Transcript Review of modes - Kingwood Application Server

Review of modes of
mechanical ventilation
By Elizabeth Kelley Buzbee
A.A.S., R.R.T.-N.P.S., R.C.P.
question
 In A/C mode there are two ways
to trigger the breath.
 What are they?
ANSWER:
 In A/C mode, the ventilator has
 Time triggered
 Patient triggered
question
 Identify the two most common
patient triggers for mechanical
ventilators in A/C mode
ANSWER:
 Pressure trigger
 Flow trigger
question
 A/C mode is considered one of
the CMV modes.
 What is a CMV mode and why is
A/C classified as a CMV mode?
ANSWER:
 A/C mode is a CMV mode because it handles
100% of the work of breathing. The patient can
trigger a breath, but all breaths are controlled
by the ventilator .
 CMV modes include: A/C in PC or VC
 One of these modes is used to rest the patient
who is in respiratory failure
 He does no work at all.
question
 Identify the most common initial
ventilator setting used with the
patient in respiratory failure who
needs to rest?
ANSWER:
 A/C or VC modes will rest the
patient
 We can also use these modes
with sedation and paralysis to
“Control” the patient
question
 Identify the mode one would
select for initial ventilation of the
patient with COPD or with
asthma who needs to rest?
ANSWER:
 We would select SIMV with a rate of
10-12 to rest this patient while
minimizing chances of air trapping
that can happen during A/C.
 If the patient’s exhalation is too
long, we may need to decrease the
rate even more.
question
 Your patient is on A/C 10 and he
is breathing 15bpm.
 What has happened to his
inspiratory time?
 What has happened to his expiratory
time?
 How can you correct this situation?
What has happened to his
inspiratory time?
 The inspiratory time is
established by the inspiratory
flow rate and flow pattern.
 If those knobs don’t change,
then the inspiratory time doesn’t
increase or decrease.
What has happened to his expiratory
time?
 Because the rate increased from 10
to 15 bpm, the patient’s cycle time
decreased.
Cycle time = 60 seconds / rate
60 / 10 = 6 seconds
60 / 15 = 4 seconds
 As the cycle time decreases, and the
inspiratory time stayed the same,
the expiratory time decreased
How can you correct this situation?
 A couple of ways:
 Increase the flow rate to decrease
the inspiratory time, this gives you
more time to exhale
 Change the patient from A/C to SIMV
if you want him to breathe
 If you don’t want him to breathe,
give him sedation and paralytic
agents to return him to ‘Control’
question
 What is the advantage of control
mode?
ANSWER:
 Controlling the patient will
control the VE, thus the PaC02.
 When the patient breathes on
A/C or SIMV he will alter the VE
which will change the PaC02.
question
 What is the difference between
SIMV and IMV?
ANSWER:
 In IMV, the patient will get his time-triggered
breaths right on schedule. If he happens to be
exhaling during his spontaneous breath, then
he will ‘stack breaths.’ this leads to air trapping
& patient discomfort.
 In SIMV, the patient’s time-triggered
mandatory breath will come in just a fraction of
a second early so that the patient and the
ventilator are ‘synchronized’ to avoid stacking
breaths
question
 Under what circumstances do
we move the patient to PSV?
ANSWER:
 we add PSV to the SIMV so that the
patient can establish a spontaneous
VE without increasing his respiratory
rate to a dangerous level.
 We also select PSV when we want to
help the patient breathe, but still
allow him to use his own muscles.
question
 What is the advantage of SIMV
with PSV over SIMV alone?
ANSWER:
 In PSV, because the patient selects his
own VT, inspiratory flow rate and his own
VE, his muscle strength and coordination are encouraged
 Because the PSV ’s VT are larger than the
patient could get with spontaneous
breathing, his WOB is not as excessive
as if he was doing all the work, but it is
more than if the ventilator was doing all
the work
question
 How do we select the correct
PSV pressure?
ANSWER:
 There are three methods:
– Set up the PS pressure to get a VT of 10-15 ml/ kg
IBW
– Titrate the PS to get a spontaneous respiratory rate
of less than 25 bpm
– Give just enough PS to overcome the resistance to
the endotracheal or the tracheostomy tube
question
Compare PC ventilation to VC
ventilation
Answer
 in PC ventilation, you set the PIP
and the VT will vary based on the
patient’s compliance and RAW
 In VC ventilation, you set the VT
and the PIP will vary based on
the patient’s compliance and his
RAW
question
 Describe the effect on the return
VT of the patient on VC whose
PIP has reached the high
pressure limit?
answer
 In VC ventilation, when the patient
reached the high pressure limit, the
breath is immediately cycled off, and
exhalation starts.
– Audible and visual High pressure
alarms go off
– VT thus VE drops
– PIP rises, thus PAW rises
question
 Describe what happens to the
patient on PC ventilation when
he reaches the set PIP?
answer
 A patient on PC ventilation, who reaches
his PIP will continue to get the breath at
that pressure until it is time-cycled off.
 If however, if something happens so that
the patient reaches the high pressure
alarm [which is set higher than preset
PIP], his breath with still end immediately
on PC just as it does on VC
question
 Compare CPAP mode to PSV
ANSWER:
 In CPAP, the patient is breathing
spontaneously. His VT, inspiratory flow rate
and Ti are all determined by the patient. His
PAW and the baseline pressure are pretty much
the same.
 In PSV, the patient triggers a pressurized
breath that rises above the baseline. Again,
this patient controls his own VT, inspiratory
flow and Ti, but in this case the PAW is lower
than the PS pressure because there is more
difference between baseline and PS pressures.
question
 In what ways are CPAP and PSV
max the same?
 CPAP and PSV max both require a patient
with an intact ventilator drive, & enough
muscle strength to create a VE that can
get the PaC02 to normal levels
 In both of these modes, the clinician
must establish [1] VE alarms that will
warn of apnea and [2] high respiratory
rate alarms to warn of possible fatigue
question
 When do we select PC
ventilation rather than VC?
ANSWER:
 When VC ventilation has failed
due to excessive PIP or Pplateau
and there is real danger of
barotrauma or decreased CO.
 In infants or small children who
have gross air leaks around
uncuffed endotracheal tubes
question
 Identify the indications for SIMV
or IMV?
ANSWER:
 To wean the patient by increasing
his work load gradually
 As an initial ventilatory mode for
COPD and asthma patient to
minimize airtrapping
 To decrease the negative effects of
A/C mode on the cardiac output
questions
 Identify indications for CPAP
ANSWER:
 CPAP or N-CPAP for obstructive sleep
apnea
 Treating refractory hypoxemia without
respiratory acidosis or hypercapnia
 Weaning modality just before the patient
is extubated
 Means of keeping a patient ‘off’ the
ventilator for more than 2 hours without
risking atelectasis
question
 Describe IRV?
ANSWER:
 IRV is ‘inverse ratio ventilation’
Which is a mode where
ventilator is set up so that the
inspiratory time exceeds the
expiratory time making the ratio
1:1 up to 4:1
question
 Identify an indication for IRV.
ANSWER:
 IRV is indicated in patients with poor
compliance and normal RAW who
have failed conventional ventilation
by having PIP so high there is a real
risk of barotrauma or decreased CO.
question
 Explain what happens in ‘Bilevel
ventilation’
ANSWER:
 In bilevel ventilation, the patient
breaths at a high level of CPAP
that drops down to a lower level
of CPAP periodically so that the
patient can get rid of excessive
C02
question
 What happens to the patient on
Bilevel ventilation if he becomes
apnic?
ANSWER:
 If the patient on bilevel ventilation
has been set up properly, as he
stops breathing, the changes
between high CPAP and low CPAP
now are changes between a PIP and
a PEEP—in other words, the patient
reverts to PC ventilation
question
 How does bilevel ventilation
compare to APRV?
ANSWER
 These modes are identical except
that in APRV, the patient breaths at
the higher CPAP level for a longer
time than he breaths at the lower
CPAP level.
 In Bilevel ventilation, the time spent
at higher CPAP is less than at lower
CPAP
 Describe what happens to the
patient on APRV who goes
apnic?
ANSWER
The patient on APRV who
goes apnic will now have
alternating high and low
pressures. He will
basically revert to PC –
IRV.
question
 You have a blood gas that shows
the pH is acidic due to a higher
PaC02.
 What parameters do you adjust
to correct this?
ANSWER
 To control the PaC02 you
manipulate the VE. Parameters
that manipulate the VE are the
respiratory rate and the VT
 Once the PaC02 returns to
normal the pH will return to
normal
question
 You have an arterial blood gas in
which the patient’s Pa02 and
Sa02 are both lower than normal.
How do you adjust the ventilator
to treat hypoxemia?
ANSWER:
 To treat hypoxemia you increase
the Fi02
 If the Fi02 changes don’t work—
or your Fi02 is at a toxic level,
then you increase the PEEP level
question
 If your patient had the following
ABG what would you do to the
ventilator?
 pH 7.47
 PaC02 30
 Pa02 45
 HC03- 26
Answer
 To correct the low PaC02, you
need to decrease the VE
 That will fix the pH too
 To correct the low Pa02, you
need to increase the Fi02 or if it
is already at 50% start the
patient on a PEEP of 3-5 cmH02
Case studies

Patient is a 65 year-old WM with respiratory failure
secondary to viral pneumonia. He has a history of
COPD. He is alert and anxious with a respiratory rate
of 35 bpm.
– What ventilator mode [modes] might work with
him?
– What parameters would you monitor?
– What are the problems associated with the mode
you selected?
– What are the advantages to the mode you
selected?
What ventilator mode [modes] might
work with him?
 He needs to rest, so A/C might
be a choice but because he is at
risk for airtrapping, one might
best select SIMV for his initial
mode
What would you have to monitor with
this mode?
 Vital signs for increased WOB or
compromise of Cardiac output
 Sp02 for oxygenation
 pH and PaC02 for acid/base balance
 BBS to make sure his breath ends before
the next breath comes in to avoid air
trapping
 monitor flow/time curve for auto-PEEP
and air trapping
What are the problems associated
with the mode you selected?
 SIMV will result in the patient controlling
some of the VE, you will lose fine control
over the PaC02—unless you sedate and
paralyze him
– Then your patient will get muscle atrophy
after a few days of this CMV
 As the SIMV rate is dropped the patient
must assume more of the VE, , and we
don’t want his spontaneous respiratory
rate getting too high if his VT is too low
What are the advantages to the
mode you selected?
 SIMV will minimize chances of
air trapping,
 it will help him keep his muscle
strength
 maintain his ventilatory drive as
long as the Pa02 and PaC02 stay
at his baseline
Case study # 2

Patient is a 25 year-old BF suffering from a closed head injury.
The doctor wants to keep the PaC02 at 25-35 mmHg and the
Pa02 110-120 mmHg to minimize cerebral edema. Her breath
sounds are clear and bilateral when you bag her at a rate of 15
bpm and with 100% Fi02.
–
What ventilator mode [modes] might work with her?
–
What would you have to monitor with this mode?
–
What are the problems associated with the mode you
selected?
–
What are the advantages to the mode you selected?
What ventilator mode [modes] might
work with her?
 In situations where the clinician
needs complete control over the
PaC02 like this one, a control
mode of some kind is required.
A/C with VC is best
 Sedation and paralysis is
mandatory
What would you have to monitor with
this mode?
 In closed head injuries we worry about
sudden changes in the systemic BP
because this can change blood flow in
the head.
 We watch the PAW: PIP and PEEP
changes can alter the thoracic pressure
thus the blood flow from the head
 We watch the Sp02 for hyper-oxygenation
 We watch the VS for s/s of altered blood
pressure
What are the problems associated
with the mode you selected?
 If the patient were to wake up and start to
breathe, he can drastically alter:
 his VE thus his C02
 He could air trap as his respiratory rate rises
without the flow rate rising to keep the I:E the
same
 As he fights the ventilator, his PAW can rise
which can alter his blood flow from his head
What are the advantages to the
mode you selected?
 You have complete control over the
PaC02 so that there are no alternations in
cerebral blood flow
 You have complete control over the PAW
so that there are no changes in the
cerebral blood flow
Case study # 3

Patient is a 55 year-old LAF with respiratory failure
following cardiac arrest. She is apnic and
unresponsive with a low CO and diffuse crackles in
both lungs
– What ventilator mode [modes] might work with
her?
– What would you have to monitor with this mode?
– What are the problems associated with the mode
you selected?
– What are the advantages to the mode you
selected?
What ventilator mode [modes] might
work with her?
 While CPAP, NIPPV or PSV might be indicated
for CHF which might well be part of this
patient’s problem, she is apnic
 She needs to be intubated and ventilated
 VC or A/C is initial ventilator mode for her.
 Post-CPR patients are best started with Fi02
100% then get a gas and titrate later
What would you have to monitor with
this mode?
 Sp02 for oxygenation and good
peripheral perfusion
 BBS and P plateau for changes in lung
compliance due to CHF—or fluid
over load during CPR
 VS and heart monitor for cardiac
arrhythmias
What are the problems associated
with the mode you selected?
 If the patient were to wake up and
breathe faster, she will increase her VE
which will alter her PaC02
 If she breathes too fast, she alters her I:E
ratio which can decrease venous return
to the heart
 Each breath on A/C will result in higher
intrathoracic pressures- this could
confuse her body’s control over urine
production and blood pressure
What are the advantages to the
mode you selected?
 We control her PaC02 and her Pa02.
 She rests
 Her WOB is decreased and that will
decrease the work on her heart
 As long as she is controlled by sedation
and paralysis, her intrathoracic
pressures stay the same so that
ventilation cannot alter the blood
pressure