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Flashcards in Delivery Systems Deck (39):

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 

  1. economy of FG
  2. conservation of heat 
  3. adequate humidification
  4. lightweight
  5. convenient to use
  6. efficient for spontaneous and controlled ventilation
  7. adaptable for adults, peds, neonates
  8. 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)



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

  1. open
  2. semi-open
  3. semi-closed
  4. closed


Open system

  1. Two types
    1. insufflation(cannula)/Blow by
    2. open drop
  2. Characterized by:
    1. no gas reservoir bag
    2. no valves
    3. 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

  1. simplicity
  2. avoids direct patient contact
  3. no rebreathing of CO2
  4. no reservoir bag or valves


open system disadvantages

  1. no ability to assist or control ventilation
  2. may have CO2/O2 accumulation under drapes
  3. no control of anesthetic depth /FiO2
  4. environmental pollution


open drop method

adv vs disadv


  • simplicity
  • low cost
  • portable


  • 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

  1. facemask or ETT
  2. pop-off valve (APL valve)
  3. Reservoir tubing
  4. fresh gas inlet
  5. reservoir bag
    1. 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:


  1. FGF rate
  2. minute ventilation of patient
  3. type of ventilation (spontaneous or controlled)


Mapleson D

  1. Reverse of A
  2. can be used for both SV and CV
  3. During SV: FGF = 2-3 x MV
  4. 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
  • 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

  1. simple components
  2. lightweight
  3. can provide PPV
  4. low resistance
  5. portable
  6. more predictable anesthetic concentration and decreased room polution compared to open systems


disadvantages of Mapleson System

  1. Requires calculation of FGF
  2. Anesthetic gases diluted by FGF, can be variable, but better than open system
  3. if FGF not maintained, CO2 buildup possible from rebreathing
  4. minimal rebreathing of other gasses, poor conservation of heat and humidity
  5. FGF costly
  6. requires special assembly and function is complex.


circle system

  1. can be used as semi-open, semi-closed, or closed system
    1. depends on adjustment of APL valve
    2. and FGF rate
  2. prevents rebreathing of CO2 with scrubber
  3. allows rebreathing of other gases


standard breathing circuit = 22mm


7 components of Circle system

  1. FGF source
  2. inspiratory and expiratory unidirectional valves
  3. inspiratory and expiratory limbs/corrugated tubing (22 mm)
  4. Y- piece connector
  5. Adjustable pressure-limiting valve (APL)
  6. reservoir bag
  7. CO2 scrubber



4 rules of circle system:

  1. a unidirectional valve must be located between pt and reservoir bag on both I and E limbs
  2. FGF inflow cannot enter circuit btw Expiratory valve and pt.  Should be btw absorber and inspiratory valve
  3. APL cannot be located btw the pt and the inspiratory valve
  4. breathing bag should be on expiratory limb
    1. to decreas resistance to exhalation
    2. compression of bag will vent alveolar gas through APL, conserving absorbent


unidirectional valves

  1. gas flowing into the valve raises the disc from its seat, then passes through the valve
  2. reversing the gas flow causes the disc to contact its seat, stopping further backward flow
  3. the guide (cage) prevents lateral or vertical displacement of the disc
  4. 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



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



O2 consumption = 10 x kg¾


advantages of circle system

  1. relative stability of concentration of inspired gases
  2. conservation of moisture and heat
  3. can be used for closed-system anesthesia
  4. can be used with low flows with no rebreathing of CO2
  5. economy of anesthetics and gases
  6. can scavage waste gases
  7. prevention of OR polution


disadvantages of circle system

  1. complex design
  2. at least 10 connection
    • potential for leaks, obstruction, disconnection
    • 1/3 malpractice claims are related to disconnects or miscconects of the circuit
  3. potential of malfunctioning valves
  4. increased resistance to breathing
  5. less portable and convenient than the mapleson systems due to bulkiness


Circle System (circuit) Check

(done between every case)

  1. 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
  2. Flow Test - assesses integrity of unidirectional valves
    • attach breathing bag to Y-piece, turn on ventilator and assess that the valves open/close appropriately