Anesthesia Circuits Flashcards
dead space
any portion of the airway that doesn’t participate in gas exchange
breathing normally do we rebreathe CO2?
yes b/c of dead space
if you increase someones dead space do you increase or decrease the amount of CO2 rebreathed?
increase
what is the amount of anatomic deadspace in patients in upright position?
2mL/kg
~ 1/3 of patients Vt
Physiologic dead space
alveolar spaces that receive air but no blood flow
What patients have more physiologic dead space?
smokers, elderly
What is special about the physiology of smokers (airway)?
1- alveolar sacs fuse into blebs
2- excess mucus in bronchioles
3- pulmonary capillaries destroyed
Mechanical dead space
circuit tubing
humidifiers
ETT
etc
normal extrathoracic anatomic deadspace adults
70-75mL
ETT dead space
12.6mL
~60mL less than a non intubated pt
LMA dead space
90mL of dead space
Face mask dead space
162mL
Y piece dead space
8mL (peds= 4mL)
Is dead space fixed?
yes
pulmonary shunt
some blood vessels bypass alveoli and doesn’t pick up alveoli
What is the normal healthy person % of shunting?
up to 3%
Could we increase pulmonary shunting?
yes by ventilating only one
Capital V
normal ventilation
Lowercase v
less ventilation
Capital Q
normal alveolar perfusion
Lowercase q
less alveolar perfusion
ventilation
alveolar capillary gas exchange
perfusion
delivery of blood and oxygen to the organs of the body
V/Q mismatch
decreased alveolar capillary exchange and some degree of hypoxia
V/q
dead space
ventilation without perfusion
v/Q
pulmonary shunt
perfusion without ventilation
lateral decubitus position
upper lung= more ventilation
lower lung= more perfusion
3 types of circuits used in anesthesia
- open circuit
- partial rebreathing circuit
- “non-rebreathing” circuit
3 examples of open circuit
nasal cannula
insufflation “blow by”
open drop anesthesia
example of partial rebreathing circuits
semi-open mapleson
semi closed machine
simple face mask
self inflating ambu bag
example non rebreathing circuit
t piece
non rebreather
what is the caution of using an open circuit in facial/head/eye surgery?
if using cautery then chance for fire
equation to estimate FiO2 with a nasal cannula
21% + 4% per 1L/min flow
what is the max FiO2 with nasal cannula?
44% with 6L/min
what is the top flow rate you want to use to make the patient comfortable?
4L/min
insufflation blow by
people who do not want mask around face or children
EGD
esophagogastroduodenoscopy
oxygen options for EGD
NC and blow by
special mask with hole for the scopes
how to manage a MAC case with a bovie and facial drapes
turn on air and place it under the drape
insufflation via bronchoscope
oxygen source hooked up and insufflated for brief apnea
what is the advantage for rebreathing circuits?
conserves heat and humidity
disadvantages to rebreathing
slower wake up
CO2 retention and hypercarbia
how to prevent rebreathing in partial rebreathing circuit
turn up FGF rate
adjust APL valve if has one
two common mistakes with oxygen
forgetting to turn on when transport or when preoxygenating
sedation outside OR
IV only medication
spontaneous breathing and oxygen
ambu bag on deck
limitation to NC and Facemask
not able to provide positive pressure ventilation
2 options for general outside the OR
- bring machine
2. use mapleson circuit
if the room had oxygen wall supply but no wall scavenging then could you supply volatile agent?
no, TIVA only
mapleson A
best for spontaneous
worst for control ventilation
mapleson d
best for cv
worst for sv
mapleson E
ayre’s T piece
mapleson F
jackson rees modification
advantage to mapleson circuit
ability to hook to ETT
provide positive pressure ventilation
disadvantage of mapleson circuit
- 1 tube for inhale exhale so increase deadspace
- no CO2 absorber
- no inspir. and expir. valves
how to minimize rebreathing in mapleson circuit
higher FGF (greater than minute ventilation)
- open APL
- shorten circuit volume
which maplesons are commonly used?
D,E,F
bain circuit
modification of mapleson D co-axial design inspired gas (inner) expired gas (outer)
ayre’s t piece
mapleson E
spontaneous only
close to 0 added rebreathing
advantage of t piece
no rebreathing
disadvantage of t piece
no positive pressure ventilation
when do we clinically use t piece?
when the pt is SV but not responding to commands to transport to PACU
jackson rees’ modification
mapleson F
t piece that allows PPV
popular in peds transport
what are the components of the semi closed circuit
circuit tubing elbow adapter inspir. and expir. unidirectional valves co2 absorber breathing bag humidifier
proximal to y piece
separate inspir and expir tubes
distal to y piece
inspir and expir share tubing
2 options for circuit tubing
inhalation and exhalation tubing
coaxial circuit
advantage of coaxial circuit
conserves heat and humidity
disadvantage of coaxial circuit
disconnection or breaking/kinking of inner tube lead to rebreathing/hypercarbia/hypoxia
elbow adapter
attaches y piece to ett
when is the inspiration valve open?
during inspiration
when is the expiratory valve open?
during expiration
what does the CO2 absorber convert CO2 into?
water and heat
what color is an old(non usable) CO2 absorber?
purple
change when 50-70% changed color
what are the CO2 absorber granules made of?
soda lime
silica added
large grannules
lower resistance
less absorptive capacity
small grannules
increases resistance
better absorptive capacity
what are the two things that dried out CO2 grannules will do?
degrade volatile agents to carbon monoxide (Des is most)
accelerate sevo into compound A
is the CO2 absorber a double or single canister?
double canister to decrease circuit resistance
when is the CO2 absorber unnecessary?
when FGF > 5L/min
which is more compliant lungs or breathing bag?
breathing bag
what is the humidity in the OR?
30-60%
humidifier
humidifies gases
filter to trap bacteria
adds 10mL-60mL deadspace
what is the lower weight limit for humidifiers?
2.5kg
what is the lower weight limit for filters?
3kg
what are the locations for the humidifier?
distal to elbow piece
expiratory limb
simple face mask FiO2 at 5L/min
40%
simple face mask fiO2 at 10L/min
60%
venturi/venti mask
range 24-60% fiO2
choose color for specific one
nonrebreathing mask at 10L/min and 15L/min
80% fiO2
90%
what are the two main reasons for supplemental oxygen?
compensate for:
hypoventilation
atelectasis
When are the supplemental devices usually used?
sedation
transport
pacu
two clinical uses of ambu bag?
emergency to ventilate
transport patient that is not going to be extubated
what are the four steps to take when transporting with ambu bag?
call resp therapy to get ventilator in pacu
ventilate during transport
place patient on ventilator
administer a propofol drip if paralyzed
airway resistance
you can decrease resistance by a larger diameter and shorter length equipment
