ventilator graphics

Mechanical Ventilation

Graphics

Dr.s.vijay anand

Purposes of monitoring graphics

Allow users to interpret, evaluate, and troubleshoot the ventilator and the patient’s response to the ventilator.

Monitor the patient’s disease status (C and Raw).

Assess the patient’s response to therapy.

Monitor proper ventilator function Allow fine tuning of ventilator to

decrease WOB, optimize ventilation, and maximize patient comfort

Mechanical Ventilation

GraphicsSCALARS LOOPS

SCALARS

Flow/TimePressure/Time

Volume/Time

Types of Waveforms•Scalars: Plot pressure, volume, or flow

against time. Time is the x-axis.

•

Pressure-Volume Flow-Volume

LOOPS

Loops: Plot pressure or flow against volume. (P/V or F/V). There is no time component

Basic shapes of waveforms

•Generally, the ramp waves are considered the same as exponential shapes, so you really only need to remember three: square, ramp, and sinewaves.

Square wave:Represents a constant or set parameter. For example, pressure setting in PC mode or

flowrate setting in VC mode. Ramp wave:Represents a variable parameterWill vary with changes in lung characteristicsCan be accelerating or decelerating Sine wave:Seen with spontaneous, unsupported breathing

Pressure Waveform In Volume modes, the shape of the pressure

wave will be a ramp for mandatory breaths•In Volume modes, adding an inspiratory

pause (or hold) will add a small plateau to the waveform.

•This is thought to improve distribution of ventilation

Pressure Waveform In Pressure modes, the shape of the pressure

wave will be a square shape.•This means that pressure is constant during

inspiration or pressure is a set parameter.

Distinguishing breath typeTrigger SensitivityPlateau pressureRate & I:EPeak Flow [VC]PS characteristicsLung mechanics

Application of a P/T curve

Y axis – Pressure X axis – Time A-B = Inspiration B – C = Expiration MAP = Area under

curve PIP = Max insp

Pressure PEEP = baseline

Pressure

Pressure / Time Curves - Overview

Press wave is square [constant]P wave is not affected by lung mechanics or pt

flow demandFlow rate is according to lung mechanics, set P, &

Insp effort by ptFlow wave rises rapidly to meet set P, then

decreases to a point necessary to maintain set P. [ expo decay or continuously variable decelerating pattern]

Note the P & V plateaus in regard to the Flow which ends before Ti is overThis condition provides the greatest volume

possible for that set PIndicates the lung has met equilibrium [Plateau]

Pressure / Time Curves - Overview

PC

This condix has a much shorter Ti [not allowing for Plateau] but for a longer Te

Delivered volume is slightly decreased

Pressure / Time Curves -Overview

A-B Inspiration B-C Expiration D shows second breath beginning before 1st

breath has exhaled fully Indicates needing to decrease rate, increase Te,

or decrease Ti

Pressure / Time Curves - Application

• Adequate Rate, I:E


•Breath type Mechanical breath [volume]

• Note at point A – there is no negative deflex

• Consistent Ti & Volume delivery• Pressure continues to rise until set V is reached, then breath cycles

VC


•Breath type • Mechanical Breath [ Pressure]

Consistent Ti & Pressure delivery

• P reaches limit early in I and holds for Ti

• No Trigger

PC


•Breath type • Triggered Mechanical Volume Breath

•Note at point A – there is a negative deflection, indicating the pt initiated a triggered breath

VC

Identified by negative inflex triggering breath varying Inspiratory timesNote the different times of the above curves

VC-SIMV w/ PS


•Breath type • Pressure Support breaths

PSVC

A – represents Inspirax of a spontaneous Breath B – represents Expirax of a Spontaneous breath Spontaneous Mode – Every breath is pt

triggered & spontaneous in nature

Pressure / Time Curves – Application

•Breath type • Spontaneous breath

A – scooped out waveform b/c inadequate flow for pt demand

B – bulging indicates too much flow


• Adjusting Peak Flow [ VC]

Note the Exp Volume is not = insp VolIndicating a leak Flow & Press both return to zero

Volume / Time Curves - Applic• Air Trapping v. Air Leaks

Note the Exp Volume > Insp VolumeIndicating active Ex due to air trappingNote the flow & Press never return to zero

Volume / Time Curves - Applic

•Active Exhalation

Y axis = flowX axis = TimeA-B = inspiration

Above x axis

B-C = ExpiraxBelow X axis

D- Peak Inspiratory Flow

E = Peak Expiratory Flow [ PEFR]

Flow / Time Curves - Overview

B-D = Ti B-C = INSP FLOW C-D = INSP PAUSE D-F = Te D-E = EXP FLOW E-F = EXP FLOW has

ended Rate could be

increased until insp begins at point E on this pt without air trapping

Flow / Time Curves - Overview

1 2 3 4 5 6

SEC

120

-120

V

.LPM

Expiratory Flow Rate and Changes

in Expiratory Resistance

Exp flow is low & slow, taking a long time to rid the lungs of volume.

Te is barely adequate to allow for lung emptying before next breath

This pt may have COPD or severe asthma Bronchodilator response

may be helpful to evaluate

Evaluation of Raw

A – Insp flow does return to zeroAdequate Ti

B – Insp flow does NOT return to zero Inadequate TiAllows for increasing Ti this will increase Vt without increasing Pressure

Evaluation of Ti [ PC]

Pressure remains constant at level set

Flow increases as pt demand increases in order to maintain the set Pressure level

Volume increases

Active Inhalation during PC

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

InspirationExpiration

0 20 40 602040-60

0.2

LITERS

0.4

0.6

Paw

cmH2O

VT

Clockwise

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

Dashed line plotted based on the Static Compliance calculation drawn from zero to peak PAPeak PA – Pstatic or

PplatNote that the

point at which Peak PA is also the point where the volume plateaus

PTA = xairway pressure [difference b/w the

airway opening(Pawo) and the Alveoli (PA)]

Static Compliance Line

Triangle APAE Represents the amount

of mechanical work to overcome the compliance [elastic forces] of the chest

Area ACBPA represents amount of work to overcome Raw during Insp

Triangle APAD represents amount of work to overcome Raw during Exp

The insp area [area w/in the hysteresis] represents total WOB due to Raw

PTA = xairway pressure [difference b/w the airway opening(Pawo) and the Alveoli (PA)]

Represents the amount of pressure needed to overcome resistance of the lung

If Raw increases this distance will increase

If flow [turbulence] increases, so does this distance

Triangle ABETotal WOBElastance & Resistance

More on WOB

Slope = line drawn from zero through the Pplat

As slope increases [ Pplat decreases] compliance increases for a set volume

As slope decreases [ Pplat increase] compliance decreases for a set volume

Assessing Compliance

Decreased compliance dz’s Fibrosis, ARDS, pna,

Pulm edema, Atelectasis, etc.

Short Time constant states(fast lung units)

Increased compliance dz’s Emphysema,

uncomplicated COPD, etc.

Long Time constant states(slow lung units)

Pressure remains constant while volumes differ

Assessing Compliance - PC

Volume remains Constant

Pressures change

Assessing Compliance - VC

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

X axis – VolumeY axis – Flow Insp – above x

axisExp – below x

axis Opposite of a PFT tracing

Peak Exp Flow Rate

Peak insp flow

Flow / Volume Loop – Overview

•The shape of the inspiratory portion of the curve will match the flow waveform.

•The shape of the exp flow curve represents passive exhalation.

•Can be used to determine the PIF, PEF, and Vt

•Looks circular with spontaneous breaths

Flow / Volume Loop - Application

•Air trapping •Airway Obstruction •Airway Resistance •Bronchodilator Response •Insp/Exp Flow •Flow Starvation •Leaks •Water or Secretion accumulation •Asynchrony

Flow -Volume Loops

Volume Control

Flow

Volume

Tidal Volume

Inspiration

Expiration

Flow -Volume Loops

Volume Control

Flow

Volume

Peak Expiratory Flow

Peak Inspiratory Flow

Tidal Volume

Inspiration

Expiration

A – normal Raw & exp flow

B – increased Raw & reduced exp flow

C – markedly increased Raw & reduced exp flow

Insp flow is unaffected by Raw b/c the vent is delivering a constant flow [square waveform]

Assessing Raw

Inner loop – increased airway resistance

Outer Loop – after BD therapy

Spike an artifact that reflects the release of gas trapped in the patient circuit during inspiration

compressible volume release It should not be valued

as PEFR

Assessing Bronchodilator therapy

Note the severe scooping of the exp waveform

Assessing Obstruction

Exp volume does not return to zeroCircuit or pt leak

Assessing Leaks

Exp flow does not return to zeroPt still exhaling volume when next breath begins

Air Trapping

Bronchodilator Response

2

1

1

2

3

3

VLPS

.

BEFORE

VLPS

.


2

1

1

2

3

3

VLPS

.

BEFORE AFTER

Worse

2

1

1

2

3

3

VLPS

.


2

1

1

2

3

3

VLPS

.VT

INSP

EXH

BEFORE AFTER

Worse Better

2

1

1

2

3

3

VLPS

.

2

1

1

2

3

3

VLPS

.

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.

Reference

Susan philbeam textbook of mechanical ventilation

ventilator graphics

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