Review of modes of mechanical ventilation

1
Review of modes of mechanical ventilation

• By Elizabeth Kelley Buzbee A.A.S., R.R.T.-N.P.S.,
  R.C.P.

2
question

• In A/C mode there are two ways to trigger the
  breath.
• What are they?

3
ANSWER

• In A/C mode, the ventilator has
• Time triggered
• Patient triggered
• Flow triggered
• Pressure triggered
• Volume triggered
• NAVA

4
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?

5
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.

6
question

• Identify the most common initial ventilator
  setting used with the patient in respiratory
  failure who needs to rest?

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ANSWER

• A/C or VC modes will rest the patient
• We can also use these modes with sedation and
  paralysis to Control the patient

8
question

• What is the function of a PAV mode?

9
answer

• The PAV proportional assist ventilation mode is
  one in which the ventilator collects data about
  elasticity and RAW and his flow and volume
  demands to moderate the PS to maintain a more or
  less consistent breathing pattern

10
question

• Under what conditions would you want to select
  ATC mode?

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answer

• Automatic tube compensation is a mode in which
  the PS will be set by the machine based on the
  RAW of the ET tube.

12
question

• Identify the mode one would select for initial
  ventilation of the patient with COPD or with
  asthma who needs to rest?

13
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 patients exhalation is too long, we may
  need to decrease the rate even more.

14
question

• Your patient on A/C 10 bpm and he is assisting at
  a total f of 15 bpm.
• What has happened to his inspiratory time?
• What has happened to his expiratory time?
• How can you correct this situation?

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What has happened to his inspiratory time?

• The inspiratory time is established by the
  inspiratory flow rate and flow pattern.
• If those knobs dont change, then the inspiratory
  time doesnt increase or decrease.

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What has happened to his expiratory time?

• Because the rate increased from 10 to 15 bpm, the
  patients 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

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How can you correct this situation?

• A couple of ways
• Increase the flow rate to decrease the Ti, this
  gives you more time to exhale
• Change the patient from A/C to SIMV if you want
  him to breathe
• If you dont want him to breathe, give him
  sedation and paralytic agents to return him to
  Control

18
question

• What is the advantage of control mode?

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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.

20
question

• What is the difference between SIMV and IMV?

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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 patients 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

22
question

• Under what circumstances do we move the patient
  to pressure support ventilation PSV?

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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.

24
question

• What is the advantage of SIMV with PSV over SIMV
  alone?

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ANSWER

• In PS, because the patient selects his own VT,
  inspiratory flow rate and his own VE, his muscle
  strength and co-ordination are encouraged
• Because the PS 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

26
question

• How do we select the correct PSV pressure?

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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

28
question

• Compare pressure control PC ventilation to
  volume Control VC ventilation

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Answer

• in PC ventilation, you set the PIP and the VT
  will vary based on the patients time constants
• In VC ventilation, you set the VT and the PIP
  will vary based on the patients time constants

30
question

• Describe the effect on the return VT of the
  patient on VC whose PIP has reached the high
  pressure limit?

31
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

32
question

• Describe what happens to the patient on PC
  ventilation when he reaches the set PIP?

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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 end
  immediately on PC just as it does on VC

34
question

• Compare CPAP mode to PSV

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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.

36
question

• In what ways are CPAP and PSV max the same?

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• 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

38
question

• When do we select PC ventilation rather than VC?

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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

40
question

• Identify the indications for SIMV or IMV?

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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

42
questions

• Identify indications for CPAP

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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

44
question

• Describe IRV?

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ANSWER

• IRV is inverse ratio ventilation this is a mode
  in which ventilator is set up so that the
  inspiratory time exceeds the expiratory time
  making the ratio 11 up to 41

46
question

• Identify an indication for IRV.

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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.

48
question

• Identify the normal settings for the non-invasive
  positive pressure ventilation via the BiPap
  machine

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answer

• IPAP 8 cmH20
• EPAP 4 cmH20
• Spontaneous mode/ Spontaneous timed
• Added 02 via 02 line to mask

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Question

• Discuss the indications for NIPPV BiPap

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answer

• Indications for NIPPV are the patient who
• Acute management of CHF, COPD patient who doesnt
  want to get intubated ,recently extubated person
  who fails the immunosupressed patient.
• Long term management of the patient with
  neuromuscular disorders, with obstructive
  central Sleep Apnea and COPD with hx of
  hypoventilation at night

52
question

• Identify the patient who would handle NIPPV best.

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answer

• The patient who would be most successful being
  placed on NIPPV would be the patient who
• Can protect his airway remember no ET tube
• Is alert
• Is not claustrophobic nor vomiting
• Has an intact ventilatory drive
• Requires only a little extra driving pressure to
  keep his VE reasonable PaC02 and pH at base
  line

54
question

• Explain what happens in Bilevel ventilation

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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

56
question

• What happens to the patient on Bilevel
  ventilation if he becomes apnic?

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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 PEEPin other words,
  if the rate is set approprately the patient
  reverts to PC ventilation

58
question

• How does bilevel ventilation compare to airway
  pressure release ventilation APRV?

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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

60

• Describe what happens to the patient on APRV who
  goes apnic?

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ANSWER

• The patient on APRV who goes apnic will now have
  alternating high and low pressures. If the rate
  is set appropriately, He will basically revert to
  PC IRV.

62
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?

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ANSWER

• To control the PaC02 you manipulate the VE.
  Parameters that manipulate the VE are the
  respiratory rate f and the VT
• Once the PaC02 returns to norma,l the pH will
  return to normal assuming the bicarb is normal

64
question

• You have an arterial blood gas in which the
  patients Pa02 and Sa02 are both lower than
  normal. How do you adjust the ventilator to treat
  hypoxemia?

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ANSWER

• To treat hypoxemia you increase the Fi02
• If the Fi02 changes dont workor your Fi02 is at
  a toxic level, then you increase the PEEP level

66
question

• If your patient had the following ABG what would
  you do to the ventilator?
• pH 7.47
• PaC02 30
• Pa02 45
• HC03- 26

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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

68
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?

69
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

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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

71
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
  PaC02unless 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 dont want his
  spontaneous respiratory rate getting too high if
  his VT is too low

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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

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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?

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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

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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

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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 IE the
  same
• As he fights the ventilator, his PAW can rise
  which can alter his blood flow from his head

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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
• As long as the patient has no changes in his RAW
  and compliance, because he is sedated, you have
  control over the PAW so that there are minimal
  changes in the cerebral blood flow

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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?

79
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 patients
  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

80
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 CHFor fluid over load during CPR
• VS and heart monitor for cardiac arrhythmias

81
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 IE
  ratio which can decrease venous return to the
  heart
• Each breath on A/C will result in higher
  intrathoracic pressures- this could confuse her
  bodys control over urine production and blood
  pressure

82
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

83
question

• When would we want to select HFV high frequency
  ventilation?

84
answer

• We would select HFV for a patient who needs high
  mPAW but whose lung compliance is so low that his
  PIP is excessive and there is a risk of
  barotrauma and decreased CO.
• We would raise the mPAW with rate rather than VT
  PIP or PEEP

85
question

• Under what conditions do we want to select a
  pressure regulated, volume control PRVC mode?

86
answer

• We would select PRVC when we want the advantages
  of VC guaranteed VE and VT, but we dont like
  the PIP that this mode might create.
• We can set a lower PIP, so that the inspiration
  is limited to a PIP that is 5 cmH20 lower than
  the preset pressure.
• The flow rate will decrease so that the PIP stays
  lower

87
question

• Under what circumstances might we want to select
  an auto-mode?

88
answer

• Auto-mode is a choice for the patient who is
  expected to start to breath on his own and we
  dont anticipate issues with muscle weakness.
• Auto mode is a form of automatic weaning from a
  CMV to a spontaneous mode.
• It is best used with the basically healthy
  patient who is s/p surgery for who we expect to
  get off the ventilator in less than 24-48 hours

89
question

• How does auto-mode work?

90
answer

• This is a duel mode that only work in when the
  RCP has selected a CMV mode PC or VC .
• If the patient is resting quietly, the ventilator
  stays at the CMV mode
• Once the patient starts to breath on his own
  increased assisted breaths the machine will
  revert to a spontaneous mode such as PS/CPAP or
  CPAP.
• If the patient fails to breath the machine
  reverts to the previous mode

91
question

• How does auto mode differ from apnea parameters?

92
answer

• When the patient is on apnea parameters, the
  ventilator gives a few breaths then allows him to
  start breathing again, then alarms audibly if he
  doesnt.
• Apnea parameters are clearly an alarm situation
  while auto-mode is simply the machine going back
  and forth between CMV and spontaneous modes

93
question

• What patient would do well on MMV?

94
answer

• In mandatory minute ventilation, the ventilator
  is in a partial mode SIMV at a low rate and if
  the patient cannot maintain a minimal VE, there
  will be help to get this VE back up
• Extra PS to increase the spontaneous VT
• Extra breathes

95
question

• Discuss the use of the ASV mode.

96
answer

• Adaptive support ventilation mode is a mode in
  which the RCP set the patients IBW and a percent
  of work VE that she wants the patient to get
  from the ventilator
• If she picks 100, the ventilator is in full
  support with all VE needs from the ventilator.
• If she picks 50, the patient is in a partial
  mode in which the half the VE comes from
  spontaneous efforts PS and half from the
  ventilator