VENTILATOR WAVEFORM ANALYSIS

By Dr. M. V. Nagarjuna 1 Seminar Overview

1. Basic Terminology ( Types of variables,,, Breaths, modes of ventilation) 2. Ideal ventilator waveforms (()Scalars) 3. Diagnosing altered physiological states 4. Ventilator Patient Asynchrony and its management. 5. Loops (Pressure volume and Flow volume)

2 Basics phase variables…………..

A. Trigger ……. BC What causes the breath to begin? B. Limit …… A What regulates gas flow during the breath? C. Cycle ……. What causes the breath to end? VARIABLES 1. TRIGGER VARIABLE : Initiates the breath  Flow (Assist breath)  Pressure (Assist Breath)  Time (Control Breath)  Newer variables (Volume, Shape signal, neural)

Flow trigge r b etter th an Pr essure tri gger . With the newer ventilators, difference in work of triggering is of minimal clinical significance. British Journal of Anaesthesia, 2003

4 2. TARGET VARIABLE : Controls the gas delivery during the breath  Flow ( Volume Control modes)  Pressure ( Pressure Control modes)

3. CYCLE VARIABLE : Cycled from inspiration into expiiiration  Volume ( Volume control)  Time (Pressure control)  Flow (pressure Support)  Pressure (S(Sftafety cycling varibl)iable)

5 Modes of Ventilation

Mode of ventilation Breath types available

Volume Assist Control Volume Control, Volume Assist

Pressure Assist Control Pressure Control, Pressure Assist

Volume SIMV Volume Control, Volume Assist, Pressure Support

Pressure SIMV Pressure Control, Pressure Assist, Pressure Support

Pressure Support Pressure support

6 SCALARS

7 FLOW vs TIME

8 Flow versus time

Never forget to look at the expiratory limb of the flow waveform The expiratory flow is determined by the elastic recoil of the respiratory system and resistance of intubated airways

9 Types of Inspiratory flow waveforms

a. Square wave flow b. Ascending ramp flow c. Descending ramp flow d. Sinusoidal flow e. Decay flow 10 Which form to use??

 Pressure con tltrol mode : Always DltiDecelerating or decay flow. Cannot be changed.

 Volume control mode : Flow waveform can be changed ddidepending on the ventilator options.

11 SQUARE FLOW WAVEFORM : • Inspiratory time is shortest for Square wave flow form. • Highest Peak Inspiratory pressures •Low Mean Inspiratory pressure,, thus better venous return and cardiac output

DESCENDING RAMP FLOW : • Increases inspiratory time (if not fixed) or peak inspiratory flow rate (if insppyiratory time is fixed) •Least Peak inspiratory pressures (19% decrease). •High mean airway pressure , helps lung inflation and oxygenation.

12 Sinusoidal and ascending ramp flow :  Initial flow rates are slow and hence cause dyssynchrony – FLOW STARVATION.  Should not be used in assist modes.

Descending ramp and Square wave flow :  Usually preferred as the initial flow rate meets the flow demand of the patient. Decreases air hunger.

13 DECSENDING RAMP SQUARE WAVE FLOW FLOW 14 Decelerating flow waveform

 Advantages :  Decreases Peak inspiratory pressures  Increases oxygenation, decreases A-aDo2  Improves patient ventilator synchrony (more physiological)  Disadvantages :  Decreases expiratory time , potential for auto PEEP  Increases mean airway pressure, decreases cardiac output  Increased intracranial pressures

Egan's Fundamentals of Respiratory Care. 8th ed. 2003:1064. Mechanical Ventilation; Physiological and Clinical Applications.4thed.2006:113 .

15 Intensive Care Med. 1985;11:68-75. Expiratory flow waveform

 Passive and determined by compliance of the lung and resistance of the airways.

 Four points to be observed : 1. Peak Expiratory Flow 2. Slope of the exp iratory lim b 3. Expiratory time 4. Does the wavef orm reach the base line ?

16 PRESSURE vs TIME

17 Pressure vs Time Scalar

18 No active breathing TtTreats lung as s ilingle unit PIP

resistance flow Pplat end-inspiratory Driving alveolar pressure Pressure (PIP-PEEP) compliance tidal volume volume

PEEP

PIP- PEEP= (Flow x Resistance) + (Vt/Compliance RS) Respiratory System Compliance tidal volume C = Pplat - PEEP Decreased with: Pulmonary Disorder: Extra Pulmonary Disorder:  mainstem intubation  abdominal distension  congestive heart failure  ARDS  chest wall edema/Obesity  Atelectasis, consolidation  thoracic deformity  fibrosis  Hyperinflation  Tension pneumothorax  pllleural effusion Normal : 100 mL/cm H2O PltPplat – PEEP = Vt/ Comp liance

 P plateau increased by a) Decreasinggp compliance of lung : Pulm edema, ARDS, Atelectasis, Pneumonia. b) Decreasing compliance of the chest wall : Morbid obesity, ascites, stiff chest wall. c) Increasing Tidal volume d) Patient ventilator dyssynchrony

21 Inspiratory Resistance PIP - Pplat R = i flow Increased with:  Airways : Secretions, Mucus plugging, Bronchospasm  ET tube : Small size, ET block  Ventilator Circuit: Kinking, Clogged HME

Normal: 5 - 10 cm H2O///L/s for intubated ventilated adults measured with 60 L/min (1 L/s) constant flow P peak – P p la t = Flow x Res is tance

 Increased by a) Increasinggp resistance : Bronchospasm, Mucus plugging/secretions, ET block , Biting the ET tube, Tube kinking, Clogged HME. b) Increasing flow : Increasing Vt, Increasing Insp.pause, Increasing I:E ratio

23 PIP tidal volume Crs = PltPplat - PEEP tidal volume Ppl Ccw = (Peso) Peso tidal volume Palv CL = (Pplat) ((pPplat – PEEP) - Peso PIP - Pplat Ri = flow STRESS INDEX (ARDS)

Increase PEEP Ideal PEEP Decrease PEEP (Recruitment) (Overdistension) 25 DECSENDING RAMP SQUARE WAVE FLOW FLOW 26 VOLUME vs TIME

27 Information derived from VolumeTime Scalar

Tidal Volume Volume on y axis

Air leak Expiratory limb fails to return to x axis

Active Expiration Tracing continues beyond the baseline

Auto PEEP Expiratory llbimb flfails to reac h the base line

28 HOW TO USE THE GRAPHS FOR DIAGNOSIS OF DISEASE STATES ?

29 Which waveforms to monitor ?

Mode of Independent Dependent Waveforms that will be Wavefor ms that ventilation variables variables useful normally remain unchanged Volume Tidal volume,RR, P Pressure-time: Volume-time Control/ Flow rate, PEEP, aw Changes in Pip, Pplat Flow time (inspiratory) Assist-Control I/E ratio Flow-time (expiratory): Changes in comp liance Pressure-volume loop: Overdistension, optimal PEEP

Pressure P , Inspiratory Volume-time and flow- Pressure-time aw Vt, flow Control time (RR), PEEP time: Changes in Vt and and I/E ratio compliance Pressure-volume loop: Overdistension, optimal PEEP

Pressure PS and PEEP Volume- time Vt,and RR, support/ flow, I/E Flow- time CPAP Ratio (for Vt and VE)

30 Increased airway resistance (ACMV- VC)

 Pressure Time Waveform :  Increased difference between Ppeak and Pplat  Normal P plat  Expiratory flow waveform :  Decreased PEFR  Increased expiratory time  Scooped out appearance of expiratory limb  Potential for auto PEEP  Loss of peak (emphysema)  Volume Time Waveform :  Expiratory limb long

31 A patient with Endotracheal Tube block (When received from Dialysis room)

32 A patient with acute severe asthma on ventilator

33 Decreased Compliance of Respiratory System

 Pressure Time Waveform :  Increased P plat and Ppeak.  Normal P peak – Pplat

 Flow Time Waveform :  Increased PEFR  Shortened expiratory time

34 Auto PEEP/Intrinsic PEEP

Notice how the expiratory flow fails to return to the baseline indicating air trapping (Auto PEEP)

Also notice how air trapping causes an increase in airwayyp pressure due to increasing end expiratory pressure and end inspiratory lung volume.

35 A patient of acute severe asthma. Note failure of expiratory limb to return to baseline

36 37 AUTO- PEEP : Consequences  Increases the work of Triggering  Ineffective triggering  Worsens Oxygenation  Lung Hyperinflation- barotrauma  Hemodynamic Compromise

AUTO PEEP : Recognition  Analysis of ventilator graphics:

 Delay between start of Inspiratory effort and Pressure drop  No increase in P peak with increase in Applied PEEP

38 39 VENTILATOR PATIENT SYNCHRONY VS DYS-SSCOYNCHRONY

40 What is Ventil at or Pati ent Synch rony? The ventilator should start inspiration at the time of onset of patients inspiration. The flow provid ed by the ven tila tor s hou ld meet the flow demand of the patient. The Ventilator Inspiratory time should match with the pa tien ts insp ira tory time.

41 Ventilator Patient Dys-synchrony

TRIGGER FLOW CYCLE ASYNCHRONY ASYNCHRONY ASYNCHRONY

1. Ineffective Triggering 2. Auto 1. Delayed Triggering Cycling 3. Double 2. Premature Triggering Cycling 4. Delayed triiiggering 42 INEFFECTIVE TRIGGGERING  One of the most common asynchronies  Failure of the patients inspiratory effort to initiate a ventilator breath.  Identified by  Visua l inspecti on of pati ent s expandi ng thoraci c vol ume but without delivery of ventilator breath.  Ventilator graphics which show a decrease in airway pressure with an increase in flow but no initiation of breath.

43 Ineffective triggering  What causes this?  Improper sensitivity of trigger threshold  Respiratory muscle weakness (disease related, critical illness neuromyopathy, electrolyte imbalances)  Intrinsic PEEP in COPD patients  Decreased respiratory drive ( Excessive sedatives)  Alkaline pH  External nebulizers  Higggpppyh Tidal volumes/High Pressure support decrease respiratory drive.

44 AUTO TRIGGERING Definition : Ventilator delivers an assisted breath that was not initiated by the patient

Causes : 1. Circui t lea ks (ET cu ff, ICTD wi th BPF etc ) 2. Fluid in the circuit 3. Cardiac oscillations (High cardiac output states) 4. Very low trigger threshold .

45 DOUBLE TRIGGERING  Patients inspiration continues after the ventilator inspiration and triggers another breath immediately after the inspiration.  Also called Breath Stacking Causes : 1. Hig h Vent ilatory deman d o f t he pat ient (ARDS) 2. Inappropriate settings ( Low tidal volume, Short inspi ratory time, Hig h cyc le thres ho ld)

46 A case of Morbid Obesityyyypy with Obesity hypoventilation syndrome. Note the low tidal volumes generated on PSV mode 47 DELAYED TRIGGERING Components of Triggering :  Trigger threshold : The pressure/flow that must be attained by the patients breath to trigger the v entilator.  Inspiratory Trigger Time (ITT) : Time from the initiation of effort to the Trigger thresh old .  Rise Time to Baseline Pressure (RTBP)

Insppyyiratory Delay Time ( ()IDT) = ITT + RTBP

48 DELAYED TRIGGERING

 An Inh erent probl em with all the conven tiona l mo des o f ventilation

 Can be overcome by  Newer modes of ventilation ( NAVA)  Newer methods of triggering ( Shape signal triggering)

49 Neurally Adjusted Ventilatory Assist (NAVA)

Diaphragmatic Electrical activity is sensed by an electrode placed in the esophagus and is used to trigger the breath and cycle into expiration.

50 Sinderby Nature Med 1999;5:1433 NEJM 2001;344 : 1986-1996 FLOW ASYNCHRONY Causes :  High Ventilatory demand (ALI/ARDS)  Low ventilatory settings ( Flow rate, Tidal volume, Pramp) What to do :  Treat reversible causes of air hunger (fever, acidosis)  Increase the tidal volume ( if feasible)  Increase the flow rate ( directly, or by decreasing inspiratory time, increasing pause)  Changgpe to pressure control mode with variable flow  Sedate /Paralyze the patient (last resort)

52 Patient of ARDS being ventilated using ARDS Network strategy (Tidal volume = 6 ml/kg, Body weight = 66 kg)

53 Tidal volume increased to 440 ml from 400 ml to improve the flow synchrony

54 Same patient during a spike of fever 39.2 C showing severe flow dyssynchrony

55 CYCLING ASYNCHRONY

 Delayed Cycling : Ventilator Ti > Patient Ti Ven tila tor continues IiInspira tion when actuall y expira tion has started.

 Premature Cycling : Ventilator Ti < Patient Ti Patients inspiratory effort continue into the expiratory phase of ventilator breath.

56 DELAYED CYCLING

Patient while weaning . Expiratory trigger sensitivity of 25 %

57 How to Manage :

 Decrease IIitnspiratory time  Decrease Tidal volume ( SCMV mode)  Increase Expiratory Trigger Sensitivity ( PSV mode)

58 Expiratory trigger sensitivity increased to 60 % to improve cycling synchrony.

59 A case of Acute severe asthma on SCMV mode. I : E ratio kept at 1: 3.3 to avoid auto PEEP. Ventilator shows double triggering 60 I : E ratio decreased to 1 : 2.5 along with control of bronchospasm. None of the other parameters changed. No further double triggering. Illustrates double triggering due to short inspiratory time and premature cycling

61 PATIENT VENTILATOR DYS-SYNCHRONY CLINICAL SIGNIFICANCE ??  Increases Work Of Breathing  Causes Ultra structural damage to the respiratory muscles.  Worsens Respiratory mechanics ( Auto PEEP)  Alters gas exchange ( Auto, double triggering – lower CO2)  Increased need for sedation  Longer duration of mechanical ventilation  Difficulty in weaning  Confounds lung protective ventilation ( Double breaths)  Sleep Fragmentation  Inability to tolerate NIV

62 Loops

 Pressure-Volume Loops

 Flow-Volume Loops Pressure-Volume Loop

VT LITERS 0.6

0.4

0.2

Paw cmH2O -60 40 20 0204060 Spontaneous Breath

VT Clockwise

0.6 CPAP

IitiInspiration 0.4 Expiration

0.2

Pressure cmH2O -60 40 20 0204060 Controlled Breath

Anticlockwise

VT LITERS 0.6

Expiration 0.4

Inspiration 0.2

Paw cmH2O -60 40 20 0204060 PEEP

P-V loop and PEEP….. Assisted Breath

VT Clockwise to LITERS Counterclockwise 0.6 Expiration 0.4

0.2 Assisted Breath Inspiration

Paw cmH2O -60 40 20 0204060

PEEP Lung Compliance Changes and the P-V Loop…. (Volume mode)

↑C C ↓C Preset VT

Volume

Pressure PIP levels

Constant VT………. Variable Pressure Lunggp Compliance Chan ggging in P-V Loop (pressure mode)………….

1.With surfactant 2. Emphysematous L ls ee lev T V RDS… lung

Volume

Pressure Preset PIP

Constant PIP……… variable VT Overdistension

V A = inspiratory pressure T LITERS B = upper inflection point 060.6 C = lower inflection point A

040.4

B 020.2

Paw C -60 -40 -20 0 20 40 60 cmH2O Insufficient flow

Normal Insufficient Flow olume VV

Cusping

Pressure

Flow-Volume Loop

Inspiration PIFR

Volume (ml)

VT

FRC

PEFR EitiExpiration Air Trapping

Inspiration PIFR

Volume (ml) Does not return VT to baseline

PEFR EitiExpiration Bronchodilator Response….. F-V loop AFTER Normal Bronchospasm Relief 3 3 3

2 2 2

1 1 1 . V . . V V V T LPS 1 1 1

2 2 2

3 3 3 SUMMARY

 Identify the correct waveforms to monitor  Spen d more time a t the bed sid e  Never Ignore any ventilator alarm

 Monitor P peak, P plat and expiratory limb of flow volume loop to diagnose changes in lung resistance or compliance.

 Identify Dys synchrony early and correct the cause.

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