What is the delivery component of the SPDD model?
How we control and monitor the interaction of gases with the patient
What determines if the circuit is semi-open or semi-closed in a circle circuit?
Dependent on the amount of fresh gas flow put into the system
What type of circuit is created if the fresh gas flows are greater than minute ventilation?
Semi-open, No rebreathing
How do you calculate minute ventilation?
Take the breaths per minute and multiply it by the tidal volume
What is an example of a closed circuit?
Circle with pop off valve closed
What type of circuit is created if the fresh gas flows are less than minute ventilation?
Semi-closed, partial rebreathing
What does APL stand for?
Adjustable pressure limiting valve (pop off valve)
After exhalation, what two places can the gas go?
CO2 absorber
Anesthesia reservoir bag
What are the seven components of a circle system?
- Fresh gas inflow source
- Unidirectional valves
- Two corrugated tubes
- Y-piece connector
- Overflow valve
- Gas reservoir bag
- CO2 absorber
What size is the corrugated tubing used in the circle system?
22 mm diameter in adults
What are the two types of unidirectional valves in the circle system?
Inspiration
Expiration
How does a floating valve work?
Opens with pressure and closes with pressure, it moves in the direction its being pushed by gas
What type of valves are the inspiratory and expiratory valves in the circle system?
Floating valves
What should be avoided between the patient and the inspiratory limb?
Avoid overflow valve
What should be avoided between the expiratory limb and the patient?
Avoid fresh gas inflow
How much rebreathing occurs in a closed circle system?
Complete rebreathing
What are some advantage of utilizing a circle system?
Constant inspired concentrations Conserve respiratory heat and humidity Useful for all ages Useful for closed system or low flow Low resistance
What are some disadvantage of utilizing a circle system?
Relatively complex
Opportunities for misconnections/disconnections
Malfunction of unidirectional valves
Less convenient and portable than NRB circuit
Where is headspace located in the circle system?
Dead space is located between y-piece and the patient
When does no rebreathing occur in the circle system?
1-1.5 x minute ventilation no rebreathing occurs
What times during anesthetic practice would we want no rebreathing to occur?
Preoxygenation
Induction (wash-in)
Emergence (washout)
When would be a good time to administer low flows to a patient?
Maintenance, it conserves heat, humidity and volatile agent
What are the tasks of the CO2 absorption system?
Makes rebreathing possible
Conserves gases and volatile agents
Decreases OR pollution
Avoids hazards of CO2 rebreathing
What is the composition of Soda Lime?
CaOH 94% NaOH 5% KOH <1% Silica 0.2% Moisture content 14-19%
What is the soda lime chemical reaction?
CO2 + H2O H2CO3
H2CO3 + NaOH Na2CO3 + H2O + Energy
Na2CO3 + CaOH CaCO3 + NaOH
What is the absorptive capacity of soda lime?
26L of CO2 per 100g of absorbent
What tells us the Soda lime and baralyme absorbents have been exhausted?
pH become less alkaline < 10.3 ethyl violets indicator changes from colorless to blue
What does the term mesh refer to?
The number of openings per linear inch, 4 mesh and 8 mesh
Why is there a mixture of 4 mesh and 8 mesh in the CO2 absorber?
Compromise between resistance to airflow and surface area for absorptive capacity
What anesthetic is incompatible with soda lime?
Trichloroethylene
What are the two products if trichloroethylene and soda lime are combined?
Dichloroacetylene (cranial neurotoxin)
Phosgene (pulmonary irritant)
This is mostly seen in developing countries
What can be produced if Sevoflurance is run with FGF < 2?
Compound A, potential renal injury
What anesthetic has the greatest potential to produce carbon monoxide?
Desflurane
What two things does a circle system have that a non-rebreathing system lacks?
Unidirectional valves
Carbon dioxide absorption
What is a benefit to utilizing a non-rebreathing system?
Without CO2 absorbers and unidirectional valves the resistance (work of breathing) is low
What are advantages of using a non-rebreathing system (semi-open)?
Portability Low resistance = low work of breathing Absence of rebreathing Inexpensive, few moving parts Allow rapid changes in anesthetic
What are disadvantages of using a non-rebreathing system (semi-open)?
Lack of conservation of moisture or heat
Requires high FGF, not economical (lots of agent used
How doe non-rebreathing systems work?
Exhales gas enters expiratory limb
APL opens
Inspiration draws in gas from expiratory limb (only has fresh gas if flow is high enough)
Professor who described five different seem-open systems?
Mapleson
What is the basic composition of the Mapleson systems?
Various arrangements of fresh gas inflow, tubing, reservoir bag and expiratory valve
What are the characteristics of the Mapleson A system?
No rebreathing if FGF > alveolar ventilation, Overflow valve opens during expiration when maximum pressure is reached
Insufficient with controlled ventilation
What are the characteristics of the Mapleson B system?
Fresh gas inlet and overflow valve closer together to prevent rebreathing
Requires FGF > 2-2.5 times the minute ventilation
What are the characteristics of the Mapleson C system?
Shorter expiratory limb than Mapleson B
Requires FGF 2-2.5 times minute ventilation
What are the characteristics of the Mapleson D system?
Fresh gas inlet and overflow valve opposite Mapleson A
Requires FGF 2-3 times minute ventilation
What are the characteristics of the Mapleson E system?
Valveless and bagless (basically T piece)
Expiratory limb must be greater than patient’s tidal volume
FGF 3 times greater than minute ventilation to prevent hypercarbia
On the Mapleson E system, why must the expiratory limb be greater than the patient’s tidal volume?
To prevent entrainment of room air
What are the characteristics of the Mapleson F system?
Requires FGF 2-3 times minute ventilation
Minimal dead space/ low resistance
The Mapeson __ is a Jackson-Rees modification of the Mapleson ___
Mapleson F
Mapleson D
What does the term Coaxial refer to?
“A tube within a tube”
What is the adaptor called that connects the Coaxial Mapleson D to the anesthesia machine?
Bain
What are major benefits to the Bain Mapleson D circuit?
Designed to conserve some heat and humidity
What patient population is the Bain Mapleson D typically seen in?
Pediatrics
What are some advantages of the Bain Circuit?
FGF warmed by exhaled gases
Improved humidification
Ease of scavenging waste gases
Lightweight
What are some disadvantages to the Bain Circuit?
Kinking of inner tube
Rebreathing if inner tube disconnected
Increased resistance
FGF 200-300mL/Kg prevent hypercarbia
What is the name of the test to use on a Bain Circuit if kinking or disconnect is suspected?
Pethick test (inner gas hose integrity kinked or disconnected)
How do you perform the Pethick test?
Occlude end of circuit Close APL valve Fill circuit with O2 flush valve Release occlusion at elbow and flush Venturi bag flattens bag if inner tube is patent
What type of ventilators do not require a driving gas?
Piston Ventilators
What are some hazards of ventilators?
Disconnection Occlusion/obstruction of breathing circuit Misconnection Failure of emergency O2 supply Infection
What type of ventilator setting limits the tidal volume by the amount of pressure within the circuit?
Pressure Control Ventilation
What is the pressure limit on pressure control ventilation?
Pressure limit 20cm H2O
What ventilator mode delivers a set volume at a set rate?
Controlled Mandatory Volume
What can the CRNA control on the ventilator?
Inspiratory flow control
I:E ratio control
Rate Control
Tidal Volume Control
