1. “…an opening must be attempted in the trunk
of the trachea, into which a tube of reed or cane
should be put; you will blow into this, so that the
lung may rise again… and the heart becomes
strong…”
Andreas Vesalius (1555)
MODES OF MECHANICAL VENTILATION
Dr. Nikhil Yadav

2. Introduction
Mechanical ventilation forms a mainstay of critical care in patients
with respiratory insufficiency.
Ventilator must generate inspiratory flow to deliver tidal volume.
Transairway pressure (PTA) = PAO – PALV
PTA = 0, at the end of expiration and beginning of inspiration.
Mechanical ventilator produce either negative or positive pressure
gradient.

3. Negative pressure ventilation
PTA gradient is created by decreasing PALV to below
PAO
e.g.-
Iron lungs
Disadvantages- poor patient access,
bulky size, cost, dec. cardiac output
(Tank shock).
Chest cuirass or chest shell

4. Positive pressure ventilation
Achieved by applying positive pressure at airway
opening which produces PTA gradient that generates
inspiratory flow.
Inspiratory flow results in the delivery of tidal volume.

5. Modes of ventilation
Ventilator mode is a set of operating characteristics that controls
how the ventilator functions.
An operating mode describes the way a ventilator is-
• triggered into inspiration
• cycled into exhalation
• what variables are limited during inspiration
• allowing mandatory or spontaneous breaths or both

6. Controlled Mode Ventilation
Volume control
The ventilator delivers a preset TV at a specific R/R and
inspiratory flow rate.
It is irrespective of patients’ respiratory efforts.
In between the ventilator delivered breaths the inspiratory valve
is closed so patient doesn’t take additional breaths.
PIP developed depends on lung compliance and respiratory
passage resistance.

7. Controlled Mode Ventilation

8. Volume controlled CMV
Indications-
• In initial stage when patients “fighting” or “bucking” with the
ventilator
• Tetanus or other seizure activity
• Crushed chest injury
Disadvantages-
• Asynchrony
• Barotrauma d/t high PAW & dec. lung compliance
• Haemodynamic disturbances
• V/Q mismatch
• Total dependence on ventilator

9. Pressure Controlled CMV
Ventilator gives pressure limited, time cycled breaths thus
preset inspiratory pressure is maintained.
Decelerating flow pattern.
Peak airway/alveolar pressure is controlled but TV, minute
volume & alveolar volume depends on lung compliance, airway
resistance, R/R & I:E ratio.

10. PC- CMV

11. PC-CMV
Advantages-
Less PAW, thus chances of barotrauma and hemodynamic
disturbances are less.
Even distribution of gases in alveoli
In case of leakage, compensation for loss of ventilation is better
as gaseous flow increases to maintain preset pressure.
Disadvantages-
Asynchrony
TV dec. if there is dec. lung compliance or inc. airway resistance,
thus causes hypoventilation and alveolar collapse.
V/Q mismatch.

12. ASSIST-CONTROL MODE Ventilation
(A-C Mode)
Ventilator assists patient’s initiated breath, but if not
triggered, it will deliver preset TV at a preset
respiratory rate (control).
Mandatory mechanical breaths may be either patient
triggered (assist) or time triggered (control)
If R/R > preset rate, ventilator will assist, otherwise it
will control the ventilation.

13. A-C Mode Ventilation

14. A-C Mode Ventilation
Advantages-
Dec. patients work of breathing.
Better patient ventilator synchrony.
Less V/Q mismatch.
Prevents disuse atrophy of diaphragmatic muscle.
Disadvantages-
Alveolar hyperventilation
Development of high intrinsic PEEP in obstructed pts.
Inc. mean airway pressure causes hemodynamic disturbances.

15. Intermittent Mandatory Ventilation
(IMV)
Ventilator delivers preset number of time cycled mandatory
breaths & allows patient to breath spontaneously at any tidal
volume in between.
Advantages-
Lesser sedation
Lesser V/Q mismatch
Lesser hemodynamic disturbances
Disadvantage-
Breath stacking- lung volume and pressure could increase
significantly, causing barotrauma.

16. IMV

17. Synchronized Intermittent
Mandatory Ventilation (SIMV)
Ventilator delivers either assisted breaths to the patient at the
beginning of a spontaneous breath or time triggered mandatory
breaths.
Synchronization window- time interval just prior to time
triggering.
Breath stacking is avoided as mandatory breaths are
synchronized with spontaneous breaths.
In between mandatory breaths patient is allowed to take
spontaneous breath at any TV.

18. SIMV

19. SIMV

20. SIMV
It provides partial ventilatory support
Advantages-
Maintain respiratory muscle strength and avoid atrophy.
Reduce V/Q mismatch d/t spontaneous ventilation.
Decreases mean airway pressure d/t lower PIP & inspiratory
time
Facilitates weaning.

21. SIMV
Disadvantages-
Desire to wean too rapidly results in high work of spontaneous
breathing & muscle fatigue & thus weaning failure.

22. Positive End Expiratory Pressure
(PEEP)
An airway pressure strategy in ventilation that increases the end
expiratory or baseline airway pressure greater than atmospheric
pressure.
Used to treat refractory hypoxemia caused by intrapulmonary
shunting.
Not a stand-alone mode, used in conjugation with other modes.
Indications-
Refractory hypoxemia d/t intrapulmonary shunting.
Decreased FRC and lung compliance

23. Physiology of PEEP
PEEP reinflates collapsed alveoli & maintain alveolar inflation during exhalation.
PEEP
Increases alveolar distending pressure
Increases FRC by alveolar recruitment
Improves ventilation
Increases V/Q
Improves oxygenation
Decreases work of breathing

24. PEEP

25. PEEP
Complications
Dec. venous return and cardiac output.
Barotrauma
Inc. ICP d/t impedance of venous return from head.
Alteration of renal function & water imbalance.

26. Continuous Positive Airway Pressure
(CPAP)
PEEP applied to airway of patient breathing spontaneously
Indications are similar to PEEP, to ensure patient must have
adequate lung functions that can sustain eucapnic ventilation.

27. Mandatory Minute Ventilation
(MMV)
Similar to IMV mode except that minimum minute volume is set
rather than R/R.
Ventilator measures spontaneous minute volume, if found less
than preset mandatory minute volume, the difference b/w two is
delivered as mandatory breaths by ventilator at preset flow &
TV.
Suited for patients with variable respiratory drive
Disadvantage-
Hypoventilation as either minute volume recorded is not
necessary alveolar ventilation.

28. Pressure Support Ventilation (PSV)
Supports spontaneous breathing of the patients.
Each inspiratory effort is augmented by ventilator at a preset
level of inspiratory pressure.
Patient triggered, flow cycled and pressure controlled mode.
Decelerating flow pattern.
Applies pressure plateau to patient airway during spontaneus br.
Can be used in conjugation with spontaneous breathing in any
ventilator mode.

29. PSV
Commonly applied to SIMV mode during spontaneous
ventilation to facilitate weaning
With SIMV, PS-
Inc. patient’s spontaneous tidal volume.
Dec. spontaneous respiratory rate.
Decreases work of breathing.
Addition of extrinsic PEEP to PS increases its efficacy.

30. SIMV (VC) -PS

31. PSV
Disadvantages-
Not suitable for patients with central apnea. (hypoventilation)
Development of high airway pressure. (hemodynamic
distubances)
Hypoventilation, if inspiratory time is short.

32. Adaptive Support Ventilation (ASV)
Available on Galileo ventilator.
Patient body weight (deadspace) & percent minute volume are
feed in ventilator.
Ventilator has pre determined setting of 100ml/kg/min.
Test breath measures compliance, airway resistance & i. PEEP.
Ventilator selects and provide the frequency, inspiratory time, I:E
& sets high pressure limit for mandatory and spontaneous
breaths.
May be either time triggered or patient triggered.

33. Proportional Assist Ventilation (PAV)
PAV is a spontaneous breathing mode that offers assistance to
the patient in proportion to the patient’s effort.
Inspiratory flow, volume & pressure are variable & pressure
support changes according to elastance & airflow resistance &
patients demand (volume or flow).
PAV is set to overcome 80% of elastance & airflow resistance.
PAV instantaneously measures the flow and volume being pulled
in by the patient, and automatically calculates the compliance
and resistance of the respiratory system to determine how much
pressure to provide for each breath.

34. PAV
Flow Assist (FA)-
Pressure is provided to meet patient’s inspiratory flow demand.
Dec. inspiratory effort to overcome airflow resistance.
Volume Assist (VA)-
Pressure is provided meet patient’s volume requirement.
Dec. inspiratory efforts to overcome systemic elastance.
Indications-
Spontaneously breathing patient
Intact respiratory drive
Intact neuromuscular function
Generally, a patient considered suitable for pressure support
ventilation could be considered for PAV.

35. PAV
Advantage-
The patient ‘drives’ the ventilator
Better patient ventilator synchrony as pressure vary to augment
flow & demand.
Disadvantage-
Barotrauma- if elastance & resistance show sudden
improvement.

36. Volume Assured Pressure Support
(VAPS)
Incorporates inspiratory pressure support ventilation &
conventional volume assisted cycles to provide optimal
inspiratory flow during assisted/controlled ventilation.
Desired TV & pressure support level are preset.
Once triggered desired PS level reaches asap & delivered volume
is compared with preset TV.
If volume delivered = 0r > preset volume, it is PS breath.
If volume < preset volume, ventilator switches to volume
limited, resulting in longer inspiratory time until preset TV is
delivered

37. Pressure Regulated Volume Control
(PRVC)
Used to achieve volume support while keeping PIP to lowest
level.
Achieved by altering the peak flow & inspiratory time in
response to changing airway or compliance characteristics.
At constant flow PIP increases d/t inc. airflow resistance, so
decreasing flow reduces the airflow resistance.
To compensate for lower flow, inspiratory time is prolonged.

38. Airway Pressure Release Ventilation
(APRV)
Similar to CPAP as patient breathes spontaneously.
Airway pressure is maintained at moderately high level (15-20 cmH2O)
throughout most of respiratory cycle with brief periods of lower pressure to
allow deflation of lungs.
Inc. pressure ensures alveolar recruitment & oxygenation & brief deflation
allows CO2 elimination without alveolar collapse.
Indicated as an alternative to conventional volume cycled ventilation for
patients with decreased lung compliance (ARDS), as chances of barotrauma is
less d/t less PAW.

39. APRV

40. Inverse Ratio Ventilation (IRV)
Used to promote oxygenation esp. in ARDS.
Normal I:E ratio is 1:1.5 – 1:3, in IRV I:E is 2:1 – 4:1
Improves oxygenation by
• Reducing intrapulmonary shunting.
• Improving V/Q mismatch.
• Decreasing deadspace ventilation.
• Increasing mean airway pressure.
• Presence of auto PEEP.
Disadvantages-
Barotrauma d/t inc. mPaw & auto PEEP.
High rate of transvascular fluid flow. May worsen pulm. oedema

41. Tracheal Gas Insufflation (TGI)
Adjuvant to mechanical ventilation in which O2 enriched gas is
insufflated into trachea to ventilate anatomical dead space
during expiration.
Decreases PaCO2 at any level of inspiratory minute ventilation.
Extra flow may cause inc. airway pressure and hyperinflation.

42. Independent Lung Ventilation (ILV)
It is simultaneous separate ventilation of individual lung.
Separation achieved by double lumen tube and two ventilators-
synchronized or asynchronized.
Indication-
Severely diseased one lung which can not be treated with
conventional ventilation.
e.g.- unilateral pulmonary contusion, aspiration pneumonia,
bronchopleural fistula, massive unilateral pulmonary embolism etc.

43. High frequency ventilation (HFV)
For all high frequency techniques during which tidal volume
equals or less than anatomical dead space volume and
respiratory frequency between 60 to 3000 breaths / minutes.
They are 3 types:
HFPPV …..60 to 110 breaths/min
HFJV…….110 to 600 breaths/min
HFO……..600 to 3000 breaths/min
Advantages-
Low PAW, less V/Q mismatch, less barotrauma

44. THANK YOU