Anesthesia Circuits Flashcards
Any portion of the airway that does not participate in gas exchange
Dead space
True/false: Dead spaces causes us to rebreathe CO2 with every breath
True
Anatomic dead space
Pharynx, trachea, bronchi
2ml/kg
Physiologic dead space
Alveolar spaces that receive air but no blood flow
Physiology of smokers
- Alveolar sacs fuse into blebs (bullae)
- Excess mucus forms in the bronchioles
- Pulmonary capillaries get destroyed
Mechanical dead space
Anesthesia airway equipment (circuit tubing, humidifiers, ETT)
Which has less dead space? Masks, LMAs, or ETT?
ETTs have less, then LMAs, then masks
True/false: Even though dead space is fixed, when a patient takes a larger breath, a lower percentage of that will be dead space?
True
Perfused, but not ventilated
Pulmonary shunt
v/Q
Ventilated, not perfused
Dead space
V/q
Most common cause of hypoxemia
V/Q mismatch most likely due to atelectasis (v/Q, shunt)
v/Q
Pulmonary shunt
V/q
Dead space
Is a pneumothorax a shunt or dead space?
v/Q, pulmonary shunt
Pulmonary embolism: shunt or dead space?
V/q, dead space
Pulmonary edema: shunt or dead space?
v/Q, pulmonary shunt
Atelectasis: shunt or dead space?
v/Q, pulmonary shunt
Increase in pulmonary vascular resistance: shunt or dead space?
V/q, dead space
R mainstem intubation: shunt or dead space?
v/Q pulmonary shunt
Top lung in lateral decubitus position: shunt or dead space?
V/q, dead space
Lower lung in lateral decubitus position: shunt or dead space?
v/Q, pulmonary shunt
Emphysema: shunt or dead space?
Both (due to bullae and mucus plugs)
Spontaneous ventilation under GA: shunt or dead space?
v/Q, pulmonary shunt
NTG (inc pulmonary vasculature and blood flow): shunt or dead space?
v/Q, pulmonary shunt
Drop in cardiac output due to internal hemorrhage: shunt or dead space?
V/q, dead space
Types of circuits used in anesthesia
- Open circuits (nasal cannula, insufflation/blow by, open drop anesthesia
- Partial re-breathing circuits (anesthesia circuits, oxygen masks)
- Non-rebreathing circuits (T-piece, nonrebreather mask)
What are open circuits primarily used for?
Oxygen delivery
Max FiO2 for nasal cannula
44% (reached at 6L/min)
How to calculate FiO2 with nasal cannula
21% + 4% for each L/min
Hazards of nasal cannula use
- Dries out nares at >4L/min flows
2. Can increase risk of fire for facial surgeries/where cautery is used near face
When is insufflation (blow by) used?
When a patient is claustrophobic, anxious, or won’t tolerate the mask well
During sedation/scope cases
Facial surgeries to prevent CO2 accumulation under the drapes (use air, NOT O2)
Types of partial rebreathing circuits
- Semi-closed partial rebreathing circuits (used on our machines)
- Semi-open partial rebreathing circuits (Mapleson)
- Partial rebreathing O2 masks (simple face mask, venturi mask, ambu bag, “nonrebreathing” mask on lower flows
Advantages and disadvantages to rebreathing circuits
Advantage: Conserves heat and humidity
Disadvantage: Slower wake up on emergence and potential for CO2 retention/hypercarbia
How can you prevent rebreathing in partial rebreathing circuits?
Increase fresh gas flow, or by opening the APL valve if applicable
What do you do if you want to use an LMA or ETT outside of the operating room?
Transport an anesthesia machine to the room and hook it up to scavenging
Use a mapleson circuit
Best mapleson circuit for spontaneous ventilation
Mapleson A -APL valve closer to patient, FGF at end of circuit
Best mapleson circuit for control ventilation
Mapleson D -FGF closer to patient, APL valve at end of circuit
Mapleson circuits are primarily used for:
Delivering oxygen
Advantage of Mapleson Circuits
Can hook them up to ETT or LMA for GA (TIVA)
Can deliver positive pressure ventilation
Disadvantage of Mapleson Circuits
More dead space = more potential to rebreathe CO2
No CO2 absorber and no inspiratory or expiratory valves
Purpose of T piece
When a patient is breathing on their own but not ready to wake up yet
To limit/decrease rebreathing CO2. Oxygen goes in one side and CO2 comes out the other
Disadvantage of T piece
Cannot use positive pressure
Advantages of a coaxial circuit
Conserves heat and humidity
Disadvantage to a coaxial circuit
Possibility of disconnection or kink in tubing
Open during inspiration, closed during expiration
Inspiratory valve
Open during expiration, closed during inspiration
Expiratory valve
Purpose of unidirectional valves
So the patient does not rebreathe CO2
When is a CO2 absorber practically unneccesary?
When fresh gas flows over 5L/min are running
Desiccated “old school” granules will:
- Degrade all volatile agents into carbon monoxide (desflurane is the worst)
- Accelerate the degradation of sevoflurane into compound A
AIAAAH recommends a humidity range of ___ for the OR
30-60%
FiO2 for a simple face mask
40% at 5L/min
60% at 10L/min
FiO2 for nonrebreathing mask
80s at 10L/min
90s at 15L/min
Maximum FiO2 of venturi mask
60%
also depends on the adapter
Purpose of supplemental oxygen
To compensate for:
- atelectasis
- anesthetic induced hypoventilation
Supplemental oxygen is most often given:
During MAC
In transport from OR to PACU
In the PACU
Airway resistance equation (and what each variable means)
R= 8ul/π(r^4)
R: resistance
u: viscosity of air
l: length of circuit
r: radius
What does the Hagen Poiseuille equation tell us?
- Adding dead space (length) to a circuit increases resistance
- Resistance can minimized if: the diameter of the equipment is bigger or the length of the equipment is shorter (diameter has a bigger effect than length)
