This document defines key terms and concepts related to mechanical ventilation. It discusses pressures such as airway opening pressure, intrapleural pressure, transpulmonary pressure, and others. It also describes lung characteristics like compliance and resistance. The document outlines the basics of negative and positive pressure ventilation. It discusses variables that control the ventilator cycle, including triggers, limits, and cycles. Finally, it examines various waveforms produced by mechanical ventilation like pressure/time scalars and esophageal pressure curves.
Basic information on the Graphics displayed on the Ventilators. Prepared to educate about the graphics to train the professionals who work with Ventilators.
Basic information on the Graphics displayed on the Ventilators. Prepared to educate about the graphics to train the professionals who work with Ventilators.
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THIS IS THE BASIC POINTS REGARDING NIV, THIS IS COMPILED AND ARRANGED FROM DIFFERENT BOOKS, JOURNALS AND PPTs.
The author is grateful to the teachers and authors of pulmonology and critical care.
HERE IS A SEMINAR BASED ON ALL THE NEWER MODES OF MECHANICAL VENTILATION .
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Final newer modes and facts niv chandanChandan Sheet
THIS IS THE BASIC POINTS REGARDING NIV, THIS IS COMPILED AND ARRANGED FROM DIFFERENT BOOKS, JOURNALS AND PPTs.
The author is grateful to the teachers and authors of pulmonology and critical care.
HERE IS A SEMINAR BASED ON ALL THE NEWER MODES OF MECHANICAL VENTILATION .
MY SINCERE APOLOGIES , BECAUSE I HAD TO TAKE INFORMATION FROM OTHERS SLIDES TOO , SINCE THERE IS VERY LESS INFORMATION AVAILABLE ABOUT THIS TOPIC
Learning Objectives Covered1. Explain the importance of monitor.docxsmile790243
Learning Objectives Covered:
1. Explain the importance of monitoring plateau pressures and its use in calculating static compliance
2. Explain the use of volume-controlled ventilation and pressure-controlled ventilation
3. List and describe ventilatory support treatment plans for patient’s based on their clinical diagnosis
Background
Compliance is a measurement of the distensibility of the lung or the ability of the lung to distend. It is expressed as a change in volume divided by a change in pressure using the standard units of Liters/cmH20. The normal lung + thorax compliance of an adult is around 0.1 L/cmH20. When the compliance is low, more pressure will be needed to deliver a given volume of gas to a patient. Diseases that cause low lung compliance are classified as restrictive diseases and include Adult Respiratory Distress Syndrome (ARDS), pulmonary edema, pneumonectomy, pleural effusion, pulmonary fibrosis, and pneumonia among others. Emphysema is a typical cause of increased lung compliance.
When measuring lung compliance one must know the delivered tidal volume and must also know the change in alveolar pressure that results from the addition of that known tidal volume. Alveolar pressure is the pressure in the distensible parts of the respiratory tract and is determined by the tidal volume and the lung/chest compliance. Airway pressure is the pressure measured at the patient’s airway during mechanical ventilation. Airway pressure is equal to alveolar pressure when there is no occurrence of airflow. At the end of a mechanical inspiration, flow to the distal parts of the lungs continues even after inspiratory flow from the ventilator stops, as time is required for gas to reach the periphery of the lung. To measure alveolar pressure, one must measure the airway pressure at a time when both pressures are equal, i.e. when there is no flow.
We normally assume that alveolar and airway pressure starts out at atmospheric (our zero reference) before an inspiration starts. To equalize airway and alveolar pressures, we only have to prevent exhalation after inspiration has ceased by utilizing an inspiratory hold maneuver. The actual calculation is to divide the delivered tidal volume by the plateau pressure where the plateau pressure is the steady-state pressure measured during an inspiratory hold maneuver. Since approximate values are adequate for clinical use, clinicians use the plateau pressure minus the end expiratory pressure that is then divided into the exhaled tidal volume as measured by the ventilator. This compliance measurement is referred to as static compliance since it is measured after an inspiratory hold and there is no gas flow during its measurement.
Cstatic = exhaled VT (ml)
Pplat (cmH2O) – PEEP (cmH2O)
Where:
VT – Tidal Volume
Pplat = Plateau Pressure
A spontaneously breathing person has a normal compliance of approximately 100mL/cmH2O. In intubated patients, normal comp ...
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3. Definition of Pressures and Gradients
in the Lungs
Airway opening pressure (Pawo), is most often called mouth pressure (PM) or
airway pressure (Paw). Other terms that are often used to describe the airway
opening pressure include upper- airway pressure, mask pressure, or
proximal airway pressure. Unless pressure is applied at the airway opening,
Pawo is zero or atmospheric pressure.
Intrapleural pressure (Ppl) is the pressure in the potential space between the
parietal and visceral pleurae. Ppl is normally about −5 cm H2O at the end of
expiration during spontaneous breathing. It is about −10 cm H2O at the end of
inspiration.
Because Ppl is difficult to measure in a patient, a related measurement is used,
the esophageal pressure (Pes), which is obtained by placing a specially
designed balloon in the esophagus; changes in the balloon pressure
are used to estimate pressure and pressure changes in the pleural space.
4.
5. Transthoracic pressure (PW) is the pressure difference
between the alveolar space or lung and the body’s
surface (Pbs): PW = Palv − Pbs. It represents the pressure
required to expand or contract the lungs and the chest
wall at the same time. It is sometimes abbreviated to
PTT, meaning transthoracic).
Transpulmonary pressure (PL or PTP), or transalveolar pressure, is
the pressure difference between the alveolar space and the pleural
space (Ppl): PL = Palv − Ppl.
alveolar inflation and is therefore sometimes called the alveolar
distending pressure. All modes of ventilation increase PL during
inspiration, either by decreasing Ppl (negative pressure ventilators) or
increasing Palv by increasing pressure at the upper airway (positive
pressure ventilators). The term transmural pressure is often used to
describe pleural pressure minus body surface pressure
6. Transrespiratory pressure (PTR) is the pressure difference between
the airway opening and the body surface: PTR = Pawo − Pbs.
Transrespiratory pressure is used to describe the pressure required to
inflate the lungs and airways during positive pressure ventilation. In this
situation, the body surface pressure (Pbs) is atmospheric and usually is
given the value zero; thus Pawo becomes the pressure reading on a
ventilator gauge (Paw).
Transairway pressure (PTA) is the pressure difference between the
airway opening and the alveolus: PTA = Paw − Palv. It is therefore the
pressure gradient required to produce airflow in the conductive airways.
It represents the pressure that must be generated to overcome
resistance to gas flow in the airways (i.e., airway resistance).
7.
8. LUNG CHARACTERISTICS
The compliance (C) of any structure
can be described as the relative
ease with which the structure
distends. It can be defined as the
opposite, or inverse, of elastance
(e), where elastance is the tendency
of a structure to return to its original
form after being stretched or acted
on by an outside force. Thus, C = 1/e
or e = 1/C.
Resistance is a measurement of the
frictional forces that must be
overcome during breathing. These
frictional forces are the result of the
anatomical structure of the airways
and the tissue viscous resis- tance
offered by the lungs and adjacent
tissues and organs.
Normal compliance in
spontaneously breathing patients:
0.05 to 0.17 L/cm H O or 50 to 170
mL/cm H O
Normal compliance in intubated
patients: Males: 40 to 50 mL/cm H2O,
up to
100 mL/cm H2O; Females: 35 to 45
mL/cm H2O, up to 100 mL/cm H2O
NORMAL RESISTANCE VALUES
Unintubated Patient
0.6 to 2.4 cm H2O/(L/s) at 0.5 L/s flow
Intubated Patient
Approximately 6 cm H2O/(L/s) or higher
(airway resistance increases as
endotracheal tube size decreases)
9. Measuring Airway Resistance
PTA = PIP − Pplateau.
Raw = (PIP − Pplateau)/flow• STATIC COMPLIANCE is measured when
there is no airflow (using plateau pressure –
PEEP
• STATIC COMPLIANCE
= (exhaled tidal volume)/(plateau
pressure − EEP)
= VT/(Pplateau − EEP)
•DYNAMIC COMPLIANCE is measured
when airflow is present(using the peak
airway pressure- PEEP)
• DYNAMIC COMPLIANCE =
tidal volume / peak airway pressure- PEEP
Measuring Lung Compliance
10. CLINICAL CONDITIONS THAT
AFFECT THE COMPLIANCE
DECREASED COMPLIANCE
STATIC DYNAMIC
Atelectasis
ARDS
Pneumothorax
Obesity
Retained
secretions
Bronchospasm
Kinking of ET tube
Airway obstruction
INCREASED COMPLIANCE
Emphysema
Surfactant therapy
11. NEGATIVE AND POSITIVE PRESSURE
VENTILATION
A. NEGATIVE PRESSURE VENTILATION
• Negative pressure ventilation creates a transairway
pressure gradient by decreasing the alveolar
pressures to a level below the airway opening
pressure (i. e., below the 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
12.
13. B. POSITIVE PRESSURE VENTILATION
• Positive pressure ventilation is achieved by
applying positive pressure (a pressure greater
than atmospheric pressure) at the airway
opening.
16. TRIGGERING (INITIATION OF A BREATH)
• 1. Patient Triggered or Assisted Ventilation where a
mechanical breath results from an inspiratory effort
made by the patient.
17. • 2. Time Triggered or Controlled Ventilation is a term
used when a mechanical breath is generated by a timer
allowing delivery of breaths at fixed time intervals.
• For example, if the ventilator frequency is preset at 12
breaths per minute (60 sec), the time-triggering interval
for each complete breath is 5 sec.
• At this time-trigger interval, the ventilator
automatically delivers one mechanical breath every 5
sec without regard to the patient’s breathing effort or
requirement
18. • 3. Triggering can be secondary to a negative pressure
generated by the patient (Pressure triggering) or it
results when patient removes a specific amount of
flow from the circuit during inspiratory effort (Flow
triggering).
19. • For example, if the sensitivity for pressure triggering is
set at -3 cm H2O, then the patient must generate a
pressure of -3 cm H2O at the airway opening to trigger
the ventilator into inspiration.
• If the sensitivity for pressure triggering is changed from
-3 to -5 cm H2O, the ventilator becomes less sensitive
to the patient’s inspiratory effort as more effort is
needed to trigger the ventilator into inspiration.
• Changing the sensitivity from -3 to -5 cm H2O is
decreasing the sensitivity setting on the ventilator
20. • If the ventilator is made more sensitive to the
patient’s efforts (pressure, flow, or volume), it is
easier for the patient to trigger a breath. The
converse is also true.
21. • 4. Flow-Triggered. Some ventilators are able to
measure inspiratory and expiratory flows. When the
patient’s inspiratory flow reaches a specific value, a
ventilator-supported breath is delivered. Flow
triggering has been shown to be more sensitive and
responsive to a patient’s efforts than pressure
triggering.
• How hard the patient must work to initiate or trigger
a breath is termed the ventilator sensitivity.
22. LIMIT VARIABLE (Safety)
• During a ventilator-supported breath, volume
pressure and inspiratory flow all rise above their
respective baseline values.
• Inspiratory time is defined as the time interval
between the start of inspiratory flow and the
beginning of expiratory flow.
• If one or more variables (pressure, flow, or volume) is
not allowed to rise above a preset value during the
inspiratory time, it is termed a limit variable.
25. • 1. PRESSURE CYCLED
Inspiration is terminated when the preset pressure
reaches.
• 2. VOLUME CYCLED
Inspiration is terminated when the preset volume is
delivered by the ventilator.
26. • 3. Time-Cycled
When the preset inspiratory time elapses, inspiration is
terminated.
• 4. Flow-Cycled:
Inspiration is terminated when flow decreases to a
system specific flow rate.
30. Types of Waveforms
Scalars: plot pressure/volume/flow against time…
time is the x axis
Loops: plot pressure/volume/flow against each
other…there is no time component
Six basic waveforms:
• Square: AKA rectangular or constant wave
• Ascending Ramp: AKA accelerating ramp
• Descending Ramp: AKA decelerating ramp
• Sinusoidal: AKA sine wave
• Exponential rising
• Exponential decaying
•Generally, the ascending/descending ramps are considered the same as the exponential
ramps.
31. Scalars
• Scalars waveform representations of pressure, flow
or volume on the y axis vs time on the x axis
• Ventilators measure airway pressure and airway flow
• Volume is derived from the flow measurement
• Pressure and flow provide all the information
necessary to explain the physical interaction
between ventilator and patient
• Volume scalar – tidal volume delivered during
inspiration and expiration
32.
33.
34. Types of Waveforms
Volume Modes Pressure Modes
Volume Control/ SIMV (Vol. Control) Pressure Control/ PRVC
SIMV (PRVC)
SIMV (Press. Control)
Pressure Support/
Volume Support
Pressur
e
FlowVolume
Pressur
e
FlowVolume
35. Pressure/Time Scalar
• In Volume modes,
the shape will be
an exponential
rise or an
accelerating ramp
for mandatory
breaths.
In Pressure modes, the
shape will be rectangular
or square.
This means that pressure
remains constant
throughout the breath
cycle.
•In Volume modes, adding an inspiratory pause may improve distribution of ventilation.
36. Pressure/Time Scalar
Can be used to assess:
•Air trapping (auto-PEEP)
•Airway Obstruction
•Bronchodilator Response
•Respiratory Mechanics (C/Raw)
•Active Exhalation
•Breath Type (Pressure vs. Volume)
•PIP, Pplat
•CPAP, PEEP
•Asynchrony
•Triggering Effort
37. Pressure/Time Scalar
A
B
Inspiratory pause
1
2
= MAP
1=Peak Inspiratory Pressure (PIP)
2=Plateau Pressure(Pplat)
A =Airway Resistance (Raw)
B=Alveolar DistendingPressure
• The area under the entire curve represents the mean airway pressure (MAP).
38. Pressure/Time Scalar
Decreased Compliance
Pplat
PIP
Pplat
Increased Airway Resistance
A.
PIP
B
.
•A-An increase in airway resistance causes the PIP to increase, but Pplat pressure
remains normal.
•B-A decrease in lung compliance causes the entire waveform to increase in size.
The difference between PIP and Pplat remain normal.
39. Pressure-time waveformsusinga
‘squarewave’ flow pattern
Normal pressure-time waveform With
normal peak pressures ( Ppeak) ;
plateau pressures (Pplat )and
airway resistance pressures (Pres)
time
pressure
Ppe
ak
Pr
es
Ppl
at
Pr
es
#
1
Paw = Flow x Resistance + Volume
Compliance
tim
e
flow
‘Square
wave’
Normal
values:
Ppeak < 40
cm H2O
Pplat < 30
cm H2O
Pres < 10
cm H2O
40. time
pressure
Ppe
ak
Pr
es
Ppl
at
Pr
es
#
2
Increase in peak airway
pressure
driven by an increase in
the airways resistance
e.g. ET
tube
blocka
ge
Paw = Flow x Resistance + Volume + PEEP
Compliance
tim
e
flow
‘Square
wave’
flow
pattern
Nor
mal
Pressure-timewaveform-
obstruction
42. time
pressure
Ppe
ak
Pr
es
Ppl
at
Pr
es
#
3
Increase in the peak airway pressure driven
entirely by an increase in the
airways resistance pressure
caused by excessive flow rates
shortened inspiratory time and
high flow
e.g. high
flow
rates
tim
e
flow
‘Square
wave’
Nor
mal
Normal
(low)
flow
rate
Pressuretime waveform–highflow
44. time
pressure
Pre
s
Ppl
at
Ppeak
P
re
s
#
4
Increase in the peak airway
pressure is driven entirely by
the decrease in the lung
compliance
e.g.
ARDS
Paw = Flow x Resistance + Volume + PEEP
Compliance
Norm
al
tim
e
flow
‘Square
wave’
Pressuretime waveform–reducedCompliance
47. Stressindex–Pressuretime
waveform
• At constant flow, the slope of the airway pressure-
time curve is proportional to elastance (inversely
proportional to resistance)
• In passively breathing patients and at constant flow –
shape of the pressure time curve provide overview
about compliance/recruitable/overdistension
• When rate of pressure increase with time is
small indicating a recruitable lung (Curve
convex upwards)
• When rate of pressure change is higher indicating
overdistention
51. Overdistension
• Stress index upward concavity of the pressure time
scalar
• Increased Ppeak and Pplat
• High peak expiratory flow
52. Meanairwaypressure
• Average pressure over a ventilatory cycle (one
inspiration and one expiration)
• Area below the pressure-time curve divided by the
ventilatory period (inspiratory time plus expiratory
time)
• Numerically, calculated as the average of many
pressure samples taken over the ventilatory
period
• PaO2 is proportional to mean airway pressure
• Cardiac output may be inversely proportional
• Increase airway pressure or increases the I:E ratio
(increasing inspiratory time or decreasing expiratory
time) increases mean airway pressure
53. Esophagealpressurecurve
• Esophageal pressure is measured by a
catheter with a balloon that is placed at the
lower end of the esophagus
• Estimate the pleural pressure
• Passive patient esophageal pressure
increases with each mechanical insufflation
• Spontaneously breathing patients
esophageal pressure becomes negative
during insufflation
• Positioning is key
57. Clinicalapplication
• Measuring transpulmonary pressure at end inspiration and
expiration
• Open lung strategy in ARDS ventilation and prevention of lung
injury
• End inspiratory transpulmonary pressure≤25(≤20 cm)
• End expiratory transpulmonary pressure 0-5 cm
• Spontaneously breathing
• Inspiratory effort
• AutoPEEP
• Asynchrony assessment
58. Volume/Time Scalar
The Volume waveform will generally have a “mountain peak”
appearance at the top. It may also have a plateau, or “flattened”
area at the peak of the waveform.
•There will also be a plateau if an inspiratory pause set or inspiratory hold maneuver is
applied to the breath.
59. Volume/Time Scalar
Can be used to assess:
•Air trapping (auto-PEEP)
•Leaks
•Tidal Volume
•Active Exhalation
•Asynchrony
61. Volume/Time Scalar
Air-Trapping or Leak
•If the exhalation side of the waveform doesn’t return to baseline, it could be
from air-trapping or there could be a leak (ETT, vent circuit, chest tube, etc.)
Loss of volume
62. Flow/Time Scalar
In Volume modes, the shape of the
waveform will be square or
rectangular.
This means that flow remains
constant throughout the
breath cycle.
• In Pressure modes,
(PC, PS, PRVC)
• the shape of the
waveform will have a
decelerating ramp
flow pattern.
65. Flow/Time Scalar
Can be used to assess:
•Air trapping (auto-PEEP)
•Airway Obstruction
•Bronchodilator Response
•Active Exhalation
•Breath Type (Pressure vs. Volume)
•Flow Waveform Shape
•Inspiratory Flow
•Asynchrony
•Triggering Effort
67. Flow/Time Scalar
•The decelerating flow pattern may be preferred over the constant flow pattern. The same
tidal volume is delivered, but with a lower peak pressure.
68.
69. Flow/Time Scalar
Auto-Peep (air trapping)
•If expiratory flow doesn’t return to baseline before the next breath starts, there’s auto-
PEEP(air trapping) present , e.g. emphysema.
Start of next breath
Expiratory flow
doesn’t return to
baseline
=Normal
70. AutoPEEP
• Expiration is interrupted before its natural end
by the next inspiration some un-expired
residual gas remains in thorax
• Exerts a pressure onto the respiratory circuit
• As a result, the alveolar pressure at the end
of expiration is higher than zero
(atmospheric pressure = 0)
• This incomplete emptying is called dynamic
hyperinflation, and the positive alveolar
pressure is called PEEPi or auto PEEP
74. Auto PEEPDetection
• End-expiratory occlusion is used to measure
auto PEEP
• Pressure in the lungs equilibrates with the
pressure ventilator circuit
• Pressure measured at the proximal
airways is equal to the end- expiratory
alveolar pressure
• Auto PEEP is the difference between total
PEEP and set PEEP
77. Flow/Time Scalar
Peak Exp. Flow
Improved Peak Exp. Flow
•To assess response to bronchodilator therapy, you should see an increase in peak
expiratory flow rate.
•The expiratory curve should return to baseline sooner.
Shorter
E-time
Longer
E-time
Bronchodilator Response
Pre-Bronchodilator Post-Bronchodilator
78. •Notice the area of no flow indicated by the red line. This is known as a “zero-flow state”.
•This indicates that I-time is too long for this patient.
Zero flow state
79. Waveformsobservedin pressure
support
• Flow or pressure triggered, pressure targeted
and flow cycled
• Pressure curve may be shaped by a set rise
time
• Flow curve characteristics determined by
Inspiratory time constant (compliance,
resistance) and patients effort
86. Rise Time
•The inspiratory rise time determines the amount of
time it takes to reach the desired airway pressure or
peak flow rate.
•Used to assess if ventilator is meeting patient’s demand in Pressure Support mode.
•In SIMV, rise time becomes a % of the breath cycle.
87. Rise Time
If rise time is too fast, you can get an overshoot in the pressure wave,
creating a pressure “spike”. If this occurs, you need to increase the rise
time. This makes the flow valve open a bit more slowly.
If rise time is too slow, the pressure wave becomes rounded or
slanted, when it should be more square. This will decrease Vt delivery
and may not meet the patient’s inspiratory demands. If this occurs,
you will need to decrease the rise time to open the valve faster
Hence rise time is set according to patients demand.
too slowtoo fast
pressure spike
88. Inspiratory Cycle Off
•The flow-cycling variable is given different names depending on the type of ventilator.
•The inspiratory cycle off determines when the
ventilator flow cycles from inspiration to expiration, in
Pressure Support mode.
Also know as–
•Inspiratory flow termination,
•Expiratory flow sensitivity,
•Inspiratory flow cycle %,
•E-cycle etc…
89. Inspiratory Cycle Off
•The breath ends when the ventilator detects inspiratory flow has dropped to a specific
flow value.
Inspiration ends
pressure
flow
90. Inspiratory Cycle Off
•In the above example, the machine is set to cycle inspiration off at 30%of the patient’s
peak inspiratory flow.
100%ofPatient’s
Peak Inspiratory FlowFlow
100%
75%
50%
30%
91. Inspiratory Cycle Off
60%
10%
•A –The cycle off percentage is too high, cycling off too soon. This makes the breath too
small. (not enough Vt.)
•B–The cycle off percentage is too low, making the breath too long. This forces the
patient to actively exhale (increase WOB), creating an exhalation “spike”.
Exhalation
spike
A B
100% 100%
94. Early cycling
• Flow from ventilator ends but patient still making
insp effort
• Distortion of flow and pressure wave form at
onset of expiration
• Abrupt initial reversal of expiratory flow toward
zero, indicating patient’s inspiratory effort is
prolonged
• Exaggeration of same = autotrigger
96. Ineffectivetrigger
• Respiratory muscular effort which is insufficient to
initiate mechanical breath
• Manifests as a decrease in airway pressure
associated with a simultaneous increase in
airflow
• Ventilator factors– effort not able to meet the set
trigger, large pressure drops across smaller tubes
• Patient related- Auto PEEP, resp muscle weakness
and decreased drive
98. Autotrigger
• Assisted breaths delivered which were not patient triggered
• Cause
• Fluid in circuit, leak, cardiac oscillations, low trigger threshhold
99. Doubletrigger
• Patients inspiration continues after the
ventilator inspiration and triggers another
breath immediately after the inspiration
• High ventilatory demand of the patient (ARDS)
• Inappropriate settings ( Low tidal volume, short
inspiratory time, high ETS)
101. Reverse triggering
• Unique type asynchrony in which diaphragmatic
muscle contractions triggered by ventilator
insufflations constitute a form of patient- ventilator
interaction referred to as“entrainment”
• In heavily sedated patients it is suggested
that patients had entrainment of neural
breaths within mandatory breaths.
• This entrainment occurred at a ratio of 1:1 up to 1:3.
They occur at the transition from the ventilator
inspiration to expiration.
• Breath stacking , overdistention and VIDD
107. Pressure/Volume Loops
Volume is plotted on the y-axis, Pressure on the x-
axis.
Inspiratory curve is upward, Expiratory curve is
downward.
Spontaneous breaths go clockwise and positive
pressure breaths go counterclockwise.
The bottom of the loop will be at the set PEEP level.
It will be at 0if there’s no PEEP set.
If an imaginary line is drawn down the middle of
the loop, the area to the right represents inspiratory
resistance and the area to the left represents
expiratory resistance.
113. 15 305
A
A =Inspiratory
Resistance/
Resistive WOB
B
Pressure/Volume Loops
Dynamic
Compliance
(Cdyn)
•The top part of the P/V loop represents Dynamic compliance (Cdyn).
• Cdyn = Δvolume/Δpressure
500
250
B = Exp.
Resistance/
Elastic WOB
114. Pressure/Volume Loops
Can be used to assess:
•Lung Overdistention
•Airway Obstruction
•Bronchodilator Response
•Respiratory Mechanics (C/Raw)
•WOB
•Flow Starvation
•Leaks
•Triggering Effort
118. 15 305
Pressure/Volume Loops
Airway Resistance
•As airway resistance increases, the loop will become wider.
•An increase in expiratory resistance is more commonly seen. Increased inspiratory
resistance is usually from a kinked ETT or patient biting.
500
250
120. 15 305
Pressure/Volume Loops
A Leak
•The expiratory portion of the loop doesn’t return to baseline. This indicates a leak.
500
250
121. 15 305 Lower
Inflection Point
•The lower inflection point represents the point of alveolar opening (recruitment).
•Some lung protection strategies for treating ARDS, suggest setting PEEPjust above the
lower inflection point.
Pressure/Volume Loops
Inflection
Points
250
500
122. Point of upper inflection (Ipu)
C lt changed later during
Vt because of
overinflation of the alveoli
The reduction in Clt late
in inspiratory cycle is
called Ipu
The appearance of upper
shape PAO curve indicating
the presence of Ipu is
known as duck bill PVC
124. Flow/Volume Loops
Flow is plotted on the y axis and volume on the x axis
Flow volume loops used for ventilator graphics are the
same as ones used for Pulmonary Function Testing,
(usually upside down).
Inspiration is above the horizontal line and expiration is
below.
The shape of the inspiratory curve will match what’s set on
the ventilator.
The shape of the exp flow curve represents passive
exhalation…it’s long and more drawn out in patients with
less recoil.
Can be used to determine the PIF, PEF,and Vt
Looks circular with spontaneous breaths
130. Flow/Volume Loops
Can be used to assess:
•Air trapping
•Airway Obstruction
•Airway Resistance
•Bronchodilator Response
•Insp/Exp Flow
•Flow Starvation
•Leaks
•Water or Secretion accumulation
•Asynchrony
131. Flow/Volume Loops
0
200 400 600
20
40
60
-20
-40
-60
Expiratory
portion of loop
does not
return to starting
point, indicating
a leak.
Air Leak
•If there is a leak, the loop will not meet at the starting point where inhalation starts and
exhalation ends. It can also occur with air-trapping.
=Normal
136. Air Trapping (auto-PEEP)
Causes:
•
•
Insufficient expiratory time
Early collapse of unstable alveoli/airways during exhalation
How to Identify it on the graphics
•
• Pressure wave: while performing an expiratory hold, the waveform rises
above baseline.
Flow wave: the expiratory flow doesn’t return to baseline before the next
breath begins.
• Volume wave: the expiratory portion doesn’t return to baseline.
• Flow/Volume Loop: the loop doesn’t meet at the baseline
• Pressure/Volume Loop: the loop doesn’t meet at the baseline
137. Airway Resistance Changes
Causes:
•
•
•
•
•
•
Bronchospasm
ETT problems (too small, kinked, obstructed, patient biting)
High flow rate
Secretion build-up
Damp or blocked expiratory valve/filter
Water in the HME
How to Identify it on the graphics
• Pressure wave: PIP increases, but the plateau stays the same
• Flow wave: it takes longer for the exp side to reach baseline/exp flow rate
is reduced
• Volume wave: it takes longer for the exp curve to reach the baseline
• Pressure/Volume loop: the loop will be wider. Increase Insp. Resistance
will cause it to bulge to the right. Exp resistance, bulges to the left.
• Flow/Volume loop: decreased exp flow with a scoop in the exp curve
How to fix
• Give a treatment, suction patient, drain water, change HME, change ETT,
add a bite block, reduce PF rate, change exp filter.
138. Leaks
Causes
•
• Expiratory leak: ETT cuff leak , chest tube leak, BP fistula, NG tube
in trachea
Inspiratory leak: loose connections, ventilator malfunction, faulty
flow sensor
How to ID it
•
•
•
•
•
Pressure wave: Decreased PIP
Volume wave: Expiratory side of wave doesn’t return to baseline
Flow wave: PEF decreased
Pressure/Volume loop: exp side doesn’t return to the baseline
Flow/Volume loop: exp side doesn’t return to baseline
How to fix it
• Check possible causes listed above
• Do a leak test and make sure all connections are tight
139. Asynchrony
Causes (Flow, Rate, or Triggering)
• Air hunger (flow starvation)
• Neurological Injury
• Improperly set sensitivity
How to Identify it•
•
Pressure wave: patient tries to inhale/exhale in the middle of the
waveform causing a dip in the pressure
Flow wave: patient tries to inhale/exhale in the middle of the
waveform, causing erratic flows/dips in the waveform
Pressure/Volume loop: patient makes effort to breath causing dips in
loop either Insp/Exp.
Flow/Volume loop: patient makes effort to breath causing dips in
loop.
141. Asynchrony
• How to fix it:
• Try increasing the flow rate, decreasing
the I-time, or increasing the set rate to
“capture” the patient.
• Change the mode - sometimes changing
from partial to full support will solve the
problem
If neurological, may need paralytic or
sedative
Adjust sensitivity
