Anesthesia Circuits Flashcards
Dead space
“Dead space” refers to any portion of the airway that does not participate in gas exchange (pharynx, trachea, bronchi)
Dead space in our airway causes all of us to rebreathe CO2 on every single breath
Dead space can also be thought of as any portion of the airway that causes us to rebreathe CO2
“Ventilated, but not perfused”
Anatomic dead space
Anatomic dead space includes the trachea, bronchi, pharynx, etc
2mL/kg in patients in the upright position
Physiological dead space
Physiologic dead space refers to alveolar spaces that receive air but no blood flow, usually from pulmonary alveoli that are destroyed (smokers, elderly, etc.)
What happens to the physiology of smokers?
- Alveolar sac fuse into “blebs” or bullae
- Excess mucous forms in the bronchioles
- Pulmonary capillaries get destroyed
Use lower tidal volumes with smokers and higher respiratory rates
Mechanical dead space
Mechanical dead space includesanesthesia airway equipment (circuit tubing, humidifiers, endotracheal tubes, etc)
Pulmonary shunt
A pulmonary shunt means that, although MOST of the blood passing our alveoli picks up oxygen, SOME of the blood in our body “bypasses” the alveoli and doesn’t pick up oxygen
Usually around 3% of cardiac output
V/Q ratios
“Ventilation,” or “V” refers to “air flow” to an area
Perfusion,” or “Q” refers to ALVEOLAR blood flow
Capital letter is normal, lowercase refers to reduced
V/Q mismatch
Anytime we get a v (less ventilation) or a q (less perfusion), we have a “V/Q mismatch”
What is the most common cause of hypoxia in the recovery room?
The most common cause of hypoxemia in the recovery room is “V/Q mismatch,” most likely due to atelectasis
V/q
In anesthesia, instead of “V/q,” we would say “ventilation without perfusion”
v/Q
In anesthesia, instead of “v/Q,” we would say, “perfusion without ventilation”
Would V/q (normal ventilation, but less alveolar blood flow) represent dead space or a pulmonary shunt?
Dead space
Would v/Q (less ventilation, but normal alveolar blood flow) represent airway dead space or a pulmonary shunt?
Pulmonary shunt
Is this an example of dead space (V/q) or pulmonary shunt (v/Q)?
Pulmonary shunt (v/Q)?
Is this (pulmonary embolism) an example of dead space (V/q)or pulmonary shunt (v/Q)?
Dead space (V/q)
Is this an example of dead space (V/q) or pulmonary shunt (v/Q)?
Pulmonary shunt (v/Q)
Is this an example of dead space (V/q) or pulmonary shunt (v/Q)?
Pulmonary shunt (v/Q)
Will this lead to an increase in dead space (V/q) or pulmonary shunt (v/Q)?
Pulmonary shunt (v/Q)
Is emphysema an example of dead space (V/q) or pulmonary shunt (v/Q)?
Both!
Bullae, along with destroyed pulmonary capillaries
Will spontaneous ventilation under GA lead to an increase in dead space (V/q) or pulmonary shunt (v/Q)?
Pulmonary shunt (v/Q)
A patient has a profound drop in cardiac output (from internal hemorrhage), will this cause more dead space (V/q) or pulmonary shunting (v/Q)?
Dead space (V/q)
Examples of open circuits?
- Nasal cannula
- Insufflation/”blow by”
- Open drop anesthesia
An “open circuit” is open to the atmosphere, meaning that, in addition to going into the patient’s airway, it freely disperses around the face and into the room (because there is nothing to confine the gas to the patient’s airway)
Examples of partial re-breathing circuits?
- Anesthesia circuits
- Semi-open (Mapleson)
- Semi-closed (the kinds on our anesthesia machine) - Oxygen masks
- Simple face mask, “non-rebreather” mask, Venturi (“Venti” mask), self-inflating Ambu bag
Examples of non-rebreathing circuits?
- A T-piece
- A “nonrebreather” mask
Why should you be catious with open circuits?
Since open circuits are primarily used for oxygen delivery, and since the oxygen is dispersed around the face and into the room, and since oxygen is one of the three elements (fuel, ignition source, and oxygen) that kindle fires, there is a higher risk for surgical fires with open circuits, especially if the surgery is around the face.
Contraindicated with facial surgery with drapes
The anesthesia provider needs to communicate with the patient that, because they will not be able to use oxygen, that they won’t be able to give as much sedation