Delivery Systems

Question 1

Basic function of a breathing circuit

Answer 1

The Circuit is :

• Interface between the anesthesia machine and the patient
• Deliver O2 and other gases
• Eliminates carbon dioxide
• CO2 absorbents eliminate CO2 in circle systems
• Other breathing circuits require fresh gas flow (FGF) for elimination of CO2

Question 2

3 essential components of the Basic function breathing circuit.

Answer 2

3 essential components:
low resistance conduit for gas flow
reservoir for gas that meets inspiratory flow demand
expiratory port or valve to vent excess gas

Question 3

Requirements of a Breathing System

Answer 3

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

Question 4

Breathing System Features Desirable

Answer 4

Desirable:
provision to reduce environmental pollution- safe disposal of waste gas
light weight
adequate humidification of inspired gas
adaptability for adults, children and mechanical ventilators
conservation of heat (adequately warm gases)
convenience during use
economy of fresh gas
efficiency during spontaneous as well as controlled ventilation.

Question 5

Considerations: Resistance and Rebreathing.

Answer 5

Resistance- want low resistance
Short tubing, large diameter tubing, avoid sharp bends, caution with valves, minimize connections
Rebreathing- may be beneficial
Cost reduction
Adds humidification/heat to gases
BUT: Do not want rebreathing of CO2
*Higher FGF is associated with less rebreathing in any type of circuit

Question 6

Consideration: 
Dead space
Dry gases/Humidification
Manipulation of inspired content
Bacterial Colonizaton

Answer 6

Dead Space- increases the chance of rebreathing CO2
Dead space ends where the inspiratory and expiratory gas streams diverge
Apparatus dead space can be minimized by separating the inspiratory and expiratory streams as close to the patient as possible
Dry gases/humidification
Manipulation of inspired content
The concentration inspired most closely resembles that delivered from the common gas outlet when rebreathing is minimal or absent
-Bacterial colonization
ASA recommendation“bacterial filter with an efficiency rating of more than 95% for particle sizes of 0.3 μm
Sampling sites for gas analysis.

Question 7

Classification of Anesthetic Delivery Systems

Answer 7

Open- no reservoir; no rebreathing
Semi-Open- reservoir; no rebreathing
Semi-Closed- reservoir; partial rebreathing
Closed- reservoir; complete rebreathing

Question 8

Open System

Answer 8

-No Reservoir
-No Rebreathing
Characterized by:
NO gas reservoir bag
NO valves
NO rebreathing of exhaled gas
2 Types:
1. Insufflation/Blow by
2. Open drop

Question 9

Describe Open Systems and FGF in the elimination of CO2. (Minute Ventilation)

Answer 9

When FGFs are 1 to 1.5 times the minute volume (approximately 10 L/min in an adult), dilution alone is sufficient to remove carbon dioxide. Such systems then behave the same as a non-rebreathing system.

Question 10

Inhalation Induction (steal)

Answer 10

child is already asleep on arrival in the OR
the child is not touched or disturbed
breathing circuit is primed with N2O in O2 and the mask is gently placed near the child’s face and gradually brought closer and closer until it is gently applied to the face.

Question 11

Insufflation examples:

Answer 11

Examples: Blow-by (or insufflation under OR drapes), tent, bronchoscopy port, nasal cannula, “steal” induction

Question 12

Advantages and disadvantages of Insufflation

Answer 12

Advantages: Simplicity
Avoids direct patient contact
No rebreathing of CO2
No reservoir bag or valves 
Disadvantages: 
No ability to assist or control ventilation
May have CO2/ O2 accumulation under drapes
No control of anesthetic depth /FiO2
Environmental pollution

Question 13

What is a Semi Open system? Gives examples

Answer 13

Has reservoir and no rebreathing
SOME Mapleson systems (FGF depends on design )
Circle system (FGF is >Minute Ventilation)

Question 14

What are the components Mapleson Systems

Answer 14

Connection point to a facemark or ETT
Reservoir Tubing
Fresh gas inflow tubing
Expiratory pop-off valve or port

Question 15

Differences in a Mapleson Systems

Answer 15

locations of pop-off valve, fresh gas input, and whether or not a gas reservoir bag is present.
Mapelson systems EXCEPT E also have a reservoir bag

Question 16

When are Mapleson Systems used?

Answer 16

pediatrics
transport of patients
procedural sedation
weaning tracheal intubation (the T-piece)
Pre-02 during out-of-the-OR airway management

Question 17

Best measure of optimal FGF to prevent

Answer 17

rebreathing: etCO2

Question 18

Mapleson Pros

Answer 18

Advantages:

1. simplicity of design
2. ability to change the depth of anesthesia rapidly
3. portability
4. lack of rebreathing of exhaled gases NOTE: ONLY if FGF is adequate

Question 19

Mapleson Cons

Answer 19

Disadvantages:

1. lack of conservation of heat and moisture
2. limited ability to scavenge waste gases
3. high requirements for FGF

Question 20

3 Functional Groups and describe location of FGF inlet and pop-off valve location

Answer 20

Mapleson A:
pop-off located near facemask, FGF located at opposite end

Mapleson B & C:
pop-off and FGF located near facemask

Mapleson D, E, F:
FGF located near facemask and pop-off located at opposite end (OPPOSITE OF MAPLESON A)

Question 21

Rank Mapleson systems in efficiency during controlled ventilation

Answer 21

Controlled: D > B > C > A (mnemonic:DogBitesCanAche)

Question 22

Rank Mapleson systems in efficiency during spontaneous ventilation

Answer 22

Spontaneous: A > D > C > B (mnemonic:AllDogsCanBite)

Question 23

CO2 Rebreathing will depend on:

Answer 23

• Fresh gas inflow rate
• Minute ventilation of patient (MV=TVxRR)
• Mode of ventilation (spont v controlled)
• CO2 production of individual patient (increased with fever, catabolism, etc)
• Respiratory waveform characteristics
  e. g., inspiratory flow, inspiratory and expiratory times, I:E ratio, and expiratory pause.
• Type of ventilation (spontaneous or controlled)

Question 24

Mapleson A “Magill”

Answer 24

MOST EFFICIENT FOR SV
Least efficient for controlled ventilation- requires up to 20L/min
No rebreathing during SV when the fresh-gas flow is at least 1x minute ventilation
-Requires a larger fresh-gas flow to eliminate rebreathing during controlled ventilation
Impractical design in the operating room
proximal location of the overflow valve makes scavenging difficult
difficult to adjust during head and neck surgery
heavy valve can dislodge a small tracheal tube

Question 25

Mapleson B & C

Answer 25

Require high FGF, limiting there use - The ‘B’ circuit has a length of corrugated tubing connecting the rest of the system to the reservoir bag * inefficient * impractical for clinical use for either spontaneous or controlled ventilation - The FGF in both systems needs to be very high in order to prevent rebreathing – the close proximity of the APL valve to the fresh gas port provides the potential for mixing of inspiratory and expiratory gases - The Mapleson C (often referred to as a ‘Water's circuit without absorber’) is used in resuscitation situations and for patient transfer

Question 26

Mapleson D

Answer 26

- Mapleson D is reversed configuration of Mapleson A - Can be used for both spontaneous and controlled ventilation - During spontaneous respiration, FGF = 2-3 x MV - During controlled ventilation, FGF = 1-2 x MV - Most efficient Mapleson during controlled ventilation

Question 27

Bain Circuit

Answer 27

Is a coaxial modification of Mapleson D FGF tubing within the large bore corrugated tubing allows the exhaled gas to warm the inspired gas therefore, preserves heat and humidity Used for controlled OR SV FGF requirements- same as Mapleson D.

Question 28

Bain Circuit advantages

Answer 28

Advantages of the Bain circuit include (1) warming of the fresh gas inflow by the surrounding exhaled gases in the corrugated expiratory tube, (2) conservation of moisture as a result of partial rebreathing, and (3) ease of scavenging waste anesthetic gases from the overflow valve. It is lightweight, easily sterilized, reusable, and useful when access to the patient is limited, such as during head and neck surgery. Disadvantages Hazards of the Bain circuit include unrecognized disconnection or kinking of the inner fresh gas tube. The outer expiratory tube should be transparent to allow inspection of the inner tube. Pethick (1975)  described an indirect test of the Bain inspiratory-limb integrity in which the O2 flush is passed through the circuit for several seconds. If the inspiratory limb is intact, the rapid flow of gas through it exerts a Venturi effect on the expiratory limb, resulting in a slight negative pressure and collapse of the breathing bag. With a leak from the inspiratory limb into the expiratory limb, the pressure in the latter rises, tending to inflate the reservoir bag

Question 29

Bain Circuit Disadvantages

Answer 29

Hazards of the Bain circuit include unrecognized disconnection or kinking of the inner fresh gas tube. The outer expiratory tube should be transparent to allow inspection of the inner tube. Pethick (1975)  described an indirect test of the Bain inspiratory-limb integrity in which the O2 flush is passed through the circuit for several seconds. If the inspiratory limb is intact, the rapid flow of gas through it exerts a Venturi effect on the expiratory limb, resulting in a slight negative pressure and collapse of the breathing bag. With a leak from the inspiratory limb into the expiratory limb, the pressure in the latter rises, tending to inflate the reservoir bag

Question 30

Bain Circuit indirect inspiratory

Answer 30

Pethick (1975) described an indirect test of the Bain inspiratory-limb integrity in which the O2 flush is passed through the circuit for several seconds. If the inspiratory limb is intact, the rapid flow of gas through it exerts a Venturi effect on the expiratory limb, resulting in a slight negative pressure and collapse of the breathing bag. With a leak from the inspiratory limb into the expiratory limb, the pressure in the latter rises, tending to inflate the reservoir bag

Question 31

Mapleson E (T-Piece)

Answer 31

Modification of Ayre’s T-Piece commonly used to administer O2 in ICU and PACU settings NO RESERVOIR BAG (the expiratory limb is the reservoir) AND NO POP-OFF VALVE!!! If SV, FGF = MV x 2-3

Question 32

Mapleson F (Jackson-Rees)

Answer 32

A modification of the Mapleson E Ayre’s T piece with an adjustable pop-off valve at the end of reservoir bag Very popular in pediatrics Allows the application of continuous positive airway pressure or hand ventilation Provides a visual indicator of respiration with the reservoir bag

Question 33

Ambu Bag

Answer 33

Manual resuscitator Critical piece of equipment and part of morning checks Contain non-rebreathing valve & self-inflating bag Capable of delivering high FiO2 with O2 reservoir attached Reservoir self filling w/intake valve CO2 wash-out depends on minute ventilation

Question 34

Mapleson Systems v. Circle Systems similarities

Answer 34

accept a FGF supply the patient with a sufficient volume of gas from a reservoir to satisfy the inspiratory flow and volume requirements eliminate carbon dioxide

Question 35

Mapleson Systems v. Circle Systems differences

Answer 35

bidirectional flow do not use an absorber depend on an appropriate rate of fresh gas inflow to eliminate carbon dioxide

Question 36

The Circle System

Answer 36

Hall mark is unidirectional gas flow via unidirectional valves Components are arranged in a circle Can be used as a semi-open, semi-closed, or closed system Depends on the adjustment of the APL valve Depends on FGF rate Prevents re-breathing of CO2 by chemical neutralization Allows re-breathing of other exhaled gases

Question 37

What are the 7 components the circle system

Answer 37

Characterized by 7 components FGF source Inspiratory and expiratory unidirectional valves Inspiratory and expiratory limbs/ corrugated tubing Y-piece connector Adjustable pressure-limiting valve (APL valve, over-flow valve, or Pop-off valve ) Reservoir bag CO2 absorber

Question 38

FGF preferred location

Answer 38

common gas outlet gas inflow incorporated with the inspiratory unidirectional valve or the carbon dioxide–absorbent canister housing preferred fresh gas inflow site is between the carbon dioxide absorber and the inspiratory valve.

Question 39

Unidirectional Valves

Answer 39

``` Gas flowing into the valve raises the disc from its seat, then passes through the valve. Reversing the gas flow causes the disc to contact its seat, stopping further retrograde flow. The guide (cage) prevents lateral or vertical displacement of the disc. The transparent dome allows observation of disc movement. ```

Question 40

Reservoir Bag

Answer 40

Made of neoprene or rubber Functions: 1) they serve as a reservoir for anesthetic gases or O2 optimally sized bag can hold a volume that exceeds the patient’s inspiratory capacity (vary 0.5 L to 6 L) 3L most common adult size bag 2) visual assessment of SV & rough estimate of the volume Visual assessment affected by FGF 3) means for manual ventilation

Question 41

APL Valve

Answer 41

AKA: pressure relief, pop-off, safety-relief valve Purpose: permits PEEP during SV or allows for pressure- limited controlled respiration Releases gases to scavenge or atmosphere exhaust port User-adjustable: clockwise – closes valve & increases pressure within system Provides control of pressure in system – pressure gauge on absorber Spontaneous Respiration: valve fully open close partially only if reservoir bag collapses Assisted Ventilation: valve partially open bag squeezed on inspiration careful & frequent adjustments necessary Mechanical Ventilation- APL left open

Question 42

Breathing Tubes

Answer 42

Large bore, non rigid corrugated tubing Clear plastic (historically rubber was used) 22 mm female fitting w/machine Patient end – T piece 22 mm male, 15 mm female coaxial fitting Functions:  Flexible, low resistance, lightweight connection  Reservoir

Question 43

Dead Space in Circle System

Answer 43

If the unidirectional valves are working properly, the only dead space in the circle system is the distal limb of the Y-connector and any tube or mask between it and the patient’s airway.

Question 44

Semi-open Circle System

Answer 44

No re-breathing occurs; very high flow of FGFs (10-15L/min) are used and eliminates rebreathing of gases No conservation of wastes gases and heat APL valve is open all the way or ventilator in use

Question 45

Semi-closed Circle System

Answer 45

Most commonly used breathing system in U.S. practice 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 is less than minute ventilation Conserves some heat and gases APL valve is partially closed and adjusted as needed; or ventilator is in use.

Question 46

Closed Circle System

Answer 46

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

Question 47

Advantages of the Circle System

Answer 47

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

Question 48

Disadvantages of Circle System

Answer 48

Complex design Has at least 10 connections This sets the stage for potential leaks, obstruction, or disconnection A third of malpractice claims are related to disconnects or misconnects of the circuit Potential of malfunctioning valves Stuck open= rebreathing Stuck closed= airway obstruction Increased resistance to breathing (above Mapleson) Less portable and convenient than the Mapleson systems due to its bulkiness Increased dead space BUT dead space ends at the Y piece

Question 49

Increased INSPIRED CO2

Answer 49

CO2 Absorbent Exhaustion Temporary fix: increase FGF above minute ventilation Incompetent Unidirectional Valve: If increasing FGF does not help then it is likely a stuck valve

Question 50

Circle System Check

Answer 50

Leak Test 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, open APL valve and ensure pressure decreases This test does not assess integrity of unidirectional valves Flow Test Attach breathing bag to Y- piece, turn on ventilator, and assess integrity of unidirectional valves

Question 51

Circuit Issues

Answer 51

``` misconnections or disconnections leaks valve failure carbon dioxide absorber defect bacterial filter occlusion ```

Question 52

Example of Which circle system has very low FGF and closed APL valve

Answer 52

Closed system

Question 53

Example of Which circle system has FGF < less than minute ventilation

Answer 53

Semi-closed

Question 54

Example of Which circle system has FGF greater > than minute ventilation and mapleson circuit.

Answer 54

Semi Open