure alarm; open APL valve and ensure pressure decreases
this does not test integrity of unidirectional valves
How do you perform flow test?
attach breathing bag to y piece, turn on ventilator, and assess integrity of unidirectional valves
what mapleson is best for spontaneous ventilation?
A
What mapleson is best for controlled ventilation?
D
With a self inflating reservoir bag, what is a disadvantage?
you cant feel if the patient is spontaneously breathing
How many liters can the reservoir bag hold?
3L
