This document discusses the classification and working of anaesthesia ventilators. It describes how ventilators are classified based on their power and cycling mechanism. The key types are discussed as being pneumatically driven bellows ventilators and mechanically driven piston ventilators. The workings of bellows ventilators are explained as using bellows to interface between gas circuits, while piston ventilators use electric motors to compress gas. Advantages and disadvantages of each type are provided. Common ventilation modes for anaesthesia like volume control, pressure control and others are also summarized.

1. ANAESTHESIA VENTILATORS
:CLASSIFICATION, PNEUMATICALLY
DRIVEN BELLOWS VENTILATORS,
MECHANICALLY DRIVEN PISTON
VENTILATORS
PRESENTOR- DR SNIGDHA
MODERATOR – DR BHAVNA GUPTA

2. DEFINITION
 A ventilator is an automatic device designed to provide
or augment patient ventilation

3. MODERN HISTORY
 John Hunter developed double bellows for resuscitation in 1775
- one for blowing air in and the other for drawing bad air out.
Draeger Medical designed an artificial breathing
device“Draeger Pulmoter” in 1911 that was used by fire and
police units

5. NEGATIVE PRESSURE VENTILATORS
 From mid 1800-1900s, devices were invented that
applied negative pressure around body or thoracic cavity.
Two successful designs became popular; one is -body of
patient was enclosed in an iron box or cylinder and
patient’s head protruded out of end 'iron lungs’.
 Second design was a box or shell that fitted over
thoracic area only (chest cuirass).

7. SCANDINAVIAN POLIO EPIDEMIC - 1952
 Between July-December of 1952, in Copenhagen, 2722
patients with poliomyelitis were treated in Community
Disease Hospital of which 315 patients required ventilatory
support. Many principles of IPPV were defined during that
time –including use of cuffed tubes, periodic breaths and
weaning by reduction of assisted breaths.

8. ERA OF RESPIRATORY INTENSIVE CARE
 Two types of ventilators and two modes of mechanical
ventilation evolved during this period-
1) Ventilator with pressure cycled (PCV).Two ventilators were
commonly used for PCV in 1960’s and 1970’s; the Bird Mark 7
and the Bennet PR2.
2) Volume cycled ventilator –VCV.
 The term ‘weaning’ was used to explain various techniques to
test the quality of patient’s spontaneous ventilation before
extubation

9. OLD ANAESTHESIA VENTILATORS
 Offers only volume control ventilation
 Separate models or different bellows assemblies were required
for adult and pediatric patients.
 DeliveredVt was affected by fresh gas flow and breathing
system compliance.
 User had to manually enable low pressure alarm when the
ventilator was turned ON.
 APL valve should have to be close and turn the bag/ventilator
switch when turning on ventilator.

10. OLD ANAESTHESIA VENTILATORS
 Could not provide as high inspiratory pressures or flows
as their ICU counterparts (eg. If positive end-expiratory
pressure (PEEP) were needed
 The anesthesia provider had to add a PEEP valve to the
anesthesia breathing system

11. NEW ANAESTHESIA VENTILATOR
 An integral PEEP valve is present , and many have several
ventilatory modes.
 High inspiratory pressures and flows can be delivered
 Ventilator can deliver volumes for a wide range of patients
from smallest child to the largest adult.
 Overcomes effect of fresh gas, breathing system
compliance and gas compression on tidal volume.
 Turning ventilator ON involves fewer steps and
automatically enables the low airway pressure alarm

12. CLASSIFICATION
A. POWER :
a) Low powered - generate only modest gas pressures required
to deliver Vt with normal and near-normal compliances and
resistances.
b) High powered - generate pressures sufficient to overcome the
increase in airways resistance and/or reduction in lung
compliance that are seen in diseased lungs;
Require addition of certain safety features to protect patients
with both normal and abnormal lungs from excessive pressures

13. B. CYCLING MECHANISM
 A ventilator cycle between two phases -inspiratory and
expiratory.
lnspiratory cycling
 During inspiratory phase, ventilator delivers- (a)a volume of
gas, over (b) a given period of time, producing (c) an increase in
airways pressure, also a change in the pattern of (d) flow
(inspiratory waveform) .

14. VOLUME CYCLING
 ventilator terminate inspiratory cycling -point at which pre-
determined volume of gas has left the ventilator and
switches its internal mechanism to allow exhalation to
occur.
TIME CYCLING
 Incorporated in most new ventilators.
 Mechanical, pneumatic or electronic timers used to control
operation of inspiratory and expiratory valves that govern
cycling of ventilator ; it functions independently of delivered
tidal volume

15. PRESSURE CYCLING
 ventilators sense predetermined airway pressure in order to
terminate inspiratory phase.
FLOW CYCLING
 Recognition of flow pattern changes has been used to cycle
ventilators.
 rarely employed nowadays.

16. Expiratory Cycling
expiratory volume-cycled ventilator have mechanism-
1. for terminating expiratory phase when reservoir bellows has filled
to desired tidal volume required for the next inspiration
2. to identify a selected airways pressure at the end of exhalation that
would trigger the next inspiratory phase
3. to switch to the inspiratory phase when desired flow rate at end of
exhalation was reached, or
4. of terminating expiratory phase after a predetermined time.

17. VENTILATION MODES IN ANAESTHESIA
VENTILATORS
 Volume control ventilation
 Pressure-controlled ventilation
 PCV volume guaranteed
 Synchronised intermittent mandatory ventilation
 Pressure-support ventilation

18. VOLUME CONTROL VENTILATION
 Preset volume is delivered with a constant flow
 Peak inflation pressure varies with patient’s compliance and
airway resistance.
 Modern anaesthesia ventilators can deliver Vt : 20-1500 ml.
 Typical ventilator settings inVCV:
•Tidal volume: 6-10 ml/kg body weight.
• Rate: 8-12 breaths/min.
• PEEP: 0-5 cm H2O to start with and titrated.

20. PRESSURE-CONTROLLED VENTILATION
Inspiratory pressure is maintained constant andVt varies.
Inspired volume varies according to changes in compliance and
airway resistance.
Target pressure is adjusted to produce a reasonableVt to avoid
extremes of atelectasis and volutrauma.
 PCV mode is useful in neonatal surgeries, in pregnancy , in
laproscopic surgery and patients with ARDS.

23. PCV VOLUME GUARANTEED
 ventilator operates as in PC- mode, but a tidal volume target is
also set.
 It ensure that patient receives uniformVt regardless of
compliance changes caused by packs, retractors, position,
surgical exposure or relaxation
 ventilator delivers presetVt with low pressure using a
decelerating flow.
 PCV-VG breaths are characterised by a decelerating flow and a
square pressure waveform.

24. INTERMITTENT MANDATORY VENTILATION
 used for weaning patients from mechanical ventilation
 IMV-ventilator delivers mechanical (mandatory, automatic)
breaths at a preset rate and permits spontaneous, unassisted
breaths of a controllable inspiratory gas mixture between
mechanical breaths.
 spontaneous breaths utilizes either continuous gas flow within
circuit or a demand valve that opens to allow gas to flow from
a reservoir.
 Continuous gas flow at a rate greater than peak inspiratory
flow involves no additional work of breathing but requires a
large volume of fresh gas.

25. SYNCHRONISED INTERMITTENT MANDATORY
VENTILATION
 Synchronizes ventilator-delivered breaths with patient's
spontaneous breaths.
 Time between end of each mandatory breath and beginning of
next is subdivided into spontaneous breathing time and trigger
time.
 Reduces incidence of patient-ventilator disharmony and need
for sedation or narcosis for patient to tolerate mechanical
ventilation.

28. MANDATORY MINUTE VENTILATION
 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
&Vt.
 Suited for patients with variable respiratory drive

29. PRESSURE SUPPORT
 designed to augment patient's spontaneous breathing by
applying positive pressure to airway in response to patient-
initiated breaths.
 Disadvantage - if patient fails to make any respiratory effort, no
pressure-supported breaths will be initiated.
 A supported breath may be pressure or flow initiated
 When selected flow or sub-baseline pressure caused by a
spontaneous breath is reached, flow from ventilator begins and
set pressure is quickly reached and modulates flow to maintain
that pressure.

30.  Desired tidal volume should be calculated and pressure support
level adjusted so that the desired volume is delivered.
 If exhaled volume is inadequate, inspiratory pressure should be
increased or inspiratory rise time decreased (if adjustable). PEEP
may cause an increase in tidal volume.
 As the patient's effort increases, inspiratory pressure can be
reduced.

31. CLASSIFICATION(according to
application)
1. MECHANICALTHUMBS
2. MINUTEVOLUME DIVIDERS
3. BAG SQEEZERS
4. INTERMITTENT BLOWERS

32. MECHANICAL THUMBS

33. MINUTE VOLUME DIVIDERS
 uses a continuous source pressurised gas fed into a ventilator
system -collected by a reservoir-continually pressurised by a
spring, a weight or its own elastic recoil.
 It has one inspiratory valve and another expiratory valve, which
are linked together and operated by a “bistable” mechanism.
 Examples of minute volume dividers are East-Freeman
automatic vent, the Flomasta and Manley MP3

35. BAG SQUEEZERS
 employed in conjunction with a circle or Mapleson D system.
 Various type of bag (bellow squeezers)-
A. rising bellows arrangement B. descending bellows
arrangement C. pneumatic piston with mechanical linkage
D. pneumatic piston E. cam driven linkage from an electric motor
F. screw threaded piston (worm drive) powered by electric
motor.
Manley servovent®, Penlon Nuffield 400 series ventilator,
Ohmeda 7800, Servo 900 series

37. INTERMITTENT BLOWERS
 Ventilators are driven by a source of gas or air, at a pressure of
45-60 psi.The driving gas is normally delivered to patient
undiluted, but it may be passed through a venturi device so that
air, oxygen or anaesthetic gases may be added to it.
 Major component is - electronically timed and activated
proportional flow valve or a pneumatically timed oscillator that
divides driving gas into tidal volumes; size and rate of which can
be adjusted.
 Pneupac and Penlon Nuffield 200 series ventilator

39. CLASSIFICATION OF INTERMITTENT BLOWERS:
A. Basic resuscitator B. Sophisticated resuscitator
C. Ventilator for intensive care D. Anaesthetic
ventilator for Mapleson D system

40. WORKING PRINCIPLE
PNEUMATICALLY DRIVEN BELLOWSVENTILATORS
bellows are analogous to reservoir bag in breathing circuit
 Act as interface between breathing system gas and
ventilator driving gas.
 driving gas circuit is located outside bellows and patient gas
circuit inside bellows.

41. FUNCTIONING OF BELLOWS-IN–BOX VENTILATOR

44. INSPIRATION

45. INSPIRATORY PAUSE

46. EXHALATION

47. EXPIRATORY PAUSE

48. WORKING PRINCIPLE OF MECHANICALLY
DRIVEN PISTON VENTILATORS
 ventilators use electric motor to compress gas in breathing
circuit; Motor’s force compresses gas within piston, raising
pressure within it- causing gas to flow into patient’s lungs
 area of piston is fixed, so volume delivered by piston directly
related to linear movement of piston.

51. SPONTANEOUS INHALATION

52. SPONTANEOUS EXHALATION

53. MANUAL

54. MECHANICAL VENTILATION (INSPIRATION)

55. MID EXHALATION

56. EXHALATION ( LATER PART)

57. ADVANTAGE AND DISADVANTAGE OF
PNEUMATICALLY DRIVEN BELLOWS
VENTILATORS OVER MECHANICALLY
DRIVEN PISTON VENTILATORS
Advantages of piston ventilators:
 Greater precision of tidal volume delivery due to rigid piston
design, decreased compliance losses
 Greater precision of pressure control with the use of pressure
sensors
 Electrical control instead of pneumatic control

58.  Economical use of wall oxygen (wall oxygen not used to compress
a bellows, only used for patient delivery)
 A perforation in the bellows can allow the driving gas to be
delivered to the patient.This can potentially cause barotrauma or
unpredictable inspired gas concentrations, including oxygen and
volatile anesthetic.
 No intrinsic PEEP (compared to ascending bellows (2-3 cm water
are mandatory due to the design of ventilator spill valve).)
 Quiet

59. Disadvantages of piston ventilators
 Leak in piston diaphragm can lead to hypoventilation
 Possible entrainment of room air as piston returns to
filled position
 Loss of the familiar visible behaviour of a standing
bellows during disconnections.
 Quiet and less easy to hear regular cycling.