1. Anesthesia Ventilators
Anesthesia Department
Anesthesia Ventilators
Raafat Abdelazim

2. Intended Learning Outcomes
By the end of this lecture, the student will be able to:
Identify the components of the anesthesia ventilator (AV)
Understand the physical principles of mechanical ventilation (MV)
Operate the AV, monitor the parameters of MV and adjust its settings as required
Apply the goals of MV
Understand the hazards of MV
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3. The motive power
Electrical
Pneumatical
Mechanism of action (Mode of operation): 4 phases
Inspiratory phase (I)
Cycling from I to E
Expiratory phase (E)
Cycling from E to I
T V P F
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4. Respiratory cycle Two phases: I & E Two phase transitions:
From I to E = expiratory cycling
Between E and I = inspiratory cycling
Inspiration can itself sometimes have two phases:
an active ‘flow’ (TI flow) phase during which gas is being delivered to the patient
an end-inspiratory pause (TI pause )
The total duration of inspiration is made of the sum of these two:
TI = TI flow + TI pause

5. Relationship of the Ventilator to the Breathing System
It replaces the reservoir bag in the BS
It may be connected to the breathing system:
using a hose that is attached at
the bag mount
the bag/ventilator selector valve
without a hose (newer)
During MV, the APL valve in the BS must be closed or isolated
Most selector valves when turned for MV isolate the APL valve (no need to close) V B
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6. B / V
APL
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7. B / V
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8. The flow arrangement of a basic two-gas anesthesia machine
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9. Low pressure circuit P
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13. Pipeline
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14. Back O2
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15. O2 O2 Ventilator – Control unit Anesthesia machine Side Back
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16. Bellows assembly Control Unit
Rigid housing
Distensible bellows
Control Unit
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17. Control Unit Bellows assembly Distensible bellows Rigid housing
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18. Driving Gas
Flow valve BS
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19. Driving Gas BS Spill valve Safety relief valve Exhaust valve
Insp
Spill valve
Safety relief valve
Exhaust valve
Driving Gas
Flow valve BS
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20. BS Spill valve Safety relief valve Exhaust valve Flow valve
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21. BS Spill valve Safety relief valve Exhaust valve Flow valve
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22. Overpressure at any time
To atmosphere
Safety relief valve BS
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23. Exp
To atmosphere
Exhaust valve BS
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24. Scavenging
Spill valve
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25. Spill Valve
To scavenging system
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26. Spill Valve I & beginning E End E (2-4 cmH2O) Driving gas
To scavenging system
Patient’s gas
I & beginning E
End E (2-4 cmH2O)
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27. Raafat Abdel-Azim

28. Traditional circle system
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29. Traditional circle system
In a system with no significant leaks, the amount of excess gas vented by the spill valve should approximate the incoming FGF
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30. Raafat Abdel-Azim

31. Components of the Ventilator
Driving Gas Supply
Injector (some)
Controls (F, V, T, P)
Alarms
Safety-Relief Valve
Bellows Assembly
Exhaust Valve
Spill Valve
Ventilator Hose Connection
preset cmH2O
adjustable
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32. Injector Air Driving gas Air
Some ventilators use a device called an injector (Venturi mechanism) to increase the flow of driving gas. As the gas flow meets restriction, its lateral pressure drops (Bernoulli principle). Air will be entrained when the lateral pressure drops below atmospheric. The end result is an increase in the total gas flow leaving the outlet of the injector but no increase in consumption of driving gas
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33. Control of Parameters of VentilationVT VM
f (frequency= rate)
I:E ratio
IFR (Insp. Flow Rate)
Maximum Working Pressure
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36. Narkomed - Drager
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37. Fabius - Drager
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38. Cisero - Drager
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39. Dameca
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40. Penlon a800/80
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41. Penlon Nuffield 200
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42. Raafat Abdel-Azim

43. IFR (Inspiratory Flow Rate)
VT (ml)
f (b/min)
Cycle time (s)
IFR
TI (s)
TE (s)
I:E
L/min
L/s
ml/s
500 20
60/20 = 3 60 1
1000
0.5
2.5
1:5 30 2
1:2
60 L/min
600
Volume (ml)
30 L/min
500
400
300
200
100
0.5 1
1.5 2
2.5 3
3.5 4
4.5 5
5.5 6
Time (sec)
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44. Inspiratory Waveforms
Constant
Decelerating
Accelerating (ramp)
Sinusoidal
Inspiration 60
Flow (L/min) 30
Expiration
shorter TI TI TI TI
shorter 30 60
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46. The Ventilation Cycle
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47. t Cycling Limiting Triggering - Volume - Flow - Flow - Time - Pressure
- Patient (assisted)
- Machine (controlled)
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48. IPPV
Paw
Pmax
Pplat 20
Pause IF E t
ZEEP I E
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49. T V P F Duration of ventilation cycle (sec) f (60/duration)
I phase (IF period, IP period)
E phase
VT, VM
TI, TE, I:E
T V P F
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50. R C Inspiratory Phase During the IF period: Paw depends on:
The airway resistance (R)
The total thoracic compliance (C) (V/P)
R C
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51. P P P P P P P P Resistance P P P P Flow Rate: FRP P P
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52. Resistance
Paw 20 t N
R F
R F
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53. Raw = (PIP – Pplat) / Flow
Calculation of Airway Resistance (Raw) in a Ventilated Patient
Raw = (PIP – Pplat) / Flow
Examples: If in a given situation,
PIP = 40 cm H2O,
Pplat = 38 cmH2O,
flow = 60 L/min (i.e., 1 L/s),
Raw will be:
= (40 − 38)/1
= 2 cmH2O/L/s
PIP = 40 cm H2O,
Pplat = 25 cmH2O,
flow = 60 L/min (i.e., 1 L/s),
Raw will be:
= (40 − 25)/1
= 15 cmH2O/L/s
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54. Compliance P P
Volume C C
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55. Compliance P P
Volume: VP
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56. During I pause
Pause
No gas F into or out of the lungs  Paw depends only on VI & CT
Gas redistributes among alveoli
This improves gas distribution in the lungs of patients with small AWD (BA, smokers).
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57. C R Paw t EB intubation CW rigidity Pulmonary edema Secretions
Bronchospasm
Kinked ETT
Paw 20 t C R
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58. Compliance = V/P Dynamic compliance: = VT/(PIP-PEEP) L/cmH2O
Static compliance:
= VT/(Pplat-PEEP) L/cmH2O
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59. Compliance represents a volume change per unit change in pressure (200 ml/cm H2O in the normal lung).
The total respiratory compliance consists of combined lung and chest wall compliance and is normally 70–80 ml/cm H2O.
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61. Raafat Abdel-Azim

62. Time Constants of the Lung
In most diseases, the involvement of the lung is not uniform. Regional differences in C and R occur.
Owing to this, alveoli in different parts of the lung behave differently; diseased alveoli take longer to fill and to empty.
The rate of filling of an individual lung unit is referred to as its time constant.
For a particular lung unit
Time Constant = R x C
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63. It takes the equivalent of 5 time constants for the lung to completely fill (or to empty).
In the time afforded by one time constant, 63% of the lung will fill (or empty); two time constants allow 86% of the inspiratory or expiratory phase to be completed; three time constants allow for 95%, and four time constants for 98%.
100 5 98 95 4 86 3 63 2 1
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64. A lung unit with a normal Raw of 1 cm H2O/L/s
Example:
A lung unit with a normal Raw of 1 cm H2O/L/s
and a normal compliance of 0.1 L/cm H2O would have a time constant of:
= 1 × 0.1
= 0.1 s
Five times this is 0.5 s, which would be the time required for this unit to fill or empty satisfactorily.
This information comes useful while setting a ventilator’s TI and TE
Since diseased air units take longer to fill, deliberately
prolonging the TI may enable such units to participate
more meaningfully in gas exchange
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65. Compliance, Time Constant and WOB in Anaesthesia UK
MV slide show
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66. During the expiratory phaseVT I E
FRC
FRC
PEEP
PaO2
FRC
IA contents
Pulmonary edema
ARDS
PaO2
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67. Goals of Pulmonary Ventilation
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68. necessary to maintain the desired PaCO2
To provide adequate minute alveolar ventilation
and to  side effects
necessary to maintain the desired PaCO2
PPV   ITP
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69. Adequate Ventilation PaCO2 of 40 mmHg = 5.3% of 760 mmHg
Goals
Adequate Ventilation
PaCO2 of 40 mmHg = 5.3% of 760 mmHg
40/760 = 0.053
Normal resting VCO2= 200 ml/min= 0.2 L/min
This requires VM of 3.8 L
0.2/ ? = 0.053
0.2/ =
Add dead space (VD)
3.8 L/min
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70.  150 ml in a 70 Kg (154 pound) adult = 0.15 x 10 (f) =
Goals, Adequate Ventilation
N = 2.2 ml/Kg (1 ml/pound)
 150 ml in a 70 Kg (154 pound) adult
= 0.15 x 10 (f) =
Required VM = =
A larger VM is required for patients who have VD or VCO2
1.5 L/min
5.3 L
For VCO2
For VD
VD phys = VD ana + VD alv
VD ana = conducting airways = 150 ml in a 70 Kg adult
VD alv is created when non-perfused alveoli are ventilated (negligible in health, expands in disease)
This 150 ml of VD ana is reduced by ETT and can be cut down to about 60% by tracheostomy
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71. When VCO2 & VD are stable: VM  1/ PaCO2 VM x PaCO2 = constant
Goals, Adequate Ventilation
When VCO2 & VD are stable:
VM  1/ PaCO2
VM x PaCO2 = constant
e.g., PaCO2 = 50 mmHg with VM = 5 L/min
 VM to 7 L/min   PaCO2 to 36 mmHg
V1 x P1aCO2 = V2 x P2aCO2
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72. VM =VT x f
Manipulation of VT has a different effect on the PaCO2 than does altering f.
Consider the following:
A set VT of 500 ml and f of 10 b/min results in a VM of 500 × 10 = 5,000 ml/min.
The same VM can be produced by a VT of 250 ml delivered at f of 20 b/min, i.e., 250 × 20 = 5,000 ml/min.
If, however, the VD is taken into consideration, the implications of these two settings are vastly different.
Assuming a VD phys of 150 ml, the alveolar ventilation (the effective ventilation or the ventilation that takes part in gas exchange) in the first example would be:
(500 – 150) × 10 = 3,500,
and in the second example would be:
(250 – 150) × 20 = 2,000.
PaCO2 is inversely proportional not to all of the VM, but to that part of the ventilation that is independent of VD (i.e., the alveolar ventilation VA)
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73.  Side effects  CO PPV  ITP  PVR  RVA  VR  EDV Goals
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74. Goals,  Side Effects
PPV
 ITP VD
PA > PAP
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75. All these effects  mean Paw
Goals
All these effects  mean Paw
Therefore, a goal of PPV is to  mean Paw while maintaining adequate ventilation and oxygenation
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76. Modes of Pulmonary Ventilation
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77. SB Paw t +ve -ve Anesthesia ICU: demand valve   WOB  CPAPt
-ve
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78. CPAP
Paw t
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79. IPPV Paw t Anesthesia (or sedation) + MR Few days  muscle atrophyt
ZEEP
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80. IPPV + PEEP
Paw
PEEP t
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81. Assisted Ventilation (A)
Paw
Patient  f and timing
Hazard: hypoventilation A
No A t S
If  or No S
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82. Assisted Ventilation (A)
Paw
Patient  f and timing
Hazard: hypoventilation A
No A
CPAP t
If  or No S
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83. Assist-Control (AC) Paw A+C Provides a minimum f below which  C
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84. AC Conscious patients are more comfortable on A & AC > C
Muscle atrophy is still a problem
Most AV don’t provide A or AC
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85. IMV   PaCO2 < apneic threshold  no SB  IMV = IPPV
Preset VT and f
Paw
SB is allowed
Muscle atrophy is less likely S t
IMV   PaCO2 < apneic threshold  no SB  IMV = IPPV
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86. SIMV Paw t Preset VT and f Synch. Mandatory Mandatory NO St
Triggering window
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87. Pressure-limited ventilation (PLV) (PCV)
Paw
Pmax
Pplat t
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88. Ventilator Classification
Pressure versus Volume Ventilators
Single-Circuit versus Double-Circuit Ventilators
Bellows Assembly:
Ascending (=upright = standing) versus descending (=hanging)
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89. P vs V Ventilators P Ventilators V Ventilators Changes in R & C changeVT P
Commonly used in
Neonates
 Barotrauma
 Compressible V
ICU
Most AV
Other names
P generators
P-limited
P-stable
Flow generators
V-stable
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90. ICU
Anesthesia
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91. Bellows assembly Distensible bellows Rigid housing E Driving gas I
BS to patient
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92. VT VT
Drager (End-insp.)
Ohmeda (End-exp.)
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93. E Expands partially Fully expands I Empties completely
NA Drager bellows
Ohmeda bellows E
Expands partially
Fully expands I
Empties completely
Partially empties
Spill valve
External (visible)
Hidden in housing
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94. E Ascending bellows Descending bellows Attachment Movement EEP
VT adjustment
Disconnection or leak
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95. Interaction between the Ventilator and Breathing Circuits
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96. Preset / delivered VT difference due to:
Interaction
Preset / delivered VT difference due to:
Effect of circuit compliance
for all V ventilators: both single circuit and double circuit
Effect of FGFR
only for double circuit ventilators
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97. Effect of Circuit Compliance
Interaction
Effect of Circuit Compliance
 PIP   Delivered VT
Circuit compliance = Compressible volume (gas compression, tubing distension)
CC= the V of gas that must be injected into a closed circuit to cause a unit  in the circuit P
It is related to the volume of the circuit
 P V
Ventilator tubing V C
Anesthesia
6 L
9 ml/cmH2O
ICU 
 (1.5 ml/cmH2O)
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98. Del VT = Preset VT – [(PIP - PEEP) x CC]
Interaction, Circuit Compliance
Preset – Del VT difference  CC and PIP
Del VT = Preset VT – [(PIP - PEEP) x CC]
(i.e, VT loss = P x CC)
Example:
Ventilator tubing CC
(ml/cmH2O)
PIP
(cmH2O)
V Loss
(ml)
Anesthesia 9 20 30
180
270
ICU
1.5 45
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99. Volume loss is specially important in:
Interaction, Circuit Compliance
Volume loss is specially important in:
Patients with  PIP
ICU patients
Patients with small VT
Neonates  PLV
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100. Effect of Fresh Gas Flow Rate (from anesthesia machine)
Interaction
Effect of Fresh Gas Flow Rate (from anesthesia machine)
 FGFR   Delivered VT V
FGF from AM
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101. Volume added = TI x FGFR At a certain I:E,  f   TI   V added
Interaction, FGFR
Volume added = TI x FGFR
TI depends on
I:E  I fraction of the respiratory cycle  f
TI = 60/f x I fraction
Example: I:E = 1:2, f = 20, FGFR = 6 L/min
TI = 60/20 x 1/3 = 1 s
FGFR = 6000 ml/min = 100 ml/s
V added = 1 x 100 = 100 ml
At a certain I:E,  f   TI   V added
I:E
I fr
1:1
1:2
1/3
1:3
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102. Interaction, FGFR
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103. Volume added is specially important:
Interaction, FGFR
Volume added is specially important:
When making large changes in FGFR
O2 flush  L/min (don’t use during insp.)
When delivering small VT
For a neonate, changing FGFR from 1 to 5 L/min  double VT
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104. Delivered VT = Preset VT - V lost (compression)
Interaction
Delivered VT = Preset VT
- V lost (compression)
+ V added (An. machine)
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105. FGF Independent of Ventilation
Fresh gas compensation – GE
Compensate for FGF
Active, feedback controls bellows movement
Fresh gas decoupling – Draeger
FGF goes to reservoir bag during inspiration
Fresh gas accommodation – Maquet Flow-i
Fresh gas flows only during inspiration
Ventilation by circuit flow interruption – Draeger Zeus, Perseus
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106. Fresh Gas Decoupling (FGD)
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107. Fresh Gas Decoupling (FGD)
Circle system with piston ventilator and fresh gas decoupling (FGD)
(Dräger Narkomed 6000)
During the I phase the FG coming from the AWS through the fresh gas inlet is diverted into a separate reservoir by a “decoupling valve” (located between the fresh gas source & the circle BS). In the case of the NM 6000 series, the reservoir bag serves as an accumulator for FG storage until the E phase begins.
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108. NPR valve = negative pressure relief valve
During the E phase, the decoupling valve opens, allowing the accumulated FG in the reservoir bag to be drawn into the circle system to refill the piston ventilator chamber. Because the ventilator exhaust valve also opens during the E phase, excess FG & exhaled patient gases are vented into the scavenging system
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109. Most FGD systems are designed with either piston-type or descending bellows-type ventilators.
Because the ventilator piston unit or bellows in either of these type systems refills under slight negative pressure, it allows the accumulated fresh gas from the reservoir to be drawn into the breathing circuit for delivery to the patient during the next ventilator cycle.
As a result of this design requirement, it is not possible for FGD to be used with conventional ascending bellows ventilators, which refill under slight +ve pressure
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110.  risk of barotrauma & volutrauma
Advantage of FGD
 risk of barotrauma & volutrauma
With a traditional circle system, in FGF from the flow meters, or from inappropriate activation of the oxygen flush valve, may contribute directly to VT  excessive FG  pneumothorax, pneumomediastinum, other serious patient injury, or even death.
Because systems with FGD isolate the patient from FG coming into the system while the ventilator is in I phase, delivered VT tends to remain stable over a broad range of FGF rates, and the potential risk of barotrauma to the patient is greatly reduced.
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111. Disadvantages of FGD
The possibility of entraining room air into the patient gas circuit
In a FGD system, the ventilator piston unit (or descending bellows) refills under slight -ve pressure. If the total volume of gas contained in the reservoir bag + that returning as exhaled gas from the patient’s lungs is inadequate to refill the ventilator piston unit, -ve patient Paw could develop.
To prevent this, a negative pressure relief valve is placed in the FGD BS.
If BS P  < a preset threshold value, then the relief valve opens and ambient air is allowed to enter into the patient gas circuit.
If this goes undetected, the entrained atmospheric gases could lead to dilution of either or both the inhaled anesthetic agent(s) or an enriched oxygen mixture (lowering an enriched oxygen concentration toward 21%).
If allowed to continue, this could lead to intraoperative awareness and/or hypoxia.
High-priority alarms with both audible and visual alerts should notify the user that fresh gas flow is inadequate and room air is being entrained.
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112. If the reservoir bag is removed during mechanical ventilation, or if it develops a significant leak (from poor fit on the bag mount or a bag perforation), room air may enter the breathing circuit as the ventilator piston unit refills during the expiratory phase.
This could also result in dilution of either the inhaled anesthetic agent(s) concentration and/or the enriched oxygen mixture. This type of a disruption could lead to significant pollution of the operating room with anesthetic escaping into the atmosphere.
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113. Hazards of Ventilators
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114. Apnea Erroneous setting of ventilator selector switch
Hazards
Apnea
Erroneous setting of ventilator selector switch
Ventilator switched off
Disconnection
Obstruction of inspiratory gas pathway
Ventilator failure V B
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115. Hypoventilation Circuit leak Incompetent spill valve
Hazards
Hypoventilation
Circuit leak
Incompetent spill valve
Open APL valve in circuit
Driving gas leak
Improper settings
Ventilator limitation at high airway pressure PL S
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116. Raafat Abdel-Azim

117. Hyperventilation & dilution of anesthetic gases
Bellows leak
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118. Obstruction of expiratory gas pathway Ventilator cycling failure
Hazards
High airway pressure
Exhaust obstruction
Obstruction of expiratory gas pathway
Ventilator cycling failure
Improper settings
Oxygen flush during inspiration
Bellows leak
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119. Summary of important points
Driving gas and patient gas don’t mix
The ventilation cycle is controlled by F, V, P and T
During the I phase, Paw depends on R and CT
Goals of MV are to provide adequate VM (necessary to maintain the desired PaCO2) and to side effects
Modern AV provide a range of ventilatory modes
The difference between the delivered VT and the preset VT depends on CC and FGF
FGD decreases the risk of barotrauma and volutrauma
Hazards of MV can be avoided
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120. Examples of questions to assess the ILOs
Describe causes and ventilatory management of high airway pressure during inspiratory phase of mechanical ventilation
Discuss goals of pulmonary ventilation under anesthesia
With IPPV: if f (rate) = 10/min, I: E= 1:1 and FGF= 3 LPM
What will be the volume added to the preset tidal volume?
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121. APL = adjustable pressure limiting BS = breathing system
I = inspiration
E = expiration
TI = inspiratory time
TE = expiratory time
f = respiratory rate (frequency)
VT = tidal volume
VM = VE = minute volume (minute ventilation)
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122. Thank you
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