ventilators and airway monitors Flashcards
stages of ventilation cycle
1 - inspiration
2 - transition from inspiration to expiration
3 - expiration
4 - transition from expiration to inspiration
constant flow
- deliver constant insp gas flow regardless of a/w circuit pressure
- hi pressure gas source (5-50) allow stay sam regardless of changes in a/w resistance or compliance
- lo pressure (venturi) gas source varies to some degree w a/w pressure
non constant flow
consistently vary flow w each insp cycle
constant pressure generators
maintains constant a/w pressure throughout insp, irrespective of insp gas flow
gas flow ceases when a/w pressure equals the set insp pressure
time cycled
- cycle tot the exp phase once predetermined interval elapses from start of insp
- TV product of set insp time and insp flow rate
vol cycled
- terminate insp when preselected TV delivered (most are V cycled bu thane second limit on insp, pressure to guard against barotrauma)
- percentage of TV always lost to compliance of the system, 4-5cc
pressure cycled
cycle into exp phase when a/w pressure reaches a predetermined level
TV & insp time vary
flow cycled
BOTH pressure sand flow sensors that plow the vent to monitor insp flow at preselected fixed insp pressure
when flow reachers predetermined level, vent cycles from insp to exp
power source
1 - compressed gas-gas only
2 - piston - power only (quiet, can’t hear things change)
3 - compressible bellows - gas & power ( most)
drive mechanism
- double circuit bellows compressed by driving gas and pneumatically driven
- piston bellows comprised by electricity
cycling mechanism in older machines
most vents are time cycled, electronically controlled w lvl limiting aspect
bellows
direction of bellows movement during EXPIRATION determined classification
1 - ascending, ascend during exp
2 - descending, descend during expiration (gravity)
pressure
impedance to gas flow rate
1 - breathing circuit
2 - pt airway and lungs
amt back pressure generated as result of airway resistance and lung thorax compliance (tube, elasticity)
flow rate
rate at which gas vol delivered to pt, from pt connection of breathing system to pt,
vol change/time
during expiration
- drive gas exits bellows chamber, pressure in bellows and pillot drop to zero, vent relief (ball) open
- exhaped pt gas fills bellows before any scavenging occurs (ball 2-3cm H2O), which occurs only after bellows filled completely
- relief valve only open during exp
TV
10-15ml/kg
RR
8-12
flow rate
4-6/min vent
MV
TV X RR
I:E
- physiologic 1:2
TI
TV/flow rate
500ml/30,000ml/min = .0167 X 60sec = 1 sec
TE
determined by flow rate and RR/min
first figure out total tim elf ea vent for 1 min cycle…
60sec/12bpm = 5sec
exp time = 5-1 1:E = 1:4
inspiratory pause
- inhalation time increased by 25%
- drive gas flow stops
- gas pressure in bellow housing system stays the same
- col of gas to pt is held inputs lungs until exhalation begins
- changes ratio to get exp you want (shorter exp)
FiO2
delivery - COxO2 content
content - (hgb x %sat x 1.39) + (PaO2 x .0031)
how much O2 to give?
- ## hypoventilation reduces PaO2 except when subject breathes enriched O2 mix
PaO2
PiO2 - PaCO2/ R+F
R = extraction ratio (0.8) F = correction factory (negligible)
each time you increase FiO2 by 10%, increase PaO2 by 50mmHg
low pressure alarm
“disconnect alarm”
detected by drop in peak circuit pressure
sub atm pressure alarm
pressure =/< -10
pt starting to breath on mating, creating neg pressure
sustained/continuing pressure alarm
15 for more than 10 sec
high peak airway pressure alarm
normal 35-40
detects excess pressure in system activated at 60 (or set by practitioner)
vent setting alarm
vent inability to deliver desired MV set
ETCO2 monitor
capnography is best for revealing disconnect
O2 analyzers
most important monitor on machine
calibrate at 21% in ambient air
determine how much you’re giving pt
respirometer
vent setting, PAP monitors
keep from delivering too much pressure
- transducer cartrige and TV sensor clip
- gas flow converted to electrical pulses
- cartridge in exp limb
- sensor clip snaps ionto transducer cartrige
- exhaled vt expect to measure is…
Vt = Vt set on vent + Vt fresh gas flow - Vt lost in system
exhaled vol monitor
activated automatically once breaths are sensed and always active during mechanical vent
reverse flow
alarm in flow toward patient
apnea
if insufficient breath, based on TV setting, not achieved w/in 30sec
ICU vs
- ICU vent more powerful, greater insp pressure & TV
- CO2 absorber (pt rebreathing in OR)
- ICU vent support more modes of vent
- gas in ICU vent directly vent patient (OR, driving gas)
CV
controlled ventilation by vent
IMV
vent delivers preset vol at specific interval, while also providing cont flow of gas for spontaneous vent
pt breaths spontaneously, while the vent delivers preset TV at predetermined interval through parallel vent circuit
use as weaning technique
fixed rate, NOT synch w pt
SIMV
IMV, but synch w pts effort
pt breaths spontaneously and at a predetermined interval the spontaneous breath is assisted by machine
it times mechanical breath w the BEGINNING of spontaneous effort
waking pt up in OR
generates rest of breath for patient as soon as it detects pt breathing
AC
intermittent mode of pos pressure vent
pts insp effort creates sub baseline pressur ein insp limb of vent circuit that then triggers vent to deliver predetermined TV
if pt rate drops below ppeset min rate, machine takes over w controlled vent mode
all breaths pt takes are full assisted vent breaths
can be pressure controlled or vol controlled
pressure support
aid in normal breathing w predetermined level pos a/w pressure
similar to IMV except than a/w pressure held constant throughout insp
objective is to increase pt spon TV by delivering a/w pressure to achieve vol = 10-12
1- decrease work of breathing
2 - delay muscle fatigue
high frequency vent
low total vol, less than dead space w high rate (60-300)
typical settings 100-200bpm, IT 33%, drive pressure 15-30psi
goal to maintain plum gas exchange at lower mean a/w pressures
used in ESWL, ARDS
must allow for exhalation
pressure control
pt or time triggered pressure limited, time-ccyled mode of vent support
gas flow decreases as a/w pressure rises and ceases when a/w pressure equals the set peak inflation pressure
- TV not fixed
- used in situation where pressure can be high
- useful in neonates/premies
CPAP
continuous pos pressure
maintained during both insp & exp, only when pt is spent breathing
can be provided w mask
caution - if pressure > 15 can cause regurgitation & aspiration.
