Pediatric Acute Respiratory Distress Syndrome

Dr. Mohammad AvaisUPRIMS&R Saifai

Bismillahirehmaniraheem

ARDS: Old Definition

Criteria:1. Acute onset (<7 days)2. Bilateral CXR infiltrates3. Absence of left atrial hypertension • PAWP pressure < 18 mm Hg.

4. Severe hypoxemiaa) Acute lung injury - PaO2 : F1O2 < 300b) Acute respiratory distress syndrome - PaO2 : F1O2 < 200

1994 American – European Consensus Conference

Adult Respiratory Distress Syndrome Acute Respiratory Distress Syndrome

Berlin Definition of ARDS 2012

The significant changes in New Berlin definitions:Improvement:a)The ALI category was eliminated and replaced with a gradation of ARDS severity (mild, moderate, and severe) based on the degree of oxygenation disturbance.

b)A minimum of 5 cm of water positive end-expiratory pressure (PEEP) was required.

c)The determination of cardiac failure was rendered more subjective in view of the decreased utilization of pulmonary artery catheters.

Limitations:a)Necessity of invasive measurement of arterial oxygen.

b)The PaO2/FIO2 (P/F) ratio is influenced by ventilator pressures (4–7).

c)The differences in risk factors, aetiology, pathophysiology, and outcomes between adults and children were not considered

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Pediatric Critical Care Medicine 2015

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• Oxygenation Index = (FIO2 × mean airway pressure × 100)/PaO2.

• Oxygenation Saturation Index = (FIO2 × mean airway pressure × 100)/SpO2.

When To Suspect ARDS

Causing Direct Injury • Pneumonia• Gastric aspiration• Less Common

• Pulmonary contusion• Fat emboli• Near drowning• Inhalational injury

Causing Indirect Injury• Sepsis• Shock after severe trauma• Less Common

• Cardiopulmonary bypass• Drug overdose• Acute pancreatitis• Massive blood

transfusions

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+ persistent hypoxemia refractory to oxygen

ARDS - Pathogenesis

Intensive Care Medicine, 2005

Pulmonary Edema

Breakdown of barriers

Lymphatic movement

ALVEOLAR EDEMA

Alveolar lumen

FULL of fluid

Interstitial fluid

Pulmonary capillary

NORMAL ALVEOLI

Alveolar lumen

EMPTY of fluid

Pulmonary capillary

Protein

Phases of ARDS

•Acute - exudative, inflammatory(0 - 3 days)

• Subacute - proliferative (4 - 10 days)

• Chronic - fibrosing alveolitis( > 10 days)

Diagnosis

• Pulse oximetry• Arterial Blood Gas.• Capnography (end-tidal CO2 measurement)• A-aO2 gradient: Calculated by subtracting arterial

Po2 from alveolar. For the comparison to be valid, it must be at the same Fio2.

NELSON 19TH EDITION

MANAGEMENT•Control of causative factor• Infection- early antibiotic therapy.• Shock- intravascular volume expansion with crystalloids and

vasopressors.

•Careful fluid administration• Goal-directed fluid management.

•Analgesia and sedation.•Nutrition.• Blood Transfusion.• Psychosocial support.

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Oxygen Administration

•Nasal cannula• Flow rate <5 L/min.• FIO2 = 21%+ (nasal cannula flow (L min) × 3)

• Simple mask• Flow rate 5 to 10 L/min.

•Venturi mask• Adapter can be chosen to provide between 30 and

50% oxygen.• Flow rates of 5-10 L/min

•Airway Adjuncts.• Oropharyngeal Airway.• Nasopharyngeal airway, or Nasal trumpet.

•Positive Pressure Respiratory Support.• High-flow nasal cannula delivers gas flow at 4-16 L/min.• Bi-level positive airway pressure (BiPAP)

•Mechanical ventilation• Controlled oxygen exposure (FiO2)• Avoidance of volutrauma (low VT) and atelectrauma

(appropriate PEEP)

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•Non-conventional ventilation• High frequency ventilation• Liquid ventilation

•Drug-based therapies• Nitric oxide• Surfactant• Corticosteroids and other anti-inflammatory agents

• Positioning (Prone ventilation)

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Ventilation strategies

•Controlled Oxygen Exposure (FiO2)• PaO2 target is 55 to 80 mm Hg (SpO2 target 88%-95%).• Decrease FiO2 below 0.6 as soon as possible.

• Permissive Hypercapnia• Target arterial pH levels - 7.30 to 7.45.

•Mode of Ventilation • Time-cycled, pressure regulated, volume controlled mode.

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Kinder, gentler” forms of ventilation

“Open lung” Higher PEEP, lower PIP

Ventilator Goals

• Predicted body weight should be used, based on calculation

from gender and from height or length or from ulna length.

• Set the PEEP slightly higher than the lower inflection point

• Lower tidal volume (generally < 6 mL/kg)

• Static peak pressure <40 cm H20

• Wean oxygen to <60%

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• Tidal Volume (VT)• Patient-specific tidal volumes according to disease severity.• VT 3–6 mL/Kg of predicted body weight and plateau pressure 28 cmH2O.• In pressure controlled mode, VT should be accurately monitored.

• Positive End-Respiratory Pressure (PEEP)• Moderately elevated levels of PEEP (10–15 cm H2O) titrated to the

observed oxygenation and hemodynamic response in patients with severe ARDS.

• In absence of routine static PV curve measurement PEEP is increased by 2–3 cm H2O increments to maintain saturation between 90-95% with FiO2<0.6.

• If PV loops monitoring are available, then it is desirable to keep the PEEP above the lower inflection point.

• markers of oxygen delivery, respiratory system compliance, and hemodynamics should be closely monitored as PEEP is increased.

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• Inspiratory Time• The I:E ratio may be increased to 1:1 or 2:1 (inverse ratio ventilation) to

improve oxygenation.

• The exhaled tidal volume should be continuously monitored to prevent injurious ventilation and monitoring of ventilatory inspiratory pressure is important to prevent ventilator-induced lung injury.• At least daily assessment of predefined clinical and

physiologic criteria of extubation readiness in order to avoid unnecessary prolonged ventilation.

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•Weaning• In volume-controlled ventilation, the VT is usually reduced to

about 4–6 ml/kg. • In pressure-controlled ventilation, the PIP is gradually

reduced in steps of 1–2 cm H2O. • PEEP and FiO2 are reduced while monitoring the PaO2.

• Extubation• FiO2 of less than 40%, PEEP of 4–5 cm H2O, rate of 15/min

or less, PIP of less than 15 cm H2O; the child is hemodynamically stable and sensorium is normal/near normal with presence of protective reflexes.• Expert clinical judgment is best for extubation.

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Lung Injury Zones

0

10

20

13 33 38Airway Pressure (cmH20)

Lung

Vol

ume (

ml/k

g)

Atelectasis

“Sweet Spot”

Overdistention

Dangers

The Dangers of Over distention

• Repetitive shear stressa) Inflammatory Response

b) Air Trapping

• Phasic volume swings: volutrauma

• Injury to normal alveoli

The Dangers of Atelectasis

Compliance

Intrapulmonary shunt

FiO2

WOB

Inflammatory response

Indications for HFOV

• High-frequency oscillatory ventilation uses high-frequency very-low tidal volumes and laminar air flow to protect the lung and maintain open lung at minimal volume swings

• Severe persistent air leak- pneumothorax, bronchopleural fistulae

• Neonatal: HMD (*)

Pneumonia

Meconium aspiration

Lung hypoplasia

• Secretion-induced lung collapse

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It’s not absolute pressure, but volume or pressure swings that promote lung injury or atelectasis. - Reese Clark

Differences Between CMV and HFOV

CMV

HFV

Rate (BPM) Tidal volume (cc/kg) Alveolar pressure swings (cmH20) End exp. lung volume

0-120 4-20 5-50

low

120-1200 0.1-5 0.1-5

high

HFOV is the easiest way to find the ventilation “sweet spot”

Is turning the patient “prone” helpful?

no significant benefit of prone positioning (20 hrs./day for 7 days)

Permissive Hypercapnia

• Presence of hypercapnia in the setting of a mechanically ventilated

patient receiving limited inspiratory pressures and reduced tidal

volumes• Permissive hypercapnia should be considered for moderate-to-severe

PARDS to minimize ventilator-induced lung injury and maintaining pH 7.15–7.30 within lung protective strategy

• Exceptions to permissive hypercapnia should include intracranial hypertension, severe pulmonary hypertension, selected congenital heart disease lesions, hemodynamic instability and significant ventricular dysfunction.

www.pccmjournal.org

Pediatric ECMO

• Potential candidates•Neonate - 18 years• Reversible disease process• Severe respiratory/cardiac failure• < 10 days mechanical ventilation•Acute, life-threatening deterioration

ECMO

Pneumonia, sepsis, drowning, trauma,blood transfusion, pancreatitis, drugoverdose, DIC, burns

1. Acute onset2. Severe hypoxemia (PaO 2/FiO2 ratio

200 for ARDS and 300 for ALI)3. Bilateral pulmonary infiltrate4. No evidence of left atrial hypertension

Child with respiratory distress

Clinical assessment, pulse oximetry, CXR and ABG

Confirm diagnosis of ALI/ARDS

Identify underlying risk factors

Management

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Non-respiratory management

Respiratory management

Management

1. Intravascular volume resuscitation & inotropes

2. Blood transfusion3. Corticosteroids4. Nutrition5. Analgesia, sedation

Control of underlyingcause if possible e.g.antibiotics for sepsisand pneumonia

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Respiratory Management in Pediatric ARDS

Non-conventional ventilation

stable monitorEvaluation for Respiratory failure

Respiratory failure

Ventilatory support

Conventional ventilation

•PRVC mode•VT <6 ml/Kg•PEEP above the lower inflection point•Recruitment maneuvers•FiO2 below 0.6•Peak inspiratory pressure < 30 cm H2O

HFOV, CPAP

Target•PaO2 of 60 to 80 mm Hg•pH of 7.30 to 7.45

a) Prone positioningb) High frequency ventilationc) Surfactantd) Inhaled NO, prostacycline) ECMO

FAILURE

Stable

MonitorWean and extubateIndian J Pediatr (2010) 77:1296–1302

Berlin ARDS Taskforce 2012

ARDS- “Mechanical” Therapies

no benefit

Low tidal volumes Outcome benefit in large study

Prone positioning Unproven outcome benefit

Open-lung strategy Outcome benefit in small study

HFOV Outcome benefit in small study

ECMO Proven in neonates Unproven in children

SteroidAcuteFibrosing Alveolitis

No benefitLowered mortality, small study

Surfactant possible benefit in children

Inhaled NOPLV

No benefitNo benefit

Outcome

• Average mortality in children with an oxygenation index ≥13 at study entry was 36% vs. 20% in those with an oxygenation index ≤12.

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