ventilator waveform analysis

Chest Conference

Teerapat Yingchoncharoen M.D.

Department of Internal Medicine PSU

Content

• Pressure-Time Curve

• Flow-Time Curve

• Volume-Time Curve

• Step Approach to waveform analysis

• Combined curve

• Flow-Volume Loop

• Post-test examination

Physician

Mechanical ventilator patient

clinical ?

Waveform

Signal generation

Waveform generation

Role of Ventilator Waveforms in

Ventilator-Dependent Patients

1. Identify pathophysiologic process

2. Recognize a “real time” change in patient’s condition

3. Optimize ventilator setting and treatment

4. Determine effectiveness of ventilator settings

5. Detect adverse effects of mechanical ventilation

6. Minimize risk of ventilator-induced complications

Respir Care 2005;50(2):246-259

Pressure-Time Curve

Inspiration Expiration

PEEP/CPAP

TV

Pressure-Time Curve

Applications :-

• Breath type identification

• Work required to trigger the breath

• Breath timing (inspiration Vs exhalation)

• Adequacy of inspiration

• Adequacy of inspiratory plateau

• Adequacy of inspiratory flow

• Results and adequacy of a static mechanics maneuver

• Adequacy of the Rise Time Setting

Identifying breath type

Five different breath types can be identified

by viewing pressure-time curve :-

1. Ventilator-initiated mandatory breaths

2. Patient-initiated mandatory breaths

3. Spontaneous breaths

4. Pressure support breaths (PSV)

5. Pressure control breaths (PCV)

1. Ventilator-Initiated Mandatory Breaths (Controlled Ventilation)

A pressure rise without a pressure deflection below baseline

2. Patient-Initiated Mandatory Breaths (Assisted Ventilation)

A pressure deflection below baseline

3. Spontaneous breaths

Pressure below baseline = Inspiration

Pressure above baseline = expiration

4. Pressure Support Breaths (PSV)

Ti Ti

4. Pressure Control Breaths (PCV)

Ti Ti

Quiz # 1: What is this mode of ventilation

BiLevel Ventilation With Spontaneous Breathing at PEEPH and PEEPL

Quiz # 2: What is this mode of ventilation

Airway Pressure Release Ventilation (APRV)

Assessing Plateau Pressure

Airway Pressure Ppeak = Pairway + Pplateau

Change in Airway Resistance Change in Compliance

Basic Lung Mechanic

Ppl

Palv

Pr Paw = Pr+Palv+Ppl

Ppl ~ 0

then Paw=Pr+Palv

Pr=0 :flow =0

then Paw =Palv=Pplat

High Pressure Alarm

high pressure alarm

low Pplat

High resistive stage

High Pplat

PEEP application

increase compliance decrease compliance

parenchymal disease pleural disease

High Pressure Alarm

• Resistance load

- bronchospasm

- secretion

- airway disease

- artificial airway

problem

• Compliance load

- parenchymal

injury

- ARDS

- Pneumonia

- Pulmonary edema

- increase pleural

pressure

Quiz # 3: Is this Pplt reliable ?

No !! This is unstable pressure plateau, possibly due to a leak or the patient’s inspiratory effort.

Assessing the work to trigger

PT = Triggering time, DTOT = Delayed time

Assessing rise time

•Rise in target pressure depend on lung impedence and/or patient’s demand •The ideal waveform for pts receiving pressure ventilation is roughly square in shape (Figure B) satisfy the pt’s flow demand while contributing to a higher mean airway pressure. • Figure A = Low compliance or high flow demand • Figure C = High compliance or low flow demand (Overshoot)

Setting Rise Time

Increase rise time Decrease rise time

Assessing Auto-PEEP maneuver

Point of equilibration

12 32

Quiz #4

A 22-year-old patient presented with acute severe asthma

with respiratory failure. He was intubated and mechanically

ventilated. After the initial setting of ventilatory support, the

patient was still discomfort. The pressure-time curve was

shown below. What is the most-likely cause?

Thai Board

A. Too high PEEP level

B. Insufficient inspiratory flow

C. Auto trigger of ventilator

D. Air leak in ventilatory system

E. High tidal volume

Thai Board

Quiz #4

P-T curve in VCV

Flow-Time Curve

Applications :-

• Waveform shape

• Type of breathing

• Presence of Auto-PEEP

• Patient’s response to bronchodilators

• Adequacy of inspiratory time in pressure

control ventilation

• Presence and rate of continuous air leaks

Flow-Time Curve

= PEFR

Actual expiratory time

Total available expiratory time

Verifying Flow Waveform Shape

Detecting the type of breathing

Quiz # 5

A 65-year-old man with COPD had developed dyspnea for

5 days. A volume-controlled respirator was applied with

an FiO2 of 0.6, RR 20/min, Vt of 600 cc and PIF 40 L/min.

ABG was then performed and revealed pH of 7.30,

PaCO2 60 mmHg and PaO2 60 mmHg. The flow-time curve is shown as follows.

Flow

Time

Thai Board

What is the most appropriate next step of

management ?

A. Decrease PIF

B. Increase Vt

C. Increase RR

D. Increase PEEP

E. Increase FiO2

Thai Board

Determining the presence of Auto-PEEP

Effects of Change in Rate

Effects of Change in Flow

Management of Auto-PEEP

• Sedation and paralysis

• Decreasing airway resistance with

medications

• Increasing inspiratory flow rates (ie,

decreasing I:E ratio)

• Applying small amounts of external PEEP

Evaluating Bronchodilators Response

Quiz # 7

A patient with pneumothorax S/P ICD insertion

breathing with PCV Setting = Rate 20/min

PEEP 15 IT 0.8 RR 24-28 FiO2 0.6 TV 300

The waveform showed the following, what would

you do next ?

pressure

flow

time

time

Quiz # 7

A. Decrease PEEP

B. Decrease RR

C. Increase RR

D. Increase IT

E. Decrease IT

Quiz # 7

A patient with pneumothorax S/P ICD insertion

breathing with PCV Setting = Rate 20/min

PEEP 15 IT 0.8 RR 24-28 FiO2 0.6 TV 300

The waveform showed the following, what would

you do next ?

pressure

flow

time

time

In PC Inspired flow not = 0

(underventilation)

Inspiratory time setting in PCV

PCV Changes in Ti

Quiz # 8 : What happened ?

Water in expiratory tube of ventilator circuit

Volume-Time Curve

Applications :-

• Air-trapping detection

• Leaks in the patient circuit detection

Volume-Time Curve

Leak or Air-Trapping

Expiratory volume does not return to baseline

Air-trapping in COPD

Quiz # 9 : What happened ?

Excessive inspired tidal volume

Step-Approach for Waveform Analysis

Analyzing waveform – step 1

• determine the CPAP level

– baseline position from which there is a downward

deflection on, at least, beginning of inspiration, and

to which the airway pressure returns at the end of

expiration


• is the patient triggering?

– There will be a negative deflection into the CPAP line

just before inspiration


• what is the shape of the pressure wave?

– If the curve has a flat top, then the breath is pressure

limited, if it has a triangular or shark’s fin top, then it

is not pressure limited and is a volume breath


• what is the flow pattern?

– If it is constant flow (square shaped) this must be

volume controlled, if decelerating, it can be any mode


• Is the patient gas trapping?

– expiratory flow does not return to baseline before

inspiration commences (i.e. gas is trapped in the

airways at end-expiration)


• the patient is triggering – is this a pressure supported or SIMV or VAC breath? – This is easy, the pressure supported breath looks completely

differently than the volume control or synchronized breath: the PS breath has a decelerating flow pattern, and has a flat topped airway pressure wave. The synchronized breath has a triangular shaped pressure wave


• the patient is triggering – is this pressure support or pressure control? – The fundamental difference between pressure support and

pressure control is the length of the breath – in PC, the ventilator determined this (the inspired time) and all breaths have an equal “i” time. In PS, the patient determined the duration of inspiration, and this varies from breath to breath


• is the patient synchronizing with the ventilator? – Each time the ventilator is triggered a breath should be

delivered. If the number of triggering episodes is greater than the number of breaths, the patient is asynchronous with the ventilator. Further, if the peak flow rate of the ventilator is inadequate, then the inspiratory flow will be "scooped" inwards, and the patient appears to be fighting the ventilator

Combining the graphics

PEEP5

Assisted

Square wave = VCV

Controlled

A/CMV (constant flow) + PEEP 5

PEEP5

Pressure preset

End inspiratory flow reach baseline

PCV with PEEP 5 cmH2O

PEEP5

Non-Pressure preset

Decelerating (Ramp) flow

VCV (decelerating flow) with PEEP

PEEP 6

Pressure preset

End-inspiratory flow

Not return to baseline

Pressure support with CPAP 6

Negative reflection CPAP

Volume target SIMV

Pressure target SIMV

CPAP with Volume- target SIMV

Flow-Volume Loop

Applications :-

• Inspiratory area calculations

• Work to trigger a breath

• Changes in compliances and resistance

• Lung overdistention

• Adjustments to pressure support

• Inflection points

• Adequacy of peak flow rates

Flow-Volume Loop: Introduction •The calculation of the area of the loop to the left of the volume axis. •An approximation of the work imposed by the ventilator.

PEEP

Breath type


Trigger tail


Trigger tail : Too high pressure sensitivity

Assessing compliance

Increased Resistance

Lung overdistention

What happened: “Figure eight”

Insufficient inspiratory flow

Case Pressure-Volume Loop

Post-test exams

A patient is agitated during mechanical ventilation and

interventions are undertaken to achieve better patient-ventilator

synchrony. Flow and pressure curves from before (top panel) and

after (bottom panel) the intervention are shown in Figure 1. Based

on the change shown, which of the following best describes the

intervention?

A. Matching intrinsic PEEP with extrinsic PEEP to facilitate triggering each breath.

B. Increasing flow rate and respiratory rate to accommodate increased respiratory drive.

C. Switching the mode to pressure support. D. Switching the mode to airway pressure release. E. Paralysis.

ACCP-SEEK 2006

Which of the following best describes the

mechanical ventilation mode depicted in Figure 1?

A. Pressure assist-control ventilation

(PACV).

B. Volume assist-control ventilation

(VACV).

C. Pressure support ventilation (PSV).

D. Pressure-targeted synchronized

intermittent mandatory

(SIMV).

E. Continuous positive airway pressure

(CPAP).

ACCP-SEEK 2006

You have been asked to assist in the ventilatory management of

a 70-year-old man with ARDS complicating urosepsis. He

weighs 70 kg, is deeply sedated, and has been paralyzed with a

nondepolarizing agent. Figure 1 shows an airway pressure/lung

volume loop recorded during volume preset mechanical

ventilation with constant inspiratory flow of 0.6 L/s.

ACCP-SEEK 2006

A. Positive end-expiratory pressure (PEEP) should be raised to 18 cm H2O.

B. Some units of the lung are being inflated close to total lung capacity.

C. The deflation compliance of this patient’s lungs is 0.3 L/cm H2O.

D. The area between the inflation and deflation limb reflects lung hysteresis and is determined by recruitment and surface tension phenomena.

E. The vital capacity of this patient is probably <0.5 L.

ACCP-SEEK 2006

Which of the following statements concerning the figure is correct?

A 50-kg, 30-year-old patient with acute, severe asthma is receiving

volume preset ventilation in the assist/control mode. She is

spontaneously breathing with a rate of 30, inspiratory flow rate 60

L/min, tidal volume 0.5 L, FIO2 0.4, and PEEP 0.0. Monitoring of

airflow reveals the profile shown in Figure 1. Pulse is 100 and blood

pressure is 90/60 mm Hg with a pulsus paradoxus of 28 mm Hg.

ACCP-SEEK 2006

A. Pericardiocentesis. B. Placing a chest tube.

C. Withdrawing the endotracheal tube from right mainstem bronchus.

D. Decreasing inspiratory flow rate. E. Sedation and paralysis.

ACCP-SEEK 2006

Which of the following actions should be taken immediately in an attempt to reverse the hypotension?

A patient is receiving volume assist control mechanical

ventilatory support for the acute respiratory distress

syndrome (ARDS). He is heavily sedated and not triggering

ventilator breaths. His ventilator graphics are shown in

Figure 1. Over the last several hours, his peak airway

pressure has slowly risen and finally the high pressure alarm

is activated. A chest radiograph reveals bilateral fluffy

infiltrates. You examine him and determine that significant

pulmonary edema has developed. Which set of graphics in

Figure 2 is most consistent with these changes?

A. Breath A. B. Breath B C. Breath C. D. Breath D. E. Breath E.

ACCP-SEEK 2006

ventilator waveform analysis

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