MODES OF MECHANICAL VENTILATION, NEGATIVE PRESSURE VENTILATION, POSITIVE PRESSURE VENTILATION, INDICATION OF MECHANICAL VENTILATION

1. DR. SHASHIKANT SHARMA
MD ANAESTHESIOLOGY & CRITICAL CARE
Modes of Mechanical
Ventilation

2. NEGATIVE AND POSITIVE PRESSURE
VENTILATION
 Every ventilator must generate an inspiratory flow in
order to deliver a tidal volume. Since gas flow requires a
pressure gradient, a mechanical ventilator must produce
a pressure gradient b/w airway opening and alveoli in
order to produce inspiratory flow and volume delivery.
 At end-exhalation and prior to the beginning of
inspiration, pressures at the airway opening and the
alveoli are both equal to atmospheric pressure. Since
these two pressures are equal at this point, there is no
pressure gradient and therefore no flow.
 Since a pressure gradient is needed to generate gas flow
and volume mechanical ventilators achieve this condition
by creating either a negative or positive pressure
gradient.

3. Negative Pressure Ventilation
 Negative pressure ventilation creates a
transairway pressure gradient by decreasing
alveolar pressures to a level below i. e. below
atmospheric pressure.
 Unless airway obstruction is present, negative
pressure ventilation does not require an artificial
airway.
 Two classical devices that provide negative
pressure ventilation are the “iron lung” and the
chest cuirass or chest shell.

4.  Encloses the patient’s body except for the head and neck in a
tank, and air in it is evacuated to produce a negative pressure
around the chest cage. This negative pressure surrounding the
chest and underlying alveoli results in chest wall and alveolar
expansion.
 Tidal volume delivered to patient is directly related to negative
pressure gradient. For example, a more negative pressure applied
to chest wall will yield a larger tidal volume. Since negative
pressure ventilation does not require tracheal intubation, this
noninvasive method of ventilation has been used extensively and
successfully to support chronic ventilatory failure.
Disadvantages:
1. Poor patient access
2. Potential for a decreased cardiac output known as “tank shock”
Iron Lungs

5. Iron Lungs

6. Chest Cuirass
The chest cuirass or chest shell is a form of negative pressure
ventilation that was intended to alleviate the problems of patient
access and tank shock associated with iron lungs.
This shell device covers only the patient’s chest and leaves the
arms and lower body exposed.
To overcome the problem of air leakage, individually designed
cuirass “respirators” minimize air leaks, and they have been used
successfully to ventilate patients with chest wall diseases such as
scoliosis.
Because of the availability of positive pressure ventilators,
chest cuirass ventilators are seldom used in an acute care facility.

7. Chest Cuirass

8. Positive Pressure Ventilation
 Positive pressure ventilation is achieved by applying positive
pressure i.e. a pressure greater than atmospheric pressure at
the airway opening.
 Increasing the pressure at the airway opening produces a
trans-airway pressure gradient that generates an inspiratory
flow. This flow, in turn, results in the delivery of a tidal volume.
 Therefore, tidal volume is directly related to the transairway
pressure gradient. All other factors being held constant,
increasing the positive pressure being applied to the lungs will
result in a larger tidal volume being delivered.

9. OPERATING MODES OF MECHANICAL
VENTILATION
 A ventilator mode can be defined as a set of operating
characteristics that control how the ventilator functions.
 Regardless of which operating mode is selected, it should achieve
four main goals:
1. Provide adequate ventilation and oxygenation
2. Avoid ventilator-induced lung injury
3. Provide patient-ventilator synchrony
4. Allow successful weaning from mechanical ventilation.
 There are at least 23 modes of ventilation available in different
ventilators. Two or more of these modes are often used together to
achieve certain desired effects.

11. 1. SPONTANEOUS
 Spontaneous setting on the ventilator is not an actual
mode since the frequency and tidal volume during
spontaneous breathing are determined by the patient.
 The ventilator simply provides the flow and
supplemental oxygen. Even though the spontaneous
mode is not a direct ventilator function, the role of the
ventilator during.
Spontaneous mode is to provide:
1. Inspiratory flow to the patient in a timely manner
2. Flow adequate to fulfill a patient inspiratory demand
3. Adjunctive modes such as PEEP to complement
4. Patient’s spontaneous breathing effort.

12. 2. POSITIVE END-EXPIRATORY
PRESSURE (PEEP)
PEEP increases the end-expiratory or baseline airway pressure
to a value greater than atmospheric. It is often used to improve
the patient’s oxygenation status, especially in hypoxemia that is
refractory to high level of FIO2.
PEEP is not commonly regarded as a “stand-alone” mode,
rather it is applied in conjunction with other ventilator modes. For
example, when PEEP is applied to spontaneous breathing
patients, the airway pressure is called continuous positive airway
pressure (CPAP).
Indications for PEEP
1. Intrapulmonary shunt and refractory hypoxemia
2. Decreased FRC & lung compliance
3. Auto-PEEP not responding to adjustments of ventilator
settings.

13. Physiology of PEEP
 PEEP reinflates collapsed alveoli and supports and
maintains alveolar inflation during exhalation. Once
“recruitment” of these alveoli occurs and is sustained,
PEEP decreases the threshold for alveolar opening and
facilitates gas diffusion and oxygenation.
 PEEP increases the alveolar end-expiratory pressure
which decreases pressure threshold for alveolar
inflation.
 Re-expansion of the collapsed alveoli improves
ventilation and reverses intrapulmonary shunting.

14. Complications of PEEP
1. Decreased Venous Return
2. Barotrauma
3. Increased ICP
4. Alteration of renal function & water metabolism

15. 3. CONTINUOUS POSITIVE AIRWAY PRESSURE
(CPAP)
 CPAP is PEEP applied to the airway of a patient who
is breathing spontaneously.
 Indications for CPAP are essentially the same as for
PEEP with additional requirement that the patient must
have adequate lung functions that can sustain
Eucapnic ventilation documented by PaCO2.
 In adults, CPAP may be given via a face mask, nasal
mask, or endotracheal tube.

16. 4. BILEVEL POSITIVE AIRWAY
PRESSURE (Bipap )
 BiPAP allows the clinician to apply independent positive airway
pressures to both inspiration and expiration.
 IPAP provides positive pressure breaths, and it improves ventilation
and hypoxemia due to hypoventilation.
 EPAP is in essence CPAP, and it improves oxygenation by increasing
the FRC and reducing intrapulmonary shunting.
INDICATIONS
1. Supporting patients with chronic ventilatory failure
2. Restrictive chest wall disease
3. Neuromuscular disease
4. Nocturnal hypoventilation
5. Appears to be of value in preventing intubation of the end-stage
COPD patient.

17. Initial Settings
Used in one of three modes:
1. Spontaneous: if the patient is breathing spontaneously, the IPAP
and EPAP
may be initially set at 8 cm H2O and 4 cm H2O, respectively. Pressures
are titrated based on needs, generally with a target of 5 to 7 mL/kg.
2. Spontaneous/timed: Used as a backup mechanism and the
frequency per min (f/min) is set two to five breaths below the patient’s
spontaneous frequency.
3. Timed mode: set IPAP and EPAP as above and the f/min slightly
higher than patient’s spontaneous frequency.
 A BiPAP device can be used as a CPAP device by
setting IPAP and EPAP at same level.

18. 5. CONTROLLED MANDATORY VENTILATION
(CMV)
 Also known as continuous mandatory ventilation or control
mode, ventilator delivers the preset tidal volume at a time-triggered
frequency. Since ventilator controls both the patient’s tidal volume
and respiratory frequency, ventilator controls the patient’s minute
volume. In the control mode, patient cannot change the ventilator
frequency or breath spontaneously.
 Control mode should only be used when the patient is properly
medicated with a combination of sedatives, respiratory
depressants, and neuromuscular blockers.
 Control mode ventilation should not be instituted by decreasing
the ventilator’s triggering sensitivity to the point that no amount of
patient effort can trigger ventilator into inspiration.

19.  Problem with this approach should be obvious since any
spontaneous inspiratory effort would be like attempting to inspire
through a completely obstructed airway. Regardless of how
vigorous the patient’s inspiratory effort is, no gas flow would be
delivered to the patient until the ventilator automatically becomes
time-triggered.
Indications for Control Mode:
1. Initial stage of mechanical ventilation
2. Tetanus
3. Crushed chest injury
4. Complete rest for patients

21. Complications of Control Mode
 Since the patient’s spontaneous respiratory drive will have
been blunted with sedation and neuromuscular block in the
control mode, the patient is totally dependent on the
ventilator for ventilation and oxygenation.
 Rapid disuse atrophy of diaphragm fibers
 Prolonged mechanical ventilation leads to diaphragmatic
oxidative injury, elevated proteolysis, and reduced function
of the diaphragm

22. 6. ASSIST/CONTROL (AC)
 With the assist/control (AC) mode, patient may increase ventilator
frequency (assist) in addition to the preset mechanical frequency (control).
 Each control breath provides the patient with a preset, Ventilator-
delivered tidal volume.
 Each assist breath also results in a preset, ventilator-delivered tidal
volume.
 The assist control mode does not allow the patient to take spontaneous
breaths.
 The mandatory mechanical breaths may be either patient-triggered by
the patient’s spontaneous inspiratory efforts (assist) or time-triggered by a
preset frequency.
 If a breath is patient-triggered, it is referred to as an assisted breath; if a
breath is time-triggered, the breath is referred to as a control breath.

25. ADVANTAGES:
 Patient’s work of breathing requirement in the AC is
very small when the triggering sensitivity is set
appropriately and the ventilator supplies an inspiratory
flow that meets or exceeds the patient’s inspiratory flow
demand.
 if the patient has an appropriate ventilatory drive, this
mode allows patient to control the frequency and
therefore the minute volume required to normalize
patient’s PaCO2.

26. 7. INTERMITTENT MANDATORY VENTILATION
(IMV)
 IMV is a mode in which ventilator delivers control (mandatory) breaths
and allows the patient to breathe spontaneously at any tidal volume the
patient is capable of in between the mandatory breaths.
 Primary complication associated with IMV was random chance for
breath stacking. This occurs when the patient is taking a spontaneous
breath and ventilator delivers a time-triggered mandatory breath at the
same time. If this occurs, patient’s lung volume and airway pressure
could increase significantly.
 Setting appropriate high pressure limits will reduce the risk of
barotrauma in the event of breath stacking. As long as the breath
stacking only occurs Occasionally, IMV mode is an acceptable mode of
ventilation with few complications.
 The sophistication of ventilator technology has progressed to the point
that no new adult ventilators offer the IMV mode. Rather, all ventilators
currently available have been designed to provide SIMV.

28. 8. SYNCHRONIZED INTERMITTENT
MANDATORY
VENTILATION (SIMV)
Mode in which ventilator delivers either assisted breaths to the patient
at beginning of a spontaneous breath or time-triggered mandatory
breaths. mandatory breaths are synchronized with the patient’s
spontaneous breathing efforts so as to avoid breath stacking.
The SIMV mandatory breaths may be either time-triggered or patient-
triggered. triggering mechanism is determined by whether or not the
patient makes a spontaneous inspiratory effort just prior to the delivery
of a time-triggered breath.
Synchronization Window: time interval just prior to time triggering in
which
ventilator is responsive to the patient’s spontaneous inspiratory effort is
commonly referred to as the synchronization window.

30. SIMV Spontaneous Breath-Triggering
Mechanism
 In between mandatory breaths, SIMV permits patient to breathe
spontaneously to any tidal volume the patient desires. Gas source
for spontaneous breathing in the SIMV mode is typically supplied
by a demand valve. Demand valve is always patient-triggered,
either by pressure or flow depending on the ventilator.
 It is important to understand that spontaneous breaths taken by
patient in SIMV mode are truly spontaneous. ventilator provides
humidified gas at selected FIO2, but spontaneous frequency and
spontaneous tidal volume are totally dependent on the patient’s
breathing effort.

31. Advantages of SIMV Mode
1. Maintains respiratory muscle strength/avoids muscle
atrophy
2. Reduces ventilation to perfusion mismatch
3. Decreases mean airway pressure
4. Facilitates weaning.
The primary disadvantage associated with SIMV is desire
to wean the patient too rapidly, leading first to a high work
of Spontaneous breathing and ultimately to muscle fatigue
and weaning failure. Without PSV, best practice is to
decrease SIMV mandatory frequency slowly and monitor
patient closely for signs of fatigue.

33. 9. MANDATORY MINUTE VENTILATION
(MMV)
 Also called minimum minute ventilation, is a feature of
some ventilators that provides a predetermined minute
ventilation when the patient’s spontaneous breathing effort
becomes inadequate.
 It is especially useful in preventing hypoventilation and
respiratory acidosis in the final stages of weaning with SIMV
when the patient’s spontaneous breathing is assuming a
significant portion of the total minute volume.

35. 10. PRESSURE SUPPORT VENTILATION
(PSV)
 PSV is used to lower the work of spontaneous breathing and
augment a patient’s spontaneous tidal volume. When PSV is used
with SIMV, it significantly lowers the oxygen consumption
requirement presumably due to the reduced work of breathing.
 PSV applies a preset pressure plateau to the patient’s airway for
the duration of a spontaneous breath.
 Pressure-supported breaths are considered spontaneous
because they are patient-triggered:
1. Tidal volume varies with patient’s inspiratory flow demand
2. Inspiration lasts only for as long as the patient actively inspires
3. Inspiration is terminated when patient’s inspiratory flow demand
decreases to a preset minimal value.

36.  A pressure-supported breath is therefore patient-triggered,
pressure-limited, and flow-cycled. It is pressure-limited because the
maximum airway pressure cannot exceed preset pressure support
level. It is flow-cycled because a pressure-supported breath cycles
to expiration when the flow reaches a minimal level.
Indications for PSV Mode:
Pressure support is typically used in the SIMV mode to facilitate
weaning in a difficult-to-wean patient.
In this application, pressure support:
1. Increases the patient’s spontaneous tidal volume
2. Decreases the patient’s spontaneous frequency
3. Decreases the work of breathing.

38. 11. ADAPTIVE SUPPORT VENTILATION
(ASV)
 Dual control mode that provides a mandatory minute
ventilation. Ventilator measures the dynamic compliance and
expiratory time constant to adjust mechanical tidal volume and
frequency for a target minute ventilation. Once the target
minute ventilation is set, ventilator uses test breaths to
measure system compliance, airway resistance, and any
intrinsic PEEP.
 Following determination of these variables, the ventilator
selects and provides the frequency, inspiratory time, I:E ratio,
and high pressure limit for mandatory and spontaneous
breaths.

39.  If there is no spontaneous triggering effort, the
ventilator determines and provides mandatory frequency,
tidal volume, and high pressure limit needed to deliver
preselected tidal volume, inspiratory time, and I:E ratio.
 As the patient begins to trigger the ventilator, the
number of mandatory breaths decreases and pressure
support level increases until a calculated tidal volume is
able to provide adequate alveolar volume.

40. 12.PROPORTIONAL ASSIST
VENTILATION (PAV)
 With PAV, there is no target flow, volume, or pressure during
mechanical ventilation. Pressure used to provide the pressure
support is variable and is in proportion to the patient’s pulmonary
characteristics (elastance and airflow resistance) and demand
(volume or flow).
 PAV is set to overcome 80% of the elastance and airflow
resistance. PAV may be flow assist (FA) or volume assist (VA). In FA,
the applied pressure is provided to meet the patient’s inspiratory flow
demand.
 FA reduces the inspiratory effort needed to overcome airflow
resistance. VA occurs when PAV provides the pressure to meet the
patient’s volume requirement. VA reduces the inspiratory effort
needed to overcome systemic elastance such as restrictive lung
defects

41.  PAV improves ventilation and reduces neuromuscular drive and
work of breathing in ventilator-dependent patients with COPD. When
PAV is used with CPAP, the reduction of inspiratory muscle work
reaches values close to those found in normal subjects.

42. 13. VOLUME-ASSURED PRESSURE
SUPPORT (VAPS)
 VAPS incorporates inspiratory PSV with conventional volume-assisted cycles
(VAV). This combination provides an optimal inspiratory flow during
assisted/controlled cycles, reducing the patient’s work of breathing commonly
seen during VAV.
 Unlike typical PSV, VAPS assures stable tidal volume in patients with irregular
breathing patterns. If the delivered volume equals preset volume, breath is
considered a pressure support breath. Since pressure support breaths are
dependent on the patient effort, delivered volume may be larger than preset
volume. It is essential to set pressure support level that provides a volume that is
lower than the preset volume.
 On the other hand, if delivered volume falls short of preset volume, ventilator
switches from a pressure-limited breath to a volume-limited breath. This results
in a longer inspiratory time until the preset volume is delivered.
 Since VAPS may prolong the inspiratory time automatically, patients with
airflow obstruction should be monitored closely in order to prevent air trapping
and other undesirable cardiovascular effects associated with prolonged
inspiratory time.

43. 14. PRESSURE-REGULATED VOLUME
CONTROL (PRVC)
 Similar modes to PRVC in subsequent ventilators are known as
adaptive pressure control (Servo-I), AutoFlow , adaptive pressure
ventilation, volume control, volume targeted pressure control and
pressure controlled volume guaranteed.
 PRVC is used primarily to achieve volume support while keeping PIP
at a lowest level possible. This is achieved by altering the peak flow and
inspiratory time in response to changing airway or compliance
characteristic.

44. Automode
 combines PRVC and volume support. This mode alters between
time-cycled and flow-cycled breaths depending on the degree of
patient effort. If there is no spontaneous triggering effort for a time
period (i.e., apnea for 12, 8, and 5 sec in adult, pediatric, and
neonatal modes, respectively), ventilator provides PRVC and
breaths are time-triggered.Delivered volume is preset with a
variable PIP up to the high pressure limit.
When the patient has two consecutive breaths that trigger the
mechanical breaths, automode switches to volume support in which
all breaths become patient triggered, pressure-limited, and flow-
cycled.

45. 15. ADAPTIVE PRESSURE CONTROL
 It combines functions of volume ventilation (stable TV) with functions
of pressure ventilation via variable flow.
 It is a PC breath that uses variable inflation pressures to deliver a
minimum targeted TV.
 Inflation pressure is variable.
 As Patient’s inspiratory effort increases inflation pressure is reduced.
This is a concern because ventilator can not distinguish between
improved pulmonary compliance and increased patient effort .
 Increasing patient’s breathing effort due to hypoxia or pain may
potentially create a greater work of breathing, due to decreasing
inflation pressure.

46. 16. VOLUME VENTILATION PLUS
(VV+)
It is an option that combines two different mode: volume control plus and volume
support.
A. Volume Control Plus
 Used to deliver mandatory breaths during AC and SIMV modes of
ventilation.
 Intended to provide a higher level of synchrony than standard volume
control ventilation.
 Clinician sets target TV and Ti. Ventilator delivers a single test breath
using standard volume and decelerating flow and plateau to determine
relative compliance. Target pressures for subsequent breaths are adjusted
accordingly to compensate for any TV differences. Flow is adjusted
automatically to reduce likelihood of inadequate flow or aggressive flow
demand.
 Active spontaneous breaths are allowed during the inspiratory phase of
a mandatory breath by way of a pressure control style of breath and use of
an active exhalation valve.
 Excessive pressure caused by breathing or coughing is vented, thus
maintaining synchrony.

47. Volume Support (VS)
 Provide a control TV & increased patient comfort. Weaning from
anesthesia is a common application for VS.
 Clinician sets target TV but not inspiratory time or mandatory
frequency. Ventilator delivers a single spontaneous pressure support
type of breath and uses variable pressure support levels to provide target
TV.
 During weaning or awakening from anesthesia, patient assumes a
higher spontaneous TV and ventilator decreases pressure support level
accordingly. When spontaneously TV decreases, ventilator increases PS
level automatically to maintain the target TV.
During VS, the ventilator frequency and MV are determined by triggering
effort of the patient. Inspiratory time is determined by patient respiratory
demand.

48. 17. PRESSURE-CONTROLLED
VENTILATION (PCV)
 Pressure-controlled breaths are time-triggered by a preset
frequency. Once inspiration begins, a pressure plateau is created and
maintained for a preset inspiratory time.
 Pressure-controlled breaths are therefore time-triggered, pressure-
limited & time-cycled.
 PCV is usually indicated for patients with severe ARDS who require
extremely high PIP during mechanical ventilation in a VC mode. As a
result of these high airway pressures, incidence of barotraumas is more
Likely.
 Advantage of switching these patients from the conventional VC
ventilation to PC is that a lower PIP can be used and maintained while
providing oxygenation and ventilation.

51. 18. AIRWAY PRESSURE RELEASE
VENTILATION (APRV)
 APRV has two CPAP or pressure levels- high pressure (Phigh
or Pinsp) and low pressure (Plow or PEEP) & patient is allowed
to breathe spontaneously without restriction at high or low
pressure levels.
 When high pressure level is dropped to low pressure level, it
simulates a mechanical exhalation. Likewise, when low pressure
level is raised to high pressure level, it simulates an inspiratory
mechanical breath.
 Patient spends most of the time at high pressure level with
less than 1.5 sec at the low pressure level.

52.  Since APRV mode is pressure-limited, for a given pressure
gradient, patient’s TV will vary directly with changes in lung
compliance and inversely with changes in airway resistance. For this
reason, exhaled TV should be closely monitored to prevent
hyperinflation.
 Patient-ventilator dyssynchrony may result when pressure release
occurs during spontaneous inspiration, or when pressure increase
occurs during spontaneous expiration.
 Primary indication for this mode is similar to that of pressure
control, namely, as an alternative to conventional VC ventilation
for patients with significantly decreased lung compliance such
as patients with ARDS.

55. 19. BIPHASIC POSITIVE AIRWAY PRESSURE
 Mode that has two baseline pressure levels (Pinp. & PEEP) and
it allows spontaneous breathing at any point in mechanical
ventilation cycle.
 Similar to APRV with one exception.
 In APRV, the patient spends most of the time at high pressure
level.
While in Biphasic PAP, Patient spends more time at low pressure
level.

57. 20. INVERSE RATIO VENTILATION
 Ratio of inspiratory time (I time) to expiratory time (E time) is known as
the I:E ratio.
 In conventional mechanical ventilation, the I-time is traditionally lower
than E-time so that I:E ratio ranges from about 1:1.5 to 1:3.
 This resembles normal I:E ratio during spontaneous breathing, and it is
considered physiologically beneficial to normal Cardiopulmonary function.
Physiology of IRV
IRV improves oxygenation by:
(1) Reduction of intrapulmonary shunting
(2) Improvement of V/Q matching
(3) Decrease of dead space ventilation

58. Two notable changes are observed during IRV are:
A. Increase of Mean Airway Pressure:
 To achieve same degree of ventilation and oxygenation, IRV requires
a lower peak airway pressure and PEEP, but a higher mean airway
pressure (mPaw) than conventional mechanical ventilation.
 Increase in mPaw during IRV helps to reduce shunting and improve
oxygenation in ARDS patients.
B. Addition of Auto-PEEP:
 Since IRV provides a longer I-time and shorter E-time, breath
stacking with an increase of end-expiratory pressure is likely when there
is not enough time for complete expiration.
Presence of auto-PEEP during IRV may help to reduce shunting and
improve oxygenation in ARDS patients.

59. Adverse Effects of IRV
A. Increase in mPaw and presence of auto-PEEP both contribute
to increase of mean alveolar pressure and volume. So
Incidence of barotrauma may be as high as that obtained by
conventional ventilation with high levels of PEEP.
B. Higher rate of transvascular fluid flow or flooding induced by an
increased alveolar pressure.
C. Patients receiving IRV are often agitated. They may require
sedation and neuromuscular blocking agents to facilitate
ventilation.

60. `
Pressure Control-IRV (PC-IRV)
 Since IRV may increase mPaw, create auto-PEEP, and
increase incidence of barotrauma. it is sometimes used in
conjunction with PC-ventilation due to its pressure-limiting
capability. By using pressure control, peak airway pressure may
be kept at a safe level.
 This strategy helps to minimize pressure induced lung injuries.
 When an inverse I:E ratio is used with pressure-controlled
ventilation, it is called PC-IRV.

61.  Several studies compare the outcomes of ARDS patients
before and after implementation of PC-IRV. Changes that may
occur when positive pressure
ventilation with PEEP (PPV + PEEP) is switched over to PC-IRV
mode of ventilation are:

62. 21. AUTOMATIC TUBE COMPENSATION
 This tubing compensation can be applied in all ventilation modes.
 ATC offsets and compensates for airflow resistance imposed by
artificial airway.
 It allows the patient to have a breathing pattern as if breathing
spontaneously without an artificial airway.
 With ATC, pressure delivered by ventilator to compensate for airflow
resistance is active during inspiration and expiration.
Example: when airway diameter decreases or flow demand increases,
pressure is raised to overcome a higher airflow resistance or increased
flow demand.

63. 22. NEURALLY ADJUSTED VENTILATORY
ASSIST
 Patient’s electrical activity of diaphragm is used to guide the
optimal functions of the ventilator.
 Neural controls of respiration originated in the patient’s respiratory
center are sent to diaphragm via phrenic nerves. In turn, bipolar
electrodes are used to pick up electrical activity.
 Electrodes are mounted on a disposable catheter and positioned in
esophagus at level of diaphragm.
 NAVA is available for adults, children, and neonates.
 Ability to wean these patients rapidly reduces or eliminates
incidence of disuse atrophy of the diaphragm.

64. Use of NAVA
1. Management & weaning of mechanically ventilated
patients with spinal cord injury.
2. Head injury
3. COPD
4. H/O of ventilator dependency.

65. 23. HIGH-FREQUENCY OSCILLATORY
VENTILATION
 Delivers extremely small volumes at high frequency.
 Its main application is to minimize development of lung injury while
providing mechanical ventilation.
 It delivers a constant flow and its piston pump oscillates at
frequencies ranging from 3 Hz to 15 Hz (180 breaths/min to 900
breaths/min).
 Adult patients are sedated to prevent deep spontaneous
breathing, as this will trigger alarms and affect ventilator
performance.

66. Ventilation can be increased by:
1. Decreasing the oscillation frequency
2. Increased by increasing amplitude of oscillation
3. Increasing inspiratory time
4. Increasing flow (with an intentional cuff leak)
Oxygenation to patient can be increased by:
1. Increasing mean airway pressure
2. Increasing the FIO2.

67. THANK YOU