BASICS OF WAVEFORM
INTERPRETATION
RET 2284
Principles of Mechanical Ventilation
Objectives
• Identify graphic display options
provided by mechanical ventilators.
• Describe how to use graphics to
more appropriately adjust the patient
ventilator interface.
Introduction
Monitoring and analysis of graphic display of
curves and loops during mechanical
ventilation has become a useful way to
determine not only how patient are being
ventilated but also a way to assess problems
occurring during ventilation.
Uses of Flow, Volume, and Pressure
Graphic Display
• Confirm mode functions
• Detect auto-PEEP
• Determine patient-ventilator synchrony
• Assess and adjust trigger levels
• Measure the work of breathing
• Adjust tidal volume and minimize overdistension
• Assess the effect of bronchodilator administration
• Detect equipment malfunctions
• Determine appropriate PEEP level
Uses of Flow, Volume, and Pressure
Graphic Display
• Evaluate adequacy of inspiratory time in pressure
control ventilation
• Detect the presence and rate of continuous leaks
• Assess inspiratory termination criteria during Pressure
Support Ventilation
• Determine appropriate Rise Time
Measured Parameters
Flow
Pressure
Volume
Time
Most Commonly Used Waveforms
(Scalars)
• Pressure vs. Time
• Flow vs. Time
• Volume vs. Time
Pressure vs. Time Curve
1 2 3 4 5 6
30
Sec
PawcmH2O
A BC
PIP
Baseline
Mean Airway Pressure
-10
Pressure-Time Curve
1 2 3 4 5 6
20
Sec
Paw
cmH2O
Pressure VentilationVolume Ventilation
Patient Triggering
1 2 3 4 5 6
30
Sec
PawcmH2O
-10
Adequate Flow During
Volume-Control Ventilation
30
Time (s)
-10
1 2
awPcmH2O
Adequate flow
3
Inadequate Flow During
Volume-Control Ventilation
30
Time (s)
-10
1 2
awPcmH2O
Adequate flow
Flow set too low
3
Patient/Ventilator SynchronyVolume Ventilator Delivering a Preset Flow and Volume
Adequate Flow
1 2 3 4 5 6
-20
SecPaw
cmH2O
Patient/Ventilator SynchronyThe Patient Outbreathing the Set Flow
Air Starvation
1 2 3 4 5 6
-20
SecPaw
cmH2O
Plateau Time
Inadequate plateau time
-20
1 2 3 4 5 6
30
SEC
Paw
cmH2O
Adequate Plateau Time
-20
1 2 3 4 5 6
30
SEC
Paw
cmH2O
Plateau Time
Flow vs.Time Curve
1 2 3 4 5 6
SEC
120
120EXH
INSP
V.
LPM
Inspiration
Flow vs.Time Curve
1 2 3 4 5 6
SEC
120
120EXH
INSP
V.
LPM
Inspiration
Expiration
Flow vs.Time Curve
1 2 3 4 5 6
SEC
120
120EXH
INSP
Inspiration
V.
LPM
Constant Flow Descending Ramp
Flow-Time Curve
1 2 3 4 5 6
SEC
120
120EXH
INSP
Insp. Pause
Expiration
V.
LPM
Inspiratory Time
Short Normal Long
1 2 3 4 5 6
SEC
120
-120
V.
LPM
Expiratory Flow Rate and Changes in Expiratory Resistance
A Higher Expiratory Flow Rate and a Decreased Expiratory Time Denote a Lower
Expiratory Resistance
1 2 3 4 5 6
SEC
120
120
V.
LPM
Obstructed Lung
Delayed flow return
Pressure-Time and Flow-Time Curves
1 2 3 4 5 6
20
Sec
Paw
cmH2O
Expiration
V.
Volume Ventilation
Pressure-Time and Flow-Time Curves
Different Inspiratory Flow Patterns
1 2 3 4 5 6
20
Sec
Paw
cmH2O
Expiration
V.
Volume Ventilation
Inspiration
20
Pressure-Time and Flow-Time Curves
1 2 3 4 5 6
Sec
Paw
cmH2O
V.
Pressure Ventilation
Inspiratory Time
Volume Ventilation
Rise Time
How quickly set pressure is reached
Time
Minimal Pressure Overshoot
Pressure Relief
Slow rise Moderate rise Fast rise
P
V.
Flow Acceleration Percent
Rise Time
Patient / Ventilator SynchronyVolume Ventilation Delivering a Preset Flow and Volume
Adequate Flow
1 2 3 4 5 6
30
-20
SecPaw
cmH2O
Air Starvation
1 2 3 4 5 6
30
-20
SecPaw
cmH2O
Patient -Ventilator SynchronyThe Patient Is Outbreathing the Set Flow
If Peak Flow Remains the Same, I-Time Increases: Could Cause Asynchrony
LPM
1 2 3 4 5 6
SEC
120
-120
V.
Changing Flow Waveform in Volume Ventilation: Effect on Inspiratory Time
1 2 3 4 5 6
SEC
120
-120
V.
LPM
Increased Peak Flow: Decreased Inspiratory Time
1 2 3 4 5 6
SEC
120
-120
V.
LPM
Note: There can still be pressure in the lung behind
airways that are completely obstructed
Detecting Auto-PEEP
LPM
Zero flow at end exhalation indicates
equilibration of lung and circuit pressure
1 2 3 4 5 6
SEC
120
-120
V.
Detecting Auto-PEEP
The transition from expiratory to inspiratory
occurs without the expiratory flow returning
to zero
1 2 3 4 5 6
SEC
120
120
V.
LPM
Volume vs.Time Curve
Inspiration
SEC
800 ml
2 3 4 5 61
VT
Volume vs.Time Curve
Expiration
SEC
800 ml
2 3 4 5 61
VT
Typical Volume Curve
1 2 3 4 5 6
SEC
1.2
-0.4
VT
Liters
I-Time
E-Time
A B
A = inspiratory volume
B = expiratory volume
Leaks
1 2 3 4 5 6
SEC
1.2
-0.4
VT
Liters
A
A = exhalation that does not return to zero
1 2 3 4 5 6
SEC
1 2 3 4 5 6
VT
600 cc
120
120
SEC
.V
LPM
0
450 cc
Setting Appropriate I-Time
Setting Appropriate I-Time
500 cc450 cc
Lost VT
1 2 3 4 5 6
SEC
1 2 3 4 5 6
VT
600 cc
120
120
SEC
.V
LPM
0
Loops
• Pressure-Volume Loops
• Flow-Volume Loops
Pressure-Volume Loop
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
VT
Mandatory Breath
Inspiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
VT
Mandatory Breath
Expiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
Inspiration
VT Counterclockwise
Spontaneous Breath
Inspiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
VT
Clockwise
Spontaneous Breath
Inspiration
Expiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
VT
Clockwise
Work of Breathing
0 20 40 60-20-40-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
VT
Assisted Breath
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
Assisted Breath
VT
Assisted Breath
Inspiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
Assisted Breath
VT
Assisted Breath
Inspiration
Expiration
0 20 40 602040-60
0.2
LITERS
0.4
0.6
Paw
cmH2O
Assisted Breath
VT Clockwise to Counterclockwise
Pressure-Volume Loop Changes
0 20 40 60-20-40-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
VT
Changes in Compliances
Indicates a drop in compliance
(higher pressure for the same
volume)
0 20 40 602040-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
VT
Overdistension
B
A
0 20 40 60-20-40-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
C
A = inspiratory pressure
B = upper inflection point
C = lower inflection point
VT
Lung Overdistension
Normal Flow-Volume Loops
Flow -Volume Loops
Volume Control
Volume
Tidal Volume
Inspiration
Expiration
Flow -Volume Loops
Volume Control
Volume
Peak Expiratory Flow
Peak Inspiratory Flow
Tidal Volume
Inspiration
Expiration
ETT or Circuit Leaks
Obstructive Pattern
Bronchodilator Response
2
1
1
2
3
3
V
LPS
.
BEFORE
V
LPS
.
Bronchodilator Response
2
1
1
2
3
3
V
LPS
.
BEFORE AFTER
Worse
2
1
1
2
3
3
V
LPS
.
Bronchodilator Response
2
1
1
2
3
3
V
LPS
.VT
INSP
EXH
BEFORE AFTER
Worse Better
2
1
1
2
3
3
V
LPS
.
2
1
1
2
3
3
V
LPS
.
Remember!Waveforms and loops are graphical representation of the data
generated by the ventilator.
Typical Tracings
Pressure-time,
Flow-time,
Volume -time
Loops
Pressure-Volume
Flow-Volume
Assessment of pressure, flow and volume
waveforms is a critical tool in the management of
the mechanically ventilated patient.