basics for any anaesthesia resident interestedd in learning about mechanical ventilation

1. BASICS OF MECHANICAL VENTILATION
PROF N.KRISHNAN
Dept of Paediatric Anaesthesiology
Institute of Child Health & Hospital for Children- Chennai
Madras Medical College

2. OBJECTIVES
 TO KNOW THE
 BASIC PHYSICS
 TERMINOLOGIES BEING USED
 PHYSIOLOGY DURING MECHANICAL VENTILATION
 PHASES OF RESPIRATION IN MECHANICAL VENTILATION

3. Major indications for mechanical ventilation
 LOW Pao2 cannot be maintained above 50mm hg despite high levels of
delivered oxygen.
 (Ards).
 HIGH PACO2 In arterial blood rises above 50 torr.
 Acute respiratory failure (arf).
 Ventilation becomes inefficient and/or exhausted.
 Bronchospasm, flail chest and impending respiratory failure.
 Airway protection
 Tracheal injury, edema, severe head injury and facial fractures.
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4. Goals of Mechanical Ventilation
Improving Oxygenation
Improving Ventilation

5. Improving Oxygenation

6. Improving Ventilation

7. NORMAL INSPIRATION
 An active process requiring musular
effort.

 75% diaphragmatic at rest.
 Intercostals used during exertion.

9. Inspiratory effort causes
• Fall in intrapleural pressure
• Fall in Alveolar pressure
• “Pressure gradient from
mouth to alveoli ”
• Gas flow down pressure
gradient

10. Normal
Expiration
 Usually a passive
process due to lung
recoil.

11. Normal Expiration
 Relaxation of
inspiratory muscles
causes:
 Intrapleural pressure
becomes less negative
 Alveolar pressure rises
 “Pressure gradient
from alveoli to mouth”
 Gas flow down
pressure gradient

12. Positive pressure ventilation
 Positive pressure applied to the
airway during inspiration to
expand the lungs and chest wall
to get Tidal Volume .
 Spontaneous ventilation

13. Basic Definitions
1. Volume.
2. Flow.
3. Time.
4. Pressure gradient.
5. Resistance.
6. Compliance

14. Volume
A volume can be defined as
Measuring the amount of space occupied by an object.
The SI unit of a volume is cubic metre [m3 ]
smaller SI unit of volume is cubic centimeter [cm3. ]

16. Pressure
Pressure (symbol: p or P)
The force applied per unit area

17. Pressure Difference (∆P)
 Difference in total pressure between
two points of a gas carrying tube .

18. FLOW
FLOW
 The motion of a gas or
liquid
FLOW RATE

• Flow Rate is defined as the
volume of gas or liquid
passing a cross sectional
area per unit of time.

19. FLOW RATE
• Flow is defined as the volume of gas or liquid passing a cross sectional
area per unit of time.
Flow = volume / time

20. Flow depends on
Pressure Difference (∆P)
Hagen–Poiseuille equation

21. Inspiratory
Time
 Inspiratory Time is
the time over which
the tidal volume is
delivered .

22. Ti (Inspiratory Time):
 Time over which the tidal
volume is delivered
 Setting:
 0.1 to 5.00 sec

 Maintain an I:E of 1:2 or
greater (1:3, 1:4, etc.)

23. T pause
 Time for no flow or pressure
delivery (%)
 Setting: 0.00 to 1.50 sec

24. Inspiratory Rise Time
or
“T insp. Rise”
 The time taken to reach the
peak inspiratory flow or
pressure at the start of each
breath.

25. Inspiratory Rise Time
or
“T insp. Rise”
 Inspiratory Rise Time, set in seconds
 Setting: 0 to 0.40
 Adults range is 0 to 0.40 seconds
 Infants range is 0 to 0.20 seconds

26. Airway resistance
Impedance to ventilation
 Limits the access of inspired air to the pulmonary alveoli.
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27. Airway resistance
 Resistance is greatest at the bronchi of intermediate size,
in between the FOURTH AND EIGHTH bifurcation.
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28. Airway Resistance
Airway Resistance is dictated by the DIAMETER of the
airways and by the DENSITY of the inspired gas.

29. Abnormal Increase In Lung resistance
A . Airway lumen occluded by foreign
material
B. Edema or hypertrophy of the airway
wall
C. Spasm
D. Collapse of the airway
Croup
Epiglotitits
Anaphylactic reactions
Asthma
Bronchitis
Bronchiectasis
Cystic fibrosis
Vocal cord problems
Goiters
Thyroid tumors

30. Compliance
 The ease in which a structure
can be expanded or stretched
 Change in volume/change in
pressure
 cc or ml/cm H20
Both the lung and thorax involved.
NK

31. Abnormal Decrease In Lung Compliance
Abdominal Factors
1. obesity
2. abdominal surgery
3. Pregnancy
Pleural Factors
1. Pneumothorax
2. Pleural Effusion
Pulmonary Factors
1. Atelectasis
2. ARDS and IRDS
3. pulmonary edema (fluid in alveoli)
4. Thoracic surgery
5. pulmonary fibrosis (increased elasticity)
6. pneumonia (fluid filled alveoli)
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32. Elastance
• THE RECIPROCAL OF
COMPLIANCE
• The quality of recoiling to an original
form after the removal of pressure.
• The degree to which LUNG, can return
to its original dimensions when a
distending PRESSURE is removed.
NK

33. PHYSIOLOGY OF POSITIVE PRESSURE VENTILATION

34. POSITIVE PRESSURE
CFG CPG
EXPANSION OF LUNG
NORMAL
INSPIRATION
OVERDISTENTION:
VOLUTRAUMA
RUPTURE :
BAROTRAUMA
PHYSIOLOGY OF POSITIVE PRESSURE VENTILATION
NK

35. Physiological changes to PPV
 Cardiovascular effects
 The heart, great vessels, and
pulmonary vasculature lie
within the chest cavity in
which the pressure is
normally negative.
 During PPV they are all
subjected to the increased
intra thoracic pressure.
NK

36. Cardiovascular effects
 Decreased venous return to
the right heart .
 Altered left ventricular
distensibility
 The result is a decrease in
cardiac output
NK

37. Renal, Hepatic, and Gastrointestinal Effects
 Decline In Renal Function :
Decreased urine volume and sodium excretion.
 Decline In Hepatic Function :
Due to decrease in cardiac output.
Increased hepatic vascular resistance.
 The Gastric Mucosal Ischemia And Secondary Bleeding :
Result from a decrease in cardiac output .
Increased gastric venous pressure
 CNS :
Raised intra cranial pressure
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38. How will you give minute ventilation to your patient
?????

39. Select - For your patient
 Type of ventilator
 Mode of ventilation
 Give Orders to be followed during Phases of respiration

40. Types of ventilator

41. Constant flow generator
[Volume Ventilator]
 Flow generators are ventilators which produces constant inspiratory flow.
A high-pressure gradient is established between the ventilator and the
patient.
 The result is a Constant Flow Pattern .
 Does not care about lung characters ,
 Will deliver set tidal volume.
Dictator

42. Constant- Pressure Generator
 Pressure generators are ventilators which produces variable inspiratory
flow.
The machine develops a constant pressure that is only slightly above the
pressure in the patient's airways.
 Flow varies with resistance & compliance of lung
DEMOCRACY

43. Anatomy of a ICU Ventilator

45. Power source
Compressed gas or electricity
 Is the force that drives gas into the patient's lungs.
 Bellows Ventilators use the force of compressed
gases, separated from patient gas by a membrane
(bellows).
 Electricity to drive a piston or turbine containing
patient gas.
 All use electricity for electronic sensors and
computer control mechanisms.

46. GENERATORS - CFG /CPG
To get tidal volume gas should flow to the alveoli from ventilator

47. Constant flow generator
[Volume Ventilator]
 Flow generators are ventilators which produces constant inspiratory flow.
A high-pressure gradient is established between the ventilator and the
patient.
 The result is a Constant Flow Pattern .
 Does not care about lung characters ,
 Will deliver set tidal volume.
Dictator

48. Drive mechanism
Generates inspiratory flow
 Piston ventilators (Apollo, Fabius
GS) do not require driving gas.
 They are driven by compression
from an electric motor to move a
piston, creating pressure which
moves the gas within the piston to
the patient's lungs.
 Thus, piston or turbine ventilators are
economical of wall oxygen .

49. Drive mechanism
Generates inspiratory flow
 Turbine ventilators (Dräger Perseus)-
electric motor used to drive a turbine
(blower) which creates inspiratory
pressure and flow.
 (Hair Dryer)

50. Drive mechanism -
Generates inspiratory flow
 Bellows vents classified as
double-circuit, pneumatically
driven.
 Double-circuit means that a
pneumatic force (driving gas)
compresses a bellows, which
empties its contents (patient gas
into the patient].
 Driving gas is oxygen or air.

51. Working of Ventilator

52.  A Mechanical ventilator
delivers tidal volume to the
patient .

54. Inspiration

55. Expiration

56. Phases of respiration
 Inspiration
 Inspiration-Expiration change over
 Expiration
 Expiration- Inspiration change over
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57. Give orders for each Phases of respiration
 Inspiration
 Inspiration-Expiration change over
 Expiration
 Expiration- Inspiration change over
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58. Inspiration

59. Trigger
Trigger (start)-
begins inspiratory
flow
 Expiration- Inspiration change
over
NK

60. Triggering
• Time triggered -
control ventilation
• Pressure triggered -
patient assisted
• Flow triggered –
patient assisted
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61. Trigger Variable- Time
 Time - Control Ventilation
 Set respiratory rate
NK

62. Trigger Variable- Pressure
 Pressure - Patient
Assisted
 A sensor SENSES A
DECREASE IN PRESS
IN INSPIRATORY
CIRCUIT & initiates
inspiration
NK

63. Trigger
Variable- Flow
 Expiratory flow starts to decrease at
the end of expiration.
 A flow sensor detects the
decrease in flow.
 When expiratory flow starts to
decrease to around
 1-3 lit / min triggering will occur.
 Ventilator initiates inspiration.
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64. SENSITIVITY
 Inspiratory effort that patient must apply to initiate
inspiration
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65. SENSITIVITY
Press drop below
baseline pressure
-0.5 to -2 cm of H2O
below baseline
pressure
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66.  HIGH SENSITIVITY [-0.5] = Little effort needed from
patients.
 Early phase of recovery
 AUTOCYCLING with HIGH SENSITIVITY during later
stages of recovery.
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67. Limiting
NK

68. Limiting
Maximum Value of a
parameter chosen to be
controlled during
inspiration.
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69. Inspiratory - Delivery Limits
 Maximum value that can be reached
but will not end the breath-
 Volume
 Flow
 Pressure
NK

70. Cycling
NK

71. Cycling
ENDS INSPIRATORY FLOW
NK

72. End of Insp…cycle
mechanisms
 The phase variable used to terminate inspiration-
 Volume
 Pressure
 Flow
 Time
NK

73. Pressure cycled
Time cycled
Volume cycled
NK

74. VCV
 Ventilator controls
inspiratory flow.
 Tidal volume
determined by
inspiratory time.
 Flow & TV are set.

75. Volume Control
 Tidal volume is
preset.
 Rate delivered is
preset.
 Pressure is
variable throughout
the delivered breath
 Flow is constant
throughout the breath

76. Volume Control — vent settings
 1.Tidal Volume (ml)
 2. Respiratory Rate (b/min)
 3. PEEP (cmH2O)
 4. Oxygen concentration (%)
 5. I:E ratio / Insp. time
 6. Pause time (s)
 7. Inspiratory rise time (s)
 8. Trigg. Flow / Trigg. Pressure

77. Volume Control
 Terminates inspiration at
preset volume
 Delivers volume at whatever
pressure is required up to
specified peak pressure
 May produce dangerously High
Intrathoracic Pressures
NK

78. VCV
 .

79. Other
names
for
Volume
Control
IPPV/CMV
VCV-A/C
Volume A/C
VC-CMV
VC-AC

80. Pressure Control
 A pressure level is preset.
 Breaths are delivered at a preset
rate.
 Tidal and minute volume are
variable.
 Flow is variable throughout the
breath

81. Pressure Control
 A pressure level is preset.
 Breaths are delivered at a preset rate.
 Pressure is constant throughout the
delivered breath.
 Tidal and minute volume are variable.
 Flow is variable throughout the breath

82. Pressure Control — vent settings:
 PC (Pressure Control level)
above PEEP (cmH2O)
 Respiratory Rate (b/min)
 PEEP (cmH2O)
 Oxygen concentration (%)

83. Pressure Control — vent settings:
 I:E ratio / Insp. Time
 Inspiratory rise time (s)

84. Pressure Control — vent
settings
 The set inspiratory
pressure level for each
mandatory breath
 Setting:
 Infant range is 0 to 80 cmH2O.
 Adult range is 0 to 120 cmH2O

85. Pressure Cycled
 Terminates inspiration at preset
pressure
 Tidal volume may vary with
changes in airway resistance,
pulmonary compliance
NK

86. PCV

87. Other names for Pressure
Control:
P-CMV
PCV-A/C
Pressure
A/C

88. Time cycled
ventilation
 Time interval fixed. [6 sec /
breath]
 Resp rate fixed. [10/ min ]
 Adjust I:E ratio, Ti
 [ TV = FLOW X TIME ]
 Adjust flow rate to achieve
tidal volume
NK

89. Time cycled
– Terminates inspiration at preset
time
– Volume determined by
• Length of inspiratory time
• Pressure limit set
• Patient airway resistance
• Patient lung compliance
– Common in neonatal units
NK

90. FLOW cycled ventilation
 Expiration begins when
inspiratory flow rate decays to
predetermined percentage of its
peak flow.
NK

91. EXPIRATION

92. Baseline- breath during
expiration
 Positive End Expiratory Pressure
 Expiratory Retard
 Negative End Expiratory Pressure
NK

93. Positive End Expiratory Pressure
 (PEEP) refers to positive
pressure maintained throughout
and at the end of exhalation.
 maintaining airway and alveolar
integrity for air flow and gas
exchange.
NK

94. Modes of ventilation

95. CATEGORIES OF VENTILATION
MODES
 Mandatory breath modes
 Support breath modes
 Spontaneous breath

96. Controlled modes
Mandatory breath modes
 Every breath delivered to patient by a mechanical breath.
 (Breath may be triggered by a timing mechanism or patient
effort).
 Volume Control
 Pressure Control
 PRVC

97. Supported (spontaneous) modes
 Every breath is spontaneous (i.e., patient triggered and
patient cycled) but supported by ventilator.
 Pressure support / CPAP
 Volume support
 NAVA- Neurally Adjusted Ventilatory Assist

98. Combination modes
 Combination of both controlled and supported
 SIMV (VC) + PS
 SIMV (PC) + PS
 SIMV (PRVC) + PS
 Bi-vent

99. Measured Parameters

100.  Vte Tidal volume, expired

 Vti Tidal volume, inspired

 Spon Vt Tidal volume, spontaneous
 Leak Difference, Vi and Vt, percent

101.  Ve Minute volume
 Spon Ve Minute volume, spontaneous
 Rate Breath rate, total
 Spon rate Rate, spontaneous
 Mand rate Rate, mandatory
 Ti Time, inspiratory
 Te Time, expiratory
 I:E Ratio, Ti/Te
 f/Vt Rapid shallow breathing index

102.  Ppeak Peak inspiratory
pressure
 Pmean Mean airway
pressure
 Pplat Plateau pressure
 PEEP Positive end
expiratory pressure
 Air inlet Pressure, air supply
 O2 inlet Pressure, oxygen
supply
 FiO2 Percent oxygen
content delivered

103. 
 Cdyn Dynamic
compliance
 Cstat Static
compliance
 Rrs Respiratory
system resistance
 PIFR Peak
inspiratory flow

104. Alarms
 Loss of O2 Oxygen supply lost
 Loss of airAir supply lost
 Low battery Internal/external batteries low
 Loss of A/C Main AC power lost
 Low PEEP Low PEEP cmH2O
 Low Ppeak Low PIP cmH2O
 Low Vte Low tidal volume
 Low Ve Low minute volume
 Low %O2 Low FiO2 reading
 High %O2 High FiO2 reading

105. Alarms
 High Ve High minute volume
 High rate High breath rate
 Max insp time Inspiratory time limit exceeded
 I:E limit I:E ratio limit exceeded
 High Vt High tidal volume
 Vol limit Volume limit exceeded
 Low EtCO2 Low end tidal CO2
 High EtCO2 High end tidal CO2

106. Implications of the
measured parameters

107. Pressures

108. The Proximal Airway
Pressure (Paw)

109. The Proximal Airway Pressure (Paw)
 The Proximal Airway Pressure (Paw) is the
PRESSURE AT THE WYE PIECE which
creates pressure difference with alveoli
for the gas to move from machine to
patient during inspiration

110. Peak inspiratory pressure
(PIP)

111. Peak inspiratory pressure (PIP)
 Peak inspiratory pressure (PIP) is the
pressure measured in the ventilator
circuit DURING MAXIMAL GAS
FLOW .
 It primarily represents the interaction
between the inspiratory flow rate and
airway resistance.

112. Peak inspiratory pressure (PIP)
 Pressure required to move air through
airways and into alveoli.
 PIP is the measurement of maximum
driving pressure required to expand
the lungs and chest wall to a given
volume.

113. Peak Inspiratory Pressure
 total pressure needed to overcome
 1.The inspiratory flow resistance
 (resistive pressure),
 2.The elastic recoil of the lung and chest wall .
 (elastic pressure),
 3.The alveolar pressure present at the beginning of the
breath
 [PEEP]

114. Peak Inspiratory
Pressure (PIP)
 This pressure A
FUNCTION OF
 THE AIRWAY
RESISTANCE
 THE COMPLIANCE
OF THE LUNG AND
THORAX


115. Peak Inspiratory
Pressure (PIP)
 (PIP) is expressed in centimeters
of water pressure (cmH2O).
 PIP should be monitored to
reduce the risk of
BAROTRAUMA.

116. Mean Airway Pressure
(MAP)

117. Mean Airway Pressure (MAP)
 The average of pressures in the airway during a complete breath.

118. Mean airway
pressure
DIRECT EFFECT ON ALVEOLAR
RECRUITMENT AND GAS EXCHANGE.
MAJOR DETERMINANT OF
INTRATHORACIC PRESSURE.
NK

119. MAP
Too low a MAP may result in
hypoventilation and
atelectasis.
Too high a Paw can
increase the risk of
barotrauma.
significantly compromise
hemodynamics.

120. Mean airway pressure
is a function of the
 Inspiratory and expiratory
time
 Peak inspiratory pressure
 PEEP
 Bias flow.

121. Ways to increase mean airway pressure
 1.Increase inspiratory flow rate
 2. Increase peak inspiratory
pressure
 3. Increase inspiratory time
 4. Increase PEEP
 5. Reduce expiratory time

122. Plateau Pressure

123. The plateau
pressure
 Pstat is generally considered to be the
 PRESSURE DISTENDING THE
ALVEOLI,
 control of the plateau pressure is
important, as excessive stretch of
alveoli has been implicated as the
cause of ventilator induced lung
injury.

124. Plateau Pressure.
THE PLATEAU PRESSURE REFLECTS
THE COMPLIANCE OF THE LUNG AND
THORAX

125. Static" Compliance
 Static" Compliance “ is a
measure of the "stiffness" of
lung and chest wall.
 Measured during inspiratory
hold and no flow of air.
NK

126. Measurement of the plateau pressure
 End-inspiratory hold
maneuver which allows
equilibration of pressure
between the mouth and alveoli.
 To determine the relative
contributions of resistive and
elastic pressures.
 The maneuver keeps the
exhalation valve closed for an
additional 0.3 to 0.5 sec after
inspiration, delaying
exhalation.
 During this time, peak airway
pressure falls from its peak
value as airflow ceases.

127. Static" Compliance
 NORMAL FOR THORAX -200
CC/CM H20
 NORMAL FOR LUNG -200
CC/CM H20
 NORMAL FOR LUNG +
THORAX- 100 cc/cm H20
NK
 Cstat = Vt /(Pp1 – PEEP)
 Vt = tidal volume
 Ppl = plateau pressure

128. Static" Compliance
 When the static compliance
decreases to approximately 25
mL/cm H2O, the work of breathing
will appreciably increase.
NK

131. NK
LINEAR COMPLIANCE AREA
 Ventilation should take place as far as
possible within the LINEAR
COMPLIANCE AREA (B), as dangerous
shear forces occur as a result of the
collaborating and reopening of
individual areas of the lung.

132. NK
LINEAR COMPLIANCE AREA
 The lower inflection point can be overcome by
setting a PEEP.
 Ventilation volume & Inspiratory pressures must
then be selected such that the UPPER
INFLECTION POINT WILL NOT BE EXCEEDED.

133. Plateau Pressure
 Generally recommended that the
 PLATEAU PRESSURE should be limited to 35 cms H2O.

134. The plateau
pressure
 Control of the plateau pressure is
important, as excessive stretch of
alveoli has been implicated as the
cause of ventilator induced lung
injury.

135. Peak Inspiratory and Plateau Pressures

136. Peak Inspiratory and Plateau Pressures
• 1. Peak Inspiratory Pressure (PIP)
• This pressure A FUNCTION OF THE COMPLIANCE OF THE LUNG
AND THORAX AND THE AIRWAY RESISTANCE
• 2. Plateau Pressure
• THE PLATEAU PRESSURE REFLECTS LUNG AND CHEST
WALL COMPLIANCE.
NK

137. An Increase In Airways Resistance will result in
1. An increase in pip.
2. A widening of the difference between pip and plateau
pressure.

138. • A fall in compliance will
1. Elevate both PIP and plateau pressure

139. Auto-PEEP
 When the expiratory time is
not sufficient for the lungs to
empty before delivery of the
next breath (Air Trapping),
then the alveolar pressure
will be greater than the
baseline at end-expiration
even though PEEP has not
been set on the ventilator
Auto PEEP
CHECK FLOW
PEEP
CHECK FLOW

140. Auto-PEEP
• Auto-PEEP may occur because
 Expiratory times are too short .
 Respiratory rates are too high.
 Because of intrinsic lung disease.
• Drug therapy, or the adjustment of rate or expiratory time, may eliminate this
condition

141. Auto-PEEP
 IF PRESSURE continues to build
in this manner, delivered tidal
volumes will drop, work of
breathing will increase .
 Patients with obstructive lung
disease are prone to the
development of auto-PEEP.

142. Detection of auto-PEEP
• To detect auto-PEEP, an
expiratory hold is performed
and the pressure measured.
• If the pressure during the
expiratory hold is greater than
the set PEEP, auto-PEEP is
present.
• To correct auto-PEEP reduce
airway obstruction or increase
expiratory time.

143. Volumes

144. Tidal Volume Vt
The amount of air which enters the lungs during inhalation .

145. The achieved tidal volume
 depend to an equal extent
on the
1. Properties and settings of
the ventilator.
2. The respiratory properties
of the lung

146. Tidal Volume
• TV is only set in volume-controlled modes of
ventilation and is usually 8-12cc/kg of body weight.
• The tidal volume is closely related to ventilation.
 The tidal volume is often manipulated to abnormal
levels of CO2.

147. Tidal Volume- types
• Mechanical Tidal Volume
represents the volume delivered
by a mechanical ventilator.
• Spontaneous Tidal Volume
depicts the amount of gas
exchanged by the patient’s own
efforts.

148. Exhaled tidal volume - EVT
 Leak in circuit.
 Around the ETT.
 Pleural leak.
 Compression of circuit.
 Normal Difference of 50 ml between VT &
EVT

149. Rate
• The set ventilatory rate is the minimum number of breaths
delivered to the patient per minute.
• The actual rate may be higher than the set rate if the patient is
initiating spontaneous breaths.
• Rate is adjusted in response to the patient’s CO2 levels.

150. Minute Ventilation
• Minute ventilation is the rate
multiplied by the tidal volume.
• Total Minute Ventilation (V) is all
mechanical and spontaneous tidal
volumes for a period of one
minute, stated in liters (L).

151. Time

152. Inspiratory
Time
 Inspiratory Time is
the time over which
the tidal volume is
delivered .
 Expiratory time is
whatever time is left
over before the next
breath

153. TIME
I : E Ratio

154. Flow Rate

155. FLOW RATE
• Flow is defined as the volume of gas or liquid passing a cross sectional
area per unit of time.
Flow = volume / time

156. Flow Waveforms
• A deflection above the baseline of
the flow waveform indicates gas is
flowing into the patient
(INSPIRATION).
• A deflection below baseline of the
flow waveform indicates that gas is
flowing out of the patient
(expiration).

157. Inspirational mechanical breath
Flow patterns

158. SINUSOIDAL
Flow gradually increases to
peak .
Tapers slowly to base.
Mimic spontaneous breath.

159. RECTANGULAR FLOW
Peak flow delivered
immediately.
Maintained throughout.
Abruptly stopped
VOLUME TARGETED
MODES

160. DECELERATING RAMP
 Peak flow at start.
 Gradually decelerates.
 Flow ceases when flow decays to a set %
of peak flow.
 Raises MAP = more recruitment of alveoli.
 Reduces PIP.
 Improve distribution

161. ACCELERATING RAMP
Gradual acceleration to set
peak flow rate.

162. Bias Flow – the basal flow rate
 Bias Flow – the basal flow rate
ALWAYS flowing through the
vent.
 circuit to assist with patient
triggering.
 Normal 0-40 lpm
 Ensures MAP and that CO2 doesn't
accumulate in the inspiratory limb
upon patient exhalation.
 A lower bias flow is the reason PS
must be used. That way patients
can more easily inhale and
overcome the negative pressure of
the vent. circuit.

163. What do we tell the ventilator to
Report ??

165. Thanks to all sources in
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