Anesthesia Delivery Systems Flashcards
The purpose of anesthesic breathing systems is to deliver __________ and___________ and to eliminate _________.
Oxygen and anesthetic gas and to eliminate CO2.
How is CO2 removed from the breathing circuit?
By washout with adequate fresh gas flow and/ or by the use of CO2 absorber
It is essential for a breathing system to have these 4 things:
1.delivery of gases from the machine to the alveoli in the same concentration as set, and in the shortest time possible. 2.effectively eliminate CO2 3.Have minimal apparatus dead space 4. have low resistance
8 desirable (not essential) breathing system components are:
- economy of fresh gas 2.conservation of heat 3.adequate humidification of inspired gas 4.light weight 5. convenience during use 6.efficiency during spontaneous as well as during controlled ventilation 7.adapatibility for adults, children, and mechanical ventilators 8. provision to reduce environmental pollution
It is ideal to have (high or low) resistance in the breathing system?
low
What are some things we can do to ensure the lowest resistance possible in the breathing system?
Short tubing with large diameter, avoidance of sharp bends,caution with valves, and minimize connections
Is rebreathing a good or a bad thing?
It’s good, if the patient rebreathes the anesthetic it will drive down cost, it adds humidification and heat to the gases, but you must have something to absorb the CO2. Rebreathing CO2 is not good.
Higher fresh gas flows are associated with (more or less) rebreathing in any type of circuit?
Less. Fresh gas flows wash out CO2
Dead space (increases or decreases) the chance of rebreathing CO2?
increases
Where does dead space end (from inside lungs out in the direction of the circuit)?
Where the inspiratory and expiratory gas streams diverge.
How can apparatus dead space be minimized?
By separating the inspiratory and expiratory streams as close the patient as possible.
When rebreathing is minimal or absent, the concentration of inspired gases most closely resembles_____________.
the gas concentrations at the common gas outlet.
What are the 4 classifications of anesthetic delivery systems?
- Open, 2. Semi-open, 3. Semi-closed, 4. Closed.
What 3 features are characteristic of an open system?
- No gas resevoir bag 2. No valves 3.No breathing of exhaled gases.
What are the 2 types of open systems?
- Insufflation/ blow-by 2. Open drop
What is the “steal” induction technique?
The mask with anesthetic is held near the patient’s face, not tightly over it, and a blow by type anesthetic is given.
What are the downsides of the steal technique?
everyone in the room gets anesthesia. You are not giving a consistent concentration of anesthesia to the patient
What is one type of necessary equipment that we use during anesthesia that adds high resistance to the breathing system?
The breathing tube.
If you use larger size tubing to decrease resistance in the breathing system, what must you be aware of?
The larger the diameter of the tubing, the increased risk of creating turbulent air flow. We want only smooth laminar flow.
What are some advantages of using the open system? (insufflation)
Avoids direct patient contact, no rebreathing of CO2, no resevoir bags or valves, simplicity.
What are some disadvantages of using an open system?
No ability to assist or control ventilation, you may have CO2/O2 accumulation under drapes, you have no control of the anesthetic depth and fio2, environmental pollution
What is the name of this device and what is it used for?
The Schimmelbusch mask or an ether mask. It is a true open system. A piece of cloth was saturated with ether, chloroform, or halothane and held over the patient’s face. Dripping a bit of anesthetic on a cloth and holding it over the face like that is called the open drop method.
What are some advantages to using the open drop method of anesthesia?
simple, low cost appartus and portable.
What are some disadvantages to using the open drop method?
poor control of inspired concentration of anesthetics, accumulation of CO2 under the mask, predisposes to hypoxia risk, spontaneous ventilation only (cannot control ventilation), OR pollution, healthcare provider risk.
Name 5 components that characterize a semi-open system?
- facemask 2. pop off valve 3. resevoir tubing 4.fresh gas inlet 5.resevoir bag
Mapleson A, B, C, D, E, F, Bain, and Circle systems are all examples of _________systems.
Semi- open
What is the big difference between the various types of Mapleson systems?
The variety among the Mapleson systems is where the fresh gas comes in and where the pop off valve is.
What 2 things are necessary on the Mapelson systems to prevent hypoxia?
In the Mapleson systems you are rebreathing the same gases (CO2) so you need a fresh gas source to flush CO2 out and you need a pop-off valve to allow exhaled gases to escape.
In this system, the fresh gas comes in from the end and the pop off valve is closest to the patient. This is an example of which Mapeson design?
Mapleson A
In this system the fresh gas comes in close the patient, but the pop off valve is still closer. Which Mapleson system is this?
Mapleson B
In this system, the fresh gas and the pop off valve are close the patient (pop off closer) but there is not corrugated tubing, just a direct connection to a resevoir bag. Which type of Mapleson system is this?
Mapleson C
In this system, the fresh gas supply is closest to the patient and the pop off valve is more distal, before the resevoir bag. This is the most common Mapleson system used in practice today. Which type is it?
Mapleson D
In this system, the fresh gas is close to the patient and there is no pop off valve. It is simply open to atomosphere. Which Mapleson system is this?
Mapleson E
In this system, the fresh gas is close to the patient. There is a resevoir bag but no pop off valve because it is open to the atomosphere at the bag. Which Mapleson system is this?
Mapleson F
There are 3 distinct funtional groups of Mapleson systems. Describe group 1.
Just Mapleson A, pop off is near the face mask and fresh gas is at the opposite end.
There are 3 distinct functional groups of Mapleson systems. Describe Group 2.
Mapleson B and C are here. The pop off valve and fresh gas are both near the face mask.
There are 3 distinct functional groups of Mapleson systems. Describe Group 3.
Mapleson D, E, F. The fresh gas is near the facemask and the pop off valve (if there is one, E and F have no valves) is at the opposite end.
Can you give a positive pressure breath with a Mapleson?
Yes, only in the models with a pop off valve. You will need to close the valve to give a positive breath and then open it again quickly to allow for exhalation of that breath.
The amount of CO2 the patient rebreathes from a Mapleson system depends on what factors?
the rate of fresh gas inflow, the minute ventilation of the patient, and the type of ventilation (spontaneous or controlled)
How do you calculate minute ventilation in a patient?
TV x RR
In a 70kg patient, breathing 10 breaths a minute, what is the minute ventilation?
Take a 70kg patient x 10mL/kg for your tidal volume. Then, 700ml x 10 = 7000mL (7 liters) minute ventilation.
The best choice of Mapleson for an awake patient who is spontaneously breathing is which model?
Mapleson A
The best choice of Mapleson for an asleep patient with controlled respirations is?
The Mapleson D (Note- the Mapleson D can be used for both spontaneous and controlled ventilation)
The Mapleson D is a reversed configuration of the Mapleson __.
A
During spontaneous respiration, the fresh gas flow in the Mapleson D has to be at least ____________
2-3 times the minute ventilation
So, in a 70kg patient breathing 10 breaths per minute, how many liters of fresh gas do we need flowing into the Mapleson D system to meet the oxygen demand of the body?
MV for this patient is 7 liters. and we need 2-3 times the MV so about 21 liters/min of O2
During controlled ventilation, the fresh gas flow through the Mapleson D has to be at least ______________.
1-2 times the minute ventilation
So, in a 70kg patient, being ventilated (no spontaneous respirations) at 10 breaths per minute via a Mapleson D how much fresh gas flow would you need?
1-2 x MV so about 7-14 liters per minute flow.
Why would you need less fresh gas flow when ventilating a patient with a Mapleson D as opposed to if they were spontaneously breathing?
When you are spontaneously breathing we have no control of the depth or quality of your respirations, the chance for rebreathing CO2 is greater in a spontaneously breathing patient so more fresh gas in needed to flush CO2 from the system.
A Mapleson E is very similar to a _________ that we used in ICU.
T-piece
What kind of fresh gas flows would you need in a Mapleson E in a spontaneously breathing person?
2-3 times minute ventilation. The end of a Mapleson E is open so let the high flows in to flush the CO2 from the system.
What is the other name for a Mapleson F?
The Jackson- Rees
How is a Mapleson F unique?
It’s pop off valve is way down at the end of the resevoir bag.
What is the most popular Mapleson system used in pediatrics?
Mapleson F
What is a Bain circuit?
It’s a Mapleson D with the fresh gas flow tube inside of a large bore corrugated tubing.
What are some advantages of a Bain circuit?
The exhaled gas will warm the inspired gas as it passes over it. It preserves heat and humidity.
Is the Bain circuit used for a controlled or a spontaneously breathing patient?
It can be used for either.
How much fresh gas would you deliver through a Bain circuit?
Same as a Mapleson D. 2-3 times MV in spontaneously breathing patient and 1-2 times MV in controlled ventilation.