principals of mechanical ventilation

8/14/2019 Principals of Mechanical Ventilation

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Principals ofPrincipals of

mechanical ventilationmechanical ventilationin Neonatesin Neonates

Dr Mohd MaghayrehDr Mohd Maghayreh

PRTH -IRBIDPRTH -IRBID


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Introductionntroduction Mechanical ventilation is an invasive life-Mechanical ventilation is an invasive life-

support procedure with many effects onsupport procedure with many effects on

the cardiopulmonary system.the cardiopulmonary system. The goal is to optimize both gasThe goal is to optimize both gas

exchange and clinical status at minimumexchange and clinical status at minimumFiO2 and ventilator pressure. TheFiO2 and ventilator pressure. The

ventilator strategy employed toventilator strategy employed toaccomplish this goal depends in part onaccomplish this goal depends in part onthe infants disease process.the infants disease process.


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Introductionntroduction Conventional positive pressureConventional positive pressure

ventilation remains the mainstay ofventilation remains the mainstay of

assisted ventilation in neonates despiteassisted ventilation in neonates despitethe development of new ventilatorythe development of new ventilatory

techniques.techniques.


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Complianceompliance Term used to describe the elastic properties ofTerm used to describe the elastic properties of

a system.a system.

It is estimated from simultaneous changes inIt is estimated from simultaneous changes involume and pressure.volume and pressure.

Compliance (mL/cmH2O) =Compliance (mL/cmH2O) = Change in volume (mL)Chan

ge in volume (mL)

Change in pressureChange in pressure (cmH2O)(cmH2O)


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Re sista ncee sista nce Term used to describe the property of theTerm used to describe the property of the

lungs that resists airflow.lungs that resists airflow.

The pressure is required to overcome theThe pressure is required to overcome the

elasticity of the respiratory system, toelasticity of the respiratory system, to

force gas through the airways (airwayforce gas through the airways (airwayresistance), and to exceed the viscousresistance), and to exceed the viscous

resistance of the lung tissue (tissueresistance of the lung tissue (tissue

resistance).resistance).


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).Re sist ance )cont.Re sist ance )contResistance (cmH2O/L/sec) =Resistance (cmH2O/L/sec) =Change in pressure (cmH2O)Change in pressure (cmH2O)

Change in flow (L/sec)Change in flow (L/sec)

Time constant of the respiratoryTime constant of the respiratory

system = Resistance X Compliancesystem = Resistance X Compliance


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Pu lm onary Me chanicsPu lm onary Me chanicsdurin g Assiste ddurin g Assiste d).Ve ntila tion )cont.Ve ntila tion ) cont

A time period equal to one time constant willA time period equal to one time constant willallow a 63% equilibration of pressure (andallow a 63% equilibration of pressure (andvolume) throughout the lungs.volume) throughout the lungs.

Not much equilibration of pressure andNot much equilibration of pressure andvolume occurs beyond 3 to 5 time constants.volume occurs beyond 3 to 5 time constants.

The time necessary for the lungs to inflate andThe time necessary for the lungs to inflate anddeflate will depend on the inspiratory anddeflate will depend on the inspiratory andexpiratory time constants.expiratory time constants.


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Pu lm onary Me chanicsPu lm onary Me chanicsdurin g Assiste ddurin g Assiste d).Ve ntila tion )cont.Ve ntila tion ) cont

ExampleExample

A healthy infant has resistance of 30cmA healthy infant has resistance of 30cmH2O/L/sec and compliance of 0.004 L/cmH2O.H2O/L/sec and compliance of 0.004 L/cmH2O.

One time constant of this infants respiratoryOne time constant of this infants respiratorysystem will be 0.12 seconds.system will be 0.12 seconds.

For complete equilibration of pressure at 5 timeFor complete equilibration of pressure at 5 time

constants or (5 X 0.12 seconds), an inspiratoryconstants or (5 X 0.12 seconds), an inspiratoryor expiratory phase of 0.6 seconds will beor expiratory phase of 0.6 seconds will benecessary, assuming equal inspiratory andnecessary, assuming equal inspiratory andexpiratory time constants.expiratory time constants.


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Pu lm onary Me chanicsPu lm onary Me chanicsdurin g Assiste ddurin g Assiste d).Ve ntila tion )cont.Ve ntila tion ) cont Infants with RDS typically have aInfants with RDS typically have a

decreased compliance, anddecreased compliance, and

consequently their time constant and theconsequently their time constant and thecorresponding time for pressure andcorresponding time for pressure andvolume equilibration will be shorter.volume equilibration will be shorter.

This means that the stiff lung in theseThis means that the stiff lung in these

infants (RDS) will complete inflation andinfants (RDS) will complete inflation anddeflation in a shorter time than normaldeflation in a shorter time than normallungs.lungs.


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Pu lm onary Me chanicsPu lm onary Me chanicsdurin g Assiste ddurin g Assiste d).Ve ntila tion )cont.Ve ntila tion ) cont Because infants with RDS have aBecause infants with RDS have a

decreased time constant, shortdecreased time constant, short

inspiratory and expiratory times may beinspiratory and expiratory times may beappropriate during the period of peakappropriate during the period of peakseverity of their disease, but theseverity of their disease, but thedifference is insignificant after recoverydifference is insignificant after recovery

from RDS when compliance is muchfrom RDS when compliance is muchhigher and the time constant becomeshigher and the time constant becomeslonger.longer.


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Lung Mechanics inLung Mechanics inDise ase St atesise ase St ates WW

orkorkV/QV/Q

matchinmatchin

gg

FRCFRC

ml/kml/k

gg

TimeTime

ConstaConsta

ntnt

secsec

ResistancResistanc

ee

cm/H20/mlcm/H20/ml

/s/s

ComplianComplian

cece

ml/cmH2Oml/cmH2O

DiseaseDisease

--------30ml/k

g

0.25sec20-40cm/H20/

ml/s

4-6ml/cmH2O

NormalNormaltermterm

RDSRDS

MASMAS


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Lung Mechanics inLung Mechanics in).Dise ase St ates ) cont.Dise ase St ates ) cont

WW

orkorkV/QV/Q

matchimatchi

ngng

FRCFRC

ml/kml/k

gg

TimeTime

ConstaConsta

ntnt

secsec

ResistanceResistance

cm/H20/ml/cm/H20/ml/

ss

CompliancComplianc

ee

ml/cmH2Oml/cmH2O

DiseasDiseas

ee

/ BPDBPD

AirAir

leakleak

VLBWVLBWapneaapnea


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont Tidal volumeTidal volume (for a given compliance) is(for a given compliance) is

determined by the pressure gradientdetermined by the pressure gradient

between inspiration and expiration, i.e.between inspiration and expiration, i.e.peak inspiratory pressure (PIP) minuspeak inspiratory pressure (PIP) minus

positive end expiratory pressure (PEEP).positive end expiratory pressure (PEEP).


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont

Inspiratory duration may partially determine theInspiratory duration may partially determine thetidal volume; very short inspiratory time maytidal volume; very short inspiratory time maynot allow pressure to be equilibratednot allow pressure to be equilibrated

throughout the respiratory system in infantsthroughout the respiratory system in infantswith normal lungs and with relatively long timewith normal lungs and with relatively long timeconstants, resulting in decreased tidal volume.constants, resulting in decreased tidal volume.So tidal volume can be decreased bySo tidal volume can be decreased byshortening the inspiratory time.shortening the inspiratory time.

Changes in ventilatorChanges in ventilatorfrequencyfrequencyhave a stronghave a strongeffect on CO2 elimination.effect on CO2 elimination.


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont OxygenOxygen

Oxygen exchange depends largely onOxygen exchange depends largely on

the matching of perfusion with ventilation.the matching of perfusion with ventilation. During assisted ventilation, oxygenationDuring assisted ventilation, oxygenation

is largely determined by the mean airwayis largely determined by the mean airway

pressure applied.pressure applied.


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont Mean airway pressureMean airway pressure is a measureis a measureofof

the average pressure to which the lungsthe average pressure to which the lungs

are exposed during the respiratory cycleare exposed during the respiratory cycleand may be calculated as:and may be calculated as:

Paw = (PIP PEEP) [Ti/ (Ti +Te)] +Paw = (PIP PEEP) [Ti/ (Ti +Te)] +

PEEPPEEP wherewhere Ti and Te are inspiratory andTi and Te are inspiratory and

expiratory times respectivelyexpiratory times respectively


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont Mean airway pressure is affected byMean airway pressure is affected by

different ventilator parameters shown indifferent ventilator parameters shown in

the graph below: (1) Flow rate (2) Peakthe graph below: (1) Flow rate (2) Peakinspiratory pressure (PIP) (3) Inspiratoryinspiratory pressure (PIP) (3) Inspiratory

time (4) Positive end expiratory airwaytime (4) Positive end expiratory airway

pressure (PEEP).pressure (PEEP).


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont Mean airway pressure will beMean airway pressure will be

augmented byaugmented by

increasing any of the following:increasing any of the following:

Inspiratory flow.Inspiratory flow.

PIP.PIP. Ratio of Ti to Te (I/E ratio).Ratio of Ti to Te (I/E ratio).

PEEP.PEEP.

Frequency (or rate) by shortening Te.Frequency (or rate) by shortening Te.


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Gas Exchange duringGas Exchange duringAssist ed Ve ntil atio nAssist ed Ve ntil atio n).) cont.) cont Special notes (cont.)Special notes (cont.)

Very high Paw may cause over-distention of airwaysVery high Paw may cause over-distention of airways

and alveoli, leading to an increase in dead space andand alveoli, leading to an increase in dead space andright-to-left shunting of blood in the lungs.right-to-left shunting of blood in the lungs.

Very high Paw can be transmitted to the intrathoracicVery high Paw can be transmitted to the intrathoracic

structures, causing decreased cardiac outputstructures, causing decreased cardiac outputsecondary to decreased venous return and increasedsecondary to decreased venous return and increased

pulmonary vascular resistance. Thus despitepulmonary vascular resistance. Thus despite

adequate PaO2 and oxygen content, oxygen transportadequate PaO2 and oxygen content, oxygen transport

may decrease.may decrease.


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Typ es of Me chanic alTyp es of Me chanic alVe ntila torse ntila tors Volume-cycled ventilators.Volume-cycled ventilators.

Pressure-limited, time-cycled,Pressure-limited, time-cycled,

continuous-flow ventilatorscontinuous-flow ventilators .. Patienttriggered ventilators (PTVPatienttriggered ventilators (PTV ).).


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Vo lu me-Cyc le dVo lu me-Cyc le dVentilatorsentilators Less frequently used attempting to ventilateLess frequently used attempting to ventilate

neonates.neonates.

Deliver a fixed volume irrespective of pressureDeliver a fixed volume irrespective of pressuregenerated unless pressure limits are set.generated unless pressure limits are set.

The tidal volume (generally 7-10 ml/kg but 4-7The tidal volume (generally 7-10 ml/kg but 4-7is usually adequate)is usually adequate)delivered to the patient isdelivered to the patient isobtained by adjusting the flow rate toobtained by adjusting the flow rate todetermine the time over which it is delivered,determine the time over which it is delivered,thus determining the I:E ratio.thus determining the I:E ratio.


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Vo lu me-Cyc le dVo lu me-Cyc le d).Ve ntila tors )cont.Ve ntila tors )cont In patients with RDS showing markedlyIn patients with RDS showing markedly

diminished compliance, the delivery of adiminished compliance, the delivery of a

normal tidal volume requires a very highnormal tidal volume requires a very highPIP.PIP.


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- ,,Tim e-Cyc le d,Tim e-Cyc le d,Co ntin uous- FlowCo ntin uous- FlowVentilatorsentilators Peak inspiratory pressure (pressure-Peak inspiratory pressure (pressure-

limited), and inspiratory timing (time-limited), and inspiratory timing (time-cycled) are selected.cycled) are selected.

Continuous flow of fresh heatedContinuous flow of fresh heatedhumidified gas is delivered to the patienthumidified gas is delivered to the patientthroughout the respiratory cycle.throughout the respiratory cycle.

It allows the infant to make spontaneousIt allows the infant to make spontaneousrespiratory efforts between ventilatorrespiratory efforts between ventilatorbreaths (Intermittent Mandatorybreaths (Intermittent MandatoryVentilation (IMV).Ventilation (IMV).


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,Cy cled, Con tin uou s-Fl owCy cl ed, Con tin uou s-Fl ow).Venti lators )cont.Venti lators )cont Spontaneously breathing infants whoSpontaneously breathing infants who

breathe out of phase with too many IMVbreathe out of phase with too many IMV

breaths thus fighting the ventilator maybreaths thus fighting the ventilator mayreceive inadequate ventilation and are atreceive inadequate ventilation and are at

an increased risk of air leak.an increased risk of air leak.


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PatientTriggeredPatientTriggered)Ve ntil ato rs ) PTVVe ntil ato rs ) PTV Modification of conventional ventilation inModification of conventional ventilation in

which the patient is able to initiatewhich the patient is able to initiate

ventilator breaths.ventilator breaths. There is a detector of thoracoabdominalThere is a detector of thoracoabdominal

movement, airflow, or airway pressure tomovement, airflow, or airway pressure to

indicate the onset of the inspiratoryindicate the onset of the inspiratoryefforts, and so triggering the ventilatorefforts, and so triggering the ventilator

setting.setting.


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PatientTriggeredPatientTriggeredVe ntila tors )PTV Ve ntila tors )PTV ).) cont.) cont If the infant does not generate anIf the infant does not generate an

adequate inspiratory effort during aadequate inspiratory effort during a

preset period, the ventilator will deliver apreset period, the ventilator will deliver anon triggered breath.non triggered breath.

Result in improved tidal volume andResult in improved tidal volume andblood gases but may lead toblood gases but may lead to

hyperventilation in tachypneic infants.hyperventilation in tachypneic infants.


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PatientTriggeredPatientTriggeredVe ntila tors )PTV Ve ntila tors )PTV ).) cont.) cont PTV is used in two modes:PTV is used in two modes:

Synchronized Intermittent MandatorySynchronized Intermittent Mandatory

Ventilation (SIMV)Ventilation (SIMV) A single triggered breath is given in equalA single triggered breath is given in equal

windows of time, with the other patientwindows of time, with the other patientbreaths occurring during each window notbreaths occurring during each window not

assisted.assisted. This way the rate can be slowly reducedThis way the rate can be slowly reduced

with all assisted breaths well-synchronized.with all assisted breaths well-synchronized.


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PatientTriggeredPatientTriggeredVe ntila tors )PTV Ve ntila tors )PTV ).) cont.) cont Assist / Control mode (A/C)Assist / Control mode (A/C)

All breaths are triggered, the patientAll breaths are triggered, the patient

controls the ventilator rate, and weaning iscontrols the ventilator rate, and weaning isaccomplished by reducing the PIP.accomplished by reducing the PIP.

Advantage is reduction in cerebral bloodAdvantage is reduction in cerebral blood

flow variability.flow variability.

Weaning from ventilator is facilitated in bothWeaning from ventilator is facilitated in both

A/C and SIMV.A/C and SIMV.

These ventilators reduce the duration ofThese ventilators reduce the duration of

assisted ventilation and facilitate weaning.assisted ventilation and facilitate weaning.


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Indic atio ns o fIndic atio ns o fMe chanic al Ve ntila tio ne chanic al Ve ntila tio n

Absolute indicationsAbsolute indications

If any of the following is present:If any of the following is present:

Severe hypoxemia with PaO2 less than 50Severe hypoxemia with PaO2 less than 50

mmHg despite FiO2 of 0.8.mmHg despite FiO2 of 0.8.

Respiratory acidosis with pH of less than 7.20Respiratory acidosis with pH of less than 7.20

to 7.25, or PaCO2 above 60 mmHg.to 7.25, or PaCO2 above 60 mmHg.

Severe prolonged apnea.Severe prolonged apnea.


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Indic atio ns o fIndic atio ns o fMe chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont Relative indicationsRelative indications

Frequent intermittent apneaFrequent intermittent apnea

unresponsive to drug therapy.unresponsive to drug therapy. Early treatment when use of mechanicalEarly treatment when use of mechanical

ventilation is anticipated because ofventilation is anticipated because of

deteriorating gas exchange.deteriorating gas exchange. Relieving work of breathing in an infantRelieving work of breathing in an infant

with signs of respiratory difficulty.with signs of respiratory difficulty.

Initiation of exogenous surfactantInitiation of exogenous surfactant


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Ef fects o f Sp ecificEf fects o f Sp ecificInterve ntio ns o n Bl oodInterve ntio ns o n Bl oodGasesases Peak inspiratory pressure (PIP):Peak inspiratory pressure (PIP):

Changes in PIP will determine the pressure gradientChanges in PIP will determine the pressure gradient

between the onset and end of inspiration and thusbetween the onset and end of inspiration and thus

affect alveolar ventilation.affect alveolar ventilation. Increase in PIP will:Increase in PIP will:

Increase tidal volume.Increase tidal volume.

Increase CO2 elimination and decrease PaCO2.Increase CO2 elimination and decrease PaCO2.

Raise Paw and thus improve oxygenation.Raise Paw and thus improve oxygenation.


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Pe ak Insp iratoryPe ak Insp iratory)Pr essu re ) PI PPr essu re ) PI P Clinical assessment of chest movement shouldClinical assessment of chest movement should

be performed before and after changes in PIP.be performed before and after changes in PIP.

High levels of PIP can cause:High levels of PIP can cause: An increased risk of barotraumas with resultant airAn increased risk of barotraumas with resultant air

leaks.leaks.

An increased risk of bronchopulmonary dysplasia.An increased risk of bronchopulmonary dysplasia.

Impaired cardiac function.Impaired cardiac function.

The magnitude of the tidal volume, rather thanThe magnitude of the tidal volume, rather thanthat of PIP, correlates best with lung injury.that of PIP, correlates best with lung injury.


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re)) PEEP) PEEP Adequate PEEP will increase PaO2 by:Adequate PEEP will increase PaO2 by:

Preventing alveolar collapse.Preventing alveolar collapse.

Maintaining lung volume at the end ofMaintaining lung volume at the end ofexpiration.expiration.

Improving the ventilation-perfusionImproving the ventilation-perfusion

relationshiprelationship


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re).) PEEP - c ont.) PEEP - cont

Elevation of PEEP will decrease tidal volume andElevation of PEEP will decrease tidal volume and

consequently increase PaCO2 by:consequently increase PaCO2 by:

Altering the pressure gradient between inspirationAltering the pressure gradient between inspiration

and expiration, and consequently affecting CO2and expiration, and consequently affecting CO2elimination.elimination.

Use of a PEEP of more than 5-6 cmH2O mayUse of a PEEP of more than 5-6 cmH2O may

decrease lung compliance, leading to a decrease indecrease lung compliance, leading to a decrease in

tidal volume and to alveolar hypoventilation, andtidal volume and to alveolar hypoventilation, andconsequently causing an increase PaCO2.consequently causing an increase PaCO2.


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re).) PEEP - c ont.) PEEP - cont

For the same magnitude of pressure change,For the same magnitude of pressure change,

decrease in PEEP has a larger effect on tidaldecrease in PEEP has a larger effect on tidal

volume than increase in PIP.volume than increase in PIP.

Thus a decrease in PEEP should beThus a decrease in PEEP should be

considered when CO2 retention occurs,considered when CO2 retention occurs,

especially if oxygenation is not a problem.especially if oxygenation is not a problem.


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re)) PEEP) PEEP Adequate PEEP will increase PaO2 by:Adequate PEEP will increase PaO2 by:

Preventing alveolar collapse.Preventing alveolar collapse.

Maintaining lung volume at the end ofMaintaining lung volume at the end ofexpiration.expiration.

Improving the ventilation-perfusionImproving the ventilation-perfusion

relationshiprelationship


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re).) PEEP - c ont.) PEEP - cont Increase in PEEP will raise Paw andIncrease in PEEP will raise Paw and

improve oxygenation, but use of veryimprove oxygenation, but use of very

high PEEP does not benefit oxygenationhigh PEEP does not benefit oxygenationmore and can cause:more and can cause:

Impaired venous return.Impaired venous return.

Decreased cardiac output.Decreased cardiac output. Decreased oxygen transport.Decreased oxygen transport.


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Po sit iv e En d-o sit iv e En d-Ex piratory Pressu reEx piratory Pressu re).) PEEP - c ont.) PEEP - cont A minimum PEEP of 3 to 4 cmH2O isA minimum PEEP of 3 to 4 cmH2O is

recommended because endotrachealrecommended because endotracheal

intubation eliminates the activeintubation eliminates the activemaintenance of functional residualmaintenance of functional residual

capacity done by the infant by vocalcapacity done by the infant by vocal

cord adduction.cord adduction.


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)F requency ) Ra teF requency ) Ra te Changes alter alveolar ventilation and thus PaCO2Changes alter alveolar ventilation and thus PaCO2

(decrease PaCO2).(decrease PaCO2).

Use of a moderately high frequency (60 breaths perUse of a moderately high frequency (60 breaths per

minute) allows for a reduction in PIP and leads to aboutminute) allows for a reduction in PIP and leads to abouta 50% decrease in the incidence of pneumothorax ina 50% decrease in the incidence of pneumothorax in

infants with RDS.infants with RDS.

Most neonates can tolerate high frequencies (60-70Most neonates can tolerate high frequencies (60-70

breaths per minute) and short expiratory times withoutbreaths per minute) and short expiratory times withoutmarked gas trapping as they have short timemarked gas trapping as they have short time

constants.constants.


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Frequency ) Ra te Frequency ) Ra te .contcont Ventilation with high frequency (> 60 breaths perVentilation with high frequency (> 60 breaths per

minute) may facilitate the synchronization of patientminute) may facilitate the synchronization of patient

effort to ventilator rate while reducing ventilator fightingeffort to ventilator rate while reducing ventilator fighting

and the need for sedation or paralysis.and the need for sedation or paralysis. When high frequency is used in conventionalWhen high frequency is used in conventional

ventilators, the resultant short Ti may decrease tidalventilators, the resultant short Ti may decrease tidal

volume.volume.

Frequency changes alone, with constant I/E ratio,Frequency changes alone, with constant I/E ratio,usually do not alter Paw, and so do not alter PaO2.usually do not alter Paw, and so do not alter PaO2.


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Ra tio o f Insp ir atory toRa tio o f Insp ir atory toEx pir atory Tim ex pir atory Tim e The major effect of changes in I:E ratio isThe major effect of changes in I:E ratio is

on Paw and thus oxygenation.on Paw and thus oxygenation.

Reversed I/E ratios (longer Ti than Te)Reversed I/E ratios (longer Ti than Te)

may increase PaO2 and may also lead tomay increase PaO2 and may also lead to

an increase in the incidence ofan increase in the incidence ofpneumothorax.pneumothorax.


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Ra tio o f Insp ir atory toRa tio o f Insp ir atory toExpiratory Timexpiratory Time For the same changes in Paw, changesFor the same changes in Paw, changes

in I:E ratio do not increase oxygenationin I:E ratio do not increase oxygenationas much as changes in PIP or PEEP.as much as changes in PIP or PEEP.

Changes in I/E ratio do not usually alterChanges in I/E ratio do not usually altertidal volume (unless Ti or Te become tootidal volume (unless Ti or Te become tooshort, and inspiration or expirationshort, and inspiration or expiration

become incomplete), so CO2 eliminationbecome incomplete), so CO2 eliminationis usually not altered by changes in theis usually not altered by changes in theI:E ratio.I:E ratio.


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Inspiratory andInspiratory andExpiratory Timesxpiratory Times The effect of changes in Ti and TeThe effect of changes in Ti and Te

largely depends on the time constants.largely depends on the time constants.

Absolute durations of Ti vary in differentAbsolute durations of Ti vary in differentdisease processes and depend on thedisease processes and depend on the

inspiratory time constant.inspiratory time constant.

Ti of 1.0 second or longer leads to activeTi of 1.0 second or longer leads to activeexpiration, fighting the ventilator, slowerexpiration, fighting the ventilator, slower

weaning, and a high incidence ofweaning, and a high incidence of

pneumothorax.pneumothorax.


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Inspiratory andInspiratory andExpiratory TimesExpiratory Times).) cont.) cont

Prolonged Ti may impede venous return and impairProlonged Ti may impede venous return and impair

oxygen transport.oxygen transport.

Inspiratory times shorter than 0.2 to 0.3 seconds canInspiratory times shorter than 0.2 to 0.3 seconds can

lead to incomplete inspiration.lead to incomplete inspiration. In very short expiratory time (Te), expiration may beIn very short expiratory time (Te), expiration may be

incomplete and gas trapping in the lungs increases,incomplete and gas trapping in the lungs increases,

leading to lung overdistention and decreasedleading to lung overdistention and decreased

compliancecompliance


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Inspiratory andInspiratory andExpiratory TimesExpiratory Times).) cont.) cont Gas trapping will produce inadvertentGas trapping will produce inadvertent

PEEP which results in a reduction in thePEEP which results in a reduction in the

pressure gradient between inspirationpressure gradient between inspirationand expiration, leading to a decrease inand expiration, leading to a decrease in

tidal volume and elevation of PaCO2,tidal volume and elevation of PaCO2,

and increases the risk of pneumothorax.and increases the risk of pneumothorax.


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Insp ir ed Oxyg enInsp ir ed Oxyg en)Co ncentra tion ) FiO2Co ncentra tion ) FiO2 Increase in FiO2 alters alveolar oxygen tension,Increase in FiO2 alters alveolar oxygen tension,

provides a larger diffusion gradient, and improvesprovides a larger diffusion gradient, and improves

oxygenation.oxygenation.

Oxygen and Paw should be balanced to minimize lungOxygen and Paw should be balanced to minimize lungdamage.damage.

During weaning, maintenance of appropriate PawDuring weaning, maintenance of appropriate Paw

allows reduction in FiO2, however Paw should beallows reduction in FiO2, however Paw should be

reduced before a very low FiO2 is reached. Ifreduced before a very low FiO2 is reached. Ifdistending pressure is not decreased until a low FiO2 isdistending pressure is not decreased until a low FiO2 is

reached, a high incidence of air leak is observed.reached, a high incidence of air leak is observed.


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Flowlo w Flow rates of 5-10 L/min are sufficientFlow rates of 5-10 L/min are sufficient

under most circumstances in neonates.under most circumstances in neonates.

Higher inspiratory flows are neededHigher inspiratory flows are neededwhen Ti is shortened in larger infants towhen Ti is shortened in larger infants to

ensure an adequate pressure rise andensure an adequate pressure rise and

delivery of the desired PIP.delivery of the desired PIP. High flows can lead to turbulence, anHigh flows can lead to turbulence, an

increase in resistance, and gas trappingincrease in resistance, and gas trapping


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Ef fects o f Ve ntila torEf fects o f Ve ntila torSe ttin g Ch anges onSe ttin g Ch anges onBlo od Ga seslo od Ga sesEffectEffect

PaO2PaO2PaCO2PaCO2Ventilator settingVentilator setting

changeschanges

IncreaseDecreaseIncrease PIPIncrease PIP

IncreaseIncreaseIncrease PEEPIncrease PEEP

IncreaseDecreaseIncrease rateIncrease rate

Increase--------Increase I:E ratioIncrease I:E ratio

Increase-------Increase FiO2Increase FiO2

IncreaseDecreaseIncrease flowIncrease flow


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Starting VentilatorSt arting Ventila torSettingetting Intubate infant with an endotracheal tubeIntubate infant with an endotracheal tube

according to body weight.according to body weight.

During intubation, infants requireDuring intubation, infants require

fractional inspired oxygen FiO2 that isfractional inspired oxygen FiO2 that is

10% higher than what they were10% higher than what they werereceiving before mechanical ventilation.receiving before mechanical ventilation.


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Guidelin es f orGuidelin es f orEn dotra cheal Tu beEn dotra cheal Tu beSizeize

Endotracheal tubeEndotracheal tube

internal diameterinternal diameterInfant weight(gm)Infant weight(gm)

2.5mm< 1,000gm

3.0mm1,000 - 2,000

3.5mm2,000 - 3,000

3.5 - 4.00mm> 3,000


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Initia l Settin g o fInitia l Settin g o fMe chanic al Ve ntila tio ne chanic al Ve ntila tio n PIP is determined by hearing good breath sounds andPIP is determined by hearing good breath sounds and

good lung expansion.good lung expansion.

FiO2 is determined according to patient need.FiO2 is determined according to patient need.

Ti should not be prolonged because of risk of alveolarTi should not be prolonged because of risk of alveolarover-distention. Start with 0.25 seconds and do notover-distention. Start with 0.25 seconds and do not

exceed 0.5 seconds (unless there are specialexceed 0.5 seconds (unless there are special

indications).indications).

Respirator rate should not ordinarily exceed 80Respirator rate should not ordinarily exceed 80breaths/min to allow sufficient time for exhalation.breaths/min to allow sufficient time for exhalation.


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Initia l Settin g o fInitia l Settin g o fMe chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont

Initial settingsInitial settings

As indicatedAs indicatedFio2Fio2

8-10l/min8-10l/minSystemic flowSystemic flow

60 breaths / min60 breaths / minRateRate

1:1.25 - 1:41:1.25 - 1:4Ti/TeTi/Te18 - 22cm H2018 - 22cm H20

Good breath soundsGood breath sounds

PIPPIP

3 - 5cm H203 - 5cm H20PEEPPEEP


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Su bsequent Se ttin gs o fSu bsequent Se ttin gs o fMe chanic al Ve ntila tio ne chanic al Ve ntila tio n Measure arterial blood gases half anMeasure arterial blood gases half an

hour after the initial setting and adjust thehour after the initial setting and adjust the

setting accordingly. (Table)setting accordingly. (Table)

Although it is tempting to try to lowerAlthough it is tempting to try to lower

PaCO2 by increasing the respiratory ratePaCO2 by increasing the respiratory raterather than by adjusting ventilatoryrather than by adjusting ventilatory

pressure, data suggest that this can notpressure, data suggest that this can not

be without risk.be without risk.


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Su bsequent Se ttin gs o fSu bsequent Se ttin gs o fMe chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont

This is because as respiratory rate increases, theThis is because as respiratory rate increases, the

absolute time for expiration decreases, and if itabsolute time for expiration decreases, and if it

decreases to less than three time constants fordecreases to less than three time constants for

expiration, gas trapping and alveolar over-distensionexpiration, gas trapping and alveolar over-distensionmay occur.may occur.

The entire cardiopulmonary status of the infant must beThe entire cardiopulmonary status of the infant must be

kept in mind as vigorous attempts to control PaCO2kept in mind as vigorous attempts to control PaCO2

may result in worsened lung injury.may result in worsened lung injury.


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Su bsequent Se ttin gs o fSu bsequent Se ttin gs o fMe chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont

One can allow the PaCO2 to increase to 45- 55 torr orOne can allow the PaCO2 to increase to 45- 55 torr or

above in infants with severe respiratory distress.above in infants with severe respiratory distress.

Infants with poor pulmonary blood flow because ofInfants with poor pulmonary blood flow because of

hypotension, hypovolemia, cardiac failure, or highhypotension, hypovolemia, cardiac failure, or highpulmonary vascular resistance may have low PaO2,pulmonary vascular resistance may have low PaO2,

and treatment should be directed to improve pulmonaryand treatment should be directed to improve pulmonary

blood flow, blood pressure and volume, and cardiacblood flow, blood pressure and volume, and cardiac

output.output.


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Su bsequent Se ttin gsSu bsequent Se ttin gsof Me chanicalof Me chanical).Ve ntila tion )cont.Ve ntila tion ) cont PIPPIPPEEPPEEPSubsequentSubsequent

settingssettings

IncreaseLow PaO2 ,Low PaO2 ,

Low PaCo2Low PaCo2IncreaseLow PaO2 ,Low PaO2 ,

High PaCo2High PaCo2

DecreaseHigh PaO2 ,High PaO2 ,High PaCo2High PaCo2

DecreaseHigh PaO2 ,High PaO2 ,

Low PaCo2Low PaCo2


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Obtain an initial blood gas within 15-30Obtain an initial blood gas within 15-30minutes of starting mechanicalminutes of starting mechanicalventilation.ventilation. Obtain a blood gas within 15-30 minutes of anyObtain a blood gas within 15-30 minutes of any

change in ventilator settings.change in ventilator settings.

Obtain a blood gas every 6 hours unless aObtain a blood gas every 6 hours unless asudden change in the infant's condition occurs.sudden change in the infant's condition occurs.

Continuous monitoring of the O2 saturationContinuous monitoring of the O2 saturation

level as well as the HR and RR is necessary.level as well as the HR and RR is necessary.

Mo nitorin g Th e InfantMo nitorin g Th e Infantdurin g Me chanic aldurin g Me chanic alVe ntil atio ne ntil atio n


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De terio ration durin gDe terio ration durin gMe chanic al Ve ntila tio ne chanic al Ve ntila tio n Sudden clinical deteriorationSudden clinical deterioration

Mechanical or electrical ventilator failure.Mechanical or electrical ventilator failure.

Disconnected tube or leaking connection.Disconnected tube or leaking connection. Endotracheal tube displacement orEndotracheal tube displacement or

blockage.blockage.

Pneumothorax.Pneumothorax.


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De terio ration durin gDe terio ration durin gMe chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont Gradual deteriorationGradual deterioration

Inappropriate ventilator setting.Inappropriate ventilator setting.

Intraventricular hemorrhage.Intraventricular hemorrhage. Baby fighting against ventilator.Baby fighting against ventilator.

PDA.PDA.

Anemia.Anemia.

Infection.Infection.


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Pa ralysis and Se datio na ralysis and Se datio n The use of neuromuscular blockade is not routinelyThe use of neuromuscular blockade is not routinely

indicated.indicated.

It has been advocated in infants requiring mechanicalIt has been advocated in infants requiring mechanicalventilation with a high rate or pressure, and whoventilation with a high rate or pressure, and who

become increasingly agitated when their spontaneousbecome increasingly agitated when their spontaneous

respiration is out of phase with the ventilator, resultingrespiration is out of phase with the ventilator, resulting

in decreased effectiveness of mechanical support.in decreased effectiveness of mechanical support.


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Pa ralysis and Se datio nPa ralysis and Se datio n).) cont.) cont Paralysis may worsen oxygenation in infants with RDSParalysis may worsen oxygenation in infants with RDS

as it may result in decreased dynamic lung compliance,as it may result in decreased dynamic lung compliance,

increased airway resistance, and the removal of theincreased airway resistance, and the removal of the

infants respiratory effort contribution to tidal breathing.infants respiratory effort contribution to tidal breathing.

As a result, it is necessary to increase ventilatorAs a result, it is necessary to increase ventilator

pressure after initiation of neuromuscular blockade.pressure after initiation of neuromuscular blockade.


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Pa ralysis and Se datio nPa ralysis and Se datio n).) cont.) cont Sedation is useful when agitationSedation is useful when agitation

interferes with ventilatory support andinterferes with ventilatory support and

when infants fight the ventilator.when infants fight the ventilator. Phenobarbital decreases the variability inPhenobarbital decreases the variability in

mean arterial pressure and intracranialmean arterial pressure and intracranial

pressure associated with endotrachealpressure associated with endotrachealsuctioning.suctioning.


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Weaningeaning When the patient is stable, FiO2 and PIP are weanedWhen the patient is stable, FiO2 and PIP are weaned

first.first.

Decrease PIP as tolerated and as chest riseDecrease PIP as tolerated and as chest rise

diminishes.diminishes. When PIP is around 20, attention is directed to FiO2When PIP is around 20, attention is directed to FiO2

and then to the respiratory rate alternating with eachand then to the respiratory rate alternating with each

other, in response to assessment of chest excursion,other, in response to assessment of chest excursion,

blood gas results, and oxygen saturation.blood gas results, and oxygen saturation.


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).W eanin g )cont.W eanin g ) cont As frequency is decreased, Te should beAs frequency is decreased, Te should be

prolonged.prolonged.

For larger infants, weaning toFor larger infants, weaning toendotracheal CPAP may begin when PIPendotracheal CPAP may begin when PIP

has been stable between 15-18has been stable between 15-18cmH2O,cmH2O,

and FiO2 is less than 0.4.and FiO2 is less than 0.4. The infant can be weaned to oxygenThe infant can be weaned to oxygen

hood when he/she requires less than 4hood when he/she requires less than 4

cmH2O of end expiratory pressure.cmH2O of end expiratory pressure.


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).W eanin g )cont.W eanin g ) cont For infants weighing less than 1,750 gm, when PIP isFor infants weighing less than 1,750 gm, when PIP is

less than 15 cmH2O and FiO2 is less than 0.3, start toless than 15 cmH2O and FiO2 is less than 0.3, start to

decrease the respiratory rate gradually to 15-20decrease the respiratory rate gradually to 15-20

breaths/min and then wean directly to nasal CPAP ifbreaths/min and then wean directly to nasal CPAP ifavailable.available.

In most infants, when ventilator frequency ofIn most infants, when ventilator frequency of

approximately 15 breaths per minute is tolerated,approximately 15 breaths per minute is tolerated,endotracheal CPAP may be tried for a short periodendotracheal CPAP may be tried for a short period

before extubation.before extubation.


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).W eanin g )cont.W eanin g ) cont Atelectasis after extubation is common in pretermAtelectasis after extubation is common in preterm

infants recovering from RDS. Use of nasal CPAP mayinfants recovering from RDS. Use of nasal CPAP may

prevent atelectasis.prevent atelectasis.

Steroids are not routine before estuation, but if thereSteroids are not routine before estuation, but if therewas prolonged intubation or previous failed attempts ofwas prolonged intubation or previous failed attempts of

extubation, a short course of steroids may facilitateextubation, a short course of steroids may facilitate

extubation.extubation.

If strider caused by laryngeal edema develops afterIf strider caused by laryngeal edema develops afterextubation, racemic epinephrine aerosols and steroidsextubation, racemic epinephrine aerosols and steroids

may be helpful.may be helpful.


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Ph ysio thera py andPh ysio thera py andSuctioninguctioning Tracheal suctioning and chest physiotherapy should beTracheal suctioning and chest physiotherapy should be

minimized in infants with HMD in the first few days afterminimized in infants with HMD in the first few days after

birth because their secretions are scant.birth because their secretions are scant.

Physiotherapy and suctioning should be done toPhysiotherapy and suctioning should be done toprevent the development of atelectasis, especially inprevent the development of atelectasis, especially in

premature infants. However, some infants show acutepremature infants. However, some infants show acute

deterioration of blood gases.deterioration of blood gases.


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Ph ysio thera py andPh ysio thera py and).Su ctio nin g )c ont.Su ctio nin g )c ont Continuous monitoring of O2 saturationContinuous monitoring of O2 saturation

by pulse oximetry is recommended ifby pulse oximetry is recommended if

physical therapy is prescribed.physical therapy is prescribed.

During suction, the catheter should notDuring suction, the catheter should not

be inserted beyond the lower end of thebe inserted beyond the lower end of theendotracheal tube to prevent damage toendotracheal tube to prevent damage to

airways.airways.


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Ph ysio thera py andPh ysio thera py and).Su ctio ning ) cont.Su ctio ning ) cont During accompanying bagging (periods of manualDuring accompanying bagging (periods of manual

ventilation), FiO2 may be increased by 10% over theventilation), FiO2 may be increased by 10% over the

infants current requirement.infants current requirement.

A pressure manometer (if available) must be in placeA pressure manometer (if available) must be in placeto ensure comparable pressures maintained off-to ensure comparable pressures maintained off-

ventilator.ventilator.

It is better to use endotracheal adapters that allowIt is better to use endotracheal adapters that allow

suctioning without interrupting assisted ventilation.suctioning without interrupting assisted ventilation.


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Complications ofComplications ofMe chanic al Ve ntila tio ne chanic al Ve ntila tio n Endotracheal tube complications andEndotracheal tube complications and

tracheal lesionstracheal lesions

Accidental displacement of theAccidental displacement of theendotracheal tube into main stemendotracheal tube into main stem

bronchus, hypopharynx, or esophagus.bronchus, hypopharynx, or esophagus.

Accidental extubation.Accidental extubation. Obstruction of endotracheal tube.Obstruction of endotracheal tube.

Complications ofComplications of


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Me chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont Airway injuryAirway injury

Subglottic stenosis.Subglottic stenosis.

Edema of the cords after extubation (mayEdema of the cords after extubation (mayresult in hoarseness and stridor).result in hoarseness and stridor).

Prolonged use of orotracheal intubationProlonged use of orotracheal intubation

associated with palatal groove formation.associated with palatal groove formation. Necrotizing tracheobronchitis.Necrotizing tracheobronchitis.



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Me chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) contInfectionInfection

Pneumonia and systemic infections withPneumonia and systemic infections with

Staphylococcus epidermidis, CandidaStaphylococcus epidermidis, Candidaorganism, gram-negative organisms, andorganism, gram-negative organisms, and

Staphylococcus aureus.Staphylococcus aureus.



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Me chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont Chronic lung disease / OxygenChronic lung disease / Oxygen

toxicitytoxicity

Bronchopulmonary dysplasia (BPD),Bronchopulmonary dysplasia (BPD),related to increased airway pressure andrelated to increased airway pressure and

changes in lung volume.changes in lung volume.

Other contributing factors are oxygenOther contributing factors are oxygen

toxicity, anatomic and physiologictoxicity, anatomic and physiologic

immaturity, and individual susceptibility.immaturity, and individual susceptibility. Complications ofComplications of


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Me chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) contAir leakAir leak

Pneumothorax, pulmonary interstitialPneumothorax, pulmonary interstitial

emphysema (PIE), andemphysema (PIE), andpneumomediastinum directly related topneumomediastinum directly related to

increased airway pressure occurringincreased airway pressure occurring

frequently at MAP >14 cmH2O.frequently at MAP >14 cmH2O.



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Me chanic al Ve ntila tio nMe chanic al Ve ntila tio n).) cont.) cont MiscellaneousMiscellaneous

Intraventricular hemorrhage.Intraventricular hemorrhage.

Decreased cardiac output.Decreased cardiac output. Feeding intoleranceFeeding intolerance

principals of mechanical ventilation

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