Delivery Systems Flashcards
Function of anesthetic breathing systems
to deliver O2 and anesthetic gases to patient and to eliminate CO2
*CO2 eliminated by FGF washout or CO2 scrubber
ESSENTIAL requirements of a breathing system
- deliver the gases form teh machine or device to the alveoli in the same concentration as set and in teh shortest possible time
- effectively eliminate CO2
- have minimal apparatus dead space
- have low resistance
DESIRABLE Requirements of a breathing system
- economy of FG
- conservation of heat
- adequate humidification
- lightweight
- convenient to use
- efficient for spontaneous and controlled ventilation
- adaptable for adults, peds, neonates
- reduce environmental polution
CONSIDERATIONS of a breathing system
- Reistance- want low resistance
- rebreathing- may be beneficial
- cost reduction/ adds humidication (NOT CO2)
- dead space- increases the chance of rebreathing CO2
- minimized by seperating the insiratory/expriatory streams as close to the pt as possible
- dry gases/humidfication
- manipulation of inspired content
- once we start rebreathing, change in concentration from what’s set on dial
- bacterial colonization
resistance in tubing
such as sharp bends, valves, lots of connections
*want short, large diameter tubing to keep flow laminate (smooth)
Rebreathing
Can be beneficial to save gases and maintain heat and moisture in system
*Do not want rebreathing of CO2
**Associated with less rebreathing in any type of circuit
dead space
deadspace ends where the inspiratory and expiratory streams diverge. Can be minimized by separating I and E as close to pt as possible
*more deadspace increases the chance of rebreathing CO2
Classifications of anesthetic delivery systems
- open
- semi-open
- semi-closed
- closed
Open system
- Two types
- insufflation(cannula)/Blow by
- open drop
- Characterized by:
- no gas reservoir bag
- no valves
- no rebreathing of exhaled gas
insufflation “steal” induction
when you hold a mask with gasses in front of pt’s face and as they start to feel affects, move it closer until it is on face.
Good for pediatrics who freak out
*lots of pollution
open system advantages
- simplicity
- avoids direct patient contact
- no rebreathing of CO2
- no reservoir bag or valves
open system disadvantages
- no ability to assist or control ventilation
- may have CO2/O2 accumulation under drapes
- no control of anesthetic depth /FiO2
- environmental pollution
open drop method
adv vs disadv
Advantages:
- simplicity
- low cost
- portable
Disadvantages
- poor control of inspired concentration of anesthetics
- accumulation of CO2 under mask
- hypoxia risk
- spontaneous ventilation only
- OR pollution
5 components of semi-open systems
- facemask or ETT
- pop-off valve (APL valve)
- Reservoir tubing
- fresh gas inlet
- reservoir bag
- 3L for adults, 2L for peds, 1L for neonates
Group 1, Mapleson A
Pop-off located near the facemask, FGF located at opposite end
*more effective for spontaneous b/c pop off valve is close to pt
Group 2, Mapleson B & C
with pop-off and FGF near facemask
*more effective for spontaneous b/c pop off valve is close to pt
Group 3, Mapleson D, E, F
FGF located near facemask and pop-off at opposite end
(opposite of Mapleson A)
With Mapleson’s, CO2 rebreathing will depend on:
- FGF rate
- minute ventilation of patient
- type of ventilation (spontaneous or controlled)
Mapleson D
- Reverse of A
- can be used for both SV and CV
- During SV: FGF = 2-3 x MV
- During CV: FGF = 1-2 x MV
*Most efficient Mapleson during controlled ventilation
Minute volume
Tidal volume * RR
*normal TV about 7 ml/kg
Mapleson E
- AKA T-piece
- No reservoir bag and NO POP OFF VALVE
- modification of T-piece commonly used in ICU/PACU
Maplesone F (Jackson-Rees)
- modification of Maplesome E (T-piece) with adjustable pop-off valve at the end of reservior bag
- little resistance/dead space
- very popular in peds
- good for controlled ventilation during transport of intubated pts
Bain circuit
- Modification of Mapleson D, FGF tubing within the large bore corrugated tubing
- allows the exhaled gas to warm the inspired gas
- preserves heat and humidity
- allows the exhaled gas to warm the inspired gas
- Used for controlled or spontaneous ventilation
- FGF requirements same as M-D
- SV: 2-3 x MV
- CV: 1-2 x MV
Ambu Bag
- Modification of Mapleson A with non-rebreathing valve
- capable of delivering high FiO2
- respivior self filling with intake valve
- requires high fresh gas flow
- CO2 wash-out depends on min ventilation
advantages of Mapleson system
- simple components
- lightweight
- can provide PPV
- low resistance
- portable
- more predictable anesthetic concentration and decreased room polution compared to open systems
disadvantages of Mapleson System
- Requires calculation of FGF
- Anesthetic gases diluted by FGF, can be variable, but better than open system
- if FGF not maintained, CO2 buildup possible from rebreathing
- minimal rebreathing of other gasses, poor conservation of heat and humidity
- FGF costly
- requires special assembly and function is complex.
circle system
- can be used as semi-open, semi-closed, or closed system
- depends on adjustment of APL valve
- and FGF rate
- prevents rebreathing of CO2 with scrubber
- allows rebreathing of other gases
standard breathing circuit = 22mm
7 components of Circle system
- FGF source
- inspiratory and expiratory unidirectional valves
- inspiratory and expiratory limbs/corrugated tubing (22 mm)
- Y- piece connector
- Adjustable pressure-limiting valve (APL)
- reservoir bag
- CO2 scrubber
4 rules of circle system:
- a unidirectional valve must be located between pt and reservoir bag on both I and E limbs
- FGF inflow cannot enter circuit btw Expiratory valve and pt. Should be btw absorber and inspiratory valve
- APL cannot be located btw the pt and the inspiratory valve
- breathing bag should be on expiratory limb
- to decreas resistance to exhalation
- compression of bag will vent alveolar gas through APL, conserving absorbent
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 backward flow
- the guide (cage) prevents lateral or vertical displacement of the disc
- transparent dome allows observation of disc movement.
breathing tubes
- large bore, non-rigid corruagted tubing (doesn’t kink easily)
- rubber or clear plastic
- 22mm female fitting wtih machine
- pt end: T-Piece 22mm Male, 15 mm female coaxial fitting
- functions:
- flexible, low resistance, lightweight connection
- reservior
APL valve:
during SV, AV, and CV
- spontaneous ventilation
- valve fully open (1-3cm H20 pressure within the system- will not reach 0 bc of the reistance of valve)
- close partially only if reservoir bag collapses
- assisted ventilation
- valve partially open (APL 20cmH20- anything over will go to scavanging system)
- bag squeezed on inspiration
- careful and frequent adjustments necessary
- mechanical ventilation
- valve closed (if machine doesnt have switch)
- APL closed- >75cm H20 pressure within the system
- valve closed (if machine doesnt have switch)
Semi-open circle system
- not often used, occasionally for sedation (mask over face to increase FiO2)
- no rebreathing occurs
- very high FGF 10-15 L/min are used to eliminate rebreathing
- no conservation of wastes
- APL valve is open all the way or ventilator in use
Semi-closed Circle system
- most commonly used system in US
- allows for some rebreathing of agents (minus CO2)
- uses low flow rates (1-3L/min)
- conserves some heat and gases
- APL partially closed and adjusted as needed or ventilator in use
closed circle system
- used often in long surgical cases and third world countries
- inflow gas exactly matches metabolic needs
- 200ml O2/min
- low flow can make it take longer for gases to get to patient
- total rebreathing after CO2 scrubbed
- APL valve is closed or ventilator in use
VO2
O2 consumption = 10 x kg¾
advantages of circle system
- relative stability of concentration of inspired gases
- conservation of moisture and heat
- can be used for closed-system anesthesia
- can be used with low flows with no rebreathing of CO2
- economy of anesthetics and gases
- can scavage waste gases
- prevention of OR polution
disadvantages of circle system
- complex design
- at least 10 connection
- potential for leaks, obstruction, disconnection
- 1/3 malpractice claims are related to disconnects or miscconects of the circuit
- potential of malfunctioning valves
- increased resistance to breathing
- less portable and convenient than the mapleson systems due to bulkiness
Circle System (circuit) Check
(done between every case)
-
Leak Test- tests integrety of the system
- set gas flows to zero, occlude othe Y-piece, close the APL valve, pressure the circuit to 30cmH2O using the O2 flush valve.
- ensure pressure holds for 10 seconds, listen for sustaned pressure alarm, open APL vavle and ensure pressure decreases
- set gas flows to zero, occlude othe Y-piece, close the APL valve, pressure the circuit to 30cmH2O using the O2 flush valve.
-
Flow Test - assesses integrity of unidirectional valves
- attach breathing bag to Y-piece, turn on ventilator and assess that the valves open/close appropriately
