6. Anesthesia Circuits Flashcards
basic parts of anesthesia circuit (9)
- inspiratory one way valve
- inspiratory tubing
- y-piece
- elbow adapter
- expiratory tubing
- expiratory one way valve
- breathing bag
- CO2 absorber
- humidifier
inspiratory valve
open during inspiration
closed during expiration
inhibits CO2 rebreathing
all inhaled gas come from inspiratory limb (free of CO2)
expiratory valve
open during expiration
closed during inspiration
inhibits CO2 rebreathing
all exhaled gas goes to expiratory limb
Y-Piece
merges the inspiratory and expiratory limbs
able to connect circuit to mask, LMA, ETT
humidifier
warms/humidifies gases
filters bacteria/viruses
prevents machine contamination
elbow adapter
connect circuit to pt airway device
not necessary
helps prevent pulling of tube
breathing bag
more compliant than lungs
- if circuit P increase, bag absorbs more P than lungs
types of anesthesia circuit tubing
circuit w/inhalation and exhalation tubing
coaxial circuit
circuit w/inhalation and exhalation tubing
most common
uses y piece
co-axial circuit
inspiratory lumen (purple) is inside expiratory lumen (clear)
co-axial circuit advantage
better conserves heat/humidity
exhaled gases in exterior lumen warm up inner lumen
co-axial circuit disadvantage
possibility of disconnecting/kinking inner fresh gas tubing
- hypoxia / hypercarbia
dead space
any portion of the airway that does not participate in gas exchange
any portion of the airway that is not alveoli (serves no respiratory function)
any portion of the airway that causes us to rebreathe CO2
increasing dead space
increases amount of CO2 rebreathed
anesthesia circuit dead space
anytime inhaled and exhaled gases occupy the same space
anything distal to the y piece:
masks
LMAs
ETT
elbow adapter
humidifier
inspiratory limb dead space
none
will not have CO2 in it
expiratory limb dead space
none
pt cant inhale CO2 from the expiratory limb
y-piece dead space
portion distal to the Y piece has inhaled and exhaled gases mixed
distal to y piece has dead space
3 types of dead space
anatomic
mechanical
physiological
anatomic dead space
portions of airway that do not participate in gas exchange
nose
trachea
bronchi
pharynx
normal Total anatomic dead space
2mL/kg
1/3 of tidal volume
upright position
mechanical dead space
anesthesia airway equipment
anything distal to y piece
physiologic dead space
alveolar space that receive air but no blood flow
damaged alveolar capillaries are dead space
lung disease pts have more dead space
physiology of smokers
alveolar sacs fuse into blebs
excess mucus in bronchioles
destroyed pulmonary capillaties
normal Extrathoracic anatomic dead space
70-75mL
nose/pharynx
endotracheal tube dead space
8.0 ETT = 12.6mL dead space
LMA dead space
90mL
face mask dead space
126mL
ypiece dead space
adult: 8mL
ped: 4mL
humidifier dead space
10-60mL
dead space ranking for ventilation
most
- facemask (162mL)
- LMA (90mL)
- ETT (12.6mL)
least
dead space ranking for circuit pieces
most
- humidifier (10-60mL)
- Y piece (4-8mL)
least
dead space volume
is fixed
(does not change)
how does tidal volume affect dead space
Tv affects the % of dead space in each breath
- larger TV = lower % of dead space
- small TV = higher % of dead space
smaller breaths are less efficient
peds and dead space
small tidal volumes
most affected by mechanical dead space (high % of ventilation)
pulmonary shunting
some blood that goes to the lungs bypasses the alveoli and dose not pickup O2
normal pulmonary shunt
3%
right mainstem intubation shunting
50%
V/Q ratio
alveolar capillary gas exchange
V
ventilation/airflow to alveoli
alveolar ventilation
Q
blood flow to alveoli
V/Q mismatch
alveolar capillary gas exchange is abnormal/decreased
causes hypoxia and/or hypercarbia
type of V/Q mismatch
v/Q: decr alveolar ventilation
or
V/q: decr alveolar blood flow
V/q
pulmonary dead space
due to reduced pulmonary blood flow
normal alveolar ventilation
larger % of the airway not participating in gas exchange
V/q causes
pulmonary embolism
profound CO drop
pulmonary vasoconstriction
v/Q
pulmonary shunting
due to reduce alveolar ventilation
normal blood flow
higher % of blood bypassing lungs w/out participating in gas exchange
v/Q causes
right mainstem intubation
pneumothorax
pulmonary edema
atelectasis
most common V/Q mismatch
atelectasis
causes hypoxemia in recovery
simultaneous
v/Q
and
V/q
lateral decubitus position
emphysema
COPD
lateral decubitus position
V/Q mismatch
upper lung: V/q
- more ventilation
- less blood flow
lower lung: v/Q
- less ventilation (compressed)
- more blood flow (gravity)
Emphysema
V/Q mismatch
bullae/mucus: v/Q
- less alveolar ventilation
- shunt
destruction of capillaries: V/q
- less pulmonary blood flow
- dead space
normal V/Q ratio
0.8
V/Q = (4L/min)/(5L/min)
normal minute ventilation
6L/min
(tidal volume 500mL x 12 RR= 6L/min)n
alveolar ventilation (V)
4 L/min
minute ventilation - dead space vent
6L/min - 2L/min == 4L/min
normal CO (Q)
5L/min
supplemental O2 circuits
nasal cannula
high flow nasal cannula
simple facemask
nonrebreathing mask
venturi msk
supplemental O2 circuit uses
sedation (MAC anesthesia)
transport to PACU
in PACU
nasal cannula
max FiO2: 44% (6L/min)
nasal cannula FiO2 calc
FiO2 = 21% + 4%(L/min flow)
nasal cannula hazards
> 4L/min can damage nares
increase risk of fires during sedation cases near the face w/cautery
high flow nasal cannul
max: 60L/min = 95% FiO2
O2 humidified
+ airway pressure: 3cmH2O
simple face mask
5L/min = 40% FiO2
10L/min = 60% FiO2
must be at least 6L/min to prevent CO2 rebreathing
nonrebreathing mask
attached bag minimizes CO2 rebreathing
10L/min = 80% FiO2
15L/min = 90% FiO2
slight rebreathing does occur (cannot reach 100% FiO2)
venturi mask
specific FiO2 between 24-60%
adapter-specific
preventing rebreathing in partial rebreathing circuits
increase O2 flow rate
O2 flow rates vs CO2 rebreathing
inversely proportional
supplemental O2 compensates for:
anesthetic induced hypoventilation
atelectasis
supplemental O2 during GA
ETT or LMA connected to anesthesia circuit
supplemental O2 outside OR under GA
mapleson circuit
mapleson circuit
delivers O2
positive pressure ventilation
w/LMA or ETT
for general anesthesia
supplemental O2 for MAC sedation
use mask or nasal cannula
cannot provide PPV
mapleson A
best for SV (pt breathing on own)
worst for CV
breathing bag
APL valve near mask
mapleson D
best for CV (breathe for pt)
worst for SV
breathing bag
APL valve near bag
bain circuit
modified mapleson D
co-axial design
inner lumen: FGF
outer lumen: expired gas
mapleson E
ayres T-piece
- hooks up to ETT
- only for SV pts
inspiratory: right
expiratory: left
minimal rebreathing of CO2
no breathing bag or APL valve
mapleson’s commonly used today
D
E
Fm
mapleson’s not commonly used
A
B
C
mapleson E advantage
minimal to no rebreathing
mapleson E disadvantage
positive pressure ventilation not possible
must be for SV pt only
common mapleson E use
transporting pt to PACU who is SV but not ready to be extubated
- good tidal volume
- not responding to commands
mapleson F
jackson-rees’ modification
t-piece w/breathing bag for PPV
tail = APL valve
peds pts for assist ventilation during transport
mapleson circuit advantages
- supp O2 via ETT or LMA
- PPV w/breathing bag
mapleson circuit disadvantages
- inspiratory/expiratory gases in same tubing (incr dead space)
- no CO2 absorber
- high dead space
- possibly high CO2 rebreathing
semi-closed breathing circut
anesthesia machine
minimal CO2 rebreathing
semi-open breathing circuit
mapleson circuit
more dead space = CO2 rebreathing
prevent rebreathing CO2 in mapleson circuits
- use high flow of O2
- shorten circuit volume
- decr dead space
open circuit
open to atmosphere
gas freely disperses around face/room
nasal cannula
O2 insufflation (mask)
open drop anesthesia
open drop anesthesia
soaking gauze in volatile agent
placing over pt face
open circuit uses
O2 delivery
O2 insufflation
blow by
blowing O2 across pt face/airway
claustrophobic pts
infants
sedation case w/scope in mouth
- EGD
- TEE
bronchoscope
facial surgery
EGD/TEE O2 mask
POM mask
procedural O2 mask
conduit for scope to pass through
bronchoscope insufflation
O2 hooks up to bronchoscope
typically dont need to use blow by method w/scope O2
facial surgery insufflation
facial drape catches CO2
place breathing circuit under drape
high AIR flow (not O2)
prevents CO2 buildup under drape
open circuit fire hazard
higher [O2] can kindle fire during procedure w/cautery
managing facial surgery under sedation
supp O2 via cannula/mask contraindicated
2 options:
- minimal sedation
- ETT or LMA for higher sedation
- higher FiO2 via tube
CO2 absorber
soda lime granules that absorb CO2 and eliminate from circuit
converts CO2 into H2O and heat
can you eliminate CO2 w/out absorber?
yes
use FGF >5L/min
minimal rebreathing
CO2 larger granules
less absorptive capacity
- less surface area
lower circuit resistance
CO2 smaller granules
more absorptive capacity
- more surface area
more circuit resistance
why is silica added to CO2 granules
increase granule hardness
minimize dust inhalation
minimize airway irritation
dessicated old school absorbent
degrade volatile agents into CO
accelerate degradation of sevo into compound A
which agent produces most CO with desicated CO2 absorbers?
Des
minimum FGF rate for Sevo with old CO2 absorbers
2L/min
to avoid compound A formation
old school absorbant
double cannister
decreases circuit resistance
changing absorbant = circuit leak
- cannot change during case
new school absorbent brands
sodasorb
drager sorb
new school absorbent advantages
- do not degrade agents into CO or compound A
- can run low/min flow w/sevo
- optimal resistance to dusting
- reduced resistance to gas flow
- single canister
- reduced induction and emergence time
- can be change out mid-operation w/out circuit leak
new school absorbant
single canister
reduced induction and emergence time
can be change out mid-operation w/out circuit leak
exhausted new school absorbant
stays purple once exhausted
when to replace old school CO2 absorbant
weekly
when 50-70% color changed
when to replace new school CO2
after 8 hrs of surgical use
inspiratory CO2 >1 mmHg
circuit humidifier
AKA
heat moisture exchanger (HME)
airway humidity normal person
air humidified by upper airway
air in alveoli is warm/moisturized
airway humidity w/ETT
air not humidified by airway
air in alveoli is cold/dry
impacts of cold/dry air (4)
- decrease pt body temp
(absorb heat from airways) - dehydrate airway
- mucus plugging
- atelectasis
Relative humidity in OR
30-60% (AIAAAH reccomends)
50-60% inhibits bacterial grow/static electricity
Humidifier properties
- humdifies dry OR gases
- filters bacteria/viruses
- adds 10-60L deadspace
weight recs for humdifier/filter deadspace in peds
HME: body weight >2.5kg
filters: body weight >3kg
humidifier locations on circuit
- distal to Y piece
- incr dead space
- incr resistance to gas flow
- best humidification
- best for adults
- inspiratory or expiratory limbs
- no dead space
- less humidification
- best for peds
Ambu bag: clinical uses
- mask vent in emergency
- transfer mech vent pts from OR to PACU/ICU
Steps when transporting w/Ambu bag
- call RT to have vent in PACU/ICU
- vent pt w/self-inflating Ambu
- place pt on vent in PACU
- admin propofol if paralyzed
self-inflating ambu bag
without reservoir
connected to supp O2
fills w/mix of O2 and air during exhale
self-inflating ambu bag
with reservoir
connected to supp O2
fills w/mostly O2 during exhale
highest FiO2
ambu bag
does not require O2
can be hooked to O2
may have reservoir bag
flow inflating anesthesia bag
requires O2 to operate
pressure controlled by APL valve
infant: 450-500mL
older child/adolescent: 1000mL
