Modes of Mechanical Ventilation Flashcards
2 types of pressure measurements
peak inspiratory pressure
plateau pressure
Peak inspiratory pressure
total pressure required to distend lungs and airways
pressure used to calculate dynamic compliance (intrinsic and extrinsic factors)
plateau pressure
distending pressure to expand only lungs (intrinsic)
measures redistribution of air flow through lungs
Pplat is used to calculate static compliance
when can you measure Pplat
only in volume control during inspiratory hold
4 parts of each breath
start of inspiration (trigger variable) inspiration itself (limit or target variable) end of inspiration (cycling variable, transition to expiration) expiration (baseline variable, end expiration, PEEP)
3 components of a breath
ti=inspiratory time
te=expiratory time
TCT=total cycle time
4 types of trigger variables
pressure
volume
flow
time
pressure trigger variable
decrease in circuit stimulates ventilator to deliver breath
volume
volume change in circuit can stimulate ventilator to deliver breath
flow
change of flow in circuit stimulates ventilator to deliver
time
set time interval triggers ventilator to deliver breath (set by RR). this occurs independent of patient effort
limit variable
controls how an inspiratory breath is maintained once threshold is reached variable will not exceed set limit. this does NOT cause termination of inspiration
pressure as limit variable
sets upper pressure limit that cannot be exceeded
volume as limit variable
set upper volume limit that cannot be exceeded
flow as limit variable
sets maximum airflow that cannot be exceeded
cycling variable
transition from inspiration to expiration. based on either volume, pressure, flow, or time
volume cycling variable
ventilator delivers flow until set volume achieved. if inspiratory pause set (typically 10-20%) this variable changes to a time based cycling variable
pressure cycling variable
once pressure is achieved, flow will transition to expiration
flow cycling variable
once inspiratory flow drops below set threshold (default at 25%), ventilator will transition to expiration. noted in pressure support ventilation mode
time cycling variable
ventilator terminated inspiratory breath after predetermined inspiratory time has been delivered
intrinsic peep
secondary to incomplete expiration, referred to as auto peep (related to air trapping, MV or RR maybe too high)
extrinsic peep
provided by a mechanical ventilator, referred to as applied peep
auto peep causes
high MV, expiratory flow limitation, expiratory resistance
volume control ventilation
trigger variable
limit variable
cycling variable
delivers set TV at set RR
time
volume
flow
VCV PIP/Plat and airflow
airway pessure (PIP/plat) will change on a breath by breath basis during this mode of ventilation based on changing respiratory compliance. airflow will remain constant. (looks like sharks tooth on vent)
why choose VCV
maintenance of set minute ventilation through direct manipulation of TV and RR
remember to set individualized alarms to protect patient
increasing airway or lung resistance will stimulate generation of higher pressure to deliver set TV
PCV
trigger variable
limit cariable
cycle variable
delivers set inspiratory pressure at set respiratory rate
time
pressure
time
TV changes on breath by breath basis based on compliance
good to control barotrauma
PCV on ventilator
decelerating wave flow (allows for homogenous distribution) pPeak plateaus (not sharks tooth like VCV)
why choose PCV
set pressure limit to avoid barotrauma from delivery of excessive pressure
decelerating flow pattern allows for homogenous distribution of inspired gas throughout lungs
theoretically improves ventilation pattern and decreases WOB
compliance change means volume delivery change
Pressure Control-Volume Guarantee (PCV-VG)
trigger variable
cycling variable
delivery variable
respiratory cycle variables mirror PCV, however ventilator adjust pressure delivered if current volume is not set volume
adjustments take 3-5 breaths to complete (can be de recruitment)
can allow for atelectasis development if compliance decreases and ventilator is delayed in providing adequate pressure to distant lungs
time is trigger variable and cycling variable
pressure is delivery variable
SIMV
trigger variable
limit variable
cycle variable
delivers set TV at a set RR in conjunction with patient initiated breaths
time or patient is trigger variable (if pt takes breath its them)
flow is limit variable
volume is cycle variable
helps demote dsynchrony
can apply this mode in many ways
patient initiated breaths are not supported unless in SIMV-PSV
SIMV modes
SIMV-VC
SIMV-PC
SIMV-PCG
SIMV-PSV
why choose SIMV
useful when weaning from controlled mechanical ventilation
less dysyncrhony with patient initiated breaths
hypoventilation can occur if set TV and RR are too low and the patients spontaneous respiration effort is inadequate
hyperventilation can also occur if using SIMV-PSV and pressured support level too high
not retimed based on pt breath
PSV
trigger variable
limit variable
cycle variable
supported mode of ventilation for spontaneously breathing patient
patient is trigger variable
pressure is limit variable
flow is cycle variable
patient controls most aspects of ventilation but the anesthetist can adjust certain variables to augment or limit support given to prepare patient for extubation
defaults to SIMV PSV if they dont breathe
why choose PSV
great for end of case in preparation for extubation
patient must be breathing spontaneously or ventilator will switch to backup mode
just like PCV, pressure is controlled, changes in respiratory system compliance will alter TV delivered
how to wean in PSV
flow trigger
slowly increase this as minute ventilation increases so once they hit the flow (.2 and up), then you know they can take an adequate breath (at least 2l/min)
how to wean in PSV
trigger window
% of time patient breath will be supported by ventilator
end of breath % peak flow
transition from inspiratory to expiratory breath
backup time
how long people can be apneic before backup mode (10-30seconds)
Tinsp
inspiratory time in seconds
