Anesthesia Delivery Systems (Mod 4) Flashcards
Function of Anesthesia machine
- Delivery of medical gas, and volatile anesthetic (known conc)
- Removal of CO2 (via CO2 absorber and scavenging system)
How does the CO2 Absorber in an Anesthesia work?
The soda lime canister contains materials that absorb the CO2, they change color to blue when the soda lime is depleted, indicating another CO2 absorber needs to be swapped
What is a scavenging system
Collects and removes vented gases from operating room into the atmosphere
- Active or passive
Electric and Pneumatic power source
- Electric powers the ventilator and associated monitors
- Pneumoatic power sources control gas flow and control medical gasses
Purpose of pressure regulators
Reduce pipeline and cylinders pressures
How does an Oxygen fail-safe device work?
Prevents delivery of hypoxic gas mixtures in the event of low or failed O2 supply
- Requires Oxygen analyzer and supply failure alarm
- Proportionately decreases (or shuts off) flow of all gases
How do O2 flush controls work
Emergency O2 flush valve
- Bypasses the flowmeters and vaporizers
- O2+, 35-75 L/min through circuit to flush out anesthetic gases
- Activated by demand, designed to prevent accidental activation
How much O2 is used to flush out anesthetic gases?
35-75 mLs
Flowmeter sequence and Oxygen placement?
- add slide 6
Oxygen is always downstream from the gases
- Oxygen delivery is preserved in the event of a leak upstream
- oxygen analyzer still needed to confirm correct delivery
What is the safest configuration of flowmeter tube arrangement?
Placement of O2, Air, and N2O are important.
- safest = O2 nearest to the manifold outlet (to the right)
- a leak upstream from the oxygen result in loss of nitrous oxide rather than oxygen
Why is arrangement of oxygen to the left dangerous and not to the right (closest to the manifold)
O2 flow can pass through the leak, while all nitrous oxide is directed to the common gas outlet
Function of the common gas line in an Anesthesia Machine?
Fresh gas outlet (Fresh gas flow)
- mixture of medical gases and volatile anesthetics
- Common gas outlet directs anesthetic mixtures to be delivered to patient
Breathing limb Function in an Anesthesia Machine?
Slide 7
Breathing circuit components
Insert slide 8
What is the purpose of vaporizers in Anesthesia machines?
Converts anesthetic from liquid to gas
- Use is precise and accurate; measured amount of volatile gas is dispensed into the fresh gas mixture (done it 2 ways; flow over method and variable bypass)
What is the flow over method of vaporization for delivery of volatile gasses to fresh gas mixtures?
Gas flows over the liquid agent, becomes saturated
What does variable bypass mean in relation to vaporizer delivery of volatile gasses to fresh gas mixtures?
The gas flowing through the vaporizer is split, it either goes into 2 direction
- The amount passing into the vaporizing chamber is variable (based on operator adjusting settings)
- The rest bypasses the vaporizing chamber
Core characteristics of Vaporizers?
- Agent specific
- Variable bypass (concentration calibrated)
- Flow over
- Temperature compensated
- Out of circuit
Colour for Sevoflurane
Yellow
Colour of Desflurane
Blue
Colour for Isoflurane
Purple
maybe add slide 13 and 14?
Vaporizer safety features
- Agent specific, colour coded
- Each bottle can only fill 1 vaporizer
- Only one vaporizer can be on at a time
Ratio of O2 and N2O in a Controller?
Ratio must always be at least 1:3 (O2:N2O)
- prevents <25% O2 delivery
- Flowmeter for O2 and N2O are linked
4 circuit classifications for anesthesia machines?
- edit add image/more info on slide 15
Open, semi open, semi closed, or closed
3 common systems for Anesthesia circuits?
- Mapleson (6 system designs; Semiopen)
- Bain (modified vers of Mapleson D system, Semiopen)
- Circle (closed or semi closed) circuit…most common in Canada
Arrangements for Mapleson circuit
- insert slide 18
6 arrangements, the components are:
- FGF
- Reservoir tubing
- Facemask
- Reservoir bag
- Expiratory valve
Details on the Mapleson circuit system (a-f)?
- circuit type (open/closed)
- caveats?
Semi open circuit (no valves to direct gas flow)
- no CO2 neutralization
- Difficult to determine optimal FGF bc amount of rebreathing depends on FGF
- Caveat: If the pt requires more FGF then the pt will be rebreathing…but no CO2 absorption system….meaning they rebreathe CO2
Best way to determine optimal FGF on a Mapleson system?
Monitor EtCO2
Configuration of the Mapleson F (Jackson-Rees) circuit?
Pressure limiting overflow valve on reservoir bag
- pediatric anesthesia (or tranpsort), Minimum dead space and resistance
- Semiopen system?
- No APL valve
Disadvantages of Mapleson F circuit?
- Requires high FGF to prevent rebreating…usually requiring 2-3x the patients MV
- Potential for high airway pressure, barotrauma (if valve is occluded)
- No humification system
- Pollution of atmosphere with anesthetic gas ( can be hooked to scavenging system)
- Semi open system (rebreathing issue?)
Bain circuit system characteristics
Mod of Mapleson D; but the coaxial version…no CO2 neutralization or valves to direct flow tho. But some pros are:
- FGF is warmed by exhaled gases
- Moisture (from partial rebreathing)
- Easy scavenging of waste gases from overflow valve
- Semi open
Disadvantages of Bain system?
- Disconnect or kinking of inner FGF tubing
- Requires high FGF
- Circuit still has no valves to direct flow (semi open system)
What kind of circuit type is a circle circuit?
Can be Semiopen, Semiclosed, or closed, it Depends on amount of FGF.
The following would apply to: Semi-closed and closed systems
- Rebreathing of exhaled gasses = conservation of moisture/heat
- Rebreathing = decreased pollution of exhaled anesthetic gas (bc its rebreathed) literally talking about the environment
Decreased disadvantages of Circle Circuits
Increased airway resistance in system
- Bulky, not portable
- Higher risk of problems/malfunction
Components of Circle Circuits
- Insp/Exp unidirectional valves
- Insp/Exp correugated tubing
- APL Valve, reservoir bag
- CO2 Absorbent
- Bag/vent selector switch , ventilator
Function closed circle circuits?
- Advantages and disadvantages
Total rebreathing of exhaled gases
- (A) Max warming and humidification of inhaled gases
- (A) less pollution of atm exhaled gases and its economical
- (D) can’t make rapid changes to delivered concentration of anesthetics or O2
- (D) Unpredictable concentrations of anesthetics and O2
Bispectral Index (BIS monitor)
Level of consciousness (EEG activity)
- Usually aim for 40-60 for healthy patient and routine anesthesia
- Non invasive monitoring
Review EtCO2 monitoring
- Slide 28 forward for EtCO2 waveforms
When is MAC measured?
As the end tidal concentration of anesthetic gas
Purpose of a APL valve?
Pressurizes the circuit; known as the pop off valve/pressure relief valve
- Regulates the pressure within the breathing circuit and protects the pt from escessive pressures during mech ventilation
Should the APL valve be left opened or closed if the patient is spontaneously breathing?
Open..the patient would be able to exhale if the valve is closed.
- The patient provides back pressure when spontaneously breathing, the valve won’t let anything through
2 ways in which measured volatile gas is dispensed into fresh gas mixtures (via vaporizers)
- Flow over method of vaporization
- Variable bypass
Why are Vaporizers out of circuit
Its so that exhaled gasses don’t recirculate
Anesthesia machine safety features (not the same as the vaporizers) 8
- Cylinders are specific, color coded with PISS connectors and safety pressure relief
- O2 flowmeter (control is diff form other gasses and is downstream in case of leaks)
- O2 fail safe valve (prevents hypoxic gas delivery, occurs when O2 is less than 30psi)
- Alarms
- Min O2/N2O controller
- Vaporizer safety features
- Back pressure check valve (prevents back pressure from PPV going into the machine)
- Machine checks and alarms (person does it)
How does the minimum O2/N2O controller work (saftey feature)
Flowmeter controls O2 and N2O are linked, it ensures that a 1:3 concentration is met
- Prevents < 25% O2 delivery
Anesthesia machine circuits are defined as open, semiopen, semiclosed, or closed, What does the classification of the systems depend on?
Whether there are the following elements present (some may not be in the circuit):
- Gas reservoir bag in circuit
- Rebreathing of exhaled gases
- Chemical neutralization of CO2
- Unidirectional valves
Since the Mapleson configuration is difficult to monitor optimtal FGF, what is the best way to manage gasses so that rebreathing is not dangerous?
Monitor EtCO2 and the amount of anesthetic gas at end exhalation…but its still not perfect
How does the Mapleson F (Jackson rees) differ from other Mapleson setups?
Modified Mapleson D configuration that has a pressure limiting overflow valve on reservoir bag (meaning minimum dead space and resistance)
What population would likely use the Mapleson F setup?
Pediatric anesthesia (or in transport)
- due to min dead space and resistance so less risk of vili
How does the Bain circuit warm and moistures the FGF?
The FGF tubing runs inside the corrugated expiratory tube
Why is the Bain Circuit better than the Mapleson circuit?
Less mixing of gases; where its separate tubing
- In controlled ventilation: you can control the inspiration, minimizing rebreathing of gasses
- FGF is warmed and moisturized
- Less rebreathing of CO2 at lower FGF flow
How do closed circuits work in a circle circuit?
The inflow of fresh gas flow exactly matches the gas being used by the patient
- You need to know the exact inspiratory need of the patient, and that’s what you’ll get
Where does the scavenging of system vent collected gas from the OR?
Out of the roof of the building, with the rest of the medical gasses that are collected and vented
When is the Closed Circle Circuit considered for use?
Once CO2 is removed, than it implies anything you give is given.
- removing the CO2 from the tissue is difficult though
Which systems include a CO2 Neutrilzer?
Semi closed and closed circles systems
Do semi open systems allow for rebreathing of exhaled gasses
Generally no, if there is its because of insufficient FGF (so its bad…)
- only semi closed or closed circle systems allow purposely allow rebreathing
What level of FGF flow rate required for open breathing systems
Unknown amount due to variable nature
What level of FGF flow rate required for Mapleson breathing systems (semi open)
High FGF rate
What level of FGF flow rate required for semi closed breathing systems?
Moderate low FGF rate
What level of FGF flow rate required for closed breathing systems
Low FGF rate
Open drop system?
Open system
Does the Mapleson (semi open) system direct flow?
Only has 1 unidirectional valve (APL valve) to direct flow.
- no valves to direct gas to and from patient
- Needs high FGF
Why is rebreathing okay in semi closed systems?
The delivery of FGF is above the patient requirement, so its not dangerous…monitoring of CO2 analyzer
What does the following EtCo2 waveform indicate
Rebreathing
What does the following EtCo2 waveform indicate
Airway Obstruction
What does the following EtCo2 waveform indicate
Muscle Relaxants
What does the following EtCo2 waveform indicate
Esophageal ETT
What does the following EtCo2 waveform indicate
Poor seal or leaky ETT or uncuffed Trach
What does the following EtCo2 waveform indicate
Increasing EtCo2 levels
- could point to a potential malignant hyperthermia if temperature also rises
What does the following EtCo2 waveform indicate
Decreasing EtCO2 levels
- hyperventilation
- decrease in metabolic rate
- decrease in body temp