ventilator graphics
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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
Pre
ssu
re
Flo
wV
olu
me
Pre
ssu
re
Flo
wV
olu
me
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:
Pressure/Time ScalarPressure/Time Scalar
•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
Pressure/Time ScalarPressure/Time Scalar
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).
Pressure/Time ScalarPressure/Time Scalar
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
Can be used to assess:
Volume/Time ScalarVolume/Time Scalar
Inspiratory Tidal Volume
Exhaled volume returns to baseline
Volume/Time ScalarVolume/Time Scalar
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
Can be used to assess:
Flow/Time ScalarFlow/Time ScalarVolume Pressure
Flow/Time ScalarFlow/Time Scalar
•The decelerating flow pattern may be preferred over the constant flow pattern. The same tidal volume is delivered, but with a lower peak pressure.
Flow/Time ScalarFlow/Time Scalar
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
Flow/Time ScalarFlow/Time Scalar
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
Pre
ssu
re
Flo
wV
olu
me
Pre
ssu
re
Flo
wV
olu
me
•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
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.
Pressure/Volume LoopsPressure/Volume Loops
•Lung Overdistention•Airway Obstruction•Bronchodilator Response•Respiratory Mechanics (C/Raw)•WOB•Flow Starvation•Leaks•Triggering Effort
Can be used to assess:
inspira
tion
expira
tion
15 305
Dynamic Compliance
AA = Inspiratory Resistance/Resistive WOB
B
Pressure/Volume LoopsPressure/Volume Loops
(Cdyn)
•The top part of the P/V loop represents Dynamic compliance (Cdyn).• Cdyn = Δvolume/Δpressure
500
250
B = Exp. Resistance/Elastic WOB
Pressure/Volume LoopsPressure/Volume Loops
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
Pressure/Volume LoopsPressure/Volume Loops
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.
“hys
teresis
”ex
p. re
sistan
ce
insp.
resis
tance
500
250
15 305
250
500
15 305
Pressure/Volume LoopsPressure/Volume Loops
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
Pressure/Volume LoopsPressure/Volume Loops
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/Volume LoopsFlow/Volume Loops
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
Flow/Volume LoopsFlow/Volume Loops
•Air trapping•Airway Obstruction•Airway Resistance•Bronchodilator Response•Insp/Exp Flow•Flow Starvation•Leaks•Water or Secretion accumulation•Asynchrony
Can be used to assess:
Flow/Volume LoopsFlow/Volume Loops
0200 400 600
20
40
60
-20
-40
-60
PEF
Start of Inspiration
Start of Expiration
0 0
Flow/Volume LoopsFlow/Volume Loops
•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
Flow/Volume LoopsFlow/Volume Loops
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”
Flow/Volume LoopsFlow/Volume Loops
•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
Inspiratory Cycle OffInspiratory Cycle Off
•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%
Inspiratory Cycle OffInspiratory Cycle Off
•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 spike
A 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!
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