A Primer A Primer ininNeonatal Assisted VentilationNeonatal Assisted Ventilation

Khalid Altirkawi, MDKhalid Altirkawi, MD

King Saud UniversityKing Saud UniversityCollege of MedicineCollege of MedicineDepartment of pediatricsDepartment of pediatricsDivision of Neonatal MedicineDivision of Neonatal Medicine

Introduction Introduction

• Control of breathingControl of breathing• Pulmonary mechanicsPulmonary mechanics• Gas exchange mechanisms Gas exchange mechanisms • Historical synopsisHistorical synopsis• Assisted Ventilation StrategiesAssisted Ventilation Strategies• Strategies for preventing lung Strategies for preventing lung

damagedamage

Control of breathingControl of breathing

• ReceptorsReceptors• ChemoreceptorsChemoreceptors• MechanoreceptorsMechanoreceptors

• Reflexes Reflexes

Control of BreathingControl of Breathing

• Ventilation (CO2 elemination) is maintained by fine adjustments in tidal volume (VVTT ) and respiratory rate (RR) that minimize the work of breathing.

• Motoneurons in the CNS regulate inspiratory and expiratory muscles activity.

• Chemoreceptors and mechanoreceptors provide feedback to these neurons to adjust ventilation continuously

Chemoreceptors Chemoreceptors

• CentralCentral (in the brain stem)(in the brain stem)• Affected by changes in PaCOAffected by changes in PaCO22

• And changes in pH (independently of PaCOAnd changes in pH (independently of PaCO22 values)values)

• PeripheralPeripheral (carotid and aortic bodies) (carotid and aortic bodies)• Stimulated by hypoxiaStimulated by hypoxia• In neonates, acute hypoxia produces a In neonates, acute hypoxia produces a

transient increase in ventilation that transient increase in ventilation that disappears quicklydisappears quickly

Mechanoreceptors Mechanoreceptors

• Stretch receptors: Stretch receptors: • Located in airway smooth muscles Located in airway smooth muscles

• Respond to changes in tidal volume (VRespond to changes in tidal volume (VTT))

• Mediate:Mediate:• Hering-Breuer inflation reflexHering-Breuer inflation reflex _ a brief period of _ a brief period of

decreased or absent respiratory effort following a decreased or absent respiratory effort following a good lung inflationgood lung inflation

• Head paradoxical reflexHead paradoxical reflex _ At slow ventilator rates, _ At slow ventilator rates, large Vlarge VTT will stimulate augmented inspirations will stimulate augmented inspirations

(may be one of the mechanisms by which caffeine helps (may be one of the mechanisms by which caffeine helps weaning from ventilator)weaning from ventilator)

MechanoreceptorsMechanoreceptors

• Juxtamedullary (J) receptors:Juxtamedullary (J) receptors:• Located in the interstitium of the Located in the interstitium of the

alveolar wallalveolar wall• Stimulated by interstitial edema, Stimulated by interstitial edema,

fibrosis and by pulmonary capillary fibrosis and by pulmonary capillary engorgement (CHF). engorgement (CHF).

• Its stimulation increases respiratory Its stimulation increases respiratory raterate

MechanoreceptorsMechanoreceptors

• Baroceptors:Baroceptors:• Located in aortic and carotid sinusesLocated in aortic and carotid sinuses• Mediate:Mediate:

• The baroreflexThe baroreflex _ _

Hypertension Hypertension hypoventilation or apnea hypoventilation or apnea

Hypotension Hypotension hyperventilation. hyperventilation.

Pulmonary Mechanics

pulmonary mechanics are dynamic, frequently changing over time

Airway Pressure GradientAirway Pressure Gradient

• Gas flows down pressure gradients Gas flows down pressure gradients between airway opening and alveolibetween airway opening and alveoli

• Pressure gradient depends on: Pressure gradient depends on: • Compliance of lung parenchyma and Compliance of lung parenchyma and

chest wallchest wall• Resistance to airflow Resistance to airflow

ComplianceCompliance

• The elasticity or distensibility of the system (lungs, chest wall):

Compliance = ∆ volume/∆ pressure

• The chest wall is compliant in neonates and does not impose a substantial elastic load compared with the lungs.

ResistanceResistance

• The capacity of the air conducting The capacity of the air conducting system (airways, ETT) and tissues to system (airways, ETT) and tissues to oppose airflow oppose airflow

Resistance = ∆ pressure/∆ flowResistance = ∆ pressure/∆ flow

• Resistance depends on:Resistance depends on:• Total cross-sectional area of the airways Total cross-sectional area of the airways

(including ETT)(including ETT)• Length of airwaysLength of airways• Flow rateFlow rate• Density and viscosity of gas breathedDensity and viscosity of gas breathed

Time constantTime constant

• A measure of the time necessary for A measure of the time necessary for the alveolar pressure to reach 63% of the alveolar pressure to reach 63% of the change in airway pressure.the change in airway pressure.

Time constant = resistance x complianceTime constant = resistance x compliance

Delivery of pressure and volume is complete (95% to 99%) Delivery of pressure and volume is complete (95% to 99%) after three to five time constantsafter three to five time constants

• Different lung regions may have different time constants due to varying compliance and resistance

Ch

an

ge i

n

pre

ssu

re (

%)

100

80

60

40

20

1 2 3 4 5

Time constant (X)

63

86

9598 99

Incomplete inspiration (short TIncomplete inspiration (short Tii))

↓↓TTVV ↓↓MAPMAP

HypercapneaHypercapnea hypoxemiahypoxemia

Incomplete expiration (short TE)

Gas trapping

↓Compliance ↓TV ↑MAP

↓TV ↓Cardiac output

Hypercapnia hyperoxemia

Gas exchangeGas exchange

Hypoxemia and Hypercapnia Hypoxemia and Hypercapnia may coexist, although some may coexist, although some disorders may affect gas disorders may affect gas exchange differentiallyexchange differentially

Gas exchangeGas exchange

• Hypercapnia usually is caused by:Hypercapnia usually is caused by:• HypoventilationHypoventilation• Severe V/Q mismatchSevere V/Q mismatch

• Hypoxemia is usually due to:Hypoxemia is usually due to:• V/Q mismatching (RDS)V/Q mismatching (RDS)• R to L shunting (PPHN)R to L shunting (PPHN)• Hypoventilation (apnea)Hypoventilation (apnea)• Diffusion abnormalitiesDiffusion abnormalities

Gas exchange: COGas exchange: CO22

• In CMV, elimination of COIn CMV, elimination of CO2 2 is is directly proportional to alveolar directly proportional to alveolar minute ventilation.minute ventilation.minute ventilation = (tidal volume - dead space) X minute ventilation = (tidal volume - dead space) X frequencyfrequency

• In high frequency ventilation:In high frequency ventilation:COCO22 elimination = (tidal volume) elimination = (tidal volume)22 x frequency x frequency

Gas exchange: OGas exchange: O22

• Oxygenation is determined by FiOOxygenation is determined by FiO22 and MAPand MAP

MAP = K (PIP - PEEP) (TI/TI + TE) + PEEPMAP = K (PIP - PEEP) (TI/TI + TE) + PEEP

• ↑↑MAP MAP ↑↑lung volume and improved lung volume and improved V/Q matching V/Q matching ↑↑oxygenationoxygenation

• Within the physiologic range, MAP is Within the physiologic range, MAP is independent of rateindependent of rate

Assisted Ventilation Assisted Ventilation StrategiesStrategies

• The principlesThe principles• Historical synopsisHistorical synopsis• Continuous Positive Airway Pressure Continuous Positive Airway Pressure (CPAP)(CPAP)• Conventional Mechanical Ventilation Conventional Mechanical Ventilation (CMV)(CMV)• High-Frequency Ventilation (HFV)High-Frequency Ventilation (HFV)• Extracorporeal Membrane Extracorporeal Membrane Oxygenation (ECMO)Oxygenation (ECMO)

CMV PrinciplesCMV Principles

• Gas flows along a pressure gradientGas flows along a pressure gradient

• In spontaneous ventilation, negative In spontaneous ventilation, negative intrathoracic pressure opposes “neutral” intrathoracic pressure opposes “neutral” atmospheric pressureatmospheric pressure

• Some mechanical ventilators attempt to Some mechanical ventilators attempt to mimic nature (negative extrathoracic mimic nature (negative extrathoracic pressure) pressure) “iron lung”“iron lung”

• In most mechanical ventilators, positive In most mechanical ventilators, positive (supra-atmospheric) machine-generated (supra-atmospheric) machine-generated pressure vs. intrathoracic pressurepressure vs. intrathoracic pressure

Characteristics ofCharacteristics ofPositive Pressure CMVPositive Pressure CMV

Ti Te

Pre

ssu

re

Begin inspiration

Cycle to expiration

Time

Flow determines rate of rise and peak pressure

Pressure limited =“PIP”

In order to prevent uncontrolled over-distention, the PIP is time-limited, pressure-limited

The Oxygenation story:The Oxygenation story:the North American experiencethe North American experience

• Focus on enhancing oxygenation Focus on enhancing oxygenation during spontaneous breathingduring spontaneous breathing

• Continuous Positive Airway Pressure (CPAP)Continuous Positive Airway Pressure (CPAP)• Continuous Negative Airway Pressure (CNAP)Continuous Negative Airway Pressure (CNAP)• Continuous Respiratory Airway Pressure Continuous Respiratory Airway Pressure

(CRAP)(CRAP)

• Addition to mechanical ventilation a Addition to mechanical ventilation a Positive End Expiratory Pressure Positive End Expiratory Pressure (PEEP)(PEEP)

Adding PEEPAdding PEEP

Ti Te

Pre

ssu

re

Time

PEEP

The Oxygenation story:The Oxygenation story:Across “The Pond”Across “The Pond”

• Focus on enhancing oxygenation during Focus on enhancing oxygenation during mechanical ventilationmechanical ventilation

• Systematically explored the “reversed Systematically explored the “reversed I:E ratio”I:E ratio”• Spontaneous breathing is characterized by Spontaneous breathing is characterized by

a shorter inspiratory time compared to a shorter inspiratory time compared to expiratory timeexpiratory time

• Improved oxygenation as one moved from Improved oxygenation as one moved from 1:2 to 1:1 to 2:1 to 4:11:2 to 1:1 to 2:1 to 4:1

Reversed I:E ratioReversed I:E ratio

Ti Te

Pre

ssu

re

Time

Reversed I:E

Eureka!Eureka!

Ti Te

Pre

ssu

re

Time

Reversed I:E

Increased PEEPIncrease flow

Raise PIP

Conventional Conventional mechanical ventilation mechanical ventilation

• The variablesThe variables• The modesThe modes• The modalities The modalities

CMV variablesCMV variables

• PIPPIP• Changes in PIP affect both PaOChanges in PIP affect both PaO22 (by (by

altering the MAP) and PaCOaltering the MAP) and PaCO22 (by its effects (by its effects on Von VTT))

• A high PIP may increase the risk of A high PIP may increase the risk of volutraumavolutrauma, with resultant air leaks and , with resultant air leaks and BPDBPD

• Larger infants tend to have more compliant lungs, therefore requiring a lower PIP

CMV variablesCMV variables

• PEEPPEEP• Adequate PEEP prevents alveolar collapse,

maintains lung volume at end expiration, and improves V/Q matching.

• ↑ PEEP MAP and FRC improving oxygenation.

• Vey high PEEP may decrease venous return, cardiac output, and increase pulmonary vascular resistance

• Increases in both PIP and PEEP have opposite effects on CO2 elimination

CMV variablesCMV variables

• Rate:• In large RCTs, relatively high rates (60 In large RCTs, relatively high rates (60

breaths/min) resulted in a decreased breaths/min) resulted in a decreased incidence of pneumothorax in preterm incidence of pneumothorax in preterm infants who had RDSinfants who had RDS

• Generally, a high rate, low VGenerally, a high rate, low VTT strategy strategy is preferredis preferred

CMV variablesCMV variables

• I:E ratio:I:E ratio:• The major effect of an increase in the I:E The major effect of an increase in the I:E

ratio is to increase MAP and improve ratio is to increase MAP and improve oxygenation. oxygenation.

• Changes in the I:E ratio are not as effective Changes in the I:E ratio are not as effective in increasing oxygenation as are changes in in increasing oxygenation as are changes in PIP or PEEPPIP or PEEP

• Changes in the I:E ratio usually do not alter Changes in the I:E ratio usually do not alter VVTT unless T unless TII and T and TEE become relatively too become relatively too shortshort

CMV variablesCMV variables

• TTI I & T& TEE

• A long TA long TII increases the risk of increases the risk of pneumothoraxpneumothorax

• Shortening TShortening TII is helpful during weaning is helpful during weaning

• In RCT: limiting TIn RCT: limiting TII to 0.5 seconds resulted in a to 0.5 seconds resulted in a significantly shorter duration of weaningsignificantly shorter duration of weaning

• In patients who have CLD a longer TIn patients who have CLD a longer TI I

(around 0.8 sec) may result in improved V(around 0.8 sec) may result in improved VTT and better COand better CO22 elimination elimination

CMV variablesCMV variables

• FiOFiO2 2

• During increasing support, increase FiODuring increasing support, increase FiO2 2 first first until it reaches about 0.6 to 0.7, then increase until it reaches about 0.6 to 0.7, then increase MAP MAP

• During weaning, decrease FiODuring weaning, decrease FiO2 2 initially (~ 0.4 to initially (~ 0.4 to 0.7) before you decrease MAP0.7) before you decrease MAPmaintaining an appropriate MAP may allow substantial reduction in maintaining an appropriate MAP may allow substantial reduction in FiOFiO22

• Reduce MAP before a very low FiOReduce MAP before a very low FiO2 2 is reachedis reached

a higher incidence of air leaks has been observed if distending a higher incidence of air leaks has been observed if distending pressures are not weaned earlierpressures are not weaned earlier

CMV variablesCMV variables

• Flow:Flow:• Changes in flow have not been well studied Changes in flow have not been well studied

in infants, but they probably affect arterial in infants, but they probably affect arterial blood gases minimally as long as a blood gases minimally as long as a sufficient flow is used.sufficient flow is used.

• In general, flows of 8 to 12 L/min are In general, flows of 8 to 12 L/min are sufficient in most neonates. sufficient in most neonates.

• High flows are needed when inspiratory High flows are needed when inspiratory time is shortened to maintain an adequate time is shortened to maintain an adequate tidal volume.tidal volume.

CMV ModalitiesCMV Modalities(Target Variable)(Target Variable)

• VolumeVolume controlled: controlled: • Set tidal volume is delivered, VSet tidal volume is delivered, VTT is is

pressure-limitedpressure-limited

• PressurePressure controlled: controlled: • Constant inspiratory pressure, ie. Constant inspiratory pressure, ie.

decelerating variable flowdecelerating variable flow• Time or flow cycled: method by which Time or flow cycled: method by which

inspiration is started/ended inspiration is started/ended • Volumes vary with lung complianceVolumes vary with lung compliance

Modes of CMVModes of CMV

UntriggeredUntriggered

• IPPV:IPPV:• Machine rate faster Machine rate faster

than spontaneousthan spontaneous

• IMV:IMV:• Slower than Slower than

spontaneous and spontaneous and asynchronousasynchronous

TriggeredTriggered

• SIMVSIMV

• SIPPV or SIPPV or Assist/ControlAssist/Control

• Pressure Supported Pressure Supported Ventilation (PSV)Ventilation (PSV)

• Volume Guaranteed Volume Guaranteed (VG)(VG)

Problems in CMVProblems in CMV

• Problem:Problem:• Asynchrony:Asynchrony:

• Ineffective ventilation and oxygenationIneffective ventilation and oxygenation• Fluctuation in BP (associated with IVH)Fluctuation in BP (associated with IVH)

• Solutions: Solutions: • Paralysis and sedationParalysis and sedation• Synchronized ventilationSynchronized ventilation

SynchronizingSynchronizing

Means of detecting the Means of detecting the initiation of a breathinitiation of a breath

• Thoracic impedanceThoracic impedance• Abdominal Abdominal

movementmovement• Change in Change in

esophageal pressureesophageal pressure• Change in airway Change in airway

pressurepressure• Change in airway Change in airway

flowflow

ProblemsProblems

• ArtifactArtifact• ““auto triggering”auto triggering”• Antiphasic Antiphasic

triggeringtriggering• Delayed response Delayed response

timetime• Lack of responseLack of response

Triggered (Synchronous) VentilationTriggered (Synchronous) Ventilation

• SIMVSIMV• Only “X” breaths per minute are supported Only “X” breaths per minute are supported

with “machine breaths” in synchronywith “machine breaths” in synchrony

• SIPPVSIPPV• Every sensed breath is supported by Every sensed breath is supported by

“machine breath”“machine breath”

• PSVPSV• Every sensed breath is supported by fixed Every sensed breath is supported by fixed

pressure, but patient controls flow and Tpressure, but patient controls flow and TII

• VGVG• Preset volume delivered every timePreset volume delivered every time

Volume Guarantee (VG)Volume Guarantee (VG)

• The ventilator delivers a specified The ventilator delivers a specified expired volume (Vexpired volume (VTT) with the lowest ) with the lowest possible pressurepossible pressure

• The preferred mode in which to use VG is The preferred mode in which to use VG is PSVPSV

• Best use is when mechanics are rapidly Best use is when mechanics are rapidly changingchanging

• Do Do NOTNOT use VG if the leak is > 40% use VG if the leak is > 40%

Volume Guarantee (VG)Volume Guarantee (VG)

• The ProblemThe Problem• Preset volume delivered may be excessive Preset volume delivered may be excessive

or inadequate in a rapidly changing clinical or inadequate in a rapidly changing clinical settingsetting

• The SolutionThe Solution• Over several breaths, records volume Over several breaths, records volume

achieved and pressure generated to achieved and pressure generated to achieve that volumeachieve that volume

• Target “new” pressure computed to Target “new” pressure computed to achieve pre-defined set volumeachieve pre-defined set volume

Characteristics of Triggered CMVCharacteristics of Triggered CMV

Machine’sSupport

Frequency of support

“Support” in untriggered

phase

A/CA/CPreset flow, TPreset flow, Tii, , PIP, PEEPPIP, PEEP

All sensed breathsAll sensed breaths Set rate Set rate “guaranteed”“guaranteed”

SIMVSIMVPreset flow, TPreset flow, Tii, , PIP, PEEPPIP, PEEP

All sensed breaths in All sensed breaths in rated-defined rated-defined “window”“window”

CPAPCPAP

Set rate Set rate “guaranteed”“guaranteed”

PSVPSVPreset PIP, PEEPPreset PIP, PEEP

Patient’s flow, TPatient’s flow, Tii

All sensed breathsAll sensed breaths +/- SIMV or CPAP+/- SIMV or CPAP

Clinical Use of Triggered CMVClinical Use of Triggered CMV

Typical SettingTypical Setting AdvantageAdvantage DisadvantageDisadvantage

A/CA/C Critically ill, unstable, Critically ill, unstable, paralyzedparalyzed ControlControl Control is an Control is an

illusionillusion

SIMVSIMVStable, spontaneously Stable, spontaneously breathing but not with breathing but not with consistent rate or MVconsistent rate or MV

Increased Increased dependence on dependence on patient = patient = “wean”“wean”

Increased Increased dependence on dependence on patient = “wean” patient = “wean”

PSVPSVActively attempting to Actively attempting to decrease ventilatory decrease ventilatory supportsupport

Greatest Greatest synchronizationsynchronization

Draeger: no SIMVDraeger: no SIMV

A/C and PSV vs. SIMVA/C and PSV vs. SIMV

High frequency High frequency

ventilationventilation

HFVHFV

Characteristics of HFVCharacteristics of HFV

• Continuous distending pressure Continuous distending pressure

• Small VSmall VTT (less than anatomic dead (less than anatomic dead space) space)

• Rapid ventilator ratesRapid ventilator rates

HFV: Examples in NatureHFV: Examples in Nature

• Humming birdHumming bird

• ~250 bpm while at ~250 bpm while at rest rest

• One-way flow via One-way flow via parabronchi and air parabronchi and air sacs (NOT tidal)sacs (NOT tidal)

• Panting dogPanting dog

• VVTT less than deadspace less than deadspace

• Very high respiratory Very high respiratory raterate

HFV: Impediment to Gas FlowHFV: Impediment to Gas Flow

frequency

Imp

ed

an

ce

Airway

HFV: Impediment to Gas Flow HFV: Impediment to Gas Flow

frequency

imp

ed

an

ce

Alveolae

HFV: Impediment to Gas FlowHFV: Impediment to Gas Flow

frequency

imp

ed

an

ce

Airway

Alveolae

Airway + Alveolae

HFV: Resonant FrequencyHFV: Resonant Frequency

frequency

imp

ed

an

ce

“Sweet spot”

So… In High Frequency VentilationSo… In High Frequency Ventilation

• Ventilation is Ventilation is control-led by control-led by frequency and frequency and (V(VTT))22

• Frequency and VFrequency and VTT are inversely are inversely related related

frequency = frequency = ETT ETT resistance, resistance, V VTT

HFV: The DesignHFV: The Design

HFOVHFOV

• Diaphragm or pistonDiaphragm or piston• Active expirationActive expiration• Single control of Single control of

PawPaw• Single deviceSingle device• Optimum volume, Optimum volume,

low pressure low pressure • Air trappingAir trapping• Fixed (rigid) circuitFixed (rigid) circuit

HFJVHFJV

• High pressure jetHigh pressure jet• Passive expirationPassive expiration• Multiple controls of Multiple controls of

PawPaw• CMV in seriesCMV in series• Low volume, low Low volume, low

pressurepressure• Air trappingAir trapping• Triple lumen ET tubeTriple lumen ET tube

HFV: The StrategyHFV: The Strategy

HFOVHFOV

• Severe Severe homogeneoushomogeneous lung lung diseasedisease• RDSRDS• Early-onset pneumoniaEarly-onset pneumonia

• PPHN (in concert PPHN (in concert with iNO)with iNO)

Target: RDSTarget: RDS

HFJVHFJV

• Severe Severe heterogeneousheterogeneous lung lung diseasedisease• MASMAS• Late-onset pneumoniaLate-onset pneumonia

• Airleak syndromesAirleak syndromes• PneumothoraxPneumothorax• PIEPIE

Target: barotraumaTarget: barotrauma

Comparative Pressure ProfilesComparative Pressure Profiles

Common Starting PointsCommon Starting Points

Starting CMVStarting CMV

• Choose mode (SIMV, PSV, ….)Choose mode (SIMV, PSV, ….)• Select PEEP based upon lung disease to Select PEEP based upon lung disease to

achieve optimal inflationachieve optimal inflation• Select PIP or volume to generate VSelect PIP or volume to generate VTT = 4-= 4-

6 ml/kg6 ml/kg

• Start with rate 30-40Start with rate 30-40• Blood gases in 30 minutes to determine Blood gases in 30 minutes to determine

baselinebaseline

Starting HFOVStarting HFOV

• FrequencyFrequency

•10 to 12 Hz for infants >1500g, 15 Hz if 10 to 12 Hz for infants >1500g, 15 Hz if <1500 g<1500 g

• ITIT

•33% of cycle33% of cycle

• Amplitude (Amplitude (P)P)

•Perceptible vibration movement down to Perceptible vibration movement down to groingroin

• Paw Paw

•Equal to CMV if restrictive diseaseEqual to CMV if restrictive disease•2-3 cm H2O above CMV if atelectatic disease2-3 cm H2O above CMV if atelectatic disease

Starting HFJVStarting HFJV

• Frequency (jet)Frequency (jet)

•420 (LBW), 240 - 360 (term or long time 420 (LBW), 240 - 360 (term or long time constant)constant)

•3-5 CMV breaths3-5 CMV breaths• ITIT

•0.02 seconds0.02 seconds

• PIP (Jet)PIP (Jet)

•To vibrate chest (~PIP on CMV)To vibrate chest (~PIP on CMV)• PEEP (CMV)PEEP (CMV)

•To maintain Paw for optimal inflationTo maintain Paw for optimal inflation

HFV: Therapeutic strategiesHFV: Therapeutic strategies

• Blood gas 20-30 minutes after initiationBlood gas 20-30 minutes after initiation

• Chest radiograph within 4 hrs after Chest radiograph within 4 hrs after initiation, and whenever lung over-initiation, and whenever lung over-inflation is suspectedinflation is suspected• Adjust Paw to maintain optimal lung volumeAdjust Paw to maintain optimal lung volume

• After improvementAfter improvement• Decrease Paw to maintain FiODecrease Paw to maintain FiO22 0.3-0.4 0.3-0.4

• Decrease VDecrease VTT if PaCO if PaCO22 lower than target lower than target

HFV: Therapeutic strategiesHFV: Therapeutic strategies

• Atelectasis?Atelectasis?• Increase Paw by 1-2 cm HIncrease Paw by 1-2 cm H22O until O until OO22

requirementrequirement

• Hypercarbia with high lung Hypercarbia with high lung volumes?volumes?• Consider air trapping/inadvertent PEEPConsider air trapping/inadvertent PEEP

HFV: Pitfalls and ComplicationsHFV: Pitfalls and Complications

• HFV is more effective at ventilation, so HFV is more effective at ventilation, so the risk of hypocarbia is greater. the risk of hypocarbia is greater. Hypocarbia is clearly correlated with PVLHypocarbia is clearly correlated with PVL

• Lung overdistention Lung overdistention airleak airleak• Air trapping Air trapping Hypercarbia Hypercarbia• Increased intrathoracic pressure Increased intrathoracic pressure

Reduced systemic venous return Reduced systemic venous return HypotensionHypotension

HFV vs. CMV in prophylaxisHFV vs. CMV in prophylaxis

• There is no evidenceThere is no evidence that elective use of HFV that elective use of HFV ( HFOV or HFFI) provides any greater benefit ( HFOV or HFFI) provides any greater benefit to premature infants who have RDS than CMVto premature infants who have RDS than CMV

• Data are limited and results are mixed as to Data are limited and results are mixed as to whether HFJV may reduce the incidence of whether HFJV may reduce the incidence of CLDCLD

• Preferential use of HFV as the initial mode of Preferential use of HFV as the initial mode of ventilation to treat RDS in premature infants ventilation to treat RDS in premature infants is not supportedis not supported

HFV vs. CMV in rescue therapyHFV vs. CMV in rescue therapy

• There is no evidence that HFV provides There is no evidence that HFV provides any long-term benefit over CMV in any long-term benefit over CMV in patients who have respiratory failurepatients who have respiratory failure

• No RCTs to support the use of HFV over No RCTs to support the use of HFV over CMV in the treatment bronchopleural or CMV in the treatment bronchopleural or tracheo-esophageal fistulatracheo-esophageal fistula

• HFV in this population appears to HFV in this population appears to diminish the amount of continuous air diminish the amount of continuous air leak and improve patient stabilizationleak and improve patient stabilization

Take Home GeneralizationsTake Home Generalizations

• ““A high frequency ventilator can A high frequency ventilator can ventilate a stone.”ventilate a stone.”

• Each underlying disease has a Each underlying disease has a pathophysiology that suggests the pathophysiology that suggests the ventilator-of-choiceventilator-of-choice• Diffuse, homogeneous vs. dishomogenousDiffuse, homogeneous vs. dishomogenous• Presence or absence of barotraumaPresence or absence of barotrauma• Underlying cardiovascular compromiseUnderlying cardiovascular compromise

Strategies to PreventStrategies to PreventLung InjuryLung Injury

Strategies to Prevent LungStrategies to Prevent LungInjuryInjury

• Permissive HypercapniaPermissive Hypercapnia• Low Tidal Volume VentilationLow Tidal Volume Ventilation• Alternative Modes of Ventilation:Alternative Modes of Ventilation:

• Patient-triggered VentilationPatient-triggered Ventilation• Synchronization Synchronization • High-frequency VentilationHigh-frequency Ventilation• Liquid ventilationLiquid ventilation• Proportional Assist VentilationProportional Assist Ventilation• Tracheal Gas InsufflationTracheal Gas Insufflation

Ventilator-associated lung injuryVentilator-associated lung injury

• Biotrauma: Biotrauma: • Barotrauma (high pressure, low volume)Barotrauma (high pressure, low volume)• Volutrauma (high volume, low pressure)Volutrauma (high volume, low pressure)

• Markers of lung injury are present with the use Markers of lung injury are present with the use of high volume and low pressure, but not with of high volume and low pressure, but not with the low volume and high pressurethe low volume and high pressure

• The heterogeneity of lung tissue involvement in The heterogeneity of lung tissue involvement in many diseases predisposes some parts of the many diseases predisposes some parts of the lung to volutraumalung to volutrauma

• Oxidant injuryOxidant injury

Permissive hypercapniaPermissive hypercapnia

• Priority is given to the prevention or Priority is given to the prevention or limitation of over-ventilation rather limitation of over-ventilation rather than to maintenance of normal blood than to maintenance of normal blood gasesgases

• Two large retrospective studies: Two large retrospective studies: • HypocapniaHypocapnia during the early neonatal during the early neonatal

course resulted in an increased risk of course resulted in an increased risk of lung injurylung injury

Permissive hypercapniaPermissive hypercapnia

• RCT: RCT: • Surfactant-treated infantsSurfactant-treated infants• BW = 854BW = 854++163 g, GA = 26163 g, GA = 26++1.4 wks 1.4 wks • Assissted ventilation during the first 24 hoursAssissted ventilation during the first 24 hours

• Two groups; Permissive hypercapnia (PaCOTwo groups; Permissive hypercapnia (PaCO22 = 45 - = 45 - 55 mm Hg) or normocapnia (PaCO55 mm Hg) or normocapnia (PaCO22 = 35 - 45 mm = 35 - 45 mm Hg)Hg)

• Results:Results: the number of patients receiving assisted the number of patients receiving assisted ventilation during the intervention period was lower ventilation during the intervention period was lower in the permissive hypercapnia group (P =0.005)in the permissive hypercapnia group (P =0.005)

• IVH risk starts to rise when PaCOIVH risk starts to rise when PaCO2 2 ~ 53-~ 53-5757

• Since IVH is an early phenomenon, we Since IVH is an early phenomenon, we need to change upper limit of PaCOneed to change upper limit of PaCO22 target range after risk period has ended target range after risk period has ended

i.e. for Premature infants in first two weeks of life, i.e. for Premature infants in first two weeks of life, PCOPCO22 goal is 45 – 55 mm Hg. after two weeks of life, goal is 45 – 55 mm Hg. after two weeks of life, PCOPCO22 goal is 55 – 65 mm Hg as long as pH > 7.20 goal is 55 – 65 mm Hg as long as pH > 7.20

When to avoid hypercapniaWhen to avoid hypercapnia

Proportional Assist VentilationProportional Assist Ventilation

• PAV matches the onset and duration of both inspiratory and expiratory support

• Support is in proportion to the volume and flow of the spontaneous breath (decrease the elastic or resistive work of breathing selectively)

• RCTs are needed

Tracheal gas insufflationTracheal gas insufflation

• The added dead space of the ETT The added dead space of the ETT ↑anatomic dead space ↑anatomic dead space ↓minute ↓minute ventilation ventilation ↑ PaCO ↑ PaCO22

• Gas delivered to the distal part of Gas delivered to the distal part of ETT during exhalation washes out ETT during exhalation washes out this dead space and the this dead space and the accompanying COaccompanying CO22

Continuous positive airwaypressure

CPAPCPAP

CPAPCPAP

PROS

• ↑ alveolar volume & FRC

• Alveolar recruitment• Alveolar stability• Improved V/Q

matching• Redistribution of

lung water

CONS

• Increased risk for air leaks

• Overdistention

• CO2 retention

• CVS impairment• Decreased compliance• Potential to increase

PVR

EarlyEarly CPAP CPAP

• Rescue therapy of Rescue therapy of establishedestablished RDS RDS

• Decreases ODecreases O22 requirements requirements

• Decreases the need for mechanical Decreases the need for mechanical ventilationventilation

• May reduce mortalityMay reduce mortality

• The optimal time to start CPAP depends The optimal time to start CPAP depends on the severity of RDS (PaOon the severity of RDS (PaO22~ 50 torr, ~ 50 torr, FiOFiO2 2 ~ 0.4)~ 0.4)

ProphylacticProphylactic CPAP CPAP

• Does not decrease the incidence or Does not decrease the incidence or severity of RDS severity of RDS

• Does not reduce the rate of Does not reduce the rate of complications or deathcomplications or death

Non-invasiveNon-invasiveventilationventilation

NIVNIV

NIV – the rationale

• One of the initial forms of respiratory support used in preterm infants with RDS

• Recently it has been reintroduced for initial management of RDS and indications such as apnea and to improve extubation success after invasive ventilation

NIV – the mechanismNIV – the mechanism

• The intermittently increased nasal The intermittently increased nasal pressure:pressure:

• Is transmitted to the lower airways enhancing VIs transmitted to the lower airways enhancing VTT

• Via the nose may act as a stimulus and reduce Via the nose may act as a stimulus and reduce apnea episodesapnea episodes

• Increases MAP Increases MAP better alveolar recruitment better alveolar recruitment and higher lung volumeand higher lung volume

• Clears the exhaled gas from the upper airway Clears the exhaled gas from the upper airway and thus reducing the anatomical dead space.and thus reducing the anatomical dead space.

NIV – the ModalitiesNIV – the Modalities

• Initially, NIV was accomplished Initially, NIV was accomplished using con-ventional IMV mode (N-using con-ventional IMV mode (N-IMV)IMV)

• By adding triggering, other By adding triggering, other modalities became available: N-A/C modalities became available: N-A/C (aka N-SIPPV), N-PSV, N-SIMV(aka N-SIPPV), N-PSV, N-SIMV

• There are no data on what are the There are no data on what are the best settings during NIVbest settings during NIV

NIV and apneaNIV and apnea

• Effects of NIV on apnea:

• Not consistent• Greater among infants who present with

a more frequent apnea while on N-CPAP• May be more effective in those infants

with poorer lung function and on N-CPAP• May not always lead to improved May not always lead to improved

ventilation and gas exchange, but can ventilation and gas exchange, but can partially reduce work of breathingpartially reduce work of breathing

The EndThe End

Suggested ReadingSuggested Reading

• Goldsmith and Karotkin. Assisted Ventilation of the Goldsmith and Karotkin. Assisted Ventilation of the Neonate 2003: 183-202Neonate 2003: 183-202

• Froese and Kinsella. High Frequency Oscillatory Froese and Kinsella. High Frequency Oscillatory Ventilation: Lessons from the neonatal/pediatric Ventilation: Lessons from the neonatal/pediatric experience. Critial Care Medicine 2005;33:S115-121experience. Critial Care Medicine 2005;33:S115-121

• Keszler. High Frequency Ventilation: Evidence-based Keszler. High Frequency Ventilation: Evidence-based Practice and Specific Clinical Indications NeoReviews Practice and Specific Clinical Indications NeoReviews 2006;7:e234-2412006;7:e234-241

Optimizing Lung VolumeOptimizing Lung Volume

• Lung hysteresis refers to the fact that lung Lung hysteresis refers to the fact that lung volume and compliance at a given volume and compliance at a given transpulmonary pressure is higher in transpulmonary pressure is higher in deflation than in inflationdeflation than in inflation

Froese AB: Neonatal and Pediatric Ventilation: Physiological and clinical perspectives. In Marini JJ, Slutsky AS (eds): Physiological Basis of Ventilatory Support. New York, Marcel Dekker, 1998. P. 1346