Lecture 7 9/5/24 Flashcards
(47 cards)
What are the boundaries of the breathing circuit?
-starts at the junction with the common gas outlet
-connects to ET tube/mask
What are the functions of the breathing circuit?
-deliver O2 and volatile agent to patient
-allow intermittent positive pressure ventilation
-deliver waste gases to scavenging system
-allow measurement of airway pressure
What is rebreathing?
inhalation of previously exhaled gases, from which CO2 may or may not have been removed
What is equipment dead space?
space in the breathing circuit where inhalation and exhalation can coincide
What is the importance of equipment dead space?
it makes it possible for patients to inhale unfiltered exhaled gas
Where are the four critical places where equipment dead space is found?
-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
What is tidal volume?
amount of air that moves in or out of the lungs with each respiratory cycle
What is minute volume?
sum of all gas volumes either inhaled or exhaled in one minute; tidal volume x resp. rate
What are the basic components of the breathing circuit?
-CO2 absorbent canister
-unidirectional valves
-APL/pop-off valve
-anesthesia breathing tubes
-reservoir bag
-pressure manometer
What are the characteristics of a non-rebreathing circuit?
-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
What are the characteristics of a rebreathing circuit?
-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
Which components are absent from a non-rebreathing circuit?
-unidirectional valve
-CO2 absorbent
What are the benefits of a non-rebreathing circuit?
-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
How could a patient end up re-breathing CO2 on a non-rebreathing circuit?
hyperventilation
What are the cons of a non-rebreathing circuit?
-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
How is the flowmeter setting chosen?
according to patient’s minute ventilation
What is minute ventilation?
resp rate/min x tidal volume
What is a Bain coaxial tube?
dual tube in which an inner tube carries fresh inspired gas and an outer tube carries expired gas
What are the disadvantages of the Bain non-rebreathing system?
-requires high fresh gas flow
-if inside tubing leaks and communicates with outside tubing, there is increased dead space and CO2 re-inhalation
What is a Bain block?
a mounted component of an anesthesia machine consisting of an APL valve and a manometer to monitor pressure in the breathing circuit
What are the benefits of a rebreathing circuit?
-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
What are the cons of a rebreathing circuit?
-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
What is the primary function of the breathing tube?
convey gases to and from the patient
How does the length of the breathing tube impact resistance and dead space?
increased length adds to resistance, but does not increase dead space
