This document discusses various modes and parameters of mechanical ventilation. It describes negative pressure ventilation techniques like iron lungs and positive pressure ventilation delivered by ventilators. Key phase and control variables are defined including trigger, limit and cycle variables. Common ventilator modes like CMV, AC, IMV, SIMV and their characteristics are outlined. Parameters like PEEP, CPAP and BiPAP used to improve oxygenation are also summarized.

1. PRESENTED BY
DR. NAYAN GUPTA
MGMMC AND MYH,
INDORE

2. • NEGATIVE PRESSURE VENTILATION – It applies
subatmospheric pressure outside of the chest to inflate the
lung that decreases the alveoli pressure and create
transairway pressure gradient.
E.g Iron lung, Chest cuirass
• POSITIVE PRESSURE VENTILATION- Ventilator applies the
pressure inside the chest to expand it or applying positive
pressure at the airway opening which develop transairway
pressure gradient.
TYPES OF VENTILATION

3. IRON LUNG CHEST CUIRASS

4. POSITIVE PRESSURE VENTILATION
• CPAP, IPAP, EPAP, NIV
• Bilevel, BiPAP
• CMV, Assist Control, IMV, SIMV
• Pressure Control, Volume Control
• PSV, ASV, MMV
• Auto mode, Spontaneous mode
• Control Variables
• Phase Variables
• Waveform

5. PHASE VARIABLES
When a variable is examined during a particular phase of
respiration process, it is termed as phase variable.
A. Trigger Variable- Variable that determine the start of
inspiration.
B. Limit Variable- Factor which control the inspiratory
flow or variable is not allowed to rise above a
preset value during the inspiratory time.
C. Cycle variable- Variable that stops the inspiration
and starts the expiration.

6. TRIGGER VARIABLE – Time, Pressure Or Flow
• Time Triggered- Breath is initiated and delivered by a ventilator, when
a preset time interval has elapsed. The ventilator will trigger regular
breaths at a frequency which will depend on set respiratory rate.
• Pressure triggered- Breath is initiated and delivered by a ventilator,
when it senses the patient’s spontaneous (negative pressure)
inspiratory efforts. The amount of Negative pressure, that a patient
must generate to trigger the ventilation is called ‘Sensitivity level’.
• Flow Triggered- when a patients inspiratory flow reaches a specific
value, a ventilator supported is delivered. More sensitive to patient’s
inspiratory efforts.
Patient may trigger the ventilator by generating a pressure gradient or
flow gradient.

7. TIME
TRIGGERED
PRESSURE
TRIGGERED
FLOW
TRIGGERED

8. LIMIT VARIABLE
• A limit variable represents
the maximum value which
that parameter can attain
during the inspiratory
phase of a mechanical
breath.
• This limits the variable, but
it does not end the
inspiratory phase, which is
the defining feature of
these variables.

9. CYCLE VARIABLE
• This variable must be measured by ventilator and used as a feedback signal to
end inspiratory flow delivery, which then allows exhalation to begin.
• The ventilator measures this variable during the inspiratory phase.
• When the set parameter for this variable is achieved, the ventilator opens the
expiratory valve, and expiration may begin.
• Typical methods of ventilator breath cycling include:
• Time-cycled ventilation
• Flow-cycled ventilation
• Pressure-cycled ventilation
• Volume-cycled ventilation
• Time-cycled ventilation is mainly used for sedated or paralysed patients, and is
typical of mandatory modes
• Flow-cycled ventilation is mainly used for spontaneously breathing patients
and is typical of spontaneous modes.

10. CONTROL VARIABLE
• The control variable is the parameter/variable which the ventilator
uses as the feedback signal for controlling inspiration
• Pressure, flow and volume are all possible control variables, but
conventionally only pressure and volume are used.

11. PRESSURE CONTROL MODES OF
VENTILATION
• The inspiratory pressure is the control variable, and is maintained
during the inspiratory phase. As a result of this, the pressure
waveform is “square”. This increases the mean airway pressure (i.e.
the area under the pressure/time graph is greater).

12. ADVANTAGE
• Increased mean airway pressure, which improves oxygenation . this
is not a massive advantage until you start using extremely
inspiration-heavy I:E ratios, eg. 1:1.5 or 1:1
• Increased duration of alveolar recruitment: with a square pressure
waveform, alveoli are opened earlier and remain open for longer,
allowing better gas exchange
• Pressure limited ventilation may protect against barotrauma; the
fixed pressure level defends against pressure-induced alveolar
injury.

13. DISADVANTAGE
• Tidal volume is dependent on respiratory compliance; and it
may vary substantially over the course of mechanical
ventilation, requiring frequent adjustments.
• Uncontrolled volume may result in volutrauma, i.e. if the lung
compliance improves suddenly the ventilator may deliver
volumes which distend the most compliant lung units beyond
their elastic limit.

14. VOLUME CONTROL MODES OF
VENTILATION
• In Volume control modes the tidal volume is the defined variable
which is used by the ventilator to give feedback to the solenoid
valve circuits. As volume and flow are inextricably linked, the
volume control modes are generally constant flow modes, i.e. the
ventilator delivers flow which is constant, and stops this flow
when the desired volume is achieved.

15. ADVANTAGES OF VOLUME CONTROL
VENTILATION
• Guaranteed tidal volumes produce a more stable minute
volume. The reliability of the minute volume makes this mode of
ventilation more appropriate in situations where careful control of
PaCO2 is of importance.
• The minute volume remains stable over a range of changing
pulmonary characteristics. If airway resistance fluctuates
significantly (e.g. in the course of therapy for status asthmaticus)
this mode has the advantage of maintaining a reliable minute
volume.
• The initial flow rate is lower than in pressure-controlled
modes. This is an advantage if airway resistance is high; blowing
more slowly into the tight bronchi does not produce a high
resistance-related early pressure peak, and potentially prevents an

16. DISADVANTAGES OF VOLUME CONTROL
VENTILATION
• The mean airway pressure is lower with volume control ventilation, due to the slopy
shape of the pressure waveform. This can theoretically be a disadvantage in
patients who have severe hypoxia; in those people one might want to use a
pressure-controlled mode instead.
• Recruitment may be poorer in lung units with poor compliance. Units with a long
time constant and poor compliance may remain unrecruited until very late in the
inspiratory phase when pressure approaches its maximum value. These units will
have little time for gas exchange before the ventilator cycles to expiration. From
this, one might expect that with a volume-controlled mode the degree of
atelectasis will be greater than with a pressure controlled mode, peak airway
pressures being equal.
• In the presence of a leak, the mean airway pressure may be unstable. The constant
flow used during VCV may not be able to compensate for an intermittent
leak. Consider: if the leak flow rate is equal to the inspiratory flow rate, there will
be no volume delivered.
• Insufficient flow may give rise to patient-ventilator dyssynchrony. In the presence
of increased respiratory demand during the course of a breath, the ventilator may

17. POINTS TO REMEMBER
• Using pressure as the control variable limits the risk of
barotrauma and can improve oxygenation (with a square
pressure waveform)
• Using volume as the control variable Promotes a stable minute
volume, and therefore a stable PaCO2 level
• In general, volume control favours the control of ventilation,
and pressure control favours the control of oxygenation

18. BASIC MODES OF VENTILATION
• Controlled Mechanical Ventilation (CMV)
• Assist Control Ventilation (AC)
• Intermittent Mandatory Ventilation (IMV)
• Synchronized Intermittent Mandatory Ventilation (SIMV)
• Continuous Positive Airway Pressure (CPAP)
• Bilevel Positive Airway Pressure (BiPAP)
• Positive End-Expiratory Pressure (PEEP)
• Spontaneous

19. CONTROLLED MANDATORY
VENTILATION
• The Ventilator delivers the preset tidal volume (or pressure) at a
time triggered frequency. i.e. Ventilators controls the patient’s
Minute Volume.
• Patient can not change the ventilator respiratory rate or Breath
spontaneously.
• It is used only when the patient is properly medicated with a
combination of sedatives, neuromuscular blockers or patient
has no breathing efforts.

20. INDICATIONS
• Fighting or Bucking the ventilator- means patient is severly
distressed and vigorously struggling to breath. Their rapid
spontaneous inspiratory efforts become asynchronous with the
ventilators inspiratory flow.
• Tetanus and other seizure activities
• Complete rest
• Patient with crushed chest injury, in which spontaneous inspiratory
efforts produce paradoxical chest movements.
DISADVANTAGE
• If not paralysed completely- Any spontaneous resp. efforts would
be like attempting to inspire through a completely obstructed
airway.
• Rapid disuse atrophy of diaphragm fibres.

21. CONTROL MODE (PRESSURE TARGETED
VENTILATION)

22. CONTROL MODE (VOLUME TARGETED
VENTILATION)

23. • Patient may increase the ventilator frequency (or resp. rate) in
addition to preset mechanical resp. rate.
• The breath may be either patient-triggered by the patients
spontaneous inspiratory efforts (ASSISTED BREATH) or time
triggered by the preset frequency (CONTROL BREATH).
• Do not allow the patient to take spontaneous breath.
• Tidal volume of each breath is the same (or breath will be identical)
whether it is assisted breath or controlled breath.
ASSIST/CONTROL VENTILATION
Controlled Breath
Assisted Breaths

24. INDICATION
• To provide full ventilator support for patients when they are first
placed on ventilator.
• Used for patients who have stable respiratory drive (Spont. Freq. of
atleast 10-12/min).
e.g. if patient has stable assist frequency of 12/min, then the patient
is triggering breaths every 5 sec. and control frequency is preset at
10/min, the ventilator would deliver time triggered breath every 6
sec. No time triggered breath would be delivered.
Time triggered breath act as a safety net in case patient stop
triggering ventilation.
The accepted minimal control frequency in AC mode is 2-4/min less
than the patient’s assist frequency or minimal control frequency of 8-
10/min.

25. ADVANTAGE
• Less asynchrony
• Patients work of breathing is low.
• Allow patient to control the frequency and therefore the minute
volume required to normalize the patients Paco2.
DISADVANTAGE
• Alveolar Hyperventilation
• Hypocapnia and Respiratory Alkalosis. (if patient has high
frequency)

26. Assist Control ventilation
(Pressure)
Assist Control ventilation
(Volume)

27. INTERMITTENT MANDATORY VENTILATION
(IMV)
• Ventilator deliver mandatory (control) breaths at a set rate and
allows the patient to breathe spontaneously in between
mandatory breaths.
• Tidal volume of spontaneously breath will determined by the
patients capability.

28. DISADVANTAGE
• Random chance for Breath Stacking – If spontaneous and
mandatory breath delivered at same time. Patient’s lung volume
and airway pressure could increase – Barotrauma
Breath
stacking

29. SYNCHRONIZED INTERMITTENT MANDATORY
VENTILATION (SIMV)
• Ventilator delivers either assisted breath at the beginning of
spontaneous breath or time-triggered mandatory breath.
• The mandatory breaths are synchronized with the patient’s
spontaneous breathing efforts so as to avoid breath stacking.
• If patient’s breath spontaneously between the mandatory breath, are
truly spontaneous and if by chance, patient begins to inspire just
prior to the point at which ventilator would be expected to time-
trigger, then the ventilator sense this spontaneous effort and delivers
the mandatory breath as an Assisted Patient-triggered breath.

30. SYNCHRONIZATION WINDOW
Time interval just prior to time triggering in which ventilator is
responsive to patient’s spontaneous inspiratory efforts.

31. • If patient makes a spontaneous insp. Efforts that fall in sync window,
ventilator is patient triggered to deliver an assisted breath. (Patient
initiated Assisted Ventilation)
• If patient does not make inspiratory effort then ventilator will deliver a
time triggered mandatory breath. (Ventilator generated controlled
Ventilation)
• If the patient triggers outside the window, vent. Will allow this
spontaneous breath but does not offer any inspiratory assistance.
(Unassisted spontaneous breath)

32. INDICATION
-To provide partial ventilator support i.e. patient is actively involved in
providing part of minute volume.
-Weaning
ADVANTAGE
• Maintain respiratory muscle strength/ Avoid muscle atrophy
• Reduce ventilation to perfusion mismatch- SIMV tends to distribute the
spontaneous tidal volume more evenly– reducing dead space ventilation
• Facilitates weaning.
DISADVANTAGE
If wean too rapidly- high work of spontaneous breathing and ultimately
muscle fatigue and weaning failure.

33. PRESSURE SUPPORT VENTILATION (PSV)
• The patient breaths spontaneously while the ventilator applies a
pre-determined amount of positive pressure to the airways upon
inspiration.
• Help to overcome airway resistance, reduce the work of breathing
and augments the tidal volume.
• Pressure Supported breaths
-Pt. triggered, pressure limited and flow cycled
-Tidal volume varies with pt’s inspiratory flow demand
-Inspiration last only for log as the patient actively Inspires
-Insp. Is terminated when the pts insp. flow demand decreases to a
preset minimal value (sp. 25% of maximum)

34. • Used in conjugation with spontaneous breath in any mode of
ventilation.
• No back up ventilation in event of apnea.
• Used in the SIMV mode to facilitate weaning, In this pressure support
- Increases the patient’s spontaneous tidal volume.
-Decrease resp. rate
-Decrease the work of Breathing
• Since an endotracheal tube increases the airway resistance and work
of breathing, pressure support has been used to overcome this gas
flow resistance.

35. SIMV with PS
Pressure
Support Curve

36. POSITIVE END EXPIRATORY PRESSURE (PEEP)
• Positive pressure applied at the end of expiration during
mandatory/ventilator breath.
• Positive end-expiratory pressure increase the end expiratory or
baseline airway pressure to a value greater than atm pr.
• It is applied in conjunction with other ventilator modes.
• Due to decrease in lung compliance, force of elastic recoil is
increased that lead to decrease in alveolar volume. If elastic recoil
force is greater than normal alveolar distending pressure
resulting in alveolar collapse.
• PEEP reinflates collapsed alveoli and supports and maintains
alveolar inflation during exhalation.

37. POSITIVE END EXPIRATORY PRESSURE
Decrease the pressure threshold for alveolar inflation
Increases FRC by alveolar recruitment
Improves Ventilation
1.Increase V/Q
2.Improves Oxygenation
3.Decrease work of Breathing
Physiology

38. INDICATION
• Intrapulmonary Shunting And Refractory Hypoxemia- The Primary
indication for PEEP is refractory hypoxemia induced by Intrapulmonary
shunting. Refractory hypoxemia is defined as when PaO2 is 60mmHg
or lower at a FiO2 of 50% or Higher.
• Decrease FRC and lung compliance – A severely diminshed FRC and
reduced lung compliance greatly increases the alveolar opening
pressure.
• Auto PEEP- Air Trapping may be caused by severe airflow obstruction
or insufficient expiratory time. Uncorrected air trapping may lead to
auto-PEEP. It increases the work of breath triggering because the
patient must over come the auto-PEEP level. It is compensated by
setting a PEEP level slight below the auto-PEEP level, which raises end
expiratory baseline pressure and reduce breath trigger efforts

39. COMPLICATION
• Barotrauma- PEEP greater than 10cm H2O ( or mean airway pressure
>30cm H2O or PIP >50cm H2O ) is associated with increased
incidence of Barotrauma.
• Decreased Venous return and Cardiac Output- During PEEP, the
pleural pressure become less negative and the pressure gradient
between central venous drainage (CVP) and pleura surrounds the
heart will decrease resulting in decreased Venous return. It occurs
mainly in patients with normal and high lung compliance.
• Dec. MAP
• Decrease Renal and Portal blood flow.

40. CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP)
• When PEEP is applied to the airway of patient who is breathing
spontaneously.
Spontaneous Breath + PEEP = CPAP
• Same indication as PEEP
• CPAP is the treatment of choice for moderate to severe
obstructive sleep apnea.

41. • It apply independent positive airway pressures to both Inspiration
(IPAP) and Expiration (EPAP).
• IPAP provide positive pressure breaths, and it improves
Ventilation and hypoxemia due to hypoventilation
• EPAP (same as PEEP) improves oxygenation by increasing the FRC
and enhance alveolar recruitment.
• BiPAP= IPAP + EPAP
• EPAP= PEEP, IPAP= PS + PEEP
BILEVEL POSITIVE AIRWAY PRESSURE (BiPAP)

42. INDICATION
• Acute Respiratory failure
• End stage COPD patients or Acute Hypercapnic exacerbation of
COPD.
• Chronic ventilator failure
• Restrictive chest wall disease
• Neuro muscular disease
• Nocturnal hypoventilation

43. INTIAL SETTINGS
• IPAP and EPAP may initially set at 8cm H2O and 4cm H2O respectively.
• 3 modes
Spontaneous
Spont./Timed – act as back up mechanism, f/min is 2-5 breaths < pt’s
spont freq.
Timed - f/min is slightly > pt’s spont freq.
• IPAP may be increased in increments of 2cm H2O to enhance the “pressure
boost” to improve Ventilation, normalize PaCO2 and reduce the work of
breathing.
• EPAP should be increased by 2cm H2O to increase functional residual
capacity and Oxygenation in pts with Intrapulmonary shunting.
• A BiPAP is used as CPAP if IPAP = EPAP.
• The % IPAP set as 33% or 50% for I:E ratio of 1:2 or 1:1 respectively. IPAP
max time should not be set longer than 50% of respiratory cycle.

44. BASIC MANAGEMENT STRATEGIES
Inc Ventilation = Dec PaCO2 Inc Oxygention = Inc PaO2

45. STRATEGIES TO IMPROVE VENTILATION

46. • Minute Ventilation =(Ventilator VT × Ventilator f) +
(Spontaneous VT × Spontaneous f)
1. Increase Ventilator frequency- Ventilator freq should not
exceed 20/min as Auto PEEP may occur abovr this.
New Freq= (frequency × PaCO2 )/ Desired PaCO2
2. Increase spont. Tidal volume -more advantageous to inc
spontaneous tidal volume than freq. which result in shallow
breathing.
3. Ventilator tidal volume is set according to patient’s body
weight gen. 10ml/kg. Excessive lead to ventilator induced
lung injury, and inadequate lead to hypoventilation and

47. STRATEGIES TO IMPROVE OXYGENATION
Oxygenation
is dependent
on well
balanced
Ventilation,
diffusion and
perfusion

48. • Increase FiO2- High FiO2 increase alveolar capillary oxygen
pressure gradient thus enhancing diffusion of oxygen.

49. FiO2 may be adjusted using the following equation:
Desired FiO2 = PaO2 desired X FiO2 known
PaO2 known
• When PaO2 remains low on high FiO2 significant shunting, V/Q
abnormalities and/or diffusion defects are present.
• Ideal to keep FiO2 < .4/.5, PaO2 60-90 mmHg

50. OXYGEN TOXICITY
• It include ciliary impairment, lung damage, Respiratory distress
syndrome and pulmonary fibrosis.
• These complication occur with in 12 to 24 hrs of exposure to
100% oxygen.
• That’s why general guideline to use FiO2 lower than 60% and limit
use of high level of FiO2 for less than 24 hr.
Weaning from PEEP and High FiO2
1.Maintain PEEP and Dec FiO2 to 40% or 50%
2.Maintain FiO2 and Decrease PEEP to abt 3cm H2O,
3.Discontinue PEEP.

51. Clinical Round
• A patient with myasthenia gravis is started on mechanical
ventilation. The CXR is normal. Breath sounds are clear. Initial
ABG’s on .25 FiO2 after 20 minutes on the ventilator are
7.31/62/58. What changes in ventilator settings might improve
this patient's ABG findings?
Ans -This patient has respiratory acidosis. The PaO2 indicates
moderate hypoxemia. A common reaction by clinicians in this
situation is to increase the FiO2. However the cause of the
hypoxemia is the elevated PaCO2. An increase in CO2 of 1mmHg
reduces the O2 by 1.25mmHg. The most appropriate action is to
increase ventilation

52. Clinical Round
• After being supported on a ventilator for 30 minutes, a patient's
PaO2 is 40mmHg on an FiO2 of 0.75. Acid-base status is
normal and all other ventilator parameters are within the
acceptable range. PEEP is 3 cmH2O. What FiO2 is required to
achieve a desired PaO2 of 60 mmHg? Is this possible?
Ans -Desired FiO2 = (60x0.75)/40=
1.13
You cannot give more than 100% O2. The appropriate change is
the FiO2 to 100% and increasing PEEP