Harish Ventilator Graphics1 110113124642 Phpapp02

BASIC PRINCIPLES OF MECHANICAL BASIC PRINCIPLES OF MECHANICAL VENTILATION ANDVENTILATOR GRAPHICSVENTILATION ANDVENTILATOR GRAPHICS

BASIC PRINCIPLES OF MECHANICAL VENTILATIONBASIC PRINCIPLES OF MECHANICAL VENTILATION Regardless of the disease states when a patient

fails to ventilate or oxygenate adequately the problem lies in 1 of 6 pathophysiological factors

1. Increased airway resistance 2. Change in lung compliance3. Hypoventilation4. V/Q mismatch5. Intrapulmonary shunting 6. Diffusion defects

AIRWAY RESISTANCE Normal airway resistance in term newborn is 20-

40cm H2O/l/sec Normal airway resistance in adults is 0.6-cm of

H2O /l/sec Resistance increases by following1. Inside the airway retained secretions2. In the wall swelling or neoplasm3. Outside the wall eg. tumor Simplified Poiseuille’s Law P=V/ r4 P= driving force V=airflow , r=radius of airway

CONDITIONS LEADING TO AIRWAY RESISTANCE EmphysemaAsthmaBronchiectasisPostintubation obstructionForeign bodyEndotracheal tube (small size and long)Condensation in vent circuitALTBBronchiolitis Epiglottitis

AIRWAY RESISTANCE AND WORK OF BREATHINGAirway resistance ( Raw) is P/ V P=peak airway pressure-plateau pressureV=flowIncrease in airway resistance means increase

in work of breathing (i.e. pressure change)Hypoventilation may result if patient is

unable to overcome the resistance by increasing the work of breathing

It leads to ventilatory and oxgenation failure

VENTILATORY FAILURE is failure of lungs to

eliminate CO2OXGENATION FAILURE is failure of lung and

heart to provide adequate oxygen for metabolic needs

LUNG COMPLIANCECompliance is lung expansion (volume change) per unit

pressure change(work of breathing) V/ PAbnormal high or low compliance impairs the patient ability to

maintain effective gas exchangeSTATIC COMPLIANCE is measured when there is no

airflow(using plateau pressure –PEEPSTATIC COMPLIANCE = tidal volume /plateau pressure- PEEPDYNAMIC COMPLIANCE is measured when airflow is

present(using the peak airway pressure- PEEP)DYNAMIC COMPLIANCE = tidal volume / peak airway

pressure- PEEPNormal range of compliance in newborn is 1.5-2 ml/cmH2O/kgNormal range of compliance in adults dynamic= 30-40

ml/cmH2ONormal range of compliance in adults static= 40-60 ml/cmH2O

LUNG COMPLIANCE CONT-Static compliance reflects the elastic

properties (elastic resistance) of lung and chest wall

Dynamic compliance reflects the airway (nonelastic)resistance and the elastic properties (elastic resistance) of lung and chest wall

Conditions causing change in static compliance invoke similar changes in dynamic compliance

Where airway resistance is the only abnormality dynamic compliance change independently

CLINICAL CONDITIONS THAT DECREASE THE COMPLIANCE

TYPE OF COMPLIANC

1. STATIC

1. DYNAMIC

CONDITIONS1. ATELECTASIS2. ARDS3. Pneumothorax4. Obesity5. Retained secretions

1. Bronchospasm2. Kinking of ET tube3. Airway obstruction

HIGH COMPLIANCEEmphysemaSurfactant therapy

VENTILATORY FAILURE 5 mechanisms lead to ventilatory failure1. Hypoventilation2. Persistent ventilation perfusion mismatch3. Persistent intrapulmonary shunting4. Diffusion defect5. Reduction in PIO2 i.e. inspired oxygen

tension

HYPOVENTILATIONCaused by depression in CNSNeuromuscular diseaseAirway obstructionIn a clinical setting hypoventilation is

characterised by a reductionof alveolar ventilation and increase in arterial CO2 tension

VENTIATION PERFUSION MISMATCHDisease process which causes obstruction or

atelectasis result in less oxygen being available leading to low V/Q

Pulmonary embolism is an example that decreases pulmonary perfusion and high V/Q

T/T in mechanical ventilation include increasing rate , tidal volume , FiO2

T/t directing towards removing obstruction,recruiting atelectatic zones and preventing closure

INTRAPULMONARY SHUNTINGCauses refractory hypoxia normal shunt is less than 10%10-20%mild shunt20-30% significant shunt>30% critical and severe shunt eg pneumonia and ARDSClassic Qs/Qt=( CcO2-CaO2)/(CcO2-CvO2)

DIFFUSION DEFECT TYPE1. Decrease in pressure

gradient

2. Thickening of A-C membrane

3. Decrease surface areaof A-C membrane

4. Insufficient time of diffusion

CLINICAL CONDITIONS

1. High altitude, fire combustion

2. Pulmonary edema and retained secretions

3. Emphysema , pulmonary fibrosis

4. tachycardia

Purpose of GraphicsPurpose of GraphicsGraphics are waveforms that reflect the patient-

ventilator system and their interaction.

Purpose of monitoring graphics includes:• Allows user to interpret, evaluate, and troubleshoot

the ventilator and the patient’s response to ventilator.

• Monitors the patient’s disease status (C and Raw).• Assesses patient’s response to therapy.• Monitors ventilator function• Allows fine tuning of ventilator to decrease WOB,

optimize ventilation, and maximize patient comfort.

Types of WaveformsTypes of WaveformsScalars: plot pressure/volume/flow against

time…time is the x axisLoops: 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.

Types of Waveforms Types of Waveforms Pressure waveforms

• Square (constant)• Exponential rise• Sinusoidal

Flow waveforms• Descending ramp• Square (constant)• Exponential decay• Sinusoidal• Ascending ramp

Volume waveforms• Ascending ramp• Sinusoidal

•Sinusoidal waves are seen with spontaneous, unsupported breathing.

Types of Waveforms Types of Waveforms Volume Modes Pressure Modes

Volume Control/ SIMV (Vol. Control) Pressure Control/ PRVC

SIMV (PRVC)SIMV (Press. Control)

Pressure Support/ Volume Support

Pres

sur

eFl

owVo

lum

e

Pres

sur

eFl

owVo

lum

e

Pressure/Time ScalarPressure/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.

Pressure/Time ScalarPressure/Time Scalar

•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

Can be used to assess:


•The baseline for the pressure waveform increases when PEEP is added.•There will be a negative deflection just before the waveform with patient triggered breaths.

5

15

No patient effort Patient effort

PEEP

+5


AB

1

2

Inspiratory pause

= MAP

1 = Peak Inspiratory Pressure (PIP) 2 = Plateau Pressure (Pplat)

A = Airway Resistance (Raw) B = Alveolar Distending Pressure

• The area under the entire curve represents the mean airway pressure (MAP).


Increased Airway Resistance

Decreased Compliance

PIP

Pplat

PIP

Pplat

A. 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.

Volume/Time ScalarVolume/Time ScalarThe 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.

Volume/Time ScalarVolume/Time Scalar

•Air trapping (auto-PEEP) •Leaks

•Tidal Volume•Active Exhalation•Asynchrony



Inspiratory Tidal Volume

Exhaled volume returns to baseline


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

Flow/Time ScalarFlow/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,

VS) the shape of the waveform will have a decelerating ramp flow pattern.

Flow/Time ScalarFlow/Time Scalar

•Air trapping (auto-PEEP)•Airway Obstruction•Bronchodilator Response•Active Exhalation•Breath Type (Pressure vs. Volume)•Flow Waveform Shape•Inspiratory Flow•Asynchrony•Triggering Effort


Flow/Time ScalarFlow/Time ScalarVolume Pressure


•The decelerating flow pattern may be preferred over the constant flow pattern. The same tidal volume is delivered, but with a lower peak pressure.


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


Bronchodilator Response

•To assess response to bronchodilator therapy, you should see an increase in peak expiratory flow rate.

•The expiratory curve should return to baseline sooner.

Peak Exp. Flow

Improved Peak Exp. Flow

Shorter E-time

Longer E-time

Pre-Bronchodilator Post-Bronchodilator

Types of Waveforms Types of Waveforms Volume Modes Pressure Modes

•In Pressure Limited, Time-cycled (control) modes, inspiratory flow should return to baseline. •In Flow-cycled (support) modes , flow does not return to baseline.

Volume Control/ SIMV (Vol. control) Pressure Control/ PRVC

SIMV (PRVC)SIMV (Press. control)

Pressure Support/ Volume Support

Pres

sur

eFl

owVo

lum

e

Pres

sur

eFl

owVo

lum

e

•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.

Types of Waveforms Types of Waveforms

15 305

250

500

Pressure/Volume LoopsPressure/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 0 if 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.


•Lung Overdistention•Airway Obstruction•Bronchodilator Response•Respiratory Mechanics (C/Raw)•WOB•Flow Starvation•Leaks•Triggering Effort


inspiration

expira

tion

15 305

Dynamic Compliance

AA = Inspiratory Resistance/Resistive WOB

B


(Cdyn)

•The top part of the P/V loop represents Dynamic compliance (Cdyn).• Cdyn = Δvolume/Δpressure

500

250

B = Exp. Resistance/Elastic WOB


15 305

Overdistention

“beaking”

•Pressure continues to rise with little or no change in volume, creating a “bird beak”.•Fix by reducing amount of tidal volume delivered

500

250


15 305

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.

“hysteresis

”ex

p. res

istan

ce

insp. re

sistan

ce

500

250

15 305

250

500

15 305


Increased Compliance

Decreased Compliance

Example: Emphysema,

Surfactant Therapy

Example: ARDS, CHF,Atelectasis

500

250

15 305

Pressure/Volume LoopsPressure/Volume LoopsA Leak

•The expiratory portion of the loop doesn’t return to baseline. This indicates a leak.

500

250

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 PEEP just above the lower inflection point.

Inflection Points

250

500

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

Flow/Volume LoopsFlow/Volume Loops

0200 400 600

20

40

60

-20

-40

-60


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 VtLooks circular with spontaneous breaths


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



0200 400 600

20

40

60

-20

-40

-60

PEF

Start of Inspiration

Start of Expiration

0 0


•The shape of the inspiratory curve will match the flow setting on the ventilator.

DIFFERENT FLOW VOLUME LOOPS

A, normal loop B ski-slop observerved in exp.

Flow limitation C Extrathoracic airway

obstruction with inspiratory and expiratory air flow limitation seen in subglotic stenosis and narrow endotracheal tube

D Intrathoracic inspiratory airflow limitationas seen with babies with intraluminal obstruction

E unstable airway eg tracheomalacia

F Erratic airflow in secretions


0200 400 600

20

40

60

-20

-40

-60

Expiratory portion of loop does notreturn to starting point, indicating a leak.

A 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

0 0

Reduced PEF

“scooping”


•The F-V loop appears “upside down” on most ventilators.

•The expiratory curve “scoops” with diseases with small airway obstruction (high expiratory resistance). e.g. asthma, emphysema.

Airway Obstruction

Air Trapping (auto-PEEP)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

Airway Resistance ChangesAirway Resistance ChangesCauses:

• 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 curveHow to fix

• Give a treatment, suction patient, drain water, change HME, change ETT, add a bite block, reduce PF rate, change exp filter.

Compliance ChangesCompliance ChangesDecreased compliance

• Causes ARDS Atelectasis Abdominal distension CHF Consolidation Fibrosis Hyperinflation Pneumothorax Pleural effusion

How to Identify it on the graphics

Pressure wave: PIP and plateau both increase

Pressure/Volume loop: lays more horizontal

• Increased compliance• Causes

Emphysema Surfactant Therapy

• How to Identify it on the graphics

Pressure wave: PIP and plateau both decrease

Pressure/Volume loop: Stands more vertical (upright)

Leaks 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

AsynchronyAsynchrony Causes (Flow, Rate, or Triggering)

• Air hunger (flow starvation)• Neurological Injury• Improperly set sensitivity

How to ID 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

either Insp/Exp. 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

AsynchronyAsynchronyFlow Starvation

•The inspiratory portion of the pressure wave shows a scooping or “dip”, due to inadequate flow.

AsynchronyAsynchrony

F/V Loop P/V Loop

Rise Time Rise Time && Inspiratory Cycle Off %Inspiratory Cycle Off %

Rise TimeRise 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.

Rise TimeRise 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.

too slowtoo fast

pressure spike

Inspiratory Cycle OffInspiratory Cycle Off•The inspiratory cycle off determines when the ventilator flow cycles from inspiration to expiration, in Pressure Support mode.

•The flow-cycling variable is given different names depending on the type of ventilator.

Also know as– •Inspiratory flow termination, •Expiratory flow sensitivity, •Inspiratory flow cycle %, •E-cycle etc…

Inspiratory Cycle OffInspiratory Cycle Off

•The breath ends when the ventilator detects inspiratory flow has dropped to a specific flow value.

Inspiration ends

pressure

flow


•In the above example, the machine is set to cycle inspiration off at 30% of the patient’s peak inspiratory flow.

100% of Patient’s Peak Inspiratory Flow

Flow

100%

50%30%

75%


•A –The cycle off percentage is too high, cycling off too soon. This makes the breath too small. (not enough Vt.)

60%10%

•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 spikeA B

100% 100%

Sources:Sources:

• Rapid Interpretation of Ventilator Waveforms Ventilator Waveform Analysis –

Susan Pearson• Golden Moments in Mechanical Ventilation –

Maquet, inc.• Servo-I Graphics – Maquet, inc.• text book of physiology- Ganong • David W Chang –clinical application of

mechanical ventilation• Pulmonary function and graphics -Goldsmith

Thank You!Thank You!

Harish Ventilator Graphics1 110113124642 Phpapp02

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