mechanical ventilator

2.  INTRODUCTION
 TRADITIONAL TYPES
 INDICATIONS
 TYPES
 CLASSIFICATION OF
VENTILATORS/VENTILATORY CYCLE.
 MODES OF VENTILATION
 ALARMS ON VENTILATORY MACHINE.

3.  mechanical ventilation is a method to
mechanically assist or replace spontaneous
breathing.
 This may involve a machine called a ventilator or
the breathing may be assisted by a physician or
other suitable person compressing a bag or set
of bellows. Traditionally divided into negative-
pressure ventilation, where air is essentially
sucked into the lungs, or positive pressure
ventilation, where air (or another gas mix) is
pushed into the trachea.

4.  It can be used as a short term measure, for
example during an operation or critical illness
(often in the setting of an intensive care unit).
It may be used at home or in a nursing or
rehabilitation institution if patients have
chronic illnesses that require long-term
ventilator assistance.

5.  Owing to the anatomy of the human pharynx,
larynx and esophagus and the circumstances for
which ventilation is required then additional
measures are often required to "secure" the
airway during positive pressure ventilation to
allow unimpeded passage of air into the trachea
and avoid air passing into the esophagus and
stomach. Commonly this is by insertion of a tube
into the trachea which provides a clear route for
the air. This can be either an endotracheal tube,
inserted through the natural openings of mouth
or nose or a tracheostomy inserted through an
artificial opening in the neck.
 If the patient is able to protect their own airway
such as in non-invasive ventilation then no
airway adjunct may be needed.

6.  The iron lung, also known as the Drinker and
Shaw tank, was developed in 1929 and was
one of the first negative-pressure machines
used for long-term ventilation. It was refined
and used in the 20th century largely as a
result of the polio epidemic that struck the
world in the 1940s. The machine is effectively
a large elongated tank, which encases the
patient up to the neck. The neck is sealed
with a rubber gasket so that the patient's face
(and airway) are exposed to the room air.

7.  While the exchange of oxygen and carbon
dioxide between the bloodstream and the
pulmonary airspace works by diffusion and
requires no external work, air must be moved
into and out of the lungs to make it available
to the gas exchange process.

9.  In the iron lung by means of a pump, the air is
withdrawn mechanically to produce a vacuum inside
the tank, thus creating negative pressure. This
negative pressure leads to expansion of the chest,
which causes a decrease in intrapulmonary pressure,
and increases flow of ambient air into the lungs. As
the vacuum is released, the pressure inside the tank
equalizes to that of the ambient pressure, and the
elastic coil of the chest and lungs leads to passive
exhalation. However, when the vacuum is created, the
abdomen also expands along with the lung, cutting
off venous flow back to the heart, leading to pooling
of venous blood in the lower extremities.

10.  The design of the modern positive-pressure
ventilators were mainly based on technical
developments by the military during World
War II to supply oxygen to fighter pilots in
high altitude. Such ventilators replaced the
iron lungs as safe endotracheal tubes with
high volume/low pressure cuffs were
developed.

12.  Positive-pressure ventilators work by
increasing the patient's airway pressure
through an endotracheal or tracheostomy
tube. The positive pressure allows air to flow
into the airway until the ventilator breath is
terminated. Subsequently, the airway
pressure drops to zero, and the elastic recoil
of the chest wall and lungs push the tidal
volume -- the breath—out through passive
exhalation.

13.  Acute lung injury (including ARDS, trauma)
 Apnea with respiratory arrest, including cases
from intoxication
 Chronic obstructive pulmonary disease (COPD)
 Acute respiratory acidosis may be due to
paralysis of the diaphragm
Guillain-Barré syndrome,
Myasthenia Gravis,
spinal cord injury, or
the effect of anaesthetic and muscle relaxant
drugs

14.  Increased work of breathing
 Hypoxemia
 Hypotension
 shock,
 congestive heart failure
 Neurological diseases such as Muscular
Dystrophy and Amyotrophic Lateral Sclerosis

15.  Hand-controlled ventilation such as:
◦ Bag valve mask
◦ Continuous-flow or Anesthesia (or T-piece) bag
 A mechanical ventilator. Types of mechanical
ventilators include:
◦ Transport ventilators. These ventilators are small,and
can be powered via AC or DC power sources.
◦ ICU ventilators. These ventilators are larger and usually
run on AC power (with battery back up). This style of
ventilator often provides greater control of a wide variety
of ventilation parameters (such as inspiratory rise time).
Many ICU ventilators also incorporate graphics to
provide visual feedback of each breath.
◦ Neonatal ventilators — Designed with the preterm
neonate in mind, these are a specialized subset of ICU
ventilators which are designed to deliver the smaller,
more precise volumes and pressures required to
ventilate these patients.

16. ◦ PAP (Positive Airway Pressure) ventilators. these
ventilators are specifically designed for non-
invasive ventilation. this includes ventilators for use
at home, in order to treat sleep apnea

18. Classification of
ventilators

19.  Inspiratory phase
 Cycling to expiration
 Expiratory phase
 Cycling to inspiration
 Pressure generator,
flow generator
 Pressure cycle, Vol
cycle, Time cycle
 PEEP, NEEP, ZEEP

20.  Pressure generators: expose the lungs to a
pressure . Gas flows into the lungs until the
pressure within the patient is equal to the
ventilator pressure, or until the cycling
mechanism interrupts the process. produce a
pre-set pressure waveform. Changes in
airway resistance (e.g.: bronchospasm) and
lung compliance (e.g.: pulmonary edema) will
alter impedance and tidal volume resulting in
hypoxia and CO2 retention

21.  Flow generators: expose the lungs to a flow of
gas, often developed by passing a very high
pressure source (e.g. pipeline supplies) through a
narrow orfice, thus making the flow virtually
constant when faced with the much lower
pressures within the chest. Gas enters the lungs
for as long as the flow continues, and the
pressure and volume rise accordingly. produce a
predetermined flow of gas irrespective of the
resistance it meets, but sometimes at the price of
high airway pressure.
Inspiratory hold can be added during this phase,
whereby the lungs can be held inflated for a
period of time, usually up to 2sec, this maneuver
can improve gas distribution in the lungs.

22. (1) Pressure cycled, when the development of a
preset pressure within the system terminates
inspiration.
Examples are Bird, Blease etc..

23. Sensitivity Control
Expiratory Timer
Air Dilution
Inspiratory Flow Rate
Pressure Control

24. (2) Volume cycled: when the machine cycles
after a preset volumes has been delivered.
E.g, Bear, Bennet, Brompton

25. (3) Time cycled: cycling after the set length of
time e.g cape, servo, phillips , brompton

26.  On the ITU volume cycled machines are often
preferred as the pressure cycled variety copes
poorly with changing compliance, needing
frequent readjustment and time cycled
machines will continue to cycle whether or
not they have delivered gas to the patient.
 If inspiratory hold is used, then a time
element is added to the basic cycling
mechanism, so that a machine could be
volume plus time cycled.

27.  During expiration, ventilators are normally
open either to atmosphere, and the patient is
allowed to exhale by normal physiological
process so that at the end of expiration the
airway pressure has returned to zero (ZEEP)
 Sometimes a predetermined pressure is
applied to the airway. This is usually positive
(PEEP) but may be rarely negative (NEEP)

28.  This is accomplished by a simple preset time
switch (either expiratory time or I:E ratio), so
that the machine adjusts the expiratory time
to fullfill the pre set ratio.
 It may also be a function of the machine rate
per minute setting so that expiration simply
takes up that part of the total cycle not
already used by inspiration

29.  Basic machine settings:
TV= MV/rate (rate and either TV or MV is
set)
the remaining variable naturally being
resultant upon the above equation.
SIGH : some machine have a built in facility for
giving the pt one or several deep breaths
analogous to the sigh of the normal subject.
It has been shown that this can improve
compliance and gas exchange .

30. The sigh may be varied as to rate and depth,
and be single or multiple. There is usually a
compensatory pause, to allow the circulatory
system time to recover from the effects of the
increased intra thoracic volume and pressure
generated transiently by the sigh, before the
machine returns to normal mode.

31.  Control
 Trigger/assist,
 IMV
 SIMV
 MMV
 CPAP

32.  Simpler and older machines
 It performs its own set function no matter
what the patient is doing(accept or resist)
 Two problems with control mode
It is in controlled manner, and machine
continue to do its work no matter what the pt
doing ( accept or resist)
weaning from ventilation is very difficult
with this mode.

33.  To over come the problem of control mode
trigger/assist mode was discovered.
 Here the device allows the pt to initiate the
inspiratory phase by his own effort.
 This meant that the machine could deliver an
extra breath when the pt required it.
 By decreasing the trigger sensitivity, and
reducing the frequency it was thought that a
pt could have to work hard to breath, and pt
could be retrained in the art of breathing
normally and gradually build up his strength

34.  Unfortunately, in most cases it does not work
and it is better to disconnect the pt
altogether and allow free spontaneous
respiration for increasing intervals in order to
wean from the machine.

35.  a mode of mechanical ventilation in which the
patient is allowed to breathe independently
except during certain prescribed intervals,
when a ventilator delivers a breath either
under positive pressure or in a measured
volume.
 No initiation of full machine breath but to
open a gas supply to the pt so that he can
take whatever sized breath he wishes and is
able to do.

36.  Machine still gives him a preset no of breaths
each minute, but in between these he can
breathe for himself.
 The IMV system can be adjusted so that
machine breaths become gradually less
frequent until the pt is breathing entirely for
himself with no machine breaths.
 Using this mode pt can be effectively weaned.

37. IMV
• Pt receives a set number of
ventilator breaths
• Different from Control: pt can
initiate own (spontaneous)
breaths
• Different from Assist:
spontaneous breaths are not
supported by machine with
fixed TV
• Ventilator always delivers
breath, even if pt exhaling

39.  In this mode the ventilator provides a pre-set
mechanical breath (pressure or volume limited)
every specified number of seconds (determined
by dividing the respiratory rate into 60 seconds -
thus a respiratory rate of 12 results in a 5 second
cycle time).
 Within that cycle time the ventilator waits for the
patient to initiate a breath using either a pressure
or flow sensor.
 When the ventilator senses the first patient
breathing attempt within the cycle, it delivers the
preset ventilator breath. If the patient fails to
initiate a breath, the ventilator delivers a
mechanical breath at the end of the breath cycle.

40.  Mandatory minute volume (MMV): The patient
breathes spontaneously. If the minute volume
falls below a preset value the ventilator gives
a mandatory breath or breaths
 Both IMV and MMV systems can be made to
give the pt some slight assistance to his own
spontaneous efforts – not true ventilation,
but assisted IMV

41. SIMV
• Most commonly used mode
• Spontaneous breaths and
mandatory breaths
• If pt has respiratory drive, the
mandatory breaths are
synchronized with the pt’s
inspiratory effort

42.  Continuous positive airway pressure (CPAP):
This helps in spontaneously breathing
patients by reducing the workload and
prevents airway collapse. It can be applied by
a close fitting nasal or a facemask or an
endotracheal tube. This is a weaning mode
from SIMV.

43. Indication
 Disconnect or low pressure ( major gas leak)
 High pressure( tube kink, sudden broncho
spasm)
 Low exhale volume (inadequate ventilation)
 Low oxygen % ( oxygen line failure)
 Mains failure / power failure

44.  An alarm signal should be both audible and
visible.
 It should be possible to silence it, but only for
a few period (long enough to perform
endotracheal suction)
 System should be reliable.

46.  http://www.thamburaj.com/assisted_ventilati
on_in_neurosurgery.htm

48.  IPPB
 CPAP
 Post operative IPPV
 Inverse ratio ventilation
- Rucha (12/3/12)
 TMT with protocols
(2to3) (19/3/12)
- Riddhi

49.  Weaning from
ventilator
Reff book – cash’s
cardio..