Delivery Systems Flashcards
What is the function of the anesthetic breathing system?
to deliver oxygen and +/- anesthetic gases to pt and eliminate CO2
4 Essential Requirements of Breathing System
1) deliver gas to alveoli in same concentration as set (and in shortest time)
2) Effectively eliminate CO2
3) minimal apparatus dead space
4) low resistance
8 Desirable requirements of breathing system
1) economy of fresh gas
2) conservation of heat
3) humidification of inspired gas
4) light weight
5) convenience during use
6) efficiency during spont and controlled ventilation
7) adaptability for kids/adults and mech ventilators
8) provision to < environmental pollution
How do we get Low resistance
short tubing large diameter tubing avoid sharp bends caution w/ valves minimize connections
Benefits of Rebreathing (2)
- cost reduction (O2 and anesthetic gas in exhaled air)
- adds humidification/heat to gases
Dead space:
location and effect on rebreathing
where inspiratory and expiratory streams diverge
dead space ^s chance of rebreathing CO2
Open System characterized by (3)
1) No gas reservoir bag
2) No valves
3) No rebreathing of exhaled gas
2 Types of Open Systems
1) Insufflation/ Blow By
- NC, head drape, steal induction, bronchoscopy port
2) Open Drop
- Schimmelbusch Mask
Insufflation Advantages (4)
simplicity
no direct pt contact
no rebreathing of CO2
no reservoir bag or valves
Insufflation Disadvantages (4)
- can’t control vent or assist with
- CO2/O2 accumulation under drapes
- No control of Anesth depth or FIO2
- Environmental pollution
Open Drop Advantages (3)
1) Simplicity
2) low cost apparatus
3) portable
Open Drop Disadvantages (5)
1) poor control of inspired anesthetic concentration
2) CO2 accumulate under mask
3) Predisposes to hypoxia risk
4) spont vent only (no controlled vent)
5) OR pollution, helalth care provider risk
(5) characteristics of Semi-Open Systems
1) facemask or ETT
2) APL valve (or pop-off)
3) Reservoir tubing
4) Fresh gas inlet
5) Reservoir Bag
Mapleson A
FG inlet by reservoir bag,
tubing,
APL valve by facemask
In Group 1
Mapleson D
Reservoir bag with APL valve by it, tubing, and FR inlet by facemask
In Group 3
Mapleson B
Reservoir Bag, tubing, FG inlet and APL valve by facemask
In Group 2
Mapleson C
Reservoir Bag, FG inlet, and APL Valve by facemask
In Group 2
CO2 Rebreathing depends on (3)
1) FG inflow rate
2) Min Ventilation of pt
3) Type of ventilation
Mapleson D FGF
Spont Respiration: FGF= 2-3 x MV
Controlled Respiration:
FGF= 1-2 x MV
*most efficient during controlled vent
Mapleson E
modification of Ayre’s T piece
no reservoir bag
no pop-off valve
for spont: FGF = MV x 2-3
Jackson-Rees
Modification of Mapleson E Ayre’s T piece
- pop-off valve @ end of reservoir bag
- popular in peds
Bain Circuit
Coaxial modification of Mapleson D
FGF (same as Mapleson D)
SV: 2-3 x MV . CV: 1-2 x MV
Bain Circuit
Advantages
Disadvantages
Good: exhaled gas warms the inspired gas preserves heat and humidity Bad: Potential for leaks, kinking, or disconnection of inner tube
Ambu Bag
Modified Mapleson A w/ non-breathing valve
- can deliver high FiO2
- reservoir self filling (w/ intake valve)
- Requires high FGF
- CO2 washout depend on MV
Advantages of Mapleson
1) simple components
2) lightweight
3) can give PPV
4) low resistance
5) portable
6) more predictable anesthetic concentration and less room pollution compared to open
Disadvantages of Mapleson 6
1) Requires calculation of FGF (varies w/ type of circuit and mode of ventilation)
2) Control of anesthetic depth is variable (anesth gas diluted w/ >FGF)
3) CO2 buildup and rebreathing (if FGF not maintained)
4) Minimal rebreathing of other gases (= poor conservation of heat/humidity)
5) FGF costly
6) Requires special assembly and fx is complex
Circle System Basics
Components arranged in a circle
Can be used as semi-open, semi-closed, or closed system
-depends on APL valve and FGF
Prevents rebreathing of CO2 by chemical neutralization
Allows rebreathing of other exhaled gases
Circle System 7 Components
1) Fresh Gas Flow source
2) Inspiratory / Expiratory unidirectional valves
3) Inspiratory / Expiratory limbs (corrugated tubing)
4) Y piece connector
5) Adjustable pressure limiting (APL) valve
6) Reservoir Bag (3L for adults)
7) CO2 absorber
Circle System Gas Flow:
Inspiration
Gas goes from reservoir bag ->
top of CO2 absorber & out bottom, mixes with FGF from common gas inlet ->
inhalation check valve/tubing -> pt
Circle System Gas Flow:
Expiration
Gas flow from pt -> expiration limb ->
reservoir bag & out APL valve
Circle System Rules #1
-Unidirectional valve must be located b/w patient & reservoir bag on insp and exp limbs of circuit
Circle System Rules #2
FGF inflow can’t enter circuit b/w exp valve & pt
-would bypass pt during exhalation & be wasted
should be b/w absorber & insp valve
If it was b/w exp valve and absorber = diluted by recirculating gas and also:
-anesth absorbed by granules & slow induction
-aneth gas released by granules & slow emergence
Circle System Rules #3
APL valve can’t be b/w pt and insp valve
Should (?not) be right before CO2 absorber to conserve absorption capacity & minimize venting of FGF
Circle System Rules #4
Breathing bag located in the expiratory limb
-decreases resistance to exhalation
Bag compression during controlled ventilation vents alveolar gas through APL valve (= conserves absorbent_
Unidirectional Valves
Gas flows in and raises disc from its seat
reversing the flow = disc contacts seat and stops further retrograde flow
Guide/cage prevents displacement of disc
Transparent dome allows observation of disc mvmt
Reservoir bag
made of neoprene or rubber
neck: 22mm female fitting
tail = end opposite neck
Reservoir Bag Functions 5
- Accumulations of gas during exhalation
- Assist/control ventilation
- Visual/tactile monitor to observe spontaneous respirations
- Protects against excessive pressure
- Reservoir of gas
Breathing Tube
- Large bore, non-rigid corrugated tubing
- rubber or clear plastic tubing
- 22mm female fitting w/ machine
- Pt end T piece w/ 22mm male and 15mm female coaxial fitting
Breathing Tube Functions
Flexible, low resistance lightweight connection
Reservoir
APL Valve
aka Pressure Relief, Pop-off, Safety-relief valve
- Releases gases to scavenge/atmosphere exhaust port
- user adjustable: clockwise =close (>P in system)
- provide control of pressure in system
APL Valve
Spontaneous vs Assisted vs Mechanical Ventilation
Spontaneous Resp:
-valve fully open
-close partially only if reservoir bag collapses
Assisted Vent:
-Valve partially open
-bag squeezed on inspiration
-Careful / frequent adjustments
Mechanical Vent:
-valve closed (if no switch)Dead Space in Circle System
If unidirectional valves working properly, only dead space is b/w Y piece and pt
Semi-Open Circle System
- Not used often, occasionally for sedation
- No rebreathing occurs (high FGFs 10-15L/min)
- No conservation of waste gases and heat
- APL valve open all the way or vent in use
Semi-Closed Circle System
- Most commonly used in US
- Allow for some rebreathing of agents & exhaled gases
- Uses relatively low flow rates (1-3 L/min)
- Conserves some heat/gases
- APL valve partially closed (or vent in use)
Closed Circle System
not used that often anymore
- Used in long surgical cases and 3rd world country
- Inflow gas exactly matches metabolic needs / O2 consumption of pt using very low flows (200ml/min)
- Total rebreathing of all exhaled gases after absorption of CO2
- APL valve closed or vent in use
O2 Consumption (VO2)
10 x Kg^(3/4)
Advantages
Circle System 7
- Relative stability of concentration of inspired gases
- Conservation of moisture/heat
- Can be used for closed-system anesthesia
- Can be used w/ low flows w/ no rebreathing of CO2
- Economy of anesthetics and gases
- Can scavenge waste gases
- Prevention of OR pollution
Disadvantages 5
Circle System
1/3 of malpractice claims r/t disconnects/misconnects of the circuit
- Complex design
- At least 10 connections
- potential leaks, obstructions, disconnections
- Potential of malfunctioning valves
- Increased resistance to breathing
- Less portable & convenient than Mapleson
Circle System Check
Leak Test:
Gas flows to 0, occlude Y piece, close APL valve, pressurize circuit to 30 cm H2O w/ O2 flush,
-ensure pressure holds 10sec
-listen for sustained pressure alarm
Open APL valve and ensure pressure decreases
Circle System Check
Flow Test
Attach breathing bag to Y piece
Turn on ventilator
Assess integrity of unidirectional valves
