Anesthesia Circuits Flashcards
any portion of the airway that does not participate in gas exchange (pharynx, trachea, bronchi) or any portion of the airway that causes us to rebreathe CO2
dead space
What is absent in dead space?
alveolar blood flow
3 structures included in dead space
trachea, bronchi, pharynx
anatomic dead space is approximately how many mL/kg in the upright position
2 mL/kg (also 1/3 of patient’s tidal volume)
refers to alveolar spaces that receive air but no blood flow
physiologic dead space
how does physiologic dead space occur?
when pulmonary capillaries are destroyed (smokers, elderly pts, etc); damaged alveolar spaces become more and more like the trachea
3 aspects of physiology of smokers
1.) alveolar sacs fuse into blebs (bullae) 2. excess mucus forms in the bronchioles 3. pulmonary capillaries get destroyed
what is included in mechanical dead space
airway equipment, circuit tubing, humidifiers, endotracheal tubes
Normal EXTRATHORACIC anatomic dead space in adults (nose and pharynx only)
70-75 mL
An 8.0 ETT tube has a dead space volume of ?
12.6 mL
total dead space in an intubated adult?
up to 60 mL
dead space with LMA
90 mL
True/ False: LMAs have larger dead space but less resistance than ETTs.
TRUE
adult Y piece dead space
8 mL
pediatric Y piece dead space
4 mL
humidifier dead space
10-60 mL
True/ False: dead space volume is FIXED.
TRUE
when pt takes a larger breath, ____ percentage of that breath will be dead space
lower
when pt takes a smaller breath, a ___ percentage of that breath will be dead space.
higher
what kinds of patients are most affected by mechanical dead space?
pediatric patients
what kind of patient’s have the most dead space? (mask ventilated, ventilated w/LMAs, ventilated w/ ETT)
mask ventilated pts
normal TOTAL anatomic dead space of a 70 kg adult
140 ml (2 ml/kg)
when SOME of the blood in our body bypasses the alveoli and doesn’t pick up oxygen
pulmonary shunt
what percentage of blood or cardiac output passes the alveoli and doesn’t participate in gas exchange?
3%
portions of the airway that don’t participate in gas exchange due to shunting are said to be ____ but not ____
perfused but not ventilated
what does Q stand for in the V/Q ratio?
alveolar blood flow; alveolar perfusion
most common cause of hypoxemia in the recovery room
V/Q mismatch
v/Q mismatch is most likely due to
atelectasis
meaning of V/q; does it represent dead space or pulmonary shunt?
ventilation without perfusion (there is reduced or absent alveolar blood flow) ; dead space
meaning of v/Q; does it represent airway dead space or a pulmonary shunt?
perfusion without ventilation ; normal alveolar blood flow but less or absent ventilation (air flow); pulmonary shunt
collapsed lung/pneumothorax is an example of dead space or pulmonary shunt?
pulmonary shunt
pulmonary embolism is an example of dead space or pulmonary shunt?
dead space
pulmonary edema is an example of dead space or pulmonary shunt?
pulmonary shunt
atelectasis is an example of dead space or pulmonary shunt?
pulmonary shunt
pt experiences an increase in pulmonary vascular resistance this will lead to an increase in dead space or pulmonary shunt?
increase in DEAD SPACE
right mainstem intubation will lead to increase in dead space or pulmonary shunt?
pulmonary shunt
in the lateral decubitus position, does the upper lung have dead space or shunt?
dead space
in the lateral decubitus position, does the lower lung have dead space or shunt?
shunt
emphysema is an example of dead space or pulmonary shunt?
BOTH
spontaneous ventilation under GA is an example of dead space or pulmonary shunt?
pulmonary shunt
pt receives a bolus of nitroglycerin which dilates pulmonary vasculature and increases pulmonary blood flow will this cause more dead space or pulmonary shunt?
pulmonary shunting
pt has a profound drop in cardiac output from internal hemorrhage will this cause more dead space or pulmonary shunting?
dead space
types of circuits used in anesthesia (3)
- open circuit 2. partial re-breathing circuit 3. non rebreathing circuit
types of OPEN circuits (3)
- nasal cannula 2. insufflation “blow by” 3. open drop anesthesia
types of rebreathing circuits (3)
- semi-closed partial rebreathing circuits (anesthesia machine circuits)
- semi open (Mapleson circuits) partial rebreathing circuit
- partial rebreathing oxygen masks (simple face mask, nonrebreather mask, Venturi mask, self inflating Ambu bag)
types of nonrebreathing circuits (2)
- T piece 2. a nonrebreather mask
type of circuit used for oxygen delivery
open circuits
what should you be cautious about with open circuits?
higher risk for surgical FIRES with open circuits especially if the surgery is around the face!!!
most common flow rate used in pts w/ nasal cannula
4 L/min
what should be communicated to the pt in facial surgery where facial drapes and cautery will be used?
b/c they will not be able to use O2 that they won’t be able to give as much sedation
if pt is NOT ok with minimal sedation.. .what can be done?
intubation or have an LMA placed
what should you do for anxious pts?
insufflate (O2 blow by) near the face until the pt is sedated
what procedures might require insufflation when an O2 mask can’t be placed?
EGD or TEE ; pt can wear NC but not mask
without oxygen under the drapes how do we prevent accumulation of CO2 under the drapes?
place breathing circuit under the drape, turn on AIR up to 15 L/min, insufflate the air around the patient’s face and create a path under the drape for the air (and Co2) to escape
what is used during bronchoscopy
insufflation via a bronchoscope
refers to provider soaking gauze in volatile anesthetic and placing it over the patient’s face
open drop anesthesia
kind of circuit in our anesthesia machine; also referred as circle system breathing circuits
semi closed partial rebreathing circuit
primarily used outside the OR and are used to deliver oxygen (not anesthetic gases)
semi open/mapleson partial rebreathing circuit
what do semi open mapleson partial rebreathing circuits NOT have? (2)
- inspiratory and expiratory unidirectional valves 2. a CO2 absorber
True/False: some exhaled gas is rebreathed whether it be in a full on circuit or in an oxygen mask
TRUE
advantage of rebreathing ?
conserved heat and humidity
disadvantage of rebreathing?
- slower wake up on emergence 2. there is a potential for CO2 retention and hypercarbia
How to adjust rebreathing is partial rebreathing circuits?
- APL valve 2. fresh gas flow
True/False: the higher the fresh gas flow, the less rebreathing
TRUE
two common method of supplemental oxygen delivery during transport or during sedation outside the OR
nasal cannula and oxygen face mask
if you want to provide general anesthesia with an ETT or LMA outside the OR what are the two options?
- transport machine to the remote location 2. use a mapleson circuit
Identify type of mapleson circuit and what its best and worst for
Mapleson A; best for SV worst for CV
Identify type of mapleson circuit and what its best and worst for
Mapleson D; best for CV worst for SV
Identify type of mapleson circuit and what its best and worst for
Mapleson E; Ayre’s T piece
Identify type of mapleson circuit and what its best and worst for
Mapleson F; Jackson Rees’ Modification
advantages of mapleson circuit for supplemental O2 delivery instead of nasal cannula or oxygen facemask (2)
- ability to be hooked up to ETT or LMA which can allow general anesthesia (with TIVA) in these locations outside the OR without an anesthesia machine
- deliver positive pressure ventilation
disadvantage of mapleson circuit
lot more dead space and there is much greater potential to rebreathe CO2 b/c:
- only one tube for inhalation and exhalation CO2 does into inspiratory tubing
- there is no CO2 absorber
- there are no inspiratory and expiratory valves
how do you minimize rebreathing in Mapleson circuits? (3)
- using a higher fresh gas flow
- opening the APL valve
- shortening the circuit volume
which mapleson circuits are commonly used today?
D,E, and F
the bain circuit is what kind of mapleson circuit and where is fresh gas flow ?
D; fresh gas flow INSIDE the breathing limb
a T piece adds how much rebreathing?
minimal or 0% rebreathing of CO2
disadvantage of T piece
positive pressure ventilation is not possible; it can only be used in pts who are spontaneously ventilating
most common use for T piece
for pt breathing on own but not yet ready to be extubated ; have good tidal volume but not responding to verbal commands
t piece that can allow postive pressure ventilation because it has a breathing bag
mapleson F
Components of semi closed circuit (6)
- circuit tubing
- elbow adapter
- inspiratory and expiratory unidirectional valves
- CO2 absorber
- breathing bag
- humidifier
anesthesia circuit tubing options
- circuit with inhalation and exhalation tubing
- coaxial circuit
what’s important before the Y piece (proximal to the Y piece) ?
separate tubes for inspiration and expiration in this portion of the circuit
what’s important after the Y piece (distal to the Y piece) ?
expiratory and inspiratory gases share the same tube (expiratory CO2 mixed with the inspired gas) in this portion of the circuit
used to connect the anesthesia circuit with pt’s airway device
elbow adapter
inspiratory valve is ___ during inhalation and ____ during expiration ; function?
open; closed; prevents exhaled gases from going into the inspiratory limb
the expiratory valve is ____ during inspiration and ____ during expiration. function?
closed; open; prevents the pt from inhaling gases from the expiratory limb
eliminates rebreathing of CO2 from the circuit (proximal to the Y piece) even with low fresh gas flows
unidirectional valves
does the dead space of a circuit increase if an anesthetist increases the length of the circuit DISTAL to the Y piece (like w/ elbow adapter, humidifier, ETT etc) ?
YES; increases the amount of CO2 that pt rebreathes they are considered DEAD space
where is air humidified in non-anesthetized pts?
upper airway
intubated pts have dry gases that absorb moisture /heat from the upper airway causing what? (2)
- a decrease in body temp
- dehydration of the airway , mucus plugging, and atelectasis
a relative humidity (%) inhibits bacterial growth and decreases the potential for static electricity?
50-60%
what is the recommended humidity range for the OR
30 to 60%
Functions of humidifier on anesthesia circuits (3)
- humidifies dry operating room gases
- a filter is also added to it in order to trap bacteria and virsues
- can add 10-60 mL dead space to circuit
Possible locations for humidifier? (2)
- distal to the Y piece/ elbow (best humidification here)
- on the expiratory limb of the circuit (less effective humidification)
When do you give supplemental O2? (3)
- during transport
- in the recovery/PACU
- sedation/MAC anesthesia cases
FiO2 with simple face mask at 5L/min
40%
FiO2 on simple face mask at 10L/min
60%
maximum FiO2 with Venturi mask
up to 60%
main purpose of supplemental oxygen is to compensate for what? (2)
- anesthetic induced hypoventilation
- atelectasis
what does the Hagen Poiseuille equation tell us? (2)
- ) adding dead space (length) to a circuit increases airway resistance
- ) resistance can be minimized if diameter of equipment is bigger and length of equipment is shorter
The compliance of pt’s breathing circuit is 12 mL/cmH20. An anesthetist is providing positive pressure ventilation to their pt on the ventilator. Vent settings are:
PIP- 30 cmH20
Respiratory rate =6
minute ventilation= 7.2 L
what is the compliance loss (in mL) in the breating circuit?
360 mL
(12 x 30)
