Waveforms, lecture about mechanical ventilation, by Prof Ahmed Tarek, Prof of Pediatrics, Abu El...

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.