Getting Gas to Patient: Breathing Systems Flashcards
what are non-rebreathing systems (3)
- lack
- T-piece
- bain
what are re-breathing systems
- circle
what are hybrid systems
humphrey ADE
what are the functions of breathing systems (4)
- deliver oxygen to patient
- deliver anesthetic gas and/or vapour to patient
- remove exhaled carbon oxide
- provide a means to ventilate patient
what is tidal volume
volume of gas exhaled in 1 breath (10-20 ml/kg)
what is minute respiratory volume
volume of gas exhaled in 1 minute
tidal volume x respiratory rate ~ 200ml/kg
what is rebreathing
inhalation of previously exhalged gas
what are the two types of rebreathing systems
- rebreathing of exhaled gas from which CO2 has been removed by an absorbent is not detrimental
- rebreathing of unchanged exhaled gas leads to build up to CO2 (hypercapnia) –> detrimental
what is apparatus dead space
volume of breathing system that may contain exhaled gas that could be rebreathed during subsequent breath
what are the breathing system components (5)
- tubing
- reservoir bag
- adjustable pressure limiting (APL) valve
- carbon dioxide absorbent (soda lime)
- unidirectional valves
what is the function of tubing
conveys gases to and from pateint
why are tubes corrugated
resist kinking
how do tubes reduce resistance of air flow
smooth internal bore reduces resistance
what are the two arrangements of tubing
- parallel: tubes arranged side by side
- coaxial: 1 tube inside the other
what are the functions of reservoir bag
- reservoir
- visual aid
- means of assisting ventilation
what are APL valves and what is their function
adjustable pressure limiting valve
“pop off” or “spill” or “expiratory valve”
provides a means of escape for excess fas preventing pressure build up
connects to scavenging system for disposal of waste gases
what is an open APL valve
slight increase in pressure during expiration lift disc and open valves
what are closed APL valves
tension in spring opposes lifting of disc and valve remains closed
how do you open an APL valve
anti-clockwise open
lefty loosey
how do you close an APL valve
clockwise close
righty tighty
when should you have the APL valve open
should always be fully open during spontaneous ventilation
only adjusted during intermittent positive pressure ventilation (IPPV) –> when we want to manually inflate the patients lungs
what can occur when the APL valve is closed
how are breathing systems classified (4)
- rebreathing or non-rebreathing
- with or without CO2 absorbent
- conway classification
- mapleson classification
what are non-rebreathing systems
no rebreathing of exhaled gases occurs
high fresh gas flow flushes out exhaled gases before the next inspiration
what are rebreathing systems
exhaled gases are rebreathed after removal of CO2 by an absorbant
allow use of lower fresh gas flows
what does removal of exhaled gases in non-rebreathing systems depend on
adequate fresh gas flow (FGF)
what are the advantages of non-rebreathing systems
- patient inspires fresh gas
- patient breathes gas of known composition
- anesthetic depth can be changed rapidly
what are the disadvantages of non-rebreathing systems (2)
- high fresh gas flow (FGF)
- increased cost
- increased potential for environmental pollution - fresh gas is cold & dry
what are the two ways to calculate FGFs
- use minute resp volume (MRV)
- use ml/kg/min
how do you calculate FGF using MRV
MRV = resp rate x tidal volume (10-20 ml/kg)
FGF = MRV x circuit factor
what are circuit factors for lack, ayre’s t-piece, bain
lack: 0.8-1
ayre’s t-piece: 2.5-3.5
bain: 1-3.5
how do you calculate FGF using ml/kg/min
lack: 150-200 ml/kg/min
ayre’s t-piece: 400-600 ml/kg/min
bain: 200-600 ml/kg/min
why are FGFs not always sufficient
noraml ventilatory pattern: inspiration, expiration & then expiratory pause
the expiratory pause is crucial –> fresh gas flushes expired gas out of system, if too short there is insufficient time for expired gas to be removed & rebreathing occurs
so increase FGF in patients with rapid resp rates
what are the classifications of the mapleson A systems
- parallel
- coaxial
what system is this
parallel lack
describe how the gas flows through this system
what system is this
parallel lack
what system is this
coaxial lack
what are the differences between the parallel and coaxial lack
coaxial: damage/disconnection of central tube leads to marked rebreathing of CO2 or if there is a leak
parallel: more bulky but probably safer, more widely used
is the lack system suitable for IPPV
no
the reservoir is on the inspiratory limb –> rebreathing & hypercapnia develop during prolonged IPPV
can be reduced but not eliminated by increasing FGF
what patients is the parallel lack used for
10kg & over
what is the recommended FGF in the parallel lack
160-200 ml/kg/min
what is the minilack
for smaller patients
undre 10kg
what is the FGF for the miniLack
200 ml/kg/min
what is the basic ayre’s t-piece
mapleson E
does the basic ayre’s t-piece have an APL valve
no
low resistance
what are the problems with basic ayre’s t-piece
no reservoir bag so difficult to observe ventilation
can IPPV be done on the basic ayre’s t-piece
yes but exposes lungs to high pressure
occlude the tube with thumb
what system is this
basic ayre’s t-piece
what is the jackson-rees modification of the basic ayre’s t-piece
addition of open ended bag
what system is this and describe how air flows through it
jackson-rees modification
what is the jackson-rees modification classified as
mapleson F
what are the benefits of the jackson-rees modification
- allows observation of respiration
- allows more control during IPPV
what is a disadvantage of jackson-rees modification
difficult to scavenge
what system is this
jackson-rees
what is the mapleson D t-piece
adaptation to facilitate scavenging
includes closed reservoir bag & APL valve
what is this system and describe the airflow through it
mapleson D t-piece
what system is this
mapleson D t-piece
what size of patients can the t-piece be used for (modified/basic/mapleson D)
up to 10kg
what is the FGF of t-piece be used for (modified/basic/mapleson D)
400-600 ml/kg/min
if the t-piece be used for (modified/basic/mapleson D) suitable for IPPV
yes
what is the bain system
mapleson D
modification of T-piece –> parallel or coaxial (most common)
what system is this and describe how air flows through it
coaxial bain system
fresh gas passes up inner tube and expired gas out via outer tube
what system is this and how does gas pass through it
fresh gas passes up the outer tube and expired gas out via inner tube
what are the disadvantages of coxaxial bain
damage/disconnection of central tube leads to marked rebreathing
but we can test integrity of inner tube in coaxial bain –> always check prior to use
what size of patient is the bain system suitable for
up to 10kg and above
what is the FGF of the bain system
200-600 ml/kg/min
is the bain system suitable for IPPV
yes
what is the bain modification t-piece used for
larger patients
FGF 400-600 ml/kg/min
slower resp rate and longer expiratory pause
what are the features of rebreathing systems (3)
- exhaled gases are rebreathed after removal of CO2 by an absorbent
- relatively low FGF can be used
- patient inspires a mixture of fresh gas & exhaled gas
what are the advantages of rebreathing systems
- lower gas flow –> more economical, less environmental contamination
- gases are warmed and humidified
what are the disadvantages of rebreathing systems (4)
- greater resistance to breathing (soda lime canister, unidirectional valves)
- unsuitable for small patients
- patient inspires a mixture of fresh gas & exhaled gas (composition of mixture unknown)
- more difficult to alter anesthetic depth
what is the usual absorbent of CO2
soda lime
80% calcium hydroxide
4% sodium hydroxide
14-20% added water
indicator dye
how do indicator dyes in CO2 absorbents
pH of soda lime changes reveals exhaustion
-exothermic reaction
what are the classification of rebreathing systems
- closed systems
- semi-closed systems (low flow)
what are the features of closed systems
oxygen supplied is just sufficient to meet the patient’s metabolic oxygen requirement ~5-10 ml/kg/min oxygen
no gas exits via the APL valve
what are the problems of closed systems (3)
- flowmeters may be inaccurate
- vaporizers may be inaccurate
- marked dilutional effect
what is the dilutional effect
inspired concentrations of inhalant & oxygen may differ from those set
can the anesthetic depth be altered quickly in closed system
slow to adjust
what are the features of semi-closed systems
use higher FGF than for closed systems but still less than in non-RB systems
excess gas spills via APL valve
what is the minimum FGF of semi-closed systems
20ml/kg/min O2
what are the differences between closed and semi-closed systems
- flowmeters should be accurate
- vaporizers should be accurate
- less dilution effect (though it still occurs) –> easier to adjust anesthetic depth, N2O can be used safely
how do you denitrogenate after post-induction in rebreathing systems
use high FGF for the first 10-15 min of anesthesia with closed or semi-closed rebreathing systems (4L/min O2)
after this lower FGF to closed/semi-closed levels (1L/min O2)
what is the concern of using nitrous oxide in rebreathing systems
N2O accumulates reducing O2 concentration
don’t use in closed systems without monitoring FiO2
can use in semi-closed systems in 1:1 mixture with O2
what system is this
to & fro system
what are the components of circle system (3)
- soda lime canister
- reservoir bag
- unidirectional valves (flow through soda lime is unidirectional)
what size of patients are circle systems used for
>15 kg (pediatric circles available)
what system is this and how does the gas flow through them
what system is this
circle
describe the main differences between non-RB and RB systems
what system should you use for patients <10kg
T-piece or miniLack
what system should you use for patients 10-15kg
bain, lack, (circle)
what system should you use for patients <15kg
bain, lack or circle
what is a hybrid system
humphrey ADE system
what is a hybrid system used for
patients 10kg and over
how does a hybrid system work for paitents 10kg and over
use a soda lime canister used as a circle
how does a hybrid system work for paitents <10kg
remove soda lime canister & use in non-RB mode
with lever up for spont breathing = miniLack
with lever down for IPPV = bain/T-piece
what are the pros and cons of humphrey ADE
pros: easy to change from spont breathing to IPPV + suitable for wide range of patient sizes + economical to run
cons: expensive to purchase
