This document provides an overview of various modes of mechanical ventilation. It begins by defining key terms like peak inspiratory pressure, plateau pressure, PEEP, and CPAP. It then describes the basic modes of ventilation: volume-controlled, pressure-controlled, and pressure support. Various advanced modes are also outlined such as SIMV, BiPAP, APRV, and ASV. Factors related to weaning a patient from mechanical ventilation are discussed. Throughout, details are provided on the objectives, physiology, advantages, and disadvantages of each ventilation mode.

1. MODE OF MECHANICAL VENTILATION
PREPARED BY
SYED UMAIR
ACADEMIC CO-ORDINATOR
ANESTHESIA AND ICU

2. OBJECTIVES
• Introduction
• How ventilator ventilates
• Basic definitions
 Peak Inspiratory Pressure (PIP)
 Plateau pressures
 Positive End Expiratory Pressure (PEEP)
 Continuous Positive Airway Pressure (CPAP)
• Modes of ventilation
 Controlled
 Pressure Control (PC)
 Volume Control (VC)
 Supported
 Continuous Positive Airway Pressure (CPAP)
 Pressure Support (PS)
 Combined
 SIMV (PC) + PS
 SIMV (VC) + PS
• Latest modes of ventilation
 CMV
 SIMV
 Spont
 APRV
 ASV
 Duopap, BiPAP
 NIV

3. INTRODUCTION
Each mode of ventilation is defined by its phase variable components:
a) Trigger
b) Target/Limit
c) Cycle.
The three basic modes of ventilation include
1. volume-controlled ventilation (VCV)
2. pressure-controlled ventilation (PCV)
3. pressure support ventilation (PSV).

4. A. Trigger
B. Limit
C. Cycling
How a ventilator ventilates ?
A
B C

5. • Patient effort- pressure triggering
• After a predetermined time-time triggering
• Manually - manual/flow triggering
Start Inflation (Trigger)

6. Pressure Triggering
•
•
•
•
Breath is delivered when ventilator senses patients
spontaneous inspiratory effort.
sensitivity refers to the amount of negative pressure the
patient must generate to receive a breath/gas flow.
If the sensitivity is set at 1 cm then the patient must
generate 1 cm H2O of negative pressure for the
machine to sense the patient's effort and deliver a
breath.
Acceptable range -1 to -5 cm H2O below patient s
baseline pressure

7. Time triggering

8. Flow Triggering
•
•
•
•
•
The flow triggered system has two preset variables for
triggering, the base flow and flow sensitivity.
The base flow consists of fresh gas that flows
continuously through the circuit. The patient’s earliest
demand for flow is satisfied by the base flow.
The flow sensitivity is computed as the difference
between the base flow and the exhaled flow
Here delivered flow= base flow- returned flow
Hence the flow sensitivity is the magnitude of the flow
diverted from the exhalation circuit into the patient’s
lungs. As the subject inhales and the set flow sensitivity
is reached the flow pressure control algorithm is
activated, the proportional valve opens, and fresh gas is
delivered.

9. • Pressure
• Volume
• Flow
• Time
Cycling

10. •
•
•
• Terminates inspiratory phase at a preset
PIP. TV varies directly with lung
compliance and inversely with airway
resistance.
Advantages: reduced barotrauma which
has been implicated secondary to high
PIP.
Disadvantages: if lung compliance is
less, will lead to respiratory acidosis.
Important to monitor patient’s expired
TV.
Pressure Cycled Ventilation

11. • Terminates inspiratory phase at a preset TV.
• Advantages: patient is guaranteed to receive a preset
TV under normal operating conditions.
• Disadvantages: PIP may rise high enough to cause
barotrauma.
Volume Cycled Ventilation

12. • Terminates the inspiratory phase when inspiratory
flow reaches a predetermined minimal level.
• Measured during spontaneous ventilation
• Mostly seen in pressure support modes of
ventilation.
Flow cycled ventilation

13. •
•
•
Terminates the inspiratory phase when a preset
inspiratory time has been reached.
Advantages: ease to regulate I:E ratio especially
when inverse ratio ventilation is desired.
Disadvantages: delivered TV is dependent on
airway resistance and compliance characteristics.
Time Cycled Ventilation

14. Basic definitions
– Peak Inspiratory Pressure (PIP)
– Plateau pressures
– Positive End Expiratory Pressure (PEEP)
– Continuous Positive Airway Pressure (CPAP)

15. • Peak Inspiratory Pressure (PIP)-
The peak pressure is the maximum pressure
obtainable during active gas delivery. This pressure
a function of the compliance of the lung and thorax
and the airway resistance including the contribution
made by the tracheal tube and the ventilator circuit.
– Maintained at <45cm H2O to minimize barotrauma
• Plateau Pressure-
The plateau pressure is defined as the end inspiratory
pressure during a period of no gas flow. The plateau
pressure reflects lung and chest wall compliance.

17. • Mean Airway Pressure-
The mean airway pressure is an average of the
system pressure over the entire ventilatory period.
• End Expiratory Pressure-
End expiratory pressure is the airway pressure at the
termination of the expiratory phase and is normally
equal to atmospheric or the applied PEEP level.

18. PEEP
•
•
•
Positive end expiratory pressure (PEEP) refers to the
application of a fixed amount of positive pressure
applied during mechanical ventilation cycle
Continuous positive airway pressure (CPAP) refers to
the addition of a fixed amount of positive airway
pressure to spontaneous respirations, in the presence
or absence of an endotracheal tube.
PEEP and CPAP are not separate modes of ventilation
as they do not provide ventilation. Rather they are
used together with other modes of ventilation or during
spontaneous breathing to improve oxygenation, recruit
alveoli, and / or decrease the work of breathing

19. Advantages
•
•
•
Ability to increase functional residual capacity (FRC)
and keep FRC above Closing Capacity.
The increase in FRC is accomplished by increasing
alveolar volume and through the recruitment of
alveoli that would not otherwise contribute to gas
exchange. Thus increasing oxygenation and lung
compliance
The potential ability of PEEP and CPAP to open
closed lung units increases lung compliance and
tends to make regional impedances to ventilation
more homogenous.

20. Physiology of PEEP
• Reinflates collapsed alveoli and maintains alveolar
inflation during exhalation
PEEP
Decreases alveolar distending pressure
Increases FRC by alveolar recruitment
Improves ventilation
Increases V/Q, improves oxygenation, decreases work of
breathing

21. Dangers of PEEP
• High intra-thoracic pressures can cause decreased
venous return and decreased cardiac output
• May produce pulmonary barotrauma
• May worsen air-trapping in obstructive pulmonary
disease
• Increases intracranial pressure
• Alterations of renal functions and water metabolism

22. AutoPEEP
• During expiration alveolar pressure is greater than
circuit pressure until expiratory flow ceases. If
expiratory flow does not cease prior to the initiation
of the next breath gas trapping may occur. Gas
trapping increases the pressure in the alveoli at the
end of expiration and has been termed:
– dynamic hyperinflation;
– autoPEEP;
– inadvertent PEEP;
– intrinsic PEEP; and
– occult PEEP

23. Effects of autoPEEP can predispose the patient to:
• Increased risk of barotrauma
• Fall in cardiac output
• Hypotension
• Fluid retention
• Increased work of breathing

24. Modes of Ventilation
•
•
•
Controlled
– Pressure Control (PC)
–Volume Control (VC)
Supported
– Continuous Positive Airway Pressure (CPAP)
–Pressure Support (PS)
Combined
– SIMV (PC) + PS
– SIMV (VC) + PS

25. • CMV
• SIMV
• Spont
• APRV
• ASV
• Duopap, BiPAP
• NIV
Modes of latest ventilation

26. • Patient receives a preset TV at a preset RR.
– Pt. Cannot increase RR or breathe spontaneously
– Should only be used if the patient is properly medicated
and paralyzed
CMV (Continuous mandatory ventilation)mode

27. • Indications:
- bucking during initial stages of vent support
- flail chests
- who otherwise need complete respiratory rest
• Complications: a disconnect will lead to apnea and
hypoxia.
• Disadvantages:
-Muscles of respiration weaken making weaning
more difficult.
CMV (Continuous mandatory ventilation)mode

28. -May lead to a rapid type of disuse atrophy involving
the diaphragmatic muscle fibers, which can develop
within the first day of mechanical ventilation.
-May cause atrophy in all respiratory related muscles
during CMV
CMV (Continuous mandatory ventilation)mode

29. •
•
•
Ventilator delivers a pre-set tidal volume at a pre-set
respiratory rate when there is not respiratory effort from
the patient.
But if the patient triggers a spontaneous respiratory
effort earlier than the time interval created by the set
respiratory rate, the ventilator will still deliver the breath
at the set tidal volume and then resets the time interval
for the next breath.
All breaths are delivered at the set tidal volume whether
it was ventilator triggered or patient triggered.
AC ( Assist control ventilation) mode

30. • Indications: Myasthenia gravis, GBS, post cardiac /
resp arrest, ARDS, pulmonary oedema.
• Advantages: minimal work of breathing and patient
controls RR which helps normalize PaCO2.
AC ( Assist control ventilation) mode

31. • 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.
• It provides partial ventilatory support
SIMV(Synchronized Intermittent Mandatory
Ventilation )

32. SIMV(Synchronized Intermittent Mandatory
Ventilation )

33. • Advantages:
– Maintain respiratory muscle strength.
– Reduce ventilation to perfusion mismatch.
– Decreases mean airway pressure.
– Facilitates weaning.
SIMV(Synchronized Intermittent Mandatory
Ventilation )

34. •
•
•
•
•
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.
Applies pressure plateau to patient airway during
spontaneous breathing.
Commonly applied to SIMV mode during
spontaneous ventilation to facilitate weaning
PSV (Pressure Support Ventilation) mode

35. PSV (Pressure Support Ventilation) mode

36. • Indications:
As an adjunct to SIMV. Not used during machine
breaths. This will increase pts. Spontaneous TV,
decrease spontaneous RR and decrease work of
breathing
• Disadvantages-
✓Not suitable for patients with central
apnea. (hypoventilation)
✓Development of high airway pressure.
(hemodynamic distubances)
✓Hypoventilation, if inspiratory time is short.
PSV (Pressure Support Ventilation) mode

37. •
•
•
•
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.
Increased pressure ensures alveolar recruitment &
oxygenation & brief deflation allows CO2elimination
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
due to less PAW.
APRV (Airway Pressure Release Ventilation) Mode

38. APRV (Airway Pressure Release Ventilation) Mode

39. • a ventilator targeting scheme in which one variable is
automatically adjusted to achieve a predetermined value
of another variable.
• Patient body weight (deadspace) & percent minute
volume are feed in ventilator.
• Inspiratory pressure is automatically adjusted by the
ventilator to achieve a minute volume target.
• Automatically adjust the inspiratory flow to maintain a
constant I:E ratio.
• Using artificial intelligence application to conduct
ventilation
ASV (Adaptive Support Ventilation ) Mode

40. • Used in conjunction with other
modes Prevents closing of alveoli
by increasing baseline airway
pressure.
• Indications: intrapulmonary shunt
and refractory hypoxemia,
decrease FRC and lung
compliance.
• Complications: decrease venous
return, barotrauma, increased ICP
and alterations in renal functions
and water metabolism.
PEEP (Positive end expiratory Pressure)

41. CPAP and BiPAP
CPAP is essentially constant PEEP; BiPAP is CPAP plus PS
• Parameters
CPAP – PEEP set at 5-10 cm H2O
BiPAP – CPAP with Pressure Support (5-20 cm H2O)
Shown to reduce need for intubation and mortality in COPD
pts
Indications
When medical therapy fails (tachypnea, hypoxemia,
respiratory acidosis)
Use in conjunction with bronchodilators, steroids,
oral/parenteral steroids, antibiotics to prevent/delay intubation
Weaning protocols
Obstructive Sleep Apnea

42. - Decrease cardiac output
- Barotrauma
- Nosocomial pneumonia
- Positive water balance
- Decrease renal perfusion
- Increase ICP
- Hepatic congestion
- Worsening of intracardiac shunt
Complications

43. •
•
Unsupported spontaneous breathing trials.
- The machine support is withdrawn
-T-Piece (or CPAP) circuit can be attached .
Intermittent mandatory ventilation (IMV) weaning.
- The ventilator delivers a preset minimum minute volume
•
-Synchronized (SIMV) to the patient's own resp efforts.
Pressure support weaning.
-Patient initiates all breaths and these are 'boosted' by the
ventilator.
- Gradually reducing the level of pressure support,
- Once the level of pressure support is low (5-10 cmH2O
above PEEP), a trial of T-Piece or CPAP weaning should
Modes of Weaning

44. • Underlying illness is treated and improving
• Respiratory function:
– Respiratory rate < 35 breaths/minute
– FiO2 < 0.5, SaO2 > 90%, PEEP <10 cmH2O
– Tidal volume > 5ml/kg
– Vital capacity > 10 ml/kg
– Minute volume < 10 l/min
• Absence of infection or fever
• Cardiovascular stability, optimal fluid balance
and electrolyte replacement
Indication of weaning