VENTILATOR SETTINGS & THEIR CLINICAL APPLICATION

Guided By-

Dr. R L Suman (Assoc. prof.)

Presented by- Jaskaran singh (Resident doctor)

Chairperson & Head-

Dr.Suresh Goyal

Objectives 1. Pulmonary physiology

2. Assisted ventilation

3. Operating mode of ventilation

4. Case scenarios in neonate

5. Case scenarios in children

Pulmonary Physiology

The Airways• From trachea, the air passes through 10- 23 generations.

• First 16 generations = CONDUCTING ZONE, Contain no alveoli, No gas exchange Anatomic dead space.

• 17th - 19th generation = TRANSITIONAL ZONE, Alveoli start to appear, in the respiratory bronchioles.

• 20th - 22nd generations = RESPIRATORY ZONE, Lined with alveoli, alveolar ducts and alveolar sacs, which terminate the tracheobronchial tree

• Gas Exchange– Oxygenation & Ventilation (CO2 removal)

• Acid-Base Balance -- Participate in acid-base balance by removing

CO2 from the body

• Phonation

• Pulmonary Defense Mechanisms

• Pulmonary Metabolism and the Handling of Bioactive Materials

Lung Functions

• Change in volume (Lung expansion) produced by per unit change in pressure (Work of Breathing)

• Denotes the Ease of Distensibility of the lung and chest wall• Compliance is inverse of elasticity or elastic recoil• Low CL= Difficult lung expansion (Stiff Lung) High WOB

1. Usually related to condition that reduces FRC

2. Have a restrictive lung defect,low lung volume,low minute ventilation

3. May be compensated by increased rate.

Eg.HMD• High CL= Incomplete exhalation (lack of elastic recoil of lung) & CO2 elimination.

1. Conditions that increases FRC.

2. Steep slope on P-V curve.

3. Have an obstructive lung defect,airflow obstruction,incomplete exhalation,poor gas exchange.

• E.g. Emphysema

Lung Compliance (CL = ΔV ÷ ΔP)

Lung Compliance Changes and the P-V LoopLung Compliance Changes and the P-V Loop

Volume (mL)Volume (mL)

Preset PIP

VT

levels

PPawaw (cm H (cm H22O)O)

COMPLIANCEIncreasedNormalDecreased

COMPLIANCEIncreasedNormalDecreased

Pre

ssu

re T

arg

ete

d

Ven

tilatio

n

OverdistensionOverdistension

Volu

me (

ml)

Pressure (cm HPressure (cm H22O)O)

With little or no change in VTWith little or no change in VT

Paw risesPaw rises

NormalAbnormal

• Change in pressure per unit change in flow of gases.

• Due to friction b/w gas and air conducting system (Airways & ET tube)

• Airway resistance = inversely proportional to its radius raised to the 4th power.

• If airway lumen decreased half the resistance/work of breathing 16 times

• Newborns and young infants have inherently smaller airways, are especially prone to increase in airway resistance from inflamed tissues and secretions.

• High Resistance in dis. with airway obstruction like MAS and BPD

• During IMV: Airway resistance varies directly with length of ET & inversely with internal diameter of ET

• Cut ET short*, Use largest appropriate ET size, Suction regularly

Airway Resistance = (PIP-PEEP) ÷ Flow

• Resistance = Pressure change/ Flow

• ∆P(PIP - PEEP) can be treated as WOB

• In clinical settings, airway obstruction is one of most frequent causes of increased WOB Decreased Airflow Decreased Minute Ventilation Hypoventilation CO2 retention

• Prolonged high resistance High WOB Respiratory muscle fatigue Ventilatory Failure & Oxygenation Failure

Airway Resistance & Work of Breathing

• Time const.= Compliance × Resistance = TV / Flow• A pressure gradient between atmosphere and alveoli must be established to move

air into or out of the alveoli.• Tc is the time taken for the transthoracic pressure change to be transmitted as the

volume change in the lungs, i.e. the time it takes for airway pressure and volume changes to equilibrate b/w the proximal airway and the alveoli.

• For practical purposes, all pressure and volume delivery (inflation/ deflation) is complete (99%) after 5 Tc.

• Inspiratory Tc << Expiratory Tc • Patients with Decreased Compliance (Shorter Tc) ventilate with Smaller TV and

Faster Rates to minimize PIP• In pts with increased resistance (Long Tc), a fast rate results in short Ti & Te

Inadequate Ti results in lower TV, whereas insufficient Te results in inadvertent PEEP/ auto-PEEP/ intrinsic PEEP best ventilated with Slower rates and Larger TV.

Time constant Tc = Cl × R = ∆V/∆P × ∆P/V

Time constant

Condition Compliance(L/cm H2O)

Resistance(cmH2O/L/sec)

Time const.(sec)

Healthy neonate

0.005 20 0.1

HMD 0.001 20 Normal 0.02

MAS 0.003 100 0.3

Implication of CL, R, Tc

• During Mechanical Ventilation, inspiratory phase is active and high flow of air Low Tc So short Ti is sufficient in most situations

• Ventilator expiratory phase is passive, so Tc values are essentially applicable to expiratory time.

• Diseases of the lung parenchyma e.g. ARDS, HMD, Atelectasis, Pneumonia, Pulmonary edema, Pulmonary hemorrhage FRC is reduced as terminal airways become fluid-filled or collapsed

• The Approach to decreased FRC is to increase MAP to recruit atelectatic areas;(usually achieved by a higher PEEP).

• Decreased compliance requires a higher pressure gradient to achieve a given TV.

• Volume-Controlled MV PIP will be higher to achieve a given TV.

• Pressure-Controlled MV Given PIP may result in a lower TV.

• May respond to higher ventilator Rates (lungs empty and fill more quickly).

• If neither PIP nor Rate is increased sufficiently Hypercarbia

DISEASES OF DECREASED COMPLIANCE (Restrictive Diseases)

• Diseases that decrease the caliber of the airway lumen by edema, spasm, or obstruction. Eg.Asthma, Bronchiolitis, Cystic fibrosis etc.

• Increased resistance Impedes gas flow, Gas Trapping Intrapulmonary shunt and Dead space Hypoxia & Hypercarbia

• Increased resistance requires higher pressure for the gas flow to reach alveoli.

• Volume-Controlled MV Higher PIP is required to deliver given TV.

• Pressure-controlled MV TV is lower at the same PIP.

• Increased resistance Increases in Tc Necessitates Long Ti & Te

• If the ventilator Rate is too high and Ti & Te are too short Gas trapping Lung hyperinflation, pneumothorax, barotrauma, and reduction in compliance.

DISEASES OF INCREASED RESISTANCE (Obstructive Disease)

A. Oxygenation Failure: Hypoxemic respiratory failure

A.Severe hypoxemia (PaO2<40) that does not respond to supplemental O2, SpO2 < 90% despite FiO2 > 0.6

B.Pneumonia, Pulmonary edema, Pulmonary hemorrhage, and RDS, HMD.

• Ventilation Failure: Hypercarbic respiratory failure

• Decreased minute ventilation or increased physiologic dead space alveolar ventilation is inadequate Inability to maintain proper removal of CO2 Hyper capnia, Respiratory Acidosis

• Neuromuscular diseases

• Diseases that cause respiratory muscle fatigue due to increased workload (Asthma, COPD and Restrictive lung disease)

Respiratory failure can be of Mixed(both oxygenation & ventilation failure)

Respiratory Failure

Lung Volumes & Capacities

Alteration in Ventilatory Functions

• FRC= Volume of gas in the lungs after a normal tidal expiration

• No muscles of respiration are contracting at the FRC

• Here, Tendency of lung to contract = Tendency of the chest wall to

expand (Balance point between the inward elastic recoil of the lungs

and the outward elastic recoil of the chest wall)

• During inhalation above FRC Inspiratory muscles active

• During active exhalation below FRC Expiratory muscles active

Concept of FRC: Basis of PEEP Therapy

• Normally alveolar end expiratory pressure equilibrates with atmospheric pressure(i.e. zero pressure) and average pleural pressure is -5 cmH2O

• So alveolar distending pressure is 5 cmH2O (Alveolar-Pleural)

• This distending pressure is sufficient to maintain a normal end expiratory alveolar volume to overcome the elastic recoil of alveolar wall.

• If decreased compliance Inward elastic recoil of alveoli is increased alveolar collapse Intrapulmonary shunting.

• PEEP increases the alveolar end expiratory pressure Increases alveolar distending pressure Re-expansion/ Recruitment of collapsed alveoli Improves ventilation

• Thus, PEEP leads to increased V/Q ratio, improves oxygenation, decreased work of breathing

Concept of FRC: Basis of PEEP Therapy

Physiologic Dead Space= Anatomic + Alveolar

1.Anatomic dead space:• Volume of conducting airways, approx. 30% of TV• 1 ml/lb ideal body wt• Decrease in TV leads to relatively higher percentage of TV lost in anatomic

dead space• E.g. Neuromuscular dis., Drug Overdose

2.Alveolar dead space:• When ventilated alveoli are not adequately perfused• E.g. Decreased cardiac output, Pulmonary vasoconstriction etc.

•In health, Physiologic DS= Anatomic DS

Dead space ventilation

Assisted Ventilation

• Normal respiratory cycle of a spontaneous breath:

• Subatmosheric (Negative) intrapleural pressure

• Forces by inspiratory muscles intrapleural pressure more negative(-6 to -

8cm H2O ) Sucking of air into lungs

• During Expiration, respiratory muscles relax, elastic recoil of chest

exhalation

• This is called Negative Pressure ventilation

• Negative pressure ventilators Iron lung machines

Negative Pressure ventilation

Iron Lung Machine

• PPV causes pressure changes opposite to that of spontaneous breathing.

• During inspiration, Ventilator generates positive pressure in the airways to drive air into lungs

• The positive pressure to set on ventilator is based on disease status (severe HMD- more stiff lung, driving pressure needed for circuit etc.)

Positive Pressure ventilation

Ventilator Breath Cycle

Ventilator Settings & their Significance

• Increased FiO2 Increases PaO2 & thus oxygenation

• Very high FiO2 directly toxic to Retina, Lungs, Brain, Gut (free radical injury)

a) For pts with severe hypoxemia/ abnormal cardiopulmonary status: initial FiO2 is 80-100%, can be decreased to 50%

• Both FiO2 & MAP determine oxygenation

• Parameter more likely to be effective and less damaging should be used to increase PaO2

• E.g.– if FiO2 is > 0.6-0.7, increase MAP

if FiO2 is < 0.3-0.4, decrease MAP

b) For pts with mild hypoxemia/Normal Cardiopulmonary status: Initial FiO2 may be set 40-50%, change as per ABG

FiO2

• No positive pressure is safe

• PIP in part determines TV & Minute Ventilation

• Initial PIP: based on Chest movement & Breath sounds• Normal neonatal lungs 12-14 cm H2O• Mild to moderate lung disease 16-20• Severe lung disease 20-25

• Increase in PIP Increases TV, Increases CO2 elimination, Decreases PaCO2, Increases PaO2

• Inappropriately high PIP Increased risk of Air leaks & Chronic lung dis.(BPD)

• Inappropriately low PIP Lung collapse & insufficient ventilation Increased PaCO2, Decreased PaO2, Atelectasis

PIP

• PEEP in part determines Lung volume during expiratory phase, improves ventilation perfusion mismatch & prevents alveolar collapse

• A minimum physiological PEEP of 3 cmH2O should be used in most newborns/Infants

• In HMD Initial PEEP= 4-5 cmH2O (increase upto 8)

• Increased PEEP improves MAP & oxygenation but also reduces TV & CO2 elimination Increases PaCO2

• Inappropriately High PEEP over distended lungs, airleaks, decreased compliance, decreased cardiac output

PEEP

Rate

• Ti : Te Ratio should be kept as physiological as possible = Close to 1:2

• Insufficient Ti Inadequate TV delivery, CO2 retention

• Insufficient Te Air trapping

• Inverse Ti : Te (3:1 or 2:1) used only when conventional strategy fails

• Prolonged Expiratory (1:2 or 1:3) in MAS, Asthma

• Ti : Te ratio can be changed by manipulating one or more: Flow rate/ Ti/

Ti percentage/ Respi. Rate/ Minute Volume (TV x RR)

Ti & Te

• A minimum gas flow as required by the machine should be used (5-7 Lt/min.)

• Generally this parameter is not altered during the ventilation

• Very high gas flow increases Resistance, causes turbulence, air trapping & air leaks

• Low Flow Rate (0.5-3 l/min): produces sine waveform, But may cause hypercapnia, may not be enough to produce required PIP at high rates (Short Ti)

• High Flow Rate (4-10 l/min): produces more square waveform, necessary to attain high PIP at high rates, But may cause Barotrauma & Airleaks

Gas Flow Rate

Sine wave: • Smoother increase of pressure• More physiologic • But lower MAP is achieved for equivalent PIP

Square wave:• Constant peak flow during entire inspiratory phase• Higher MAP is achieved for equivalent PIP • Longer time at peak pressure• May open up atelectasis and improve distribution of ventilation• High pressure if applied to normal alveoli may result in barotrauma• Can impede venous return if reverse Ti:Te ratio is used

Wave Form

• TV in health= 8-10 ml/kg body wt

• During Ventilation, Initial TV = 10-12 ml/kg

• Lower TV (5-7 ml/kg) can be used (permissive hypercapnia) in

ARDS/ HMD to minimize the airway pressures and risk of

barotrauma.

• But Lower TV may lead to Acute hypercapnia, increased work of

breathing, severe acidosis & collapse.

Tidal Volume

Goals of Assisted Ventilation

• OXYGENATION(PAO2 )

• Depends on FiO2 & MAP(Area under curve P-T graph)

• MAP=K(PIP×Ti)+(PEEP×Te)

(Ti+Te)

Oxygenation(Pao2) α Fio2

PIP

Ti

K(Gas Flow,Wave form)

Advantage Disadvantage↑ Fio2 Minimizes barotrauma

Easily administeredFails to affect V/Q matchingDirect toxicity, especially >0.6

↑ PI Critical opening pressure,Improves V/Q matching

Barotrauma: Air leak, BPD

↑ PEEP Maintains FRC, prevents collapseSplints obstructed airwaysRegularizes respiration

Shifts to stiffer compliance CurveObstructs venous returnIncreases expiratory work and CO2

Increases dead space↑ TI Increases MAP without increases PI

Critical opening timeNecessitates slower rates,Lower minute ventilation for given PI — PEEP combination

↑ Flow Square wave — maximizes MAP Greater shear force, more barotraumaGreater resistance at greater flows

Manipulations to Increase Oxygenation

2) CO2 Elimination (PaCO2 & pH)α MV α RR

α TV α Driving pressure (PIP-PEEP) α Compliance of lung

Goals of Assisted Ventilation

Advantage Disadvantage

↑ Rate Easy to titrate Minimizes barotrauma

Maintains same dead space/TVMay lead to inadvertent PEEP

↑ PIBetter bulk flow (improved dead space/TV)More barotrauma

Shifts to stiffer compliance curve

↓ PEEP Widens compression PressureDecreases dead spaceDecreases expiratory loadShifts to steeper compliance curve

Decreases MAPDecreases oxygenation (alveolar collapse)Stops splinting obstructed /closed airways

↑ Flow Permits shorter TI, longer TE More barotrauma

↑ TEAllows longer time for passive expiration in face of prolonged time Constant

Shortens TI

Decreases MAPDecreases oxygenation

Manipulations to Increase Ventilation

Adequacy Of Alveolar Ventilation

• Oxygenation Index OI= MAP×Fio2×100

PaO2

>15 means severe repiratory distress >40 min in patient on conventionl ventilation, 2 samples

30 min apart indication for ECMO.• Ventilation Index VI=RR×PIP×PCO2

1000 >90 for 4hr means poor prognosis.

Classification of Mechanical Ventilators

The mechanical ventilator can control 4 primary variables during inspiration—Pressure, Volume, Flow and Time1.Pressure controlled ventilator ventilator controls trans respiratory system pressure i.e. airway pressure-body surface pressure.•Means that pressure level that is delivered to the pt will not vary in spite of changes in compliance or resistance.•Further classified as PPV & NPV•Trans respiratory pressure gradient is generated in both Causes lung expansion

Control Variables

2. Volume controlled ventilator:• Volume delivery remains constant with changes in compliance

& resistance, while the pressure varies.• Volume measurement and feedback signal is must

3. Flow controlled ventilator:• Allows the pressure to vary with changes in compliance &

resistance while directly measuring and controlling flow

4. Time controlled ventilator:• Measure and control inspiratory & expiratory time• Allows pressure and volume to vary with changes in compliance &

resistance

PRESSURE VENTILATION VOLUME VENTILATIONParameters set by the operator

• PIP, PEEP, Rate, FIO2, Ti • TV, PEEP, Rate, FIO2, Ti

Parameters determined by the ventilator

• TV, Te • PIP, Te

Advantages • Higher MAP with the same PIP• Lung protective for noncompliant lungs

• Guaranteed minute ventilation

Disadvantages • Does not accommodate for rapid changes in pulmonary compliance

• Not optimal for patients with an endotracheal tube with large leaks

• Minute ventilation not guaranteed • PIP May reach dangerous level if compliance is worsening

PRESSURE V/S VOLUME VENTILATION

• It combines two control variables (pressure & volume), that are regulated by independent feedback loops so that delivered breath switches b/w pressure control and volume control.

• Patient receives mandatory breaths that are Volume Targeted, Pressure Limited, and Time cycled.

• PRVC (pressure regulated volume control),• VAPS(volume assured pressure support), • VG(volume guarantied) is also work on dual mode.

Dual-Control Mode

• A ventilator supported breath is divided into 4 distinct phases: 1) Change from expiration to inspiration 2) Inspiration 3) Change from inspiration to expiration 4) Expiration.

• When 1 of the 4 variables (Pressure, Volume Flow & Time) is examined during a particular phase, it is termed as “Phase variable”

• Trigger Variable

• Limit Variable

• Cycle Variable

Phase variables

• What determines the start of inspiration?1. Time triggered: Breath is initiated and delivered when a preset time

interval has elapsed.• The rate control on ventilator is a time triggering mechanism. At given time

trigger interval, the ventilator automatically delivers one mechanical breath without regard to patient’s effort or requirement

2. Pressure triggered: Beginning of spontaneous inspiratory effort by pt Drop in airway pressure Sensed by ventilator as a signal to initiate and deliver a breath.

• The amount of negative pressure, a pt must generate to trigger the ventilator is Sensitivity Level (-1 to -5 cm H2O)

3. Flow triggered: More sensitive & responsive to pt’s effort1. Continuous flow is given(delivered=returned)pt effort part of flow

goes to pt returned flow< delivered flow sensed by ventilator to initiate breath

Trigger Variable

• What is set to its upper limit during inspiration?

• If one variable (volume/pressure/flow) is not allowed to rise above a

preset value during the inspiratory time, is termed as Limit Variable

• Inspiration does not end when this variable reaches its preset value,

breath delivery continues, but the variable is held at the fixed preset

value(max.)

• Pressure limited/ Volume limited/ Flow limited

Limit Variable

• What ends inspiration?

• This variable is measured and used as feedback signal by

ventilator to end inspiratory flow delivery, which then

allows exhalation to begin

• Most newer ventilators are Flow controlled, Time cycled

Cycle Variable

Operating Modes Of Ventilator

1) Spontaneous

2) Positive End Expiratory Pressure (PEEP)

3) Continuous Positive Airway Pressure (CPAP)

4) Bi-level Positive Airway Pressure (Bi-PAP)

5) Controlled Mandatory Ventilation (CMV)

6) Assist Control (AC)

7) Intermittent Mandatory Ventilation (IMV)

8) Synchronized Intermittent Mandatory Ventilation (SIMV)

9) Mandatory Minute Ventilation (MMV)

10) Pressure Support Ventilation (PSV)

1) Spontaneous

2) Positive End Expiratory Pressure (PEEP)

3) Continuous Positive Airway Pressure (CPAP)

4) Bi-level Positive Airway Pressure (Bi-PAP)

5) Controlled Mandatory Ventilation (CMV)

6) Assist Control (AC)

7) Intermittent Mandatory Ventilation (IMV)

8) Synchronized Intermittent Mandatory Ventilation (SIMV)

9) Mandatory Minute Ventilation (MMV)

10) Pressure Support Ventilation (PSV)

Operating Modes

Operating Modes11) Adaptive Support Ventilation (ASV)

12) Proportional Assist Ventilation (PAV)

13) Volume Assured Pressure Support (VAPS)

14) Pressure Regulated Volume Control (PRVC)

15) Volume Ventilation Plus (VV+)

16) Pressure Control Ventilation (PCV)

17) Airway Pressure Release Ventilation (APRV)

18) Inverse Ratio Ventilation (IRV)

19) Automatic Tube Compensation (ATC)

11) Adaptive Support Ventilation (ASV)

12) Proportional Assist Ventilation (PAV)

13) Volume Assured Pressure Support (VAPS)

14) Pressure Regulated Volume Control (PRVC)

15) Volume Ventilation Plus (VV+)

16) Pressure Control Ventilation (PCV)

17) Airway Pressure Release Ventilation (APRV)

18) Inverse Ratio Ventilation (IRV)

19) Automatic Tube Compensation (ATC)

Modes of Ventilation

• Basically there are three breath delivery techniques used with invasive positive pressure ventilation

• CMV – controlled mode ventilation• SIMV – synchronized• Spontaneous modes

• Three basic means of providing support for continuous spontaneous breathing during mechanical ventilation

• Spontaneous breathing

• CPAP

• Bi-PAP

• PSV – Pressure Support Ventilation

Spontaneous Modes

• Patients can breathe spontaneously through a ventilator circuit; sometimes called T-Piece Method because it mimics having the patient ET tube connected to a Briggs adapter (T-piece)

• Role of ventilator in this mode is to provide:

1. Inspiratory flow in a timely manner

2. Adequate flow to meet pt’s inspiratory demand (TV & inspiratory flow)

3. Provide adjunctive mode as PEEP to complement pt’s spontaneous

breath

• Disadvantage-May increase patient’s WOB with older ventilators

Spontaneous Modes

• PEEP increases end-expiratory/ baseline airway pressure to more

than atmospheric pressure.

• Not a “Stand-alone” Mode, rather it is applied in conjugation with

other modes.

• E.g. with CPAP, AC, SIMV

• Indications for PEEP:

1. Decreased FRC & Lung compliance

2. Refractory Hypoxemia, Intrapulmonary Shunting

PEEP (Positive End Expiratory Pressure)

Modes of Ventilation-CPAP

• Ventilators can provide CPAP for spontaneously breathing patients

o Positive intrapulmonary pressure (PEEP) is applied artificially

to the airways of a spontaneously breathing baby,

throughout the respiratory cycle, so that distending

pressure is created in the alveoli

o Distinct from IPPV or IMV in which breathing is taken over

by ventilator completely and increase in pressure occurs

during both inspiratory as well as expiratory phases

separately

o CPAP ≈ Half Filled Air Balloon

o Advantages-Ventilator can monitor the patient’s breathing

and activate an alarm if something undesirable occurs

• Independent positive airway pressures to both inspiration and expiration (IPAP & EPAP)

• IPAP provides positive pressure breaths and improves ventilation & hypoxemia d/t hypoventilation.

• EPAP is in essence CPAP which increases FRC, improves alveolar recruitment Improves PaO2

• Used in cases of Advanced COPD, Chronic ventilatory failure, Neuromuscular dis., Restrictive chest wall dis.

• Bi-PAP device can be used as CPAP• Initiate with IPAP=8, EPAP=4, then gradual increments of 2cmH2O in both

Bi-PAP: Bi-level Positive Airway Pressure

• PSV applies a preset pressure plateau to the airways for the duration of a spontaneous breath.

• A Pressure supported breath is: Patient Triggered: All ventilator breaths are triggered by patient Pressure Limited: Maximum pressure level can not exceed preset pressure

support level, TV varies with inspiratory flow demand. Flow Cycled: When pt’s inspiratory flow demand decreases to a preset minimal

value, inspiration stops and expiration starts.

• PSV can be used with spontaneous breathing in any ventilator mode (usually SIMV) as a PRESSURE BOOST

• Patient has control over Rate & Ti both.• Adv.: Increases spontaneous TV, Decreases spontaneous RR, Decreases

Work of breathing.

Pressure Support Ventilation-

Pressure Support Ventilation (PSV)

PSV during SIMV• Spontaneous breaths during SIMV can be supported with PSV (reduces

the WOB)

PCV – SIMV with PSV

10 cm H2O

35 cm H2O

• Ventilator delivers preset TV/Pressure at a Time triggered rate

• Ventilator controls both the pt’s TV & RR, So ventilator controls the pt’s Minute Volume

• Pt can not change RR or breath spontaneously, so only used when pt is on sedation/ respiratory depressants/ NM blockers.

• Indications of CMV:

1. Severely distressed pt, vigorously struggling Rapid inspiratory efforts Asynchrony/ Fighting in the initial stages CMV

2. Tetanus/ status epilepticus Interrupts ventilation delivery

3. Crushed chest injuries d/t Paradoxical chest movements

Controlled Mandatory Ventilation (CMV)

• Every breath delivers a preset mechanical TV (Volume Cycled) either assisted or controlled

• If Pressure/Flow triggered by Pt’s spontaneous effort = ASSIST

• If Time triggered by ventilator = CONTROL (Safety Net)

• Adv.: 1) Work of breathing is handled by ventilator,

• 2) Pt himself can control RR & therefore minute ventilation to normalize PaCO2

• Disadv.:Pt with inappropriately high respiratory drive* High assist rate despite low PaCO2 Hypocapnia & Respiratory alkalosis

• Indi.= Mostly used for a pt. with stable respiratory drive to provide full ventilatory support when pt. first placed on ventilator.

Assist Control (ACMV)

• Ventilator delivers control/mandatory breaths at a set time interval independent of pt’s

spontaneous respiratory rate.

• Allows the pt. to breath spontaneously at any TV in b/w control breaths

• Was the first widely used mode that allowed partial ventilatory support.

• Disadv.: Ventilator Asynchrony, Breath Staking.

• Not used nowadays

• Gave birth to SIMV

Intermittent Mandatory Ventilation (IMV)

• Mandatory breaths are synchronized with pt’s spontaneous breathing efforts to avoid asynchrony.

• Ventilator delivers a mandatory breath at or near the time of a spontaneous breath.

• The time interval (just prior to time triggered ventilator breath) in which ventilator is responsive to

pt’s spontaneous breath is= “Synchronization Window”, usual window is 0.5 sec*

• SIMV permits the pt. to breath spontaneously to any tidal volume the pt’ desires.

• The gas source for spont. breathing is supplied by “demand valve” always pt. triggered

• Spontaneous breaths taken by the pt. are TRULY SPONTANEOUS Rate & TV are dependent on pt,

humidified gas at selected FiO2 is given by ventilator.

Synchronized IMV (SIMV)

• SIMV allows patients with an intact respiratory drive to exercise inspiratory muscles between assisted breaths, making it useful for both supporting and weaning intubated patients

• Indication: To provide partial ventilatory support.

• When a pt placed on ventilator Full ventilatory support is appropriate for initial 24 hrs Then Trial of partial ventilatory support on SIMV (pt is actively involved in providing part of minute volume) Gradually decrease the mandatory rate as tolerated by the pt.

• Adv:1. Maintains respiratory muscle strength/ avoids muscle atrophy2. Reduces V/Q mismatch3. Decreases MAP4. FACILITATES WEANING ( Using small decrements* in mandatory rate)

Synchronized IMV (SIMV)

• neonatal ventilation has been accomplished using traditional time-cycled pressure-limited ventilation (TCPL).

• In this mode of ventilation, a peak inspiratory pressure is set by the operator, and during inspiration gas flow is delivere to achieve that set pressure, hence the term pressure-limited (PL) ventilation.

• The volume of gas delivered to the patient in this mode however varies depending on pulmonary mechanics such as compliance or stiffness of the lungs.

• At low compliance (‘stiff lungs’) such as occurs early in the course of respiratory distress syndrome (RDS), a given pressure generates lower tidal volume as compared to later in the course of the disease when the lungs are more compliant (‘less stiff’) when the same set pressure will lead to delivery of larger tidal volumes.

• This is important clinically as with improvement in compliance such as after exogenous surfactant therapy, the ventilator pressure has to be weaned by the operator to prevent alveolar over distension resulting from excessive tidal volume delivery.

TCPL( Time cycled pressure limit) ventilation

• An additional safety function of SIMV mode, that provides a

predetermined minute ventilation when pt’s spontaneous

breathing effort becomes inadequate.

• E.g. Apnea mandatory rate increased automatically to

compensate for decrease in minute ventilation caused by apnea.

• Prevents hypercapnea by automatically ensuring a minimum preset

minute ventilation.

Mandatory Minute Ventilation (MMV)

• PRVC provides volume support with the lowest possible PIP by changing the Peak Flow & Ti

• PRVC is a Dual control mode: Both TV & PIP can be controlled at same time

• Airflow resistance = (PIP-PEEP) ÷ Flow

• At a constant flow & PEEP, increased airflow resistance requires higher PIP. PRVC lowers the flow to reduce PIP.

• At a constant PIP, increased airflow resistance lowers flow. PRVC prolongs Ti to deliver the target TV.

• Works with CMV or SIMV (in viasys ventilator) mode

• Volume cycled, Time / Pt triggered

Pressure Regulated Volume Control (PRVC)

• VV+ is an option that combines two different dual mode volume targeted breath types: VC+ and VS

a) VOLUME CONTROL PLUS (VC+):

• VC+ is used to deliver mandatory breaths during AC and SIMV modes

• Intended to provide a higher level of synchrony than standard volume control ventilation.

• Target TV & Ti is set Ventilator delivers a single test breath using standard volume & flow to determine compliance Then Target pressures for subsequent breaths are adjusted accordingly to compensate for any TV differences

Volume Ventilation Plus (VV+)

b) VOLUME SUPPORT (VS):

• Target TV is set and ventilator uses variable pressure support levels to

provide the target TV.

• Only target TV is set (not the Ti or Mandatory Rate) ventilator delivers

a single spontaneous pressure support breath and then uses variable

pressure support levels to provide target TV.

• Mandatory Rate and minute ventilation is determined by triggering effort

of the patient.

• Used during “Awakening from anesthesia”

Volume Ventilation Plus (VV+)

• Like half Filled air balloon

• Pt. is allowed to breath spontaneously at an elevated baseline (i.e. CPAP). This elevated baseline

is released periodically to facilitate expiration.

• Newer mode, indicated in patients with lower compliance e.g. ARDS in which conventional

volume controlled ventilation requires very high PIP

• APRV can provide effective partial ventilatory support with a lower PIP in these pts.

Airway Pressure Release Ventilation (APRV)

• Delivers small Tidal volumes at very high rates, reduces the risk of barotrauma.

• Limited to the situations in which conventional ventilation has failed

• Categorized by rate and the method used to deliver the TV

High Frequency Ventilation (HFV)

Type of HFV Rate per min.

HFPPV (HF Positive Pressure Ventilation) 60 - 150

HFJV (HF Jet Ventilation) 240 - 660

HFOV (HF Oscillatory Ventilation) 480 - 1800

Use pressure control rather than volume control

SIMV mode can be used for any conditionApneic – SIMV mode with normal respiratory rateSpontaneous breathing (not adequate) -Set a minimum RR of 10- 20 /minTachypneic child fighting with ventilator -Set higher rate & adequately sedate the childIn addition to SIMV, every spontaneous breath can be pressure supported provided RR is not too high

Which mode for which condition ?

Case scenarios in Neonate

Retraction moderate or severeRR > 70/minCyanosis even after oxygenationIntractable apneic spellImpending or existing shock

PaO2 < 50, PCaO2 > 60, PH < 7.25

Indication for mechanical ventilation-Neonate

Setting Infant with NORMAL LUNG

FiO2 0.5 or to target SPO2 85 – 95 %

Respiratory rate 30-40 / minute to maintain normal PaCO2(higher rate is requried if cerebral odema & Raised ICT)

PIP 10 - 12 cm H2O , just enough to produce minimal chest rise ( VT 3-5ml/kg )

PEEP 4 - 5 cm H2O ( to achieve normal FRC : 7-9 post rib)

Ti 0.3-0.4 sec

Flow rate 4-6 l/min

Suggested initial ventilator setting in Birth asphyxia & apnea (Normal lung)

Target blood gas Ph 7.3 to 7.4, PaCO2 35 to 45 , PaO2 60 - 90

Setting Infant with RDS

FiO2 0.5 or to target SPO2 85 – 95 %

Respiratory rate 40-60 / minute(higher)

PIP 12-20 cm H2O(dependa upon severity) , just enough to produce minimal chest rise ( VT 3-5ml/kg )

PEEP 4 - 7 cm H2O ( to achieve normal FRC : 7-9 post rib)

Ti 0.2 - 0.3 sec

Flow rate 6-8 l/min

Suggested initial ventilator setting in Hyaline membrane disease / RDS

Target blood gas Ph 7.25 to 7.35, PaCO2 45 to 55 , PaO2 50 - 70

Setting Infant with MAS

FiO2 FiO2 to target SPO2 90 – 95 %

Respiratory rate 40-60 / minute

PIP 12-16 cm of H2O, just enough to produce minimal chest rise ( VT 3-5ml/kg )

PEEP Low to moderate PEEP (0 - 3 cm H2O)

Ti 0.4- 0.5 sec (Te 0.5 -0.7 sec, I:E = 1:3 – 1:4)

Flow rate 6-8 l/min

Suggested initial ventilator setting in MAS

Target blood gas Ph 7.25 to 7.35, PaCO2 45 to 55 , PaO2 50 - 70

Setting Infant with PPHN

FiO2 High FiO2 to target SPO2 90 – 95 %

Respiratory rate High rate 50-70 / minute

PIP Optimal PiP , just enough to produce minimal chest rise ( VT 3-5ml/kg )

PEEP 4 - 6 cm H2O

Ti 0.3- 0.4 sec

Flow rate 6-8 l/min

Suggested initial ventilator setting in PPHN

Target blood gas Ph 7.3 to 7.4, PaCO2 40 to 45 , PaO2 80 - 100

Observe infant for cyanosis , absence of retraction, chest wall movement.If ventilation is inadequate increase PIP by 1 cm H2O every few breath until air entry & chest rise adequate.If oxygenation is inadequate increase FiO2 by 0.05 every minute Until cyanosis abolish or SPO2 = 90-95 %.Initial pressure that result in adequate chest expansion & result in tidal volume 3-5 ml/kg should be taken as initial PIP setting.PEEP should not exceed 8 cm H2O in most situation.

Initiation

CLINICAL PARAMETERPink colour Adequate chest expansionAbsence of retractionAdequate air entryPrompt capillary filling within 2 secondNormal blood pressure

PULSE OXYMETERYOxygen saturation 90-95 %

BLOOD GASESPaO2 50-80 mm HgPaCO2 40-50 mm Hg (in chronic cases up to 60 mm Hg) PH 7.35-7.45

Adequacy of ventilation

Blood gas abnormamal

ity

Corrective measureFiO2 Rate PIP PEEP Ti

Hypercapnea PaCO2 > 50 mm Hg

Hypocapnea PaCO2 < 35 mm Hg

Hyperoxia PaO2 > 100 mm Hg

Hypoxemia PaO2 < 50 mm Hg

Change in ventilatory parameters

•Change should be made in short steps

•PIP &PEEP should be altered only 1 cm H2O at time

•Rate by 2 breath/min, FiO2 – 5%

•Blood gas estimation should be performed 20-30 min after every change

•To minimize adverse effect of one parameter simultaneously step up or step down various setting

FiO2 - 0.95, PIP-18 cm, PEEP- 4 cm H2O

Peep requirement go in consonance with FiO2

Changing ventilator setting

FiO2 PEEP

0.3 3

0.4 4

0.5 5

>o.8 8

•HMD weaning attempted on 3rd or 4th day especially at time when maximum diuresis occurs.•HMD it is important to reduce setting when compliance improves if not changed barotrauma will result.•Uncomplicated MAS or pneumonia can be weaned much earliar.•Iv aminophylline is started 24 hours prior to expected time of extubation .•Dexamethasone 0.15 mk/kg IV for post extubation stridor.•Infant is attached to CPAP mode before extubation.

Weaning from ventilator

Reduce PIP to 25 cm H2O

Alternately reduce PIP& FiO2

Reach PIP 20 cm, FiO2 0.6

Pulse oxymetry and PaO2

Clinical and PCaO2

PaCO2

FiO2 and PEEP

PIP

Rate and Ti

Weaning

Case scenarios in children

Respiratory failureApnea / respiratory arrestImpending Respiratory failureCardiac insufficiency & shock Neurological dysfunctionEverything ends hereAcute ventilatory failurePH < 7.3, PaCo2 > 50 mm HgSevere hypoxemiaPaO2 < 40, SaO2 < 75%

Indication of ventilation

In shock use higher FiO2 up to 1.o initially

In encephalopathy higher RR to cause hypocarbia (30-35 mm Hg)

Setting - Normal lung

PiP 15-20 cm H2O

Vt 6-8 ml/kg

PEEP 3-4 cm H2O

Rate 40/min (infant)20-30 /min (older children)

I:E ratio 1:2

Respiratory rate higher than normal

Higher PIP

Higher PEEP

Pneumonia

Pneumonia Normal lung

PiP 20-25 cm H2O 15-20 cm H2O

Vt 6-8 ml/kg 6-8 ml/kg

PEEP 4-5 cm H2O 3-4 cm H2O

Rate 40-50/min (infant)30-40 /min (older children)

40/min (infant)20-30 /min (older children)

I:E ratio 1:2 1:2

PEEP is kept low to prevent air trapping

Lower RR and prolonged Te to ensure air expulsion

Maintain oxygenation and accept hypercarbia up to 60 cm H2O

Asthma / Bronchiolitis

asthma Pneumonia

PiP <20-25 cm H2O 20-25 cm H2O

Vt 6-8 ml/kg 6-8 ml/kg

PEEP 3-4 cm H2O 4-5 cm H2O

Rate 30-40min (infant)20-30 /min (older children)

40-50/min (infant)30-40 /min (older children)

I:E ratio 1:3 to 1:4 1:2

High degree of collapsibility & very low compliance .

Don’t exceed PIP >35 cm H2O.

FiO2 preferably kept below < o.6 .

Hypercapnea to degree is acceptable.

ARDS

PiP < 35 cm H2O

Vt 4-6 ml/kg

PEEP 5-10 cm H2O

Rate 40/min (infant)20-30 /min (older children)

I:E ratio < 1:2 to inverse ratio

Measure to reduce barotrauma -•Permissive hypercapnea Higher PaCO2 is acceptable as long as PH > 7.25.•Permissive hypoxemiaPaO2 55to 60 mm Hg SaO2 of 88 – 90 % is acceptable for limiting PEEP & FiO2Inverse ratio ventilation-•Ratio of 2:1 and 4:1•Increase in mPaw during IRV help to reduce alveolar •collapse , shunting, V/Q mismatch•To achieve same ventilation you need lesser PIP & PEEP•Auto PEEP – also reduce shunting & improve oxygenation

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Don’t just increase FIO2 , increase PIP & PEEP

Saturation worsening with PEEP, suspect low cardiac output or air leak

Don’t forget other measure to improve oxygenation

Manage shock

Normal hemoglobin

Deepen sedation

Normothermia

Hypoxia

In asthma increase expiration (Te)

Decrease PEEP

Decrease Co2 production – sedation, cooling body

Et tube blockade / malpositioned

High PaCO2

Midzolam drip - 0.2 mg/kg loading dose

1-3 mcg/kg/min

Neonate - morphine

Skeletal muscle relaxant

Vecuronium – o.o5 mg/kg/hr

Pancuronium – longer acting (0.07 mg/kg/hr)

Analgesia & sedation

Position Et tube careEt suctionChest physiotherapyMaintaince fluid – restrictedMaintain blood sugar / ElectrolyteMaintain temprature Tropic feed / TPNNaso-oropharyngeal carePrevention of IVH- sound proofing

Nursing of child on ventilator

Fixation

Skin Safety

Hyperoxygenation

Gentle atraumatic suction

Asepsis

Et tube care & suction

DOPE

D = Displacement O = Obstruction

P = Pneumothorax E = Equipment failureCheck tube placement – is chest rising ? breath sound equal ?When in doubt take ET tube out & start manual ventilationCheck ABG & Chest x ray for pneumothorax & worsoning lung pathologyExamine ventilator & circuitExamine for shock & sepsisIf no other reason for hypoxemia :

Increase sedation /muscle relaxation

Patient fighting & desaturating

1. VENTILATOR-ASSOCIATED PNEUMONIA (VAP) 2. HYPOTENSION (d/t elevated intrathoracic pressures with decreased VR)3. GI Effects: Stress ulceration, Mild to moderate cholestasis4. VOLUTRAUMA = Damage caused by over distention; sometimes called high-

volume or high end-inspiratory volume injury 5. ATELECTOTRAUMA = Lung injury associated with repeated recruitment and

collapse, theoretically prevented by using adequate PEEP, sometimes called low-volume or low end-expiratory volume injury

6. BIOTRAUMA = Pulmonary and systemic inflammation caused by the release of mediators from lungs subjected to injurious mechanical ventilation

7. OXYGEN TOXIC EFFECTS = Damage caused by a high concentration of inspired oxygen

8. BAROTRAUMA = High-pressure–induced lung damage, clinically manifest by interstitial emphysema, pneumo mediastinum, subcutaneous emphysema, or pneumothorax.

Complications of Mechanical Ventilation

No clinical need for increased support – 24 hrs

Spontaneous respiration

FiO2 requirement < 0.5

Improving breath sound, decreased secretion

Improving chest x ray

Hemodynamically stable

LGB – muscle power & cough, Gag reflex

Encephalitis – improvement in GCS scale

Airway edema – air leak at below 20 cm H2O PiP

Weaning a child begins with improvement in clinical condition

How to wean-•Decrease FiO2 by 5% to keep SPO2 > 94 % (o.6).•Decrease PEEP by 1-2 cm to 4-5 cm H20.•Alternate FiO2 & PEEP after that.•Decrease SiMV rate by 3-4 breath/min to reach SiMV rate 5 .•Decrease PiP & pressure support ( 2 cm each time by titrating with Vt – 5 ml/kg ).•Ventilator rate & PiP can be changed alternatively.•ABG is true guide what you have done.When to stop further weaning-•SPO2 falls < 94% & require to increase FiO2.•Spontaneous respiration is fast & distress.•Agitation or lethargic.•Hypercarbia in blood gases.•e.g. simv rate reduced from 20 to 15/min but patient spontaneous rate increased from 25 to 50/min.

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Extubation procedure

•Keep NBM & adequate suctioning

•Keep O2 source ready

•Nebulization with beta stimulant or adrenaline

•Dexamethasone 0.15 mk/kg IV for post extubation stridor

•CPAP may be helpful in preventing reintubation

•ABG after 20 min of extubation

•Post extubation chest x ray - if clinical deterioration

When to extubate-

•SIMV respiratory rate of 5/min.

•pressure support of 5-10 cm above PEEP.

•PEEP - 5 cm H2O

•FiO2 < 0.3 with SPO2 > 94 %

•Good breath sound, minimal secretion

•Good airway reflexes

•Air leak around tube

•Awake patient

•Adequate muscle tone

•Normal electrolyte

Retraction, tachypnea

Restlessness, lethargy

Hypoxia

Hypercarbia

Acidosis ( early sign to react)

Chest x ray

Failure of extubation