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.
What are the disadvantages of of the Bain circuit?
There could be inner tubing leaks, kinks or disconnects and you cannot see them through the corrugated exterior tubing.
An ambu bag is most similar to a Mapleson ___.
Mapleson A with a non-rebreathing valve.
5 Characteristics of an ambu bag are?
- contain non-rebreathing valves 2. capable of delivering high fiO2 3.resevoir is self-filling 4. requires high fresh gas flow 5. depends on minute ventilation
The ambu bag is self inflating, a downside of this feature is?
You cannot ‘feel’ if the patient is breathing or not. It just fills right back up. You miss out on that tactile assessment of respiration.
Name 6 advantages of the Mapleson system.
- It has simple components 2. It is lightweight 3. Can provide positive pressure ventilation 4. Low resistance 5. Portable 6. If using inhaled anesthetics you get a more predictable anesthetic concentration and decreased room pollution compared to an open system
Name 6 disadvantages of the Mapleson system.
- It requires calculation of fresh gas flow which varies with both type of circuit and mode of ventilation. 2. Control of anesthetic depth is variable (anesthetic gases will be diluted as fresh gas flow increases) 3. if fresh gas flow is not maintained, there is a possibility of CO2 buildup and rebreathing 4. minimal breathing of other gases, and less conservation of heat and humidity 5. fresh gas flow is costly 6.Mapleson requires special assemblly and the function is complex
What is one, newer piece of equipment that helps us adjust gas flow rates appropriately?
CO2 monitoring
What is the standard diameter of a tube in the breathing circuit?
22 mm
What is the standard size opening of a face mask or ETT?
15mm, so you need an elbow adaptor to connect the mask/ ETT to the breathing tube.
What length are the tubes for the breathing circuit (circle system)?
40, 60, or 72 inches
What is this?
Single limb universal F circuit. It is a type of circle system but the inspiratory limb is within the expiratory limb.
Name the 7 components of the circle system.
- Fresh gas inflow source 2. inspiratory and expiratory unidirectional valves 3. inspiratory and expiratory limbs 4.Y-piece 5. Overflow/ pop-off valve 6. reservoir bag 7. canister of CO2 absorbant
When gas flows are __________ (high/low) you get more drying of the airways.
high
Is it possible for bacteria to colonize of the breathing circuit?
Absolutely.
Giving an anesthetic by blow by is an example of?
insufflation/ open system.
Giving and anesthetic under a tent is an example of?
insufflation/ open system.
Giving an anesthetic via a bronchoscopy port is an example of?
insufflation/ open system
Giving an anesthetic by nasal cannula is an example of?
Insufflation/ open system
“Steal” induction is an example of?
Insufflation/ open system
The Mapleson E has no _________ or ____________.
No reservoir bag (the expiratory limb is the reservoir) and no pop off valve.
Which Mapleson system is a modification of the Mapleson E Ayre’s T piece with adjustable pop-off valve at the end of the reservoir bag?
Mapleson F
Which system is a coaxial modification of the Mapleson D?
Bain circuit
What is this anesthesia delivery system?
Bain Circuit
In the circle system, the components are arranged in a ___________.
circle
Which anesthesia delivery systems can be delivered via a circle system?
semi-open, semi-closed, and closed.
How would you chage from semi-open to semi-closed to closed?
By adjusting the APL valve.
Is the Fresh Gas Flow the same in each anesthesia delivery system?
No, FGF differs in each system
How do you prevent the rebreathing of CO2 in the circle system?
By chemical neutralization, but it does allow the rebreathing of other exhaled gases.
Label the circle system.
When the patient takes a spontaneous breath or we administer one by squeezing the reservoir bag, where does the gas flow from?
From the reservoir bag through the CO2 absorber, it meets fresh gas coming in and goes to the breathing circuit/ circle system.
If volume in the reservoir bag gets too high, what happens to the excess gas?
It overflows out into the scavenger system.
On expiration, where does the gas go?
Goes out the expiratory limb to the reservoir bag. Some escapes through the APL valve as the air passes it.
Fresh gas enters the circle system from:
the common gas outlet on the anesthesia machine
Before flowing through the inspiratory limb, air in the circle system goes through:
the inspiratory one way valve.
From the Y piece the air in the circle system goes to:
the patient.
From the patient’s lungs the air flows through _________ and then __________.
The expiratory limb and the expiratory one-way valve.
Once air exits through the expiratory limb and valve, where does it go?
to the reservoir bag where air can move in and out.
Wher does excess air in the circle system go?
Just past the reservoir bag is the APL pop off valve. Excess gas is vented out here and goes to the scavenging system.
When air starts it’s movement through the circle system, back toward the patient what is the first thing it hits?
From the reservoir bag, air is drawn through the CO2 absorber then onto mix with fresh gas coming in and on toward the patient.
How do the unidirectional valves work?
Gas flowing in through the valve raises the disc up off its seat then passes through.
What happens to the disc in the unidirectional valve when the gas flow is reversed?
Reversing gas flow causes the disc to be pushed down into its seat, preventing retrograde gas flow from backing up further in the circuit.
What is the purpose of the guide/cage over the disc in the unidirectional valve?
It prevents the disc from getting displaced vertically or laterally.
Why is there a transparent dome over the unidirectional valve?
So the action of the disc and its movement can be observed.
What are the 2 other names for the reservoir bag?
Breathing bag or respiratory bag
What is the reservoir bag made of?
neoprene or rubber
What size is the neck of the reservoir bag?
22 mm female fitting to male system
What is the part of the reservoir bag opposite the neck called?
the tail
What are the 5 functions of the reservoir bag?
- accumlation of gas during exhalation 2. assist/control ventilation 3. visual/ tactile monitor to observe spontaneous ventilation 4. protects against excessive pressure 5. reservoir of gas.
The breathing tubes in the circle system are _______ bore, and have____________, _____________ tubing
large bore; rigid, corrugated
What are the breathing tubes for the circle system made of?
rubber or clear plastic
What size are the breathing tubes of the circle system?
22 mm female (fitting with the machine)
What size is the T piece at the patient end of the circle system?
T-piece has a 22mm male end and 15mm female coaxial fitting.
What are the functions of the breathing tubes of the circle system?
to be a flexible, low resistance, lightweight connection, and to serve as a reservoir.
What are 3 other names for the APL valve?
pressure relief, pop-off, safety-relief valve
What role in the delivery of gases, does the APL have?
It releases gases to scavenge or atmosphere exhaust port. It provides control of pressure in the system.
How do you adjust the APL?
The APL is user adjustable and lets you control the pressure in the breathing system. By turning it clockwise you increase the pressure and vice versa.
How can you tell how much pressure is in the breathing system?
There is a pressure gauge on the absorber.
In what position should the APL valve be in someone with spontaneous respirations?
It should be fully open, close partially only if the reservoir bag totally collapses.
In what position should the APL valve be in assisted ventilation?
Partially open. The bag is squeezed on inspiration. Careful and frequent adjustments are necessary.
In what position should the APL valve be in mechanical ventilation?
The valve should be closed (if machine not equipped with a switch)
If the unidirectional valves are working properly, the only dead space in the circle system is between the ________ and the ________.
patient and the Y-piece
When you depress the oxygen flush, what is the pathway of oxygen?
It flows through the absorber out the inspiratory limb. If the Ypiece is occluded, it will travel through the expiratory valve and the reservoir bag and out the APL as well.
Circle arrangement rules: The unidirectional valves must be located between the _______ and the _________ on both the inspiratory and expiratory limbs of the circuit.
Patient and the reservoir bag
Circle arrangement rules: Fresh gas flow cannot enter the system between the _________ and the _________.
Expiratory valve and the patient
Circle arrangement rules: The APL valve cannot be located between the _________ and the _________.
patient and the inspiratory valve.
Is the semi-open system used often?
No, occasionally used for sedation (mask placed over face to increase FiO2)
Does the semi-open system have rebreathing circuits?
No
How much fresh gas flow does a semi-open system require?
Very high flows 10-15 liters/ minute to eliminate rebreathing of gases.
Is there conservation of water gases and heat in a semi-open system?
No
In what position is the APL in a semi-open system?
All the way open
What is the most common used breathing system in the USA?
semi-closed system
What flow rates does the semi-closed system require?
Low flow, about 1-3 liters/ minute
Does the semi-closed system allow for conservation of heat and gases?
Yes, some
Does the semi-closed system allow rebreathing of agents and exhaled gases?
Yes, some. Minus CO2
In what postion is the APL in a semi-closed system?
Partially closed and adjusted as needed.
Where are closed systems typically used?
In 3rd world countries
What is the inflow of gas in a closed circle system?
inflow gas matches exactly the metabolic needs (O2 consumption) of the patient using very low flows 200mL/ minute)
What is the typical gas flow through a closed system?
Low, 0.2 liters/minute
Is there rebreathing of gases in a closed system?
Yes, there is total rebreathing of gases after absorption of CO2.
Is there conservation of exhaled gases in a closed system?
Yes, total conservation of all exhaled gases.
In what position is the APL in a closed system?
closed.
What is the formula for calculating O2 consumption (VO2)?
In a 70kg patient it would be 242 mL O2/min by calculating: 10 x 703/4
What are 7 advantages of the circle system?
- Relative stability of inspired gases 2. Conservation of moisture and heat 3. Prevention of OR pollution 4. Can be used for closed system anesthesia 5.Can be used with fairly low flows with no rebreathing of CO2 6. Economy of anesthetics and gases 7. Can scavenge waste gases.
What are 6 disadvantages of the circle system?
- Complex design 2. Has at least 10 connections (sets the stage for leaks, obstructions, or disconnection) 3.A third of malpractice claims resulted from disconnects or misconnects of the circuit 4.Potential of malfunctioning valves 5.Increased resistance to breathing 6. Less portable and convenient than the Mapleson system due to its bulkiness
What two tests are part of the circle system check?
The leak test and the flow test.
What are the 8 steps to performing a leak test of the circle system?
- Set all gas flows to zero 2. Occlude the Y-piece 3. Close the APL valve 4. Pressurize the circuit to 30 cm H2O using the O2 flush valve 5. Ensure the pressure holds for 10 seconds 6. listen for sustained pressure alarm 7. open APL 8. Ensure pressure decreases.
What is the one important thing that the circle system leak test does not check?
It does not assess the integrity of the unidirectional valves, so a flow test must be done to check these.
How do you perform a flow test of the circle system?
Attach breathing bag to the Y-piece, turn on the ventilator, and assess the integrity of the unidirectional valves.
