Mechanical ventilation &Cardiopulmonary Interactions

Mechanical ventilation &Cardiopulmonary Interactions

Deborah Franzon, MDPediatric Critical Care

Lucille Packard Children’s Hospital

Deborah Franzon, MDPediatric Critical Care

Lucille Packard Children’s Hospital

OverviewOverview

Review modes of mechanical ventilationCardiopulmonary interactionsLesion specific approachesApproach to extubation

Review modes of mechanical ventilationCardiopulmonary interactionsLesion specific approachesApproach to extubation

Overview of anatomy and respiratory physiology

Overview of anatomy and respiratory physiology

AnatomyAnatomy

Infant vs adult airways Anterior and cephalad Floppy U-shaped

epiglottis Subglottic area

narrowest Increased resistance

Poiseulle’s Law R = 1/r4) Compliant chest wall Increased VO2 (8ml/kg)

Infant vs adult airways Anterior and cephalad Floppy U-shaped

epiglottis Subglottic area

narrowest Increased resistance

Poiseulle’s Law R = 1/r4) Compliant chest wall Increased VO2 (8ml/kg)

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Mechanics of ventilationMechanics of ventilation

Inspiration Active contraction of diaphragm and

intercostal muscles Generate negative intrathoracic pressure

Expiration Passive chest wall relaxation Passive lung recoil

Inspiration Active contraction of diaphragm and

intercostal muscles Generate negative intrathoracic pressure

Expiration Passive chest wall relaxation Passive lung recoil

Respiratory failureRespiratory failure

1. Compliant chest cavity limits ability to increase gas exchange

2. Increased WOB3. Increased VO24. V/Q mismatch ensues5. Indication for assisted ventilation

1. Compliant chest cavity limits ability to increase gas exchange

2. Increased WOB3. Increased VO24. V/Q mismatch ensues5. Indication for assisted ventilation

Mechanical ventilationMechanical ventilation

Oxygenation Determined by inspired oxygen and sufficient

mean airway pressure FIO2 PIP, PEEP, i-time, flow

Carbon dioxide removal Determined by (Minute ventilation - dead

space ventilation)= alveolar ventilation Rate, TV

Oxygenation Determined by inspired oxygen and sufficient

mean airway pressure FIO2 PIP, PEEP, i-time, flow

Carbon dioxide removal Determined by (Minute ventilation - dead

space ventilation)= alveolar ventilation Rate, TV

Ventilatory supportVentilatory support

Assisted breaths determined by

Trigger: time, flow, pressureCycle: time cycled breathsLimit--volume or pressure

Assisted breaths determined by

Trigger: time, flow, pressureCycle: time cycled breathsLimit--volume or pressure

Modes of VentilationModes of Ventilation

Volume-limited(SIMV) Constant flow during inspiration Square flow wave pattern Set parameters: TV, rate, PEEP, i-time PIP--dependent variable Fixed minute ventilation

Paco2 and pH remain stable

Volume-limited(SIMV) Constant flow during inspiration Square flow wave pattern Set parameters: TV, rate, PEEP, i-time PIP--dependent variable Fixed minute ventilation

Paco2 and pH remain stable

SIMV ModeSIMV Mode

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Mechanical breath Spontaneous

breath

Modes of ventilationModes of ventilation

Pressure Limited (A/C) Set parameter: PIP, PEEP, rate, IT Pressure constant throughout Tidal volume dependent variable Decelerating flow pattern Lung compliance and airway resistance

determine gas delivery Theoretically less barotrauma

Pressure Limited (A/C) Set parameter: PIP, PEEP, rate, IT Pressure constant throughout Tidal volume dependent variable Decelerating flow pattern Lung compliance and airway resistance

determine gas delivery Theoretically less barotrauma

Volume control: flow and pressure graphs

Volume control: flow and pressure graphs

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Modes of ventilationModes of ventilation

Pressure support ventilation

Decelerating inspiratory flow Patient triggers breath Constant pressure delivered Better patient-ventilator synchrony Used with volume or pressure mode or

weaning mode

Pressure support ventilation

Decelerating inspiratory flow Patient triggers breath Constant pressure delivered Better patient-ventilator synchrony Used with volume or pressure mode or

weaning mode

SIMV + Pressure SupportSIMV + Pressure Support

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Mechanical breath

Spontaneous breath

Pressure Regulated + Volume Control (PRVC)/APV

Pressure Regulated + Volume Control (PRVC)/APV

Pressure limitedTidal volume targetedDecelerating flow waveformAchieve TV goals without barotrauma,

mean airway pressure maintained

Pressure limitedTidal volume targetedDecelerating flow waveformAchieve TV goals without barotrauma,

mean airway pressure maintained

Initial ventilator settingsInitial ventilator settings

Neonates <5.0 kg IT 0.4-0.7 sec I:E ratio 1:1.5-2 PEEP 5 cmH20 PS +6-8 cmH2O TV 8-10cc/kg Rate 25-40/min PIPmax 20cmH20

Neonates <5.0 kg IT 0.4-0.7 sec I:E ratio 1:1.5-2 PEEP 5 cmH20 PS +6-8 cmH2O TV 8-10cc/kg Rate 25-40/min PIPmax 20cmH20

Infant/Child IT 0.7-1.0 sec I:E ratio 1:2-3 PEEP 5 cmH2O PS+ 5 cmH2O TV 10 ml/kg Rate 15-40/ 8-20 PIPmax 30 cmH2O

Infant/Child IT 0.7-1.0 sec I:E ratio 1:2-3 PEEP 5 cmH2O PS+ 5 cmH2O TV 10 ml/kg Rate 15-40/ 8-20 PIPmax 30 cmH2O

Pressure Volume LoopPressure Volume Loop

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Flow Volume LoopFlow Volume Loop

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Interpreting pressure/volume loops

Interpreting pressure/volume loops

Effect of PEEPIncreased resistanceAltered complianceOverdistensionAir leak

Effect of PEEPIncreased resistanceAltered complianceOverdistensionAir leak

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PEEP is ideally set at the point of lower inflection point on normal Volume-Pressure curve--shifting entire curve rightward

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As resistance increases PIP increase (A to B)--Hysteresis refers to abnormal widening of PV loop

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Alterations in compliance affect PIP. Pulmonary edema or ARDS represent decreased compliance states.

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Overdistension results in “bird-beaking”, lungs have reached capacity and for added pressure, get no additional lung volume--need to adjust set tidal volume to minimize barotrauma.

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Volume does not return to zero--representing leak in system or around endotracheal tube.

High Frequency Oscillatory Ventilation

High Frequency Oscillatory Ventilation

Pistons generate frequencies of 60-3600 cpm

Tidal volumes 1-3ml/kgTidal volumes are less than dead spaceGas exchange via diffusion, convection,

penduluft and cardiogenic oscillationsSinusoidal waveformGenerally decreases oxygenation index

Pistons generate frequencies of 60-3600 cpm

Tidal volumes 1-3ml/kgTidal volumes are less than dead spaceGas exchange via diffusion, convection,

penduluft and cardiogenic oscillationsSinusoidal waveformGenerally decreases oxygenation index

HFOVHFOV

Settings: FIO2 Frequency (Hz)-- affected by patient size

and ventilatory goals Mean airway pressure--2-5mmHg higher

than on conventional ventilation Amplitude (∆P)--necessary to provide

sufficient “jiggle”

Settings: FIO2 Frequency (Hz)-- affected by patient size

and ventilatory goals Mean airway pressure--2-5mmHg higher

than on conventional ventilation Amplitude (∆P)--necessary to provide

sufficient “jiggle”

Cardiopulmonary interactionsCardiopulmonary interactions

Effects of mechanical ventilation

Effects of mechanical ventilation

Alteration of lung volumeChanges in ITP (intrathoracic pressure)Altered acid-base balanceAltered PaO2Changes in neurohormonal activity

All can affect cardiac function

Alteration of lung volumeChanges in ITP (intrathoracic pressure)Altered acid-base balanceAltered PaO2Changes in neurohormonal activity

All can affect cardiac function

Intrathoracic pressure changes

Intrathoracic pressure changes

Venous return affects RV preloadPressure gradient between CVP and

PRA

Respiratory induced changes in ITP directly effect PRA

Venous return affects RV preloadPressure gradient between CVP and

PRA

Respiratory induced changes in ITP directly effect PRA

Venous return and RV preloadVenous return and RV preload

Spontaneous inspiration PRA falls, CVP constant, intra-abdominal

pressure increases Increased pressure gradient increases VR As PRA approaches zero venous return

maximized

Spontaneous inspiration PRA falls, CVP constant, intra-abdominal

pressure increases Increased pressure gradient increases VR As PRA approaches zero venous return

maximized

Venous return and RV preloadVenous return and RV preload

Positive pressure ventilation Inhibits venous return to RA ITP (+), decreases gradient between PRA

and mean CVP, RV filling falls More pronounced in low output state

Positive pressure ventilation Inhibits venous return to RA ITP (+), decreases gradient between PRA

and mean CVP, RV filling falls More pronounced in low output state

Effects of ITP on cardiac function

Effects of ITP on cardiac function

0

3

2

1

Venous return L/min

-5 5RA pressure

ITPITP

Mean filling pressure

Effect of PEEP on RV preloadEffect of PEEP on RV preload

Increases intrathoracic pressureIncreases intrathoracic volumeDiaphragm descendsIncreases both CVP and PRA

Venour return shifts to right

RV preload decreased

Increases intrathoracic pressureIncreases intrathoracic volumeDiaphragm descendsIncreases both CVP and PRA

Venour return shifts to right

RV preload decreased

LV PreloadLV Preload

Spontaneous Inspiration RV volume increases Intraventricular septum shifts leftward LV compliance and filling fall “Ventricular interdependence”

Spontaneous Inspiration RV volume increases Intraventricular septum shifts leftward LV compliance and filling fall “Ventricular interdependence”

LV PreloadLV Preload

Positive pressure ventilation Decreased VR--decreased LV filling Decreased RV volume--increased LV

compliance Increased lung volume--restricted LV filling

Positive pressure ventilation Decreased VR--decreased LV filling Decreased RV volume--increased LV

compliance Increased lung volume--restricted LV filling

LV afterloadLV afterload

Function of LV transmural pressure(SBP-Ppl)

Spontaneous inspiration Intrathoracic pressure falls and SBP

unchanged and afterload increases

Positive pressure inspiration intrathoracic pressure increases and

afterload decreases

Function of LV transmural pressure(SBP-Ppl)

Spontaneous inspiration Intrathoracic pressure falls and SBP

unchanged and afterload increases

Positive pressure inspiration intrathoracic pressure increases and

afterload decreases

Effect of ventilation on LV Afterload

Effect of ventilation on LV Afterload

SBP =90 SBP =90

Ptm = 100mmHg Ptm = 65 mmHg

PtmPtm

Ppl -10 Ppl +25

Spontaneous Mechanical

RV AfterloadRV Afterload

Determined by Pulmonary vascular resistance (PVR)

PVR affected by lung volume via Passive compression of pulmonary vessels Hypoxic vasoconstriction

Determined by Pulmonary vascular resistance (PVR)

PVR affected by lung volume via Passive compression of pulmonary vessels Hypoxic vasoconstriction

Pulmonary vascular resistance & functional residual capacity

Pulmonary vascular resistance & functional residual capacity

PVR lowest at FRC Below FRC (atelectasis) = PVR

Extra-alveolar vessels collapse Terminal airways close--alveoli collapse--

hypoxia--Above FRC (hyperinflation) =PVR

Intralveolar vessels compressed

PVR lowest at FRC Below FRC (atelectasis) = PVR

Extra-alveolar vessels collapse Terminal airways close--alveoli collapse--

hypoxia--Above FRC (hyperinflation) =PVR

Intralveolar vessels compressed

Lung volume and PVRLung volume and PVR

Intra-alveolar vessel resistance

Total PVR

Extra-alveolar vessel resistantceFRC

Pressure

Volume

Mechanical ventilation PVRMechanical ventilation PVR

Decrease PVR Hyperventilate Alkalosis PEEP FIO2

Decrease PVR Hyperventilate Alkalosis PEEP FIO2

Increase PVR Acidosis Hypoventilation Hyperinflation/

overdistension

Increase PVR Acidosis Hypoventilation Hyperinflation/

overdistension

Lesion specific approach to mechanical ventilationLesion specific approach to mechanical ventilation

Left-to-right shuntsLeft-to-right shunts

Increasd PBFCompression of large airways can occur

due to enlarged LA and PasTOF/PA/MAPCAS--compression of

intrapulmonary bronchi by abnormal vessels Atelectasis, wheezing, poor gas exchange

Increasd PBFCompression of large airways can occur

due to enlarged LA and PasTOF/PA/MAPCAS--compression of

intrapulmonary bronchi by abnormal vessels Atelectasis, wheezing, poor gas exchange

Left-to-right shuntsLeft-to-right shunts

Bronchiolar narrowing from high flows and venous pressure

Causes pulmonary edemaIncreased PBF associated with

decreased FEV25-75%

Prominent smooth muscle narrowing seen

Bronchiolar narrowing from high flows and venous pressure

Causes pulmonary edemaIncreased PBF associated with

decreased FEV25-75%

Prominent smooth muscle narrowing seen

Single ventricle lesions: s/p Stage I Norwood

Single ventricle lesions: s/p Stage I Norwood

Goal of balancing Qp:Qs Maneuvers to increase/decrease PVR Optimize Pulmonary Blood Flow?

Hyperventilation Alkalosis Increased Fio2 Inhaled nitric oxide

Optimize cardiac output? Mild respiratory acidosis Hypoventilation Lower Fio2

Goal of balancing Qp:Qs Maneuvers to increase/decrease PVR Optimize Pulmonary Blood Flow?

Hyperventilation Alkalosis Increased Fio2 Inhaled nitric oxide

Optimize cardiac output? Mild respiratory acidosis Hypoventilation Lower Fio2

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Bidirectional Glenn--Stage IIBidirectional Glenn--Stage II

Hypoventilation improves oxygenation after bidirectional superior cavopulmonary connection.

Bradley SM, Simsic JM, Mulvihill DM.J Thorac Cardiovasc Surg. 2003 Oct;126(4):1033-9.

The effects of carbon dioxide on oxygenation and systemic, cerebral, and pulmonary vascular hemodynamics after the bidirectional superior cavopulmonary anastomosis.

Hoskote A, Li J, Hickey C, Erickson S, Van Arsdell G, Stephens D, Holtby

H, Bohn D, AdatiaJ Am Coll Cardiol. 2004 Oct 6;44(7):1501-9. I.

Hypoventilation improves oxygenation after bidirectional superior cavopulmonary connection.

Bradley SM, Simsic JM, Mulvihill DM.J Thorac Cardiovasc Surg. 2003 Oct;126(4):1033-9.

The effects of carbon dioxide on oxygenation and systemic, cerebral, and pulmonary vascular hemodynamics after the bidirectional superior cavopulmonary anastomosis.

Hoskote A, Li J, Hickey C, Erickson S, Van Arsdell G, Stephens D, Holtby

H, Bohn D, AdatiaJ Am Coll Cardiol. 2004 Oct 6;44(7):1501-9. I.

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Bidirectional GlennBidirectional Glenn

Increased PCO2 (45-55 mmHg range)Permissive hypercarbia improves

systemic oxygenationImproves QsLittle effect on PVR

Increased PCO2 (45-55 mmHg range)Permissive hypercarbia improves

systemic oxygenationImproves QsLittle effect on PVR

Single ventricle: FontanSingle ventricle: Fontan

Venous return = PBF is “passive”Minimize positive pressure ventilation

and PEEPSpontaneous ventilation idealEarly extubationAdequately volume load ptSlow rate, adequate tidal volume

Venous return = PBF is “passive”Minimize positive pressure ventilation

and PEEPSpontaneous ventilation idealEarly extubationAdequately volume load ptSlow rate, adequate tidal volume

ExtubationExtubation

Ideal setting for post-op CVICU patientHemostasisOptimal cardiac outputStable hemodynamicsAppropriate mental statusNormothermia

Ideal setting for post-op CVICU patientHemostasisOptimal cardiac outputStable hemodynamicsAppropriate mental statusNormothermia

How to wean ventilator is variable:

dictated by practice style

How to wean ventilator is variable:

dictated by practice style

What are “extubatable” settings

What are “extubatable” settings

FIO2 < 0.4 with satisfactory PaO2 PEEP < 5.0 cm H2O pH > 7.35 PCO2 < 45 -50 mmHg Spontaneous TV 5-7ml/kg on PS <8 No significant grunting/flaring/ retracting on

CPAP or low rate Mechanical VT/spontaneous TV <0.4 NIF -20-30 cm H20

FIO2 < 0.4 with satisfactory PaO2 PEEP < 5.0 cm H2O pH > 7.35 PCO2 < 45 -50 mmHg Spontaneous TV 5-7ml/kg on PS <8 No significant grunting/flaring/ retracting on

CPAP or low rate Mechanical VT/spontaneous TV <0.4 NIF -20-30 cm H20

Extubation criteria (cont’d)Extubation criteria (cont’d)

Sinus rhythm or stably pacedOptimal perfusion and filling pressuresAdequate cardiac outputMinimal inotropic supportConsciousNo residual paralysisMinimal sedative within 2-4 hrsOptimal hematocrit

Sinus rhythm or stably pacedOptimal perfusion and filling pressuresAdequate cardiac outputMinimal inotropic supportConsciousNo residual paralysisMinimal sedative within 2-4 hrsOptimal hematocrit

Predictors of extubation success

Predictors of extubation success

Spontaneous breathing trial predicts successful extubation in infants and children.

Chavez A, dela Cruz R, Zaritsky A.Pediatr Crit Care Med. 2006 Jul;7(4):324-8.

Successful completion of the SBT has a 95% sensitivity for predicting successful extubation with a positive predictive value of 92% and an odds ratio of 12 (95% confidence interval, 1.3, 53.7)

Spontaneous breathing trial predicts successful extubation in infants and children.

Chavez A, dela Cruz R, Zaritsky A.Pediatr Crit Care Med. 2006 Jul;7(4):324-8.

Successful completion of the SBT has a 95% sensitivity for predicting successful extubation with a positive predictive value of 92% and an odds ratio of 12 (95% confidence interval, 1.3, 53.7)

Reasons why patients failReasons why patients fail

Pulmonary processes Effusions, pneumonia, atelectasis Diaphragm or vocal cord paralysis Airway obstruction, RAD

Cardiac reasons Residual anatomic leasion Poor function/low output

Neurologic reasons Oversedation, weakness CNS event--hypoxic ischemic encephalopathy,

intracranial hemorrhage.

Pulmonary processes Effusions, pneumonia, atelectasis Diaphragm or vocal cord paralysis Airway obstruction, RAD

Cardiac reasons Residual anatomic leasion Poor function/low output

Neurologic reasons Oversedation, weakness CNS event--hypoxic ischemic encephalopathy,

intracranial hemorrhage.