Modes and initiation of ventilation
Elizabeth Kelley Buzbee AAS, RRT-NPS
The modes of ventilation:
 A spontaneous breath is one that the patient
triggers and cycles the breath, and he controls
the VT . This breath could be assisted by the
application of positive pressure.
 A mandatory breath is defined as one that is
triggered and cycled by the machine. All
mandatory breaths are assisted breaths.
The modes of ventilation: full
support modes
• CMV: continuous mandatory ventilation in which
all breaths are mandatory.
• VC-CMV volume control also called
Assist/Control mode
– Set VT, f to get VE; guaranteed VT
– Default ventilatory mode for full support with adults
• PC-CMV pressure control mode. Patient can
trigger breaths just like with A/C
– Set PIP, f and TI no guaranteed VT
– Default ventilator mode for full support for infants
Indications for PC: the RCP selects
pressure ventilation when:
 The adult patient who cannot be managed with
VC In this case, we keep the PIP less than 30
 PC results in better distribution of ventilation in
persons with unequal RAW, but consistent
 There is such an airway leak so that the VT are
unstable [most common with infants and small
children with uncuffed ET or tracheostomy tubes]
Compare PC to VC
 In PC, the airway pressures; mPAW and PIP
will stay the same, but the VE and VT can vary
based on patient’s time constants
 In VC the VE and VT are basically stable
[patient can increase f so VE could vary] the
PIP and the mPAW can be altered by patient
time constants
Compare control mode to
• We control patients by giving them sedation
and paralytic agents so that the VE we set on
VC-CMV is exactly the same
• We can control their PaC02 thus their acid
base balance
• In A/C, the patient can trigger breaths that
will increase the VE, so that the VE based on
set VT and f could be lower than the actual
measured VE
Controlling the chronic
hypercapnic patient
 If your patient has a hypoxic drive,
administrate enough Fi02 to get his Pa02
between 80-100 mmHg.
 This will result in apnea and works as a form
of sedation in the first 24 hours.
 Must wean the Fi02 to get Pa02 between 5565 mmHg before weaning
Problems with A/C
 Excessively high PAW can cause problems with
hemodynamics once patient starts to breath.
 Another problem with A/C mode is the risk of
auto-PEEP and air trapping.
Inverse Ratio Ventilation [with
PC or with VC]
 This is a form of full support that uses
increased Ti to raise the mPAW when
patient’s compliance is so bad that PIP and
Pplateau are excessive
 In IRV, the expiratory time is so short that the
patient never completely exhales. This works
like PEEP to recruit alveoli
Raising mPAW with IRV
 mPAW = PIP [I] + PEEP [E]
 Because we raise the inspiratory time so
much we can decrease the PIP
 Because we create auto-PEEP with the short
TE, we can decrease the PEEP
Negative pressure
 The negative pressure ventilator is a box in
which the patient’s body [or chest wall] is
placed. A suction device is attached to the
 The NPV merely replaces the ventilatory
Problems with Negative pressure
Ventilation: patient must be able to:
 protect airway
 Handle being supine all the time
 hemodynamically stable
 be comfortable in one position all the time
 handle being disconnected from vacuum for
short time spans
More problems with NPV
 Patient can get skin lesions from movement
of body inside the device
 Patient can get cold from ‘wind’
 Best 02 device is nasal cannula because 02
can be sucked into the neck opening
 Classified as controllers, but newer models
can be A/C if there is a flow sensor placed on
the patient’s nose
 Old metal iron lungs have a constant I:E of I:I;
newer fiberglass devices can have altered I:E
Setting parameters on NPV:
 Change level of the vacuum to increase the VT
[he could use a Wright’s spirometer attached
to an IPPB mask to measure exhaled VT]
 Change the respiratory rate.
 continuous spontaneous ventilation in which
all breaths are spontaneous.
patient who can completely control his VE
and only needs a little help such as with
increased baseline pressures [CPAP]
or some application of assisted breaths such
as pressure support [PS]
or who might require monitoring of VE
Pressure support ventilation
• PSV is the most common form of pressure
cycled CSV.
• Although this does raise the airway pressure so
that we have a higher and lower pressure, we
call this PS rather than PIP because of the
specific characteristics of PS
• Flow triggered and flow cycled
• Patient controls his VT, f and inspiratory time
Indications for PS:
 When used with SIMV to reduce the WOB by
increasing the spontaneous VT. We generally
select the PS that will deliver a reasonable VT
[watch the spontaneous RR]
 Can be used alone during weaning. Once a
patient is on a PS of 5-10 cmH20, he is
considered at a level that only compensates
for RAW of the tubing, so is considered
consistent with spontaneous breathing.
PSV flow patterns
 The flow pattern is descending till it reaches
5 LPM [or 25% of the peak flow] in which the
flow stops abruptly.
 The flow slows down as the device attempts
to keep the PS at the preset pressure.
VT on PS
 There is no guaranteed VT, nor VE, but we can
increase the VT by increasing the PS pressure
 We need to set VE & high f alarms closely to
warn us of problems
 The patient sends more air to Zone III
because he is using his diaphragm more with
To choose the correct level of PSV
there are three methods:
get an appropriate VT [10-15 ml/kg] and titrate the PS level to
achieve this VT
increase the PS level till the respiratory rate is normalized [25
bpm or less]
increase the PSV until you decrease the work of breathing
through the ET tube
– To select the appropriate level of PSV to overcome the RAW use this
PSV= (PIP - Pplateau) x spont insp. Flow rate [l/sec]
Ventilator flow rate [l/sec]
• or ‘straight pressure support’ or ‘stand alone PS’ [
PS without SIMV.] In this case, the PS is not used
as a weaning modality but for initial of
mechanical ventilation.
• We generally select a PS level that will deliver 1012 ml kg IBW.
• The RCP must remember that this mode is an
assist only and the patient’s VT and VE will vary
base on lung dynamics. There is no guaranteed
• Patient must have an intact ventilatory drive
for this to work
CPAP mode
spontaneous mode
• application of PEEP without any positive
pressure breathes.
• CPAP is merely a raised baseline with a flow rate
with adjustable Fi02
• recruits alveoli which will improve diffusion of 02
• CPAP can help return a low compliant lung back
to normal once atelectasis has been resolved.
The FRC should rise.
• should decrease WOB.
• proper application of CPAP should decrease
WOB- watch respiratory rates on this
CPAP interfaces
 CPAP via the ET tube or a trach tube is called
 CPAP via a nose mask, face mask or full face
mask is called nasal-CPAP [n-CPAP]
 Obviously we select the interface based on
the patient’s ability to protect his airway
n-CPAP indications
 The successful candidate for n-CPAP would
be the patient who is oriented,
 has good ventilatory drive without excessive
 and who has the ability to protect his airway.
n-CPAP contraindications
 Persons at risk for vomiting and aspiration
 persons with skin necrosis,
 claustrophobia.
CPAP indications
Management of the person who is in hypoxemia respiratory failure.
This patient will have refractory hypoxemia without respiratory
Treatment of Congestive Heart Failure [CHF] in the patient who
has an intact ventilatory drive and can keep his PaC02 down. CPAP of
8-12 with Fi02 100% is suggested. [Egans pp, 1095]
A weaning modality This invasive CPAP may be the last step before
extubation. Generally a patient can be extubated from a CPAP of 5-7
cmH20 [or can be extubated at a stand-alone PSV of 5-7 cmH20.
Non-invasive management of persons with obstructive sleep apnea
a spontaneous mode
• airway pressure release ventilation
• Patient is breathing on two different levels of
Initial settings for APRV
• The higher CPAP is set with the Phigh, while the P low sets the
lower pressure.
The RCP should also set the time interval [Thigh] for Phigh
and the time interval [Tlow]for Plow
To initial APRV, the RCP looks to the patient’s Pplateau on
PPV and uses that figure for the Phigh.
The Thigh is started at 4 seconds for adults and can be
progressively increased to 10-15 seconds
Set the Plow at zero and use the release time [Tlow] to keep
the pressure from dropping to zero
Set the Tlow at about .5 to .8 [one time constant] so that the
breath ends with the expiratory flow at 50-75% of peak flow
What happens if the patient
goes apnic?
 During APRV ventilation if the patient was
stop breathing, the time-cycling between
high and low pressures would appear similar
to PC-IRV.
 So this is a spontaneous mode that happens
to have a back up of sorts
Contraindications to APRV
 persons with COPD or other problems
associated with air trapping.
 persons with excessively high intracranial
pressures [high ICP]
Bilevel ventilation
 An alternative to APRV is ‘bilevel ventilation.’
The only difference between bilevel
ventilation and APRV is that the patient
spends more time at the [Plow] lower airway
pressure than at the high airway pressure
 Non-invasive positive pressure ventilation
 These BiPap breathes tend to be flow or time
triggered, flow cycled off
 with the operator selecting PIP [called IPAP]
and PEEP [called EPAP] and bleeding in
supplementary 02.
 The newer Vision can get a Fi02.
contraindications/hazards of NIPPV
– do not put this device on an apnic patient because it
is NOT a ventilator—it is ‘a breath augmenter’.
Persons who cannot protect their airways
Hemodynamically unstable patients
Facial burns or trauma
Uncooperative patients
Persons at risk for aspiration: vomiting, nose bleeds,
unconscious, poor gag reflex
Copious secretions
Anatomical problems with gas exchange
Indications for NIPPV: acute
care of:
 congestive heart disease [n-CPAP or BiPap]
 COPD patient who doesn’t want to be
 recently extubated patient who is at risk of
 immune-suppression for whom we may not
want to risk VAP
Indications for long-term NIPPV
 Long-term management of both obstructive
sleep apnea and central sleep apnea
 Long-term management of patients with
skeletal or neuromuscular disorders
 Long-term management of the COPD patient
who has s/s of chronic hypoventilation
[especially at night] and who is optimally
treated with drugs and other care.
Initial settings for BiPap:
 IPAP at 8 cmH20 and EPAP at 4 cmH20.
 . Increase IPAP in increments of 2 cmH20 to
deliver more VT.
 To hypoxemia, increase the EPAP in increments
of 2 cm H20.
 Oddly enough, if the EPAP is raised without
raising the IPAP, the VT might decrease because
the VT is a function of the change in pressure or
the ‘delta P’ [ Δ P]
The BiPap ST/D
 EPAP/CPAP: in this mode, all you get is CPAP
 IPAP: in this mode, again, all you get is CPAP.
 Spontaneous mode this is a form of PSV in which
you select the PS with the IPAP and the PEEP with
the EPAP. All breaths are patient triggered
 Spontaneous/timed: is their version of A/C PC
with each breath patient or time triggered. In this
mode you select the bpm
 Timed mode: their version of control ventilation
in which you now select the rate and the
inspiratory time
What is so strange about the
BiPAP ST/D circuit?
 only a single, large-bore tubing going from
the compressor to the patient’s mask.
 constant leak at the “Whisper swivel” this
will leak a minimal amount of gas out of the
circuit and between the very high flow rates
and the leak, the patient doesn’t rebreathe
his C02. Never plug up this hole!
Adding extra 02 to the BiPap STD
without starting a fire
 add 02 at the mask,
 start machine first before adding 02 so gas
will not leak back into machine
 never exceed 15 LPM
Compare the BiPap STD to the Vision
BiPap machine
 The BiPAP ST/D has no 02 inlet
 The Respironics Vision plugs into 50 psig 02 &
can get 21% to 100% Fi02
 The BiPAP ST/D has no internal alarm, you
must buy a separate alarm
 The Respironics Vision can be used for
invasive ventilation with A/C, SIMV +PSV and
CPAP as well as NIPPV [CPAP and S/T]
Use of critical care ventilators such as
BiPap machines in the ICU.
 As a rule, we would operate these machines
in the PSV mode with PEEP to mimic the
 It is important to understand that the alarms
on these machines may have to be adjusted
out of range
Dual modes
 combine mandatory ventilation with
spontaneous ventilation
 IMV: intermittent mandatory ventilation: in
which some breaths are mandatory and
others are spontaneous.
 In this type of breath, the ventilator will give
a PPV usually based on VC at timed intervals.
The patient can breathe off a constant flow
rate or from a demand valve at a VT and flow
rate determined by his muscle strength,
ventilatory drive and lung mechanics.
Advantages of IMV/ SIMV
 patient comfort
 maintains muscle coordination & muscle
 reduces V/Q mismatch;Zone III is being
 [4] lower PAW and is an excellent weaning
 less likely to cause air-trapping
Disadvantage of IMV/ SIMV:
 If the patient’s PPV support is removed too
quickly the patient can suffer increased WOB
 We need to monitor the spontaneous VE , RR
and VT, we may need to increase support by:
 increasing the SIMV rate
 adding PS
Indications for IMV/SIMV:
 IMV is a partial mode of ventilation that
usually includes dual modes.
 weaning from CMV when the patient’s
ventilator muscles are weakened
 an initial ventilator setting when the patient is
at risk for air trapping and is breathing on his
 or if the patient who is able to breathe partially
for himself is at risk for decreased CO.
The difference between SIMV and IMV:
 SIMV stands for ‘synchronized intermittent
mandatory ventilation.’
 The mandatory breath can come in sooner if
patient triggers within the synchronization
window of fractions of seconds.
Special modes: PRVC
 In a pressure regulated volume control mode,
we are attempting to deliver the VT [because
we are in VC mode] but we want to keep the
airway pressures low.
 ventilator will attempt to deliver the VT at 5
cmH20 below a preset pressure setting.
Special modes: VAPS
 volume assured, pressure support, the ventilator
will be attempting to deliver a stable VT with PS
breaths so that the patient has the advantage of
stable VE as well as the advantages of
 If a PS breath fails to reach the pre-set VT, the
breath will continue at a constant flow until the
volume is reached. If the patient got the pre-set VT
with the PS breath, it stays PS.
 Unlike normal PS, these breaths aren’t just flow
triggered, but can be time triggered.
Special modes: MMV
 Mandatory minute ventilation
 gives the patient extra breaths or extra PS
pressure to keep a predetermined minimal VE.
 This differs from apnea parameters in that
the patient doesn’t have to actually go apneic
for 20 seconds or more for this to activate. He
merely needs to have hypoventilation.
One problem with MMV
 when the patient starts the rapid, shallow
breathing associated with respiratory
 If a patient keeps the VE up with rate only, he
can be in a lot of distress
 It is suggested to keep the maximal high
respiratory rate 10 BPM above the average
Special modes: ASV
 adaptive support ventilation: the RCP inputs
the patient’s IBW and a percentage of the VE.
 The ventilator will deliver a VE based on the
patient’s IBW.
 As the patient takes over more of the breathing
the VE is maintained with PS breaths.
 The level of PS changes to give the VT calculated
by the machine, The VT will be determined by
the patient’s IBW and VD ventilation.
Special modes: PAV
 In proportional assist ventilation mode
similar to ASV in that the ventilator will
collect data about patient’s elasticity and
resistance and flow or volume demands in
order to arrive at PS levels that varies.
High frequency ventilation
 controlled ventilation- the patient is sedated
and paralyzed
 VT of less or equal to the VD anatomical
 respiratory frequencies of 60 BPM-3600 bpm
 All HFV counts on the gas stream going down
the ET tube (inside) AT THE SAME TIME and
the gas flow existing (outside stream).
How does HFV work
 Penduluft action due to various time
constants of different portions of the lungs,
the gas moves from one lobe to another ,
 there is some bulk transfer
What are the types of HFV
 high frequency jet ventilation
 high frequency positive pressure
 high frequency oscillation
 combination of HFJ with CMV
Special modes: PRVC
 In pressure regulated volume control, an
effort is made to maintain both a safe level
of airway pressure and delivered VT.
 In PRVC, the RCP selects a PIP that will
not be exceeded.
 To keep the VT, at this safe PIP, the
inspiratory time and the flow rate must
Special modes: Auto-mode:
 in some ventilators selection of the auto-
mode will allow the ventilator to decrease
support as a patient starts to take over the
 The ventilator reverts between a CMV mode
and a spontaneous mode based on breath by
breath assessment of the patient
Special modes: ATC
 Automatic tubing compensation, in this
mode the ventilator will compensate for the
RAW of the ET tube.
VT, set f and VE
 Full support A/C or SIMV rate 12-16 BPM
 Partial support SIMV below 10 BPM
 8-10 ml/Kg IBW normal lungs
 6-8 ml/kg IBW asthma
 5-8 ml/ kg IBW for ARDS & COPD
 VE needs to be 80-100 ml/KgIBW
TI and Flow rates
 Inspiratory flow rates of 60-80 LPM for most
 If air hungry raise above 80
 COPD- 60-100 LPM
 Inspiratory times .80-1.2 seconds
Flow wave pattern
 Constant flows will decrease inspiratory time
and help with I:E ratios, but can raise the PIP.
 Descending flow curve has the advantage of
better distribution of gas into the lung, but
will increase the TI and increase the mPAW
 Sine wave: while considered more
physiological, a classic sine wave may not
have enough initial flow to satisfy a patient.
Like the descending flow pattern it will raise
the TI and change the I:E ratio
Rise time or Ramp
 : in an effort to fine-tune flow patterns, the
constant flow can be damped by a rise time
adjustments. When set high, this almost
mimics an ascending flow pattern.
Inspiratory pause
 The temporary use of the inspiratory pause
at about .5 to 1 second is generally reserved
for gathering Pplateau
 100% is a good place to
 Weaning rapidly to 40-50% after ABG
 Fi02 needs to be weaned about 20% at a step.
 may be started at zero, PEEP at 5 or less
cmH20 is considered physiological and should
not result in CV problems-but-- remember
any PEEP that causes hemodynamic
problems is excessive.
 Increase or decrease by units of 2
Humidification by HME
 is limited to persons with good fluid balances,
normal secretions and VE less than 10 LPM
and normal body temperatures.
 If the patient has a gross leak so that 30% of
the delivered VT is lost, the HME will not
Humidification by heated
 can be used with everyone but are necessary
for patients with secretions. Keep the
temperatures close to 330 C +/- 2
 multiple sighs every hour or so. These sigh
volumes were about 1.5 x the VT.
 important if VT is less than 7 ml/kg
s/p lung resection or lung
 need lower VT and faster rates to protect the
torn lung from rupture.
 Keep the Pplateau at or below 30 cmH20 [old
Egan’s 1011]
lobar pneumonia:
 place patient on the good lung side so gas goes
to the bad lung
 avoid PEEP in lobar pneumonia if possible
 Try to prolong the Ti
 Consider double lumen ET tube so we can set
two ventilators on the patient
long-term neuromuscular
 more comfortable at higher than usual VT
[decrease the RR] of 10-12 ml/kg. These
patients also tend to want higher flow rates.
 They can be managed with low Fi02-even .21
as long as Sp02 is above 90-92%
 low PEEP of 3-5 to prevent atelectasis are ok
Persons with Congestive
Heart failure
 We can start with normal settings, but if the
PIP and Pplateau are excessive, we need to
decrease the VT
 PEEP at 10 cmH20 and wean the
 Once the patient’s compliance gets better, we
must wean the PEEP
 If the patient has an intact ventilatory drive, &
good VE, he could be maintained on CPAP
Initial parameters when High RAW
is an issue?
 start with SIMV because this mode is less
likely to cause air trapping.
 minimize air trapping and auto-PEEP
 SIMV rate between 10-12 BPM : decrease this to 6-8 to
allow time to exhale
start at 60 and raise to100 LPM].
A COPD patient can be started at 40-50% Fi02
Use of PEEP with COPD is dangerous, but if the set PEEP
and the auto-PEEP are kept about the same, the gas is
more likely to leave the lung
, keep Sp02 at 90-92% and keep the PaC02 and pH close
to baseline so the patient will not suffer post-hypercapnic
Asthmatic [AHI 2005 CPR CPG pp IV 141]
 Alert? may do well on BiPap machine
 SIMV rate 6-10 BPM
 VT of 6-8 ml/ kg IBW
 80-100 LPM with a descending flow pattern to
get 1:4 or 1:5
 Start Fi02 at 100%.
 Use of PEEP with asthmatics is dangerous, but if
the set PEEP and the auto-PEEP are kept the
same, the gas is more likely to leave the lung.
 permissive hypercapnia,

Highlights of Mechanical ventilation Unit 4