Anesthesia Delivery Systems Flashcards
Describe basic functions of breathing circuit
- Interface b/w anesthesia machine and patient
- Deliver o2 and other gases( fresh gas flow)
- Eliminate CO2
- CO2 absorbent in circle system
- Other breathing circuits require FGF for elimination of CO2
- Other peripheral components: humidifiers, spirometers, pressure gauges, filters, gas analyzers, PEEP devices, waste gas scavengers, mixing and circulating devices.
Needs 3 components:
- Low resistance conduit for gas flow
- Resevoir for gas that meets inspiratory flow demand
- Expiratory port or valve to vent excess gas
DIE RVR
What are the essential components of a breathign circuit?
- Low resistance conduit for gas flow
- Resevoir for gas that meets inspiratory flow demand
- Expiratory port or valve to vent excess gas
What are the requirements of a breathing system?
- Deliver gases from machine or device to alveoli in same concentration as set in shortest time possible
- Effectively eliminate carbon dioxide
- Minimal apparatus dead space
- Low resistance to gas flow
- Rapid adjustment in gas concentration and flow rate
(MEDAL)
What are some desirable breathing system features?
- Economy of fresh gas
- Conservation of heat (adequately warmed 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
What are some considerations for a breathing circuit?
- LOW resistance
- Short tubing, large diameter, no sharp bends, caution with valves, minimize connections (1CM/H2O/1M of tubing)
- Rebreathing- might be beneficial
- Cost reduction
- Adds humidification/heat
- Do not want rebreathing of CO2! HIGHER FGF IS ASSOCIATED WITH LESS REBREATHING IN ANY TYPE OF CIRCUIT
- Dead spacE- increases chance of rebreathing CO2.
- Dead space ends at Y connector.
- Dead space minimized by separating inspiratory and expiratory streams as close to patient as possible
- Dry gases/humidification
- Manipulation of inspired content
- Concentration inspired resembles what is delivered from common gas outlet when rebreathing is minimal or absent
- Bacterial colonization
(Really Rancid Dead Dry Man Bacteria)
What are ASA recommendations for infection control?
Bacteria filter with an efficiency rating of more than 95% for particle sizes of 0.3 micrometers should be routinely placed in anesthesia circuit
What are HMEs?
Heat and moisture exchangers are filters placed on Y-piece and serve as inspiratory and expiratory barrier. Standard filters placed on expiratory limb
What else can a breathing circuit incorporate in addition to filters?
- Spirometer (measure ventilation)
- Humidifier (warmth nd moisture)
- Sampling sites for gas analysis
- Scavenging devices to control atmospheric contamination
What are classifications of anesthetic delivery systems?
Classification depends on whether reservoir is used and whether rebreathing occurs
- Open- no reservoir; no rebreathing
- Semi-open- reservoir;no rebreathing
- Semi-closed- reservoir; partial rebreathing
- Closed- reservoir; complete rebreathing
What are is an open system and what are some examples?
NO rebreathing and NO resevoir
Insufflation
Simple face mask
NC
Open drop
What is a semi open system and what are some examples?
NO rebreathing and YES to resevoir
Examples:
Mapleson (FGF dependent on design)
Circle system (FGF > MV)
Nonrebreather
What is a semi closed system and what are some examples?
YES (partial) rebreathing, YES resevoir
Circle system (FGF< MV)
What is a closed system and what is an example?
COMPLETE rebreathing and YES to resevoir
Circle system with very low FGF and APL closed
What are open systems characterized by?
NO gas resevoir bag
NO valves
NO rebreathing of exhaled gas
- When FGF is 1-1.5 x the MV (about 10L/min in adult), dilution alone is sufficient to remove CO2. At this point, these systems behave the same as nonrebreathing system
Describe a steal induction
- Inhalation induction where child is not touched or disturbed
- Mask is hovered over the child (open system) and once child is asleep, then the mask is sealed to the face (semi-open)
Adequate monitoring is institued ASAP, child then transferred to OR table
- Technique is atraumatic and avoids exposing child to strange OR sounds/surroundings while awke
Describe insufflation method and its advantages and disadvantages.
Examples:
- Blow-by (insufflation under OR drapes)
- Tent
- Bronch port
- NC
- Steal induction
Advantages:
- Simplicity
- avoids direct patient contact
- no rebreathing CO2
- No reservoid 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 determines if system is semi-open, semi closed or closed?
FGF!
IF FGF >MV, then it is semi-open
If FGF < MV, then semi-closed
If very low FGF and APL closed- closed
Describe the mapleson system components, how they might be difference, and when it might be used.
Components
- Connection point to facemask or ETT
- Reservoir tubing
- FGF inflow tubing
- Expiratory pop off valve or port
Differences: location of pop off valve, fresh gas input and whether or not a gas resevoir is present
- ALL mapelson systems have resevoir except E
When used:
- Pediatrics
- Transport of patients
- procedural sedation
- weaning tracheal intrubation (t-piece)
- pre o2 during out of OR airway management
Best measure of optimatl FGF to prevent rebreathing: CO2
Compare and contrast the various Mapleson devices
A. Pop off valve is by patient, FGF inlet by resevoir bag with corrugated tubing (AKA magill attachemnt)
B. Pop off valve and FGF right next to patient with corrugated tubing
C. FGF and Pop off valve next to patient, no corrugated tubing
D. FGF next to patient, Pop off valve next to resevoir
E. No resevoir, FGF next to patient (T-piece)
F. Pop off valve in rear of resevoir, FGF by patient with corrugated tubing between (Jackson Rees)
What are some pros and cons of the Mapleson system?
Advantages (really simple portable dick)
- simplicity of design
- ability to change depth of anesthesia rapidly
- portability
- lack of rebreathing of exhaled gases (only if FGF high enough)
Disadvantages (he’s so_f_t)
- Lack of conservation of heat and moisture
- limited ability to scavenge waste gases
- high requirement for FGF
What are the 3 funcitonal groups of the Mapleson system and how do they differ in controlled vs spontaneous ventialation?
Mapleson A
- pop off near facemask, FGF near resevoir
Mapleson B and C
- pop off and FGF near facemask (VERY wasteful system)
Mapleson D, E, F
- FGF located near facemask and pop off located at opposite end (oppostie of a)
Controlled
D>B>C>A
Dog bites can ache
Spontaneous
A>D>C>B
All Dogs Can Bite
“Dogs are friends” DF together
Why is the Mapleson A system so superior for spontaneous ventilation?
Alveolar gas is shunted off immediately via pop off valve near face mask
FGF flow inflows from opposite end of patient, near resevoir
This allows very little alveolar gas to collect in dead space, minimizing rebreathing
What setup do we want for Mapleson circuit?
FGF proximal to patient and pop off valve distal
What does CO2 rebreathing depend on in Mapleson system?
- Fresh gas flow rate
- MV of patient
- Mode of ventilation (spon v controlled)
- CO2 production of patient (increased with fever, catabolism)
- Respiratory waveform chracteristics
- inspiratory flow, I:E time, I:E ratio, expiratory pause
Adjustments to ventialtory pattern that allow FGF to constitue larger portion of inspired gas (slow inspiratory time or low flow) or that enable exhaled gases to be completely washed out (long expiratory pause or slow rate) reduce amt of rebreathing.
Describe a Mapleson A System
- MOST effecient for SV
- warm, humidified, exhaled dead space gas i resused
- Least efficient for controlled ventilation- Requires 20L/min FGF to prevent rebreathing
- No rebreathing during SV when FGF is 1X MV
- Requires larger FGF to eliminate rebreathing durign controlled ventilation
- Impractical design in the OR
- Proximal location of overflow makes scavenging difficult
- Difficult to adjust during head and neck sx
- Heavy valve can dislodge a small tracheal tube
What is the air flow in a Mapleson A system during spontaneous ventilation?
- Patient inhales fresh gas and partially empties the reservoir bag
- Patient begins to exhale, anatomical dead space gas then alveolar gas, down tube towards reservoir bag.
- as the bag fills, pressure within system opens APL valve to vent exhaled gases which are mainly alveolar
- During expiratory pause, the FGF flushes the remaining alveolar gas away from pt and out of APL valve.
- If FGF matches alveolar ventilation, then just as much gas flows into the system as is exhaled, leaving only fresh, humidified dead space, gas in the circuit
Describe air flow during IPPV in the Magil system
- With APL valve closed, the bag is squeezed, generating an inspiratory breath which partially empties the bag
- Subsequent expiratory breath fills reservoir bag and tubing with dead space and alveolar gas
- If this is not flushed out with high FGF, rebrathing of exhaled CO2 occurs
Describe common characteristics of Mapleson B and C circuits
- Require high FGF, limiting the use
- B circuit has length of corrugated tubing connecting system to rest of reservoir bag
- inefficient
- impractical for clinical use for either spontaneous or controlled ventilation
- FGF in both systems need to be high to prevent rebreathing. The proximity of APL valve and FGF provides potential for mixing of inspiratory and expiratory gases
- Mapleson C (water’s circuit without absorber) used in resuscitation situations and for patient transfer
*
Describe the Mapleson D circuit
- Reversed from configuration of Mapleson A
- Can be used for both spontaneous and controlled ventilation
- Spontaneous respirations FGF= 2-3 x MV
- Controlled FGF=1-2x MV
- Most efficient Mapleson durign controlled ventilation
- Mostly used in coaxial form known as “Bain” system
- has inner tubing of FGF directly to patient who then exhales down outer corrugated tubing into reservoir bag and APL valve.
What are some issues with the Mapleson D circuit?
- Disconnectiong of inner tubing can result in increased dead space and massive rebreathing
- Tests must be performed to check for disconnection
- inner tube of pt end is occluded using tip of finger or plunger of 2cc syringe
- if tube is connected, causes back pressure on FGF and flowmeter bobbin dips
- if disconnected, leads to venturi effect and causes reservoir bag to collapse
- inner tube of pt end is occluded using tip of finger or plunger of 2cc syringe
- Tests must be performed to check for disconnection
- High FGF needed