190708_ Delivery Systems Flashcards
(47 cards)
breathing circuit
•Interface between the anesthesia machine and the patient
•Deliver O2 and other gases (FGF?)
•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:
- low resistance conduit for gas flow
- reservoir for gas that meets inspiratory flow demand
- expiratory port or valve to vent excess gas
***Recycled gas - warms, humidifies, decrease $
***Alveolar gas + Dead space + FGF = ?
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:
economy of fresh gas
conservation of heat (adequately warm gases)
adequate humidification of inspired gas
light weight
convenience during use
efficiency during spontaneous as well as controlled ventilation
adaptability for adults, children and mechanical ventilators
provision to reduce environmental pollution- safe disposal of waste gas
Breathing System Considerations
•Resistance- want low resistance
- Short tubing, large diameter tubing (22mm int. dia.), avoid sharp bends, caution with valves, minimize connections (more connections = more potential leaks)
***Correlation = turbulent flow for better mixing of gases while minimizing resistance
•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~but….increases $
•Dead Space- increases the chance of rebreathing CO2 - - Dead space ends where the inspiratory and expiratory gas streams diverge (Y connector)
– 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
Classification - Open system
no reservoir; no rebreathing (no valves)
Insufflation (blow by) Open Drop (Simple Face Mask, Nasal Cannula)
Classification - Semi-Open
reservoir; no rebreathing
Mapleton circuit (FGF dependent on design) circle system (FGF > MV)
Classification - Semi-Closed
reservoir; partial rebreathing
circle system (FGF < MV)
Classification - Closed
reservoir; complete rebreathing
circle system w/ very low FGF and APL valve closed
Insufflation
•Examples: Blow-by (or insufflation under OR drapes), tent, bronchoscopy port, nasal cannula, “steal” induction •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
- elevated fire risk
Inhalation Induction (steal)
***open at first
• 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 (semi-opem)
Mapleson Systems
• Mapleson systems components
- connection point to a facemask or ETT (15mm)
- reservoir tubing (22mm?)
- fresh gas inflow tubing (22mm?)
- expiratory pop-off valve or port
• Differences: locations of pop-off valve, fresh gas input, and whether or not a gas reservoir bag is present
- Note: all Mapelson systems EXCEPT E also have a reservoir bag
• When are these 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
• Reservoir bag inflation requires FGF, unlike ambu bag
Mapleson Pros
•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
- lack of conservation of heat and moisture
- limited ability to scavenge waste gases
- high requirements for FGF
Mapleson A
pop-off located near facemask
FGF located at opposite end
Mapleson B & C
pop-off and FGF located near facemask
***very wasteful of FGF, not really used
Mapleson D, E, F
FGF located near facemask
popoff located at opposite end
(OPPOSITE OF MAPLESON A)
Efficiency: Controlled
D&F > B > C > A
mnemonic: Dog Bites Can Ache
Efficiency: Spontaneous
A > D&F > C > B
mnemonic: All Dogs Can Bite
CO2 Rebreathing will depend on:
•Fresh gas inflow rate
•Minute ventilation of patient
•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 their 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
- **increased RR = decreased EEP = increased RB
- **decreased IT = increased ET = increased RB?
**Conditions that increase carbon dioxide production (e.g., fever, catabolic state, or malignant hyperthermia) must be met with a proportional increase in fresh-gas flow and ventilation.
Bain system or circuit
consists of inner tubing that delivers FGF directly to the patient who then exhales down the outer corrugated tubing to the reservoir bag and APL valve.
•Is a coaxial 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 SV
•FGF requirements
- same as Mapleson D.
•Disadvantage
- Potential for inner tube leaks, kinking or disconnection
- Disconnection of the inner tubing can result in increased dead space leading to massive rebreathing so tests must be performed to check for a disconnection
- Pethic test = + leak and collapses the 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 •NO POP-OFF VALVE!!! •If SV, FGF = MV x 2-3
***see PP slide 27 for animation
