Delivery Systems Flashcards
Basic function of a breathing circuit
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
3 essential components of the Basic function breathing circuit.
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
Requirements of a Breathing System
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
Breathing System Features Desirable
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.
Considerations: Resistance and Rebreathing.
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
Consideration: Dead space Dry gases/Humidification Manipulation of inspired content Bacterial Colonizaton
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.
Classification of Anesthetic Delivery Systems
Open- no reservoir; no rebreathing
Semi-Open- reservoir; no rebreathing
Semi-Closed- reservoir; partial rebreathing
Closed- reservoir; complete rebreathing
Open System
-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
Describe Open Systems and FGF in the elimination of CO2. (Minute Ventilation)
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.
Inhalation Induction (steal)
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.
Insufflation examples:
Examples: Blow-by (or insufflation under OR drapes), tent, bronchoscopy port, nasal cannula, “steal” induction
Advantages and disadvantages of Insufflation
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
What is a Semi Open system? Gives examples
Has reservoir and no rebreathing
SOME Mapleson systems (FGF depends on design )
Circle system (FGF is >Minute Ventilation)
What are the components Mapleson Systems
Connection point to a facemark or ETT
Reservoir Tubing
Fresh gas inflow tubing
Expiratory pop-off valve or port
Differences in a Mapleson Systems
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
When are Mapleson Systems used?
pediatrics
transport of patients
procedural sedation
weaning tracheal intubation (the T-piece)
Pre-02 during out-of-the-OR airway management
Best measure of optimal FGF to prevent
rebreathing: etCO2
Mapleson Pros
Advantages:
- simplicity of design
- ability to change the depth of anesthesia rapidly
- portability
- lack of rebreathing of exhaled gases NOTE: ONLY if FGF is adequate
Mapleson Cons
Disadvantages:
- lack of conservation of heat and moisture
- limited ability to scavenge waste gases
- high requirements for FGF
3 Functional Groups and describe location of FGF inlet and pop-off valve location
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)
Rank Mapleson systems in efficiency during controlled ventilation
Controlled: D > B > C > A (mnemonic:DogBitesCanAche)
Rank Mapleson systems in efficiency during spontaneous ventilation
Spontaneous: A > D > C > B (mnemonic:AllDogsCanBite)
CO2 Rebreathing will depend on:
- 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)
Mapleson A “Magill”
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
Mapleson B & C
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
Mapleson D
- 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
Bain Circuit
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.
Bain Circuit advantages
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
Bain Circuit 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
Bain Circuit indirect inspiratory
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
Mapleson E (T-Piece)
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
Mapleson F (Jackson-Rees)
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
Ambu Bag
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
Mapleson Systems v. Circle Systems similarities
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
Mapleson Systems v. Circle Systems differences
bidirectional flow
do not use an absorber
depend on an appropriate rate of fresh gas inflow to eliminate carbon dioxide
The Circle System
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
What are the 7 components the circle system
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
FGF preferred location
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.
Unidirectional Valves
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.
Reservoir Bag
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
APL Valve
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
Breathing Tubes
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
Dead Space in Circle System
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.
Semi-open Circle System
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
Semi-closed Circle System
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.
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
Advantages of the Circle System
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
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
Increased INSPIRED CO2
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
Circle System Check
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
Circuit Issues
misconnections or disconnections leaks valve failure carbon dioxide absorber defect bacterial filter occlusion
Example of Which circle system has very low FGF and closed APL valve
Closed system
Example of Which circle system has FGF < less than minute ventilation
Semi-closed
Example of Which circle system has FGF greater > than minute ventilation and mapleson circuit.
Semi Open
