What are complications of rebreathing CO2?
- Respiratory Acidosis
- Hypoxia
- Dysrhythmias
- Decreased myocardial contractility
- Decreased BP
- Decreased SVR
- HTN & Pulmonary HTN
What are some considerations for achieving low resistance on the breathing machine?
Short tubing, large diameter tubing, avoid sharp bends, caution w/ valves, minimize connections
What is laminar flow?
Smooth and orderly flow which allows particles to move parallel to the walls of the tubing
How is apparatus dead space minimized?
minimized by separating the inspiratory and expiratory streams as close to the patient as possible
What are the 4 classifications of delivery systems?
- Open
- Semi-Open
- Semi-Closed
- Closed
What are the 2 types of Open Systems?
- Insufflation/Blow by
2. Open drop
Name the different types of Insufflation of Oxygen
“Blow-by,” Tent, Bronchoscopy port, Nasal Cannula, “steal” induction
What are some advantages of insufflation of Oxygen?
Advantages: Simplicity
Avoids direct patient contact
No rebreathing of CO2
No reservoir bag or valves
What are some disadvantages of insufflation of Oxygen?
Disadvantages:
No ability to assist or control ventilation
May have CO2/ O2 accumulation under drapes
No control of anesthetic depth /FiO2
Environmental pollution
How does the historical open drop method work?
True “open circuit” consisted of a bit of cloth saturated with either ether or chloroform or halothane and held over the patient’s face; which was placed in a metal cage device
Why isn’t the open drop method common in practice today?
Disadvantages:
Poor control of inspired concentration of anesthetics
Accumulation of CO2 under mask
Predisposes to hypoxia risk
Spontaneous ventilation only/ cannot control ventilation
OR Pollution/ Health care provider risk
What are the 5 components of the Semi-Open system?
- Facemask or ETT
- Pop-off valve/APL valve (a spring loaded valve to expel excess gas)
- Reservoir tubing
- Fresh gas inlet
- Reservoir bag (Adult bag holds 3L, Peds 2L, Neonates 1L)
What are 3 types of Semi-Open Systems?
- Mapleson (A-F)
- Bain
- Circle
Where is the pop-off valve/APL valve located in the Group 1 and 2 (Mapleson A,B,C) systems?
Is the valve open or closed?
- POP-OFF is located near the facemask or ETT
- Valve is OPEN and this system is more efficient for spontaneous ventilation
Where is the pop-off valve/APL valve located in the Group 3 (Mapleson D,E,F) systems?
Is the valve open or closed?
- FRESH GAS FLOW(FGF) is located near the facemask or ETT
- Valve is CLOSED and this system is more efficient for controlled ventilation
Is there a clear separation of inspired and expired gases in the Mapleson system?
No, both inspiration and expiration take place through the same tube which can lead to deadspace and rebreathing (i.e. inspired flow exceeds FGF)
CO2 Rebreathing will depend on:
Fresh gas inflow rate
Minute ventilation (tidal volume & RR) of patient
Type of ventilation (spontaneous or controlled)
What is the goal of the Mapleson system as it pertains to end expiration?
During exhalation, FGF will push expired alveolar gas toward the APL valve so the next inspiration will contain primarily FGF
What is the most efficient Mapleson during controlled ventilation?
Mapleson D
Can also be used for spont. ventilation but a higher FGF rate is required
Describe Mapleson E (T-Piece)
No reservoir bag
No pop-off bag
Requires high rates of FGF
Describe Mapleson F
- Adjustable pop-off at the end of reservoir bag
- Used during transport of ventilated patients (commonly in Peds)
- Not much deadspace or resistance
Describe the Bain Circuit tubing
-FGF tubing within the large bore corrugated tubing
allows exhaled gas to warm the inspired gas
- preserves heat and humidity
- for controlled OR spontaneous ventilation
What is the primary disadvantage of Bain Circuit tubing and what test do you use to assess for this problem?
Potential for inner tube leaks, kinking or disconnection
-Pethick Test assesses the integrity of the inner tubing
What are the characteristics of an Open System?
NO gas reservoir bag
NO valves
NO rebreathing of exhaled gas
