VIASYS Healthcare
Bubba Reetz
Bedside Monitoring of
Respiratory Graphics to
Optimize Mechanical
Ventilation Strategies
All names are protected copyrights of
Bird Products, Bear Medical and SensorMedics Inc.
Presentation Copyright© 2001
Run Lungs Run
Primary Goals
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Early identification of changes in patient’s condition
Optimize ventilator performance and fine-tune the
ventilator settings
Determine the effectiveness of ventilation support
Early detection of possible adverse effects of
mechanical ventilation
Minimize the risk of ventilator-induced complications or
ventilator malfunctioning
Basic Mechanism of PPV
Pressure Difference
Gas Flow
Time
Volume Change
What is measured?
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Pressure
Time
Flow (dV /dt )
Volume
Flow
Volume
(calculated)
time
Pneumotachographs

Fleisch Pneumotachograph
–

Orifice Pneumotachograph
–
–

Measures pressure drop across a known resistance
Fixed or Variable
Vortex Pneumotachograph
–

Capillary tubes and pressure transducer
Ultrasonic detection of created turbulence
Turbine Pneumotachograph
–
Photocell detects rotation of turbine
Fixed Orifice Pneumotach
Q
P1
R
D P =Q x R
Q = (P1 - P2) / R
DV=QxDt
P2
Heated Anemometers

Heated element (wire or film)
–
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Measures the current necessary to maintain the
temperature constant (cooling effect of gas flow)
Lack of moving parts
Fast and sensitive response
Virtually no resistance
+ -
Problems of flow measurement
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Moisture
Secretion
Ambient temperature
Humidity
Altitude
Placement of the sensor
Compressible volume loss
What is Displayed?

Real-time waveforms of
–
–
–

Loops
–
–
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Proximal Airway Pressure
Insp. / Expiratory Flow Rate
Insp. / Expiratory Tidal
Volume
Pressure / Volume
Flow / Volume
Calculated Parameters
–
–
–
Compliance, Resistance,
TC,
C20 / Cdyn
Work of breathing
Waveforms
PIP
Pressure
PEEP
+
0
_
Insp.
Flow
Volume
Exp.
Insp.
Exp.
Time
Loops
Volume
Flow
Expir.
Insp.
Insp.
Pressure
Expir.
Volume
Phase Variables

A/ Trigger:
–
–

C
B/ Limit:
–
–
–

Patient (assisted)
Machine (controlled)
C/ Cycle:
–
–
–
B
Flow
Pressure
Volume
Volume
Time
Flow
A
Control variables
Volume Ventilation
Pressure
Pressure
Flow
Pressure Ventilation
time
Flow
time
Volume Ventilation - Waveforms
Inspiratory Hold
Flow
Tinsp
PIP
Pressure
Plateau Pressure
PEEP
Volume Cycled
Time Cycled
Pressure Ventilation - Waveforms
Peak
Flow
25%
Flow
PIP
Tinsp.
Pressure
Pressure Control
Pressure Support
Pressure-Volume Loops
Volume
Volume
Pressure
Pressure
Flow-Volume Loops
Flow
Flow
Volume
Volume
Continuous Mandatory Ventilation

Control: Only machine initiated mandatory breaths:
Paw

Assist: Only patient initiated mandatory breaths:
Paw

Assist/Control: machine and patient initiated breaths:
Paw
Typical P-V Loops
Volume
Pressure
Controlled
Volume
Pressure
Assisted
Volume
Pressure
Spontaneous
Intermittent Mandatory Ventilation
IMV: Machine initiated + Spontaneous breaths
Paw
SIMV: Mandatory (patient or machine initiated) +
Spontaneous breaths
Paw
Spontaneous Modes
Continuous Positive Airway Pressure
Paw
CPAP
Pressure Support Ventilation
Paw
PS
SIMV + Pressure Support
Pressure supported spontaneous + Patient, or
machine-initiated mandatory breaths
Paw
Abnormalities
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Detection of air-leak
Over-distension - Gas trapping
Increased expiratory resistance
Inspiratory time adjustment
Airway obstruction
Patient-ventilator dysynchrony
Inadequate trigger sensitivity
Inadequate flow support
Inadequate PEEP
Airleak
Volume
Time
Volume
Flow
Volume
Pressure
Increased Expiratory Resistance

Prolonged expiratory flow indicates an
obstruction to exhalation and may be caused
by obstruction of a large airway,
bronchospasm, or expiratory valve failure of
the ventilator
Flow
Time
Normal Resistance
Increased Resistance
Insufficient Expiratory Time


Expiratory flow is unable to return to baseline prior
to the initiation of the next mechanical breath
Incomplete exhalation causes gas trapping,
dynamic hyper-expansion and the development of
intrinsic PEEP
Flow
Time
End-Expiratory Flow
Airway Obstruction
F
F
V
V
Before Suction
After Suction
Optimising PEEP
V
V
P
PEEP: 3 cmH2O
P
PEEP: 8 cmH2O
Trigger Sensitivity
Pressure
Time
Sensitivity level
Flow
Time
Atelectasis
Lost FRC
Replaced FRC
V
V
P
P
Overdistension

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Overdistension occurs
when the volume limit of
some components of
the lung has been
exceeded
Abrupt decrease in
compliance at the
termination of inspiration
Results in a terminal
“Beaking” of the P/V
Loop
Volume
Pressure
Mental Break
Assessment of static P-V curve

Super-syringe method:
Stepwise inflation from a
big syringe with multiple
occlusions at each
volumes to record recoil
pressure
–
–
–
–
–
Volume
Time consuming
Cumbersome to perform
Difficult to standardize
Patient must be
paralysed, connected to
a special equipment
Great risk of oxygen
desaturation
Pressure
Slow Flow Single Inflation Method


Slow (5-10 lpm) inspiratory flow
with large Vt and ZEEP
Volume
The inspiratory curve of the
dynamic P-V loop closely
approximates the static curve

The flow-resistive pressure
component could be subtracted

Easy to perform, fast and relatively
comfortable
UPIflex
LPIflex
Servillo: AJRCCM 1997
Lu: AJRCCM 1999
Pressure
Ventilation-Induced Lung Injury*
Atelectrauma:
Repetitive alveolar
collapse and reopening
of the under-recruited
alveoli
*Dreyfuss: J Appl Physiol 1992
Volutrauma:
Over-distension of
normally aerated alveoli
due to excessive volume
delivery
Inflection Points on the P-V curve in ARF

Upper Inflection Point:
Represents pressure
resulting in regional
overdistension
Volume
UPIflex

Lower Inflection Point:
Represents minimal
pressure for adequate
alveolar recruitment
LPIflex
Pressure
Lung Protective Strategy
1.
2.
3.
Set PEEP above the
lower Pflex to keep
the lung open and
avoid alveolar
collapse
Apply small Vt to
minimize stretching
forces
Set Pplat below the
upper Pflex to avoid
regional
overdistension
Volume
Pressure
THANK YOU