NUR 967 Breathing Circuits

Jackson-Rees circuit (Mapleson F) -Reservoir bag has _______ mechanism -Adjustable pop-off valve can allow for spontaneous (open) or assisted (partially closed) ventilation -_______ can be accomplished if reservoir bag empties into plastic bin that is scavenged -Primarily used for pediatric transport

-Reservoir bag has VENTING mechanism -Adjustable pop-off valve can allow for spontaneous (open) or assisted (partially closed) ventilation -SCAVENGING can be accomplished if reservoir bag empties into plastic bin that is scavenged -Primarily used for pediatric transport

What are the disadvantages of non-rebreathing circuits? (5)

1 .Unrecognized disconnection or kinking of fresh gas flow (especially hidden in Bain system - use Pethick test) 2. Pollution and increased cost of gases due to need for high flows 3. Loss of heat from patient (Bain helps with this) 4. May require disconnection of fresh gas supply hose and scavenger which can lead to improper assembly after connected 5. Use of nonrebreathing circuits has fallen dramatically with modern anesthesia machines (Accuracy of small pediatric volumes has dramatically improved; the original purpose of many nonrebreathing systems was to create adequate ventilation in pediatric patients, although can be used on adults as well)

Non-rebreathing Circuits Mapleson classification of non-rebreathing systems first occurred in 1954 and is still used. Common features: (4)

1. All lack unidirectional valves 2. All lack soda lime carbon dioxide absorbent 3. Fresh gas flow determines any amount of re-breathing (2-3x minute ventilation or at least 5 LPM = no re-breathing) 4. Resistance and work of breathing are low in all due to lack of unidirectional valves and absorbent granules

What are the advantages of Circle Systems? (5)

1. Constant inspired concentrations 2. Conservation of respiratory tract heat and humidity 3. Minimal environmental pollution 4. Useful for closed, low-flow and semi-open configurations 5. Low resistance (although not as low as nonrebreathing circuits)

There are several different types of anesthesia breathing circuits. All circuits must: (2)

1. Deliver oxygen and anesthetic gas 2. Eliminate carbon dioxide

Eliminating carbon dioxide occurs one of two ways: (2)

1. Enough fresh gas flow to wash out the carbon dioxide 2. Absorption in carbon dioxide absorbent granules

What are the relative contraindications to low-flow anesthesia? (4)

1. Face mask anesthesia 2. Rigid bronchoscopy 3. Uncuffed ETT 4. Older equipment

Bain System (Modified Mapleson D) -Bain has fresh gas flow hose that is within the corrugated limb -Because the fresh gas flow is housed within the expiratory limb, there is added ______ and ______ to the inspired gas -Primarily used for pediatric transport

-Bain has fresh gas flow hose that is within the corrugated limb -Because the fresh gas flow is housed within the expiratory limb, there is added HEAT and HUMIDITY to the inspired gas -Primarily used for pediatric transport

Interpretation of Pethick test -If the inner tube is patent, the ______ effect will cause the reservoir bag to collapse. The circuit is safe to use -If the inner tubing is occluded, the reservoir bag will remain ______. The circuit is not safe to use

-If the inner tube is patent, the VENTURI effect will cause the reservoir bag to collapse. The circuit is safe to use -If the inner tubing is occluded, the reservoir bag will remain INFLATED. The circuit is not safe to use

Fresh gas flow and re-breathing -Increased fresh gas flow = -Decreased fresh gas flow =

-Increased fresh gas flow = decreased re-breathing -Decreased fresh gas flow = increased re-breathing

Circle System -Most commonly used anesthesia circuit in the US -Prevents rebreathing of _________ while allowing rebreathing of all other gases -_________ valves allow for inspiratory and expiratory limbs to stay largely separate

-Most commonly used anesthesia circuit in the US -Prevents rebreathing of CO2 while allowing rebreathing of all other gases -UNIDIRECTIONAL valves allow for inspiratory and expiratory limbs to stay largely separate

Which circuit is best for spontaneously breathing patient?

Best: Mapleson A (the least amount of rebreathing) Worst: Mapleson B A > DFE > CB

Which circuit is best for a patient with controlled ventilation?

Best: Mapleson D Worst: Mapleson A DFE > BC > A F and E are nearly equal to D

True or False? It is important to decrease resistance to flow for comfort of unconscious patients and minimize work of breathing

FALSE, conscious patients

Airway choice changes the amount of dead space. List the airway devices from the most dead space to the least amount of dead space.

Face mask > LMA > ETT

True or False? Rebreathing does not occur in anesthesia circuits

False, rebreathing does occur -Not seen in ICU ventilators

Circle System Fresh gas flows into the circle continuously and in ____ direction only due to unidirectional valves. This forces all exhaled gas through carbon dioxide granules to remove CO2 and preventing rebreathing of _____ only.

Fresh gas flows into the circle continuously and in ONE direction only due to unidirectional valves. This forces all exhaled gas through carbon dioxide granules to remove CO2 and preventing rebreathing of CO2 only.

Is resistance of the circuit higher or lower than the resistance of the ETT?

Lower than the ETT!

Can you give low fresh gas flow with sevoflurane?

No!

What are the disadvantages of circuit rebreathing?

Can re-breathe any component -oxygen: no issue -carbon dioxide: can lead to respiratory acidosis -nitrous oxide: possibly delay emergence -volatile agent: possibly delay emergence

The Bain system is often referred to as a modified Mapleson D circuit because of the arrangement of the reservoir bag and APL valve. What is the main difference between the two?

The Bain system has a fresh has hose that is directed within the corrugated expiratory limb which gives the inhaled gases greater heat and humidity.

The more dead space that exists, the _____ re-breathing occurs

The more dead space that exists, the MORE re-breathing occurs

What is the purpose of a reservoir bag in semi-open, semi-closed and closed systems?

To provide enough gas flow to the patient during times when the patient's inspiratory flow exceeds fresh gas flow.

When would it be advantageous to increase or decrease fresh gas flow with relation to re-breathing?

To speed up induction/emergence

True or False? Modern anesthesia machines have allowed for safe anesthetics utilizing low flow techniques (<1 LPM)

True

True or False? All circuits cause resistance to gas flow

true

True or False? Dead space increases with the use of any respiratory apparatus

true

True or False? When we are talking about which circuits are better for spontaneous breathing or controlled ventilation patients, we are talking about how efficient each circuit is at preventing rebreathing in those situations

true

How does the circle system work?

1. Figure A depicts inspiration - As the bellows propels gas into the inspiratory limb past the inspiratory unidirectional valve, the lungs can inflate. -Driving gas pressure also closes the ventilator relief valve which is the route to the scavenger. 2. Figure B depicts exhalation - Lung deflation propels gas into the expiratory limb past the expiratory unidirectional valve. -The exhaled gases fill the bellows to a small pressure first then opens a ventilator relief valve and proceeds to the scavenger. -A small weight within the ventilator relief valve makes filling the bellows the path of least resistance until a small PEEP builds up which opens the valve.

When should you abandon low-flow anesthesia? (4)

1. Increase flows if equipment fails during case 2. Anesthetic agent monitor fails 3. Soda lime granules fail 4. Inspired oxygen monitor fails -more purple = more rebreathing

Checking Unidirectional Valves -Part of the daily machine check includes verifying unidirectional valves are functional -Different machines have differing ways to perform this check -What is one way to accomplish this test?

1. One method to accomplish this test: place a spare breathing bag on the elbow where you would normally connect the circuit to the patient. This will serve as your patient's lungs for the check. 2. Turning on mechanical ventilation will allow you to visualize lungs filling and collapsing (the bag) and simultaneously viewing the unidirectional valves opening/closing at the appropriate times.

What are the benefits of low fresh gas flow? (5)

1. Reduced pollution 2. Reduced cost 3. Preservation of tracheal heat and humidity 4. Delay of carbon dioxide granule drying 5. Preservation of body temperature

What are the disadvantages of Circle Systems? (5)

1. Relatively complex 2. Opportunities for disconnection 3. Malfunctioning unidirectional valves cause serious problems -Open =rebreathing -Closed = obstruction 4. Less portable than nonrebreathing circuits 5. Increased dead space (like all circuits)

What are the absolute contraindications to low-flow anesthesia? (3)

1. Smoke inhalation injury 2. Malignant hyperthermia 3. Other conditions that necessitate need for washout of dangerous gases or require high oxygen uptake

There are many factors that play into rebreathing. The three that make the biggest difference are:

1. alveolar gas 2. fresh gas 3. dead space

Why is there rebreathing in anesthesia circuits? (3)

1. cost reduction 2. increased humidity and warmth 3. decreased OR exposure to waste gas

What are the advantages of non-rebreathing circuits? (4)

1. light weight 2. convenient 3. easily sterilized and scavenged 4. exhaled gases in corrugated limb may provide heat and humidity to inspired gas (Bain system)

How do you conduct a Pethick test? (4)

1. occlude the elbow at the patient end of the circuit 2. close the APL valve 3. use the oxygen flush valve to fill the circuit 4. remove the occlusion at the elbow while flushing the circuit

How can you minimize resistance in breathing circuits? (5)

1. reducing circuit length 2. increasing circuit diameter 3. avoiding sharp bends 4. eliminating valves 5. maintaining laminar flow

When should you perform a pethick test? (2)

1. should be done as part of the pre-anesthetic checkout 2. you suspect fresh gas flow obstruction

Classification of Breathing Circuit Type: Closed Reservoir: yes Re-breathing: yes (complete) Example: (1)

Type: Closed Reservoir: Re-breathing: Example: circle at extremely low fresh gas flow with closed adjustable pressure-limiting (APL) valve

Classification of Breathing Circuit Type: Open-atmosphere Reservoir: Re-breathing: Example: (4)

Type: Open-atmosphere Reservoir: No Re-breathing: No Example: open drop (ether), insufflation, nasal cannula, simple face mask

Classification of Breathing Circuit Type: Semi-closed Reservoir: Re-breathing: Example: (1)

Type: Semi-closed Reservoir: Yes Re-breathing: Yes (partial) Example: circle at low fresh gas flow (less than minute ventilation) **used for almost every anesthetic

Classification of Breathing Circuit Type: Semi-open Reservoir: Re-breathing: Example: (2)

Type: Semi-open Reservoir: Yes Re-breathing: No Example: circle at high fresh gas flow (more than minute ventilation) and non-rebreathing circuits

Where does dead space end in a breathing circuit?

Where the inspiratory and expiratory gas streams diverge -In a circle system (our typical anesthesia circuit), dead space ends at the y-piece

Closed breathing circuits must ______ the patient demand as the APL is closed.

match