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FA2 Anesthesiology > Lecture 7 9/5/24 > Flashcards

Lecture 7 9/5/24 Flashcards

1
Q

What are the boundaries of the breathing circuit?

A

-starts at the junction with the common gas outlet
-connects to ET tube/mask

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2
Q

What are the functions of the breathing circuit?

A

-deliver O2 and volatile agent to patient
-allow intermittent positive pressure ventilation
-deliver waste gases to scavenging system
-allow measurement of airway pressure

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3
Q

What is rebreathing?

A

inhalation of previously exhaled gases, from which CO2 may or may not have been removed

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4
Q

What is equipment dead space?

A

space in the breathing circuit where inhalation and exhalation can coincide

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5
Q

What is the importance of equipment dead space?

A

it makes it possible for patients to inhale unfiltered exhaled gas

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6
Q

Where are the four critical places where equipment dead space is found?

A

-portion of ETT that extends out of the trachea
-elbow on the breathing circuit
-any connector used between the end of the ETT and the breathing circuit
-Y piece at the end of a Y circuit

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7
Q

What is tidal volume?

A

amount of air that moves in or out of the lungs with each respiratory cycle

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8
Q

What is minute volume?

A

sum of all gas volumes either inhaled or exhaled in one minute; tidal volume x resp. rate

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9
Q

What are the basic components of the breathing circuit?

A

-CO2 absorbent canister
-unidirectional valves
-APL/pop-off valve
-anesthesia breathing tubes
-reservoir bag
-pressure manometer

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10
Q

What are the characteristics of a non-rebreathing circuit?

A

-for patients smaller than 5-7 kgs
-O2 flow rate of 100-600 ml/kg/min
-more expensive
-no CO2 absorption system; fresh gas only
-faster speed of anesthesia depth changes
-minimum resistance

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11
Q

What are the characteristics of a rebreathing circuit?

A

-for patients larger than 5-7 kgs
-O2 flow rate of 10-40 ml/kg/min
-less expensive
-CO2 absorbed via soda lime
-slower speed of anesthesia depth changes
-larger resistance

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12
Q

Which components are absent from a non-rebreathing circuit?

A

-unidirectional valve
-CO2 absorbent

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13
Q

What are the benefits of a non-rebreathing circuit?

A

-no previously expired gas is re-breathed
-all gases exit the scavenge
-low resistance to ventilation
-altering the vaporizer settings results in rapid depth changes

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14
Q

How could a patient end up re-breathing CO2 on a non-rebreathing circuit?

A

hyperventilation

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15
Q

What are the cons of a non-rebreathing circuit?

A

-requires high fresh gas flows to push expired gases out to scavenging system
-high fresh gas flow contributes to patient’s heat and fluid losses
-more costly
-increases environmental pollution

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16
Q

How is the flowmeter setting chosen?

A

according to patient’s minute ventilation

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17
Q

What is minute ventilation?

A

resp rate/min x tidal volume

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18
Q

What is a Bain coaxial tube?

A

dual tube in which an inner tube carries fresh inspired gas and an outer tube carries expired gas

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19
Q

What are the disadvantages of the Bain non-rebreathing system?

A

-requires high fresh gas flow
-if inside tubing leaks and communicates with outside tubing, there is increased dead space and CO2 re-inhalation

20
Q

What is a Bain block?

A

a mounted component of an anesthesia machine consisting of an APL valve and a manometer to monitor pressure in the breathing circuit

21
Q

What are the benefits of a rebreathing circuit?

A

-more economical
-less polluting
-fresh gas flow just needs to meet metabolic oxygen requirements
-warms and moistens inspired air as heat and water are generated by CO2 absorption
-minimal apparatus dead space

22
Q

What are the cons of a rebreathing circuit?

A

-recycling of exhaled gases dilutes fresh gas and volatile anesthetic coming from the vaporizer
-slower changes in anesthesia planes
-lengthy tubing offers more resistance and work of breathing

23
Q

What is the primary function of the breathing tube?

A

convey gases to and from the patient

24
Q

How does the length of the breathing tube impact resistance and dead space?

A

increased length adds to resistance, but does not increase dead space

25
Q

Why are plastic breathing tubes better than rubber?

A

rubber can absorb the anesthetic

26
Q

Why should a coaxial tube not be used with an ET tube larger than 10mm?

A

there is too much resistance due to the inside tube being smaller than the ET tube

27
Q

What are the characteristics of the Y piece?

A

-connection between the ETT and a parallel breathing circuit
-increased mechanical dead space
-mixture of inspired and expired gases

28
Q

What are unidirectional valves?

A

one-way valves, both inspiratory and expiratory, that ensure a unidirectional flow of air to and away from the patient

29
Q

When does the inspiratory valve open and close?

A

-opens during the beginning of inspiration
-closes during expiration

30
Q

When does the expiratory valve open and close?

A

-opens during expiration
-closes during inspiration

31
Q

What is the main function of the unidirectional valves?

A

prevent the mixing of fresh gas with the CO2 rich exhaled gas

32
Q

What are the functions of the reservoir bag?

A

-allows accumulation of gas during exhalation
-helps monitor breathing
-allows IPPV
-adds compliance to the system

33
Q

How is reservoir bag size calculated?

A

patient’s weight in kg x tidal vol. x 6

34
Q

Why is it important to have an appropriate reservoir bag size?

A

-too large of a bag leads to slower changes in anesthetic depth
-too small of a bag leads to increased risk of barotrauma

35
Q

Why can a reservoir bag be used to supply patients with breaths?

A

it contains recycled gas, but the CO2 has already been filtered out

36
Q

What is the APL/pop-off valve?

A

-site of communication between the reservoir bag and the exhaust system
-principal security system of the circuit

37
Q

What is the function of the APL/pop-off valve?

A

allows the evacuation of gases in excess in the circuit over a certain pressure in order to avoid overpressure

38
Q

When should the APL valve be open vs closed?

A

-completely open during spontaneous ventilation
-closed when providing manual or mechanical positive pressure ventilation

39
Q

What happens if the APL valve is closed while the patient is spontaneously ventilating?

A

-pressure increases in circuit
-reservoir bag becomes distended
-pressure increases in resp. airways to very high positive pressure
-venous return, cardiac output, and arterial blood pressure decrease
-cardiac arrest occurs

40
Q

What are the characteristics of the pressure manometer?

A

-pressure gauge attached to the top of the absorber assembly
-calibrated in cm of water
-used to assess pressure during assisted/controlled ventilation as well as during ETT and machine leak checks

41
Q

What aer the characteristics of CO2 absorbent?

A

-removes CO2 from all expired gases, allowing rebreathing of anesthetic gases and O2 only
-contact between CO2 and soda lime produces a color change related to pH

42
Q

What is generated during the chemical reaction that removes CO2?

A

water and heat

43
Q

How can exhaustion of the CO2 absorbent be determined?

A

-pH indicator/color change
-canister cold to touch
-increased inspired CO2/hypercapnia
-increased RR, HR, and BP
-granules are hard and not crumbly

44
Q

What is the purpose of the exhaust system?

A

reduce personnel exposure to waste anesthetic agents vented from the breathing system

45
Q

What are the characteristics of passive scavenging without a filter?

A

-simple duct goes from exhaust outlet to outside air
-simple and inexpensive
-not practical in all buildings
-more polluting

46
Q

What are the characteristics of passive scavenging with a filter?

A

-activated charcoal canister connected to exhaust outlet
-removes halogenated anesthetics
-mobile and convenient
-can increase resistance to evacuation with high flow rates
-limited spare life
-does not eliminate N2O

47
Q

What is active scavenging?

A

-exhaust outlet is connected to vacuum system via an interface that controls suction with a needle valve
-has positive and negative pressure relief valves in case reservoir bag becomes empty or too full

FA2 Anesthesiology (23 decks)

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