ventilatory strategies in pediatric respiratory failure
TRANSCRIPT
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Ventilatory Strategies in Pediatric
Respiratory Failure
Shekhar T. Venkataraman MDShekhar T. Venkataraman MD
Professor
Departments of Critical Care Medicine and Pediatrics
University of Pittsburgh School of Medicine
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Gas exchange problems in ARDS
�
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Mechanism of hypoxemia in ALI/ARDS
ConsolidationAtelectasisPartially
collapsed
Normal Hyperinflated
Not at all
oxygenated
Barely
oxygenated
Partially
oxygenated
Fully
oxygenated
Fully
oxygenated
but with
increased
dead space
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Goals of management
� Lung management
� Optimizing oxygen delivery to the tissues
� Multiorgan support
� Treating infections� Treating infections
� Preventing adverse outcomes
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Some Definitions
� Inflation► Increasing the volume in the lungs
► Distribution of the volumes may not be homogenous
� Recruitment► Increasing the number of open alveoli
► Inflation not same as recruitment► Inflation not same as recruitment
� Overdistension► Overinflation of the alveoli beyond its safe capacity
� Deflation► Reduction in the volume of the lung
� Derecruitment► Open alveoli collapsing and becoming atelectatic
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Inflation, deflation, recruitment and
derecruitment
INFLATION
RECRUITMENT
DEFLATION
DERECRUITMENT
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Lung management
� Opening the lung
► Ventilatory strategies
► Other strategies
� Preventing the lungs from closing� Preventing the lungs from closing
► Ventilatory strategies
► Other strategies
� Protecting the lung
► Preventing ventilator-induced lung injury
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How to open the lung
� Recruitment
► Recruitment manuever
► PEEP
► Tidal volume
► Prone positioning
► Surfactant
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Strategies for recruitment
� Sustained high peak airway pressures
� Periodic increases in peak airway pressure
� Prone positioning
� Prone positioning combined with recruitment � Prone positioning combined with recruitment
maneuvers
� High-frequency ventilation
� Prone positioning combined with high frequency
ventilation
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Recruitment maneuvers
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Recruitment
Recruitment = Increased compliance + Decreased Shunt
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Volume
Deflection point
Recommendations based on pressure-volume loop in acute lung injury
Keep Pmax below deflection point
Volume
Pressure
Inflection point
Keep PEEP above inflection point
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Interpreting Pressure-Volume
Loop
� Inflection point
► Represents the opening pressure of most of the alveoli
► PEEP above inflection point = NO DERECRUITMENT
► No more recruitment during inflation - lung is already
openopen
� Deflection point
► Represents the point at which the alveoli are overdistended
► Keeping peak airway pressure below this point prevents
ventilator-induced lung injury
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Volume
Upper Inflection Point
INFLATION
DEFLATION
Static-Pressure Volume Loop
Volume
Lower Inflection PointEELV
ZEEP (CRITICAL OPENING PRESSURE)
(CRITICAL CLOSING PRESSURE)
DERECRUITMENT
Continued recruitment
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Important
� Static pressure-volume loops using super
syringe or quasi-static pressure-volume loops
with low-flow and long-inspiratory time inflation
(validated in adults)
� Dynamic pressure-volume loops (Ventilator
Graphics) cannot be used to identify inflection
point
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Safe zone for ventilationVolume
Keep Pmax below deflection point
Deflection point
Injury
Zone
Volume
Pressure
Keep PEEP above inflection point
Safe
Zone
Injury
Zone
Inflection point
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Modes of ventilationVolume
mean lung volume
Pressure
mean airway pressure
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Case 1
� 10 yr old with bilateral pneumonia (35 kg)
� PaO2/FiO2 – 120 (FiO2 1.0)
� Pressure control ventilation
� Effective Vt = 7 mL/kg� Effective Vt = 7 mL/kg
� Rate = 20/min
� PIP = 30
� PEEP = 6
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PEEP-Titration
PEEP Vt-UP Vt-Down Vt-UP Vt-Down Vt-UP Vt-Down
6 120 135 120 120 120 120
8 125 140 120 130 120 120
Recruitable
8 125 140 120 130 120 120
10 140 160 120 140 120 120
12 160 180 125 145 110 110
14 160 170 130 140 100 100
16 130 130 110 110 90 90
Pressure control
∆ Pressure (PIP – PEEP) was kept constant
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Case 1
� 10 yr old with bilateral pneumonia (35 kg)
� PaO2/FiO2 – 450 (FiO2 1.0)
� Pressure control ventilation
� Effective Vt = 7 mL/kg� Effective Vt = 7 mL/kg
� Rate = 20/min
� PIP = 30
� PEEP = 10
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Model 1 - Completely Recruitable lung
ATELECTASISPARTIALLY COLLAPSEDNORMAL
PARTIALLY
OVERDISTENDED
FULLY OVERDISTENDED
NO ALVEOLAR BLOOD FLOW
Increased Mean Airway Pressure = Increased Mean Lung Volume
DEAD SPACE NORMAL SHUNT
Increased Mean Airway Pressure = Increased Mean Lung Volume
ALL THE PARTIALLY COLLAPSED
AND ATECTATIC
LUNGS ARE FULLY OPEN!!
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Changes in lung mechanics
Volume
• Decreased compliance
• Derecruitment
• Alveolar and airway collapse
• High Critical Closing Pressure
• High Critical Opening Pressure
Volume
Pressure
• High Critical Opening Pressure
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Effect of PEEP on recruitable lung
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Case 2
� 2 yr old with bilateral pneumonia (15 kg)
� PaO2/FiO2 – 150 (FiO2 – 1.0)
� Pressure control ventilation
� Effective Vt = 7 mL/kg� Effective Vt = 7 mL/kg
� Rate = 20/min
� PIP = 30
� PEEP = 6
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PEEP-Titration
PEEP Vt-UP Vt-Down Vt-UP Vt-Down Vt-UP Vt-Down
6 120 135 120 120 120 120
8 125 140 120 130 120 120
Partially Recruitable
8 125 140 120 130 120 120
10 140 160 120 140 120 120
12 160 180 125 145 110 110
14 160 170 130 140 100 100
16 130 130 110 110 90 90
Pressure control
∆ Pressure (PIP – PEEP) was kept constant
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Case 2
� 2 yr old with bilateral pneumonia (15 kg)
� PaO2/FiO2 – 225 (FiO2 – 1.0)
� Pressure control ventilation
� Effective Vt = 6 mL/kgEffective Vt = 6 mL/kg
� Rate = 20/min
� PIP = 32
� PEEP = 14
� PaCO2 increased from 42 mmHg to 50 mmHg
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Model 2 – Partially Recruitable lung
ATELECTASIS CONSOLIDATIONPARTIALLY COLLAPSEDNORMAL
PARTIALLY
OVERDISTENDED
FULLY OVERDISTENDED
NO ALVEOLAR BLOOD FLOW
Increased Mean Airway Pressure = Increased Mean Lung Volume
DEAD SPACE NORMAL SHUNT
Increased Mean Airway Pressure = Increased Mean Lung Volume
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Case 3
� 6-month old with bilateral pneumonia (15 kg)
� PaO2/FiO2 – 100 (FiO2 – 1.0)
� Pressure control ventilation
� Effective Vt = 7 mL/kg� Effective Vt = 7 mL/kg
� Rate = 20/min
� PIP = 28
� PEEP = 6
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PEEP-Titration
PEEP Vt-UP Vt-Down Vt-UP Vt-Down Vt-UP Vt-Down
6 120 135 120 120 120 120
8 125 140 120 130 120 120
Not Recruitable
8 125 140 120 130 120 120
10 140 160 120 140 120 120
12 160 180 125 145 110 110
14 160 170 130 140 100 100
16 130 130 110 110 90 90
Pressure control
∆ Pressure (PIP – PEEP) was kept constant
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Case 3 – What was done at night
� 6-month old with bilateral pneumonia (15 kg)
� Pressure control ventilation
� Effective Vt = 6 mL/kg
� Rate = 20/min
� PIP = 34
� PEEP = 12� PEEP = 12
� PaO2 on 100% oxygen – 50 mmHg
� SpO2 – 85%
� HFOV Machine was brought to the room
� Inhaled NO was ordered
� ECMO team was called
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Case 3 What we did afterwards
� Effective Vt = 7 mL/kg
� Rate = 20/min
� PIP = Decreased from 34 to 28
� PEEP = Decreased from 12 to 6
� PaO2 on 100% oxygen increased from 50 to 100 mmHg
� Prone positioning – PaO2 increased from 100 to 150 mmHg
� We did try inhaled NO
� No response to NO after 2 hours of NO. So taken off NO
� I would recommend leaving this child alone. Keep checking whether the lung can be recruited twice or three times a day and if so, select an appropriate PEEP
� No role for HIGHER AIRWAY PRESSURES UNLESS THE LUNG IS SHOWN TO BE RECRUITABLE!!!!
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Non-Recruitable lung
ATELECTASIS CONSOLIDATIONPARTIALLY COLLAPSEDNORMAL
PARTIALLY
OVERDISTENDED
FULLY OVERDISTENDED
NO ALVEOLAR BLOOD FLOW
Increased Mean Airway Pressure = Increased Mean Lung Volume
DEAD SPACE NORMAL SHUNT
Increased Mean Airway Pressure = Increased Mean Lung Volume
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Summary of variables for recruitment
with PEEP
� Improved compliance
� Improved oxygenation
� Improved ventilation or no change in ventilation
� No change in hemodynamics or improved � No change in hemodynamics or improved
hemodynamics
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Yin-Yang of PEEP
Positive effects
� Recruitment
� Decreased shunt
� Decreased PVR
� Decreased LV Afterload
� Improved lung compliance
� Decreased VILI
Negative effects
� Overdistension
� Increased VILI
� Increased shunt
� Increased PVR
� Decreased venous return
� Decreased cardiac output� Decreased VILI � Decreased cardiac output
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Lung Protective Strategies
� Recruit the lung
►Minimizes Atelectotrauma
� Keep Alveolar Pressures below 35 cms H2O
► Small tidal volumes► Small tidal volumes
► HFOV
� Avoid high FiO2
►Wean FiO2as quickly as possible to <0.6
� Prone positioning (?)
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Ventilator-Induced Lung Injury
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Goals for oxygenation
� Maintain PaO2 of 50-60 mmHg or SpO2 of 90-
95%
� Mean lung volume is the primary determinant of
oxygenationoxygenation
� Optimal PEEP
� Mean airway pressure ~ mean lung volume
� Avoid "toxic" inspired oxygen concentration
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Goals for ventilation
� Small tidal volumes (6-8 mL/kg)
� Keep alveolar pressure less than 35 cms H2O
(preferably less than 30 cms H2O)
� Permissive hypercapnia� Permissive hypercapnia
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Management – Change in practice over
time
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Management – Prone positioning
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A practice algorithm for prone positioning
Relvas M S et al. Chest 2003;124:269-274
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Noninvasive ventilation
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NIV vs Control patients
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RR over time
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Outcomes
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Other Strategies
� Inverse-ratio ventilation► Increases mean airway pressure without increasing peak inspiratory pressure
� Airway-pressure release ventilation► Limits peak airway pressure► Limits peak airway pressure
► Allows spontaneous breathing
► Useful in milder lung injury
� Permissive hypercapnia► Allows limitation of peak airway pressure
► Allows PaCO2 to rise with compensation of pH
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Management - HFOV
� Is useful only when the lung is recruitable
� Start with a Mean Airway Pressure 3-6 cms H2O
higher than the Conventional Mechanical Ventilation
� Determinants of oxygenation� Determinants of oxygenation►Mean airway pressure and FiO
2
� Determinants of ventilation► Amplitude – “Adequate Chest Wiggle”
► Frequency – 6-10 Hz
► Bias flow – 20-40 L/min
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Modes of ventilationVolume
mean lung volume
Pressure
mean airway pressure
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Other Strategies
� Inverse-ratio ventilation► Increases mean airway pressure without increasing peak inspiratory pressure
� Airway-pressure release ventilation► Limits peak airway pressure► Limits peak airway pressure
► Allows spontaneous breathing
► Useful in milder lung injury
� Permissive hypercapnia► Allows limitation of peak airway pressure
► Allows PaCO2 to rise with compensation of pH
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Other Strategies
� Fluid management
► Fluid restriction with early diuresis does improve
pulmonary function and outcome (Chest 1990;97:1176,
Chest 1991;100:1068)
Optimizing oxygen transport� Optimizing oxygen transport
► Optimize oxygen delivery
► Delivery-dependent consumption in some pts
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Management - HFOV
� Is useful only when the lung is recruitable
� Start with a Mean Airway Pressure 3-6 cms H2O
higher than the Conventional Mechanical Ventilation
� Determinants of oxygenation� Determinants of oxygenation►Mean airway pressure and FiO
2
� Determinants of ventilation► Amplitude – “Adequate Chest Wiggle”
► Frequency – 6-10 Hz
► Bias flow – 20-40 L/min