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Pediatric ARDS: Understanding It and Managing It James D. Fortenberry, MD Medical Director, Pediatric and Adult ECMO Medical Director, Critical Care Medicine Children’s Healthcare of Atlanta at Egleston
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New and Improved Adult Respiratory Distress Syndrome Acute Respiratory Distress Syndrome
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ARDS: New Definition Criteria Acute onset Bilateral CXR infiltrates PA pressure < 18 mm Hg Classification Acute lung injury - P a O 2 : F 1 O 2 < 300 Acute respiratory distress syndrome - P a O 2 : F 1 O 2 < 200 - 1994 American - European Consensus Conference
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Clinical Disorders Associated with ARDS
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The Problem: Lung Injury Other 4% Hemorrhage 5% Trauma 5% Noninfectious Pneumonia 14% Cardiac Arrest 12% Septic Syndrome 32% Infectious Pneumonia 28% Davis et al., J Peds 1993;123:35
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ARDS - Pathogenesis Instigation Endothelial injury: increased permeability of alveolar - capillary barrier Epithelial injury : alveolar flood, loss of surfactant, barrier vs. infection Proinflammatory mechanisms
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ARDS Pathogenesis Resolution Equally important Alveolar edema - resolved by active sodium transport Alveolar type II cells - re- epithelialize Neutrophil clearance needed
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ARDS - Pathophysiology Decreased compliance Alveolar edema Heterogenous “Baby Lungs”
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ARDS:CT Scan View
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Phases of ARDS Acute - exudative, inflammatory (0 - 3 days) Subacute - proliferative (4 - 10 days) Chronic - fibrosing alveolitis ( > 10 days)
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ARDS - Outcomes Most studies - mortality 40% to 60%; similar for children/adults Death is usually due to sepsis/MODS rather than primary respiratory Mortality may be decreasing 53/68 % 39/36 %
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ARDS - Principles of Therapy Provide adequate gas exchange Avoid secondary injury
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Therapies for ARDS Innovations: NO PLV Proning Surfactant Anti- Inflammatory Mechanical Ventilation Gentle ventilation: Permissive hypercapnia Low tidal volume Open-lung HFOV ECMO IVOX IV gas exchange AVCO 2 R Total Implantable Artificial Lung ARDS Extrapulmonary Gas Exchange
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The Dangers of Overdistention Repetitive shear stress Injury to normal alveoli inflammatory response air trapping Phasic volume swings: volutrauma
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compliance intrapulmonary shunt FiO 2 WOB inflammatory response The Dangers of Atelectasis
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Atelectasis “Sweet Spot” Overdistention Lung Injury Zones
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ARDS: George Bush Therapy “Kinder, gentler” forms of ventilation: Low tidal volumes (6-8 vs.10-15 cc/kg) “Open lung”: Higher PEEP, lower PIP Permissive hypercapnia: tolerate higher pCO 2
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Lower Tidal Volumes for ARDS * * * p <.001 ARDS Network, NEJM, 342: 2000 22% decrease
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Is turning the ARDS patient “prone” to be helpful?
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Prone Positioning in ARDS Theory: let gravity improve matching perfusion to better ventilated areas Improvement immediate Uncertain effect on outcome
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Prone Positioning in Pediatric ARDS: Longer May Be Better Compared 6-10 hrs PP vs. 18-24 hrs PP Overall ARDS survival 79% in 40 pts. Relvas et al., Chest 2003
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Brief vs. Prolonged Prone Positioning in Children Oxygenation Index(OI) - Relvas et al., Chest 2003 * * **
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High Frequency Oscillation: A Whole Lotta Shakin’ Goin’ On
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- Reese Clark It’s not absolute pressure, but volume or pressure swings that promote lung injury or atelectasis.
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Rapid rate Low tidal volume Maintain open lung Minimal volume swings High Frequency Ventilation
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High Frequency Oscillatory Ventilation
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HFOV is the easiest way to find the ventilation “sweet spot”
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HFOV: Benefits Vs. Conventional Ventilation
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- Arnold et al, CCM, 1994 * HFOV vs. CMV in Pediatric Respiratory Failure
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Surfactant in ARDS ARDS: surfactant deficiency surfactant present is dysfunctional Surfactant replacement improves physiologic function
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Surfactant in Pediatric ARDS Current randomized multi-center trial Placebo vs calf lung surfactant (Infasurf) Children’s at Egleston is a participating center-study closed, await results
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Steroids in Unresolving ARDS Randomized, double-blind, placebo- controlled trial Adult ARDS ventilated for > 7 days without improvement Randomized: Placebo Methylprednisolone 2 mg/kg/day x 4 days, tapered over 1 month Meduri et al, JAMA 280:159, 1998
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Steroids in Unresolving ARDS * * p<.01 * - Meduri et al., JAMA, 1998
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Steroids in Unresolving ARDS Randomized, double-blind, placebo- controlled trial ARDSNetwork-180 adults Randomized: Placebo Methylprednisolone No mortality difference Decreased ventilator-free days but only if started 7-14 days Steinberg, NEJM, 354:1671,2006
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Inhaled Nitric Oxide in Respiratory Failure Neonates Beneficial in term neonates with PPHN Decreased need for ECMO Adults/Pediatrics Benefits - lowers PA pressures, improves gas exchange Randomized trials: No difference in mortality or days of ventilation
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Inhaled NO and HFOV In Pediatric ARDS Dobyns et al., J Peds, 2000 *
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Partial Liquid Ventilation
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Mechanisms of action oxygen reservoir recruitment of lung volume alveolar lavage redistribution of blood flow anti-inflammatory
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Liquid Ventilation Pediatric trials started in 1996 Partial: FRC (15 - 20 cc/kg) Study halted 1999 due to lack of benefit Adult study (2001): no effect on outcome
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ARDS- “Mechanical” Therapies Prone positioning- Unproven outcome benefit Low tidal volumes- Outcome benefit in large study Open-lung strategy- Outcome benefit in small study HFOV-Outcome benefit in small study ECMO- Proven in neonates unproven in children
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Pharmacologic Approaches to ARDS: Randomized Trials Glucocorticoids Fibrosing alveolitis- lowered mortality, small study Surfactant- possible benefit in children Inhaled NO- no benefit Partial liquid ventilation- no benefit
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“…We must discard the old approach and continue to search for ways to improve mechanical ventilation. In the meantime, there is no substitute for the clinician standing by the ventilator…” - Martin J. Tobin, MD
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