PEDIATRIC ACUTE RESPIRATORY DISTRESS SYNDROME

OBJECTIVES

• Definitions
• Pathophysiology
• Principles of Management

DEFINING ARDS

• Multiple revisions to the adult definition of ARDS since first described in 1967
• Criticized for use of the PaO2/FiO2 ratio, can be influenced by changes in mean airway pressure (PEEP)
• Pediatric-specific definition established in 2015 by PALICC (Pediatric Acute Lung Injury Consensus Conference)
• Offered specific patient management recommendations and priorities for future research

OXYGENATION INDEX (OI)

• Severity of PARDS is stratified: mild, moderate, severe
• To incorporate mean airway pressure, the OI is used

Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference. Pediatr Crit Care Med 2015;16(5):428-439.

DEFINING ARDS: PALICC

Khemani RG, Smith LS, Zimmerman JJ, Erickson S, Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress syndrome: definition, incidence, and epidemiology: proceedings from the Pediatric Acute Lung Injury Consensus Conference. Pediatr Crit Care Med 2015;16(5 Suppl 1):S23-S40.

*Mortality rate of 40% when OI >16

PATHOPHYSIOLOGY

• Initiating Factors
• Direct: pneumonia (35%), aspiration (15%), submersion (9%), pulmonary contusion, inhalation
• Indirect: sepsis (13%), shock, transfusion-related lung injury
• Phases of Disease

1) Exudative Phase: decreased pulmonary compliance and hypoxemia

2) Fibroproliferative Phase: chronic inflammation and scarring

3) Recovery Phase: restoration of alveolar epithelial barrier

​

Flori HR, Glidden DV, Rutherford GW, Matthay MA. Pediatric acute lung injury: prospective evaluation of risk factors associated with mortality. Am J Respir Crit Care Med 2005;171(9):995-1001.

​

EFFECT ON CARDIOVASCULAR FUNCTION

• Pro-inflammatory cytokines potentiates development of:
• Permeability edema
• Alveolar hypoxia
• Thrombotic obstruction of pulmonary microvasculature
• Interstitial fibrosis

RELATIONSHIP OF PVR AND LUNG VOLUME

Alveolar

Extra-Alveolar

Total

Residual Volume (RV)

Functional Residual Capacity

(FRC)

Total Lung Capacity (TLC)

Pulmonary Vascular Resistance

PRINCIPLES OF MANAGEMENT

• Conventional Mechanical Ventilation
• High-Frequency Oscillatory Ventilation
• Adjuvant Therapies
• Extracorporeal Life Support

CONVENTIONAL MECHANICAL VENTILATION

• Tidal Volume
• “Patient-specific tidal volumes according to lung severity”
• 3-6 mL/kg ideal weight for poor respiratory system compliance
• 5-8 mL/kg ideal weight (physiologic range) for better preserved compliance
• Peak Inspiratory Pressure
• Linear association between mortality and peak inspiratory pressure (PIP)
• Limit to 28 cm H2O (29-32 cm H2O if reduced chest wall compliance)
• PEEP
• Minimize atelectrauma (alveolar collapse)
• 10-15 cm H2O should be titrated in patients with severe PARDS
• *closely monitor markers of O2 delivery, respiratory compliance, and hemodynamics
• Recruitment Maneuvers (lack of pediatric data)

​

GAS EXCHANGE GOALS

• Permissive hypoxemia
• Increased systemic oxygenation is not correlated with improved outcomes
• SpO2 of 88-92% should be considered
• Permissive hypercapnia
• pH of 7.15-7.3
• *Exceptions: pulmonary HTN, intracranial hypertension, ventricular dysfunction

​

Acute Respiratory Distress Syndrome Network, Brower RG, Matthay MA, Morris A, Schoenfeld D, Thompson BT, Wheeler A. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342(18):1301-1308.

Rimensberger PC, Cheifetz IM, Pediatric Acute Lung Injury Consensus Conference Group. Ventilatory Support in Children with Pediatric Acute Respiratory Distress Syndrome: Proceedings from the Pediatric Acute Lung Injury Consensus Conference. Pediatr Crit Care Med 2015;16(5 Suppl 1):S51-S60.

HIGH FREQUENCY OSCILLATORY VENTILATION

• Used as salvage therapy for refractory hypoxemic respiratory failure
• In theory is lung protective
• Prevents atelectrauma by delivering constant applied airway pressure to maintain recruitment
• Prevents volutrauma by delivering small tidal volumes
• In adults, 2 large multi-center randomized, controlled trials:
• OSCAR: no significant difference in all cause 30-d or in-hospital mortality
• OSCILLATE: increased mortality seen with HFOV compared to control
• In pediatrics,
• RESTORE: longer duration of mechanical ventilation, increased use of sedation and paralysis
• Remains center and clinician-dependent

ADJUVANT THERAPIES: CORTICOSTEROIDS

• RCT by Drago 2015, low dose methylprednisolone infusion showed:
• No difference in mortality
• No difference in mechanical ventilation
• No difference in length of hospital stay
• Prospective, observational, single-centered study by Yehya 2015 showed corticosteroid exposure >24 hrs was associated with:
• Increased mortality
• Fewer ventilator free days (at 28 d)
• Longer length of ventilation in survivors compared to those without steroid exposure
• Used in 20-60% of PARDS patients but cannot be recommended as routine therapy
• Need more pediatric data!

Drago BB, Kimura D, Rovnaghi CR, Schwingshackl A, Rayburn M, Meduri GU, Kanwaljeet JS, Anand KJ. Double-blind, placebo-controlled pilot randomized trial of methylprednisolone infusion in pediatric acute respiratory distress syndrome. Pediatr Crit Care Med 2015;16(3):e74-e81.

Yehya N, Servaes S, Thomas NJ, Nadkarni VM, Srinivasan V. Corticosteroid exposure in pediatric acute respiratory distress syndrome. Intensive Care Med 2015;41(9):1658-1666.

​

ADJUVANT THERAPIES: PRONING

• Curley 2005, pediatric RCT:
• Stopped early for futility demonstrating no benefit
• Included mild to severe ARDS and mandated use of HFOV as disease progressed
• Guerin 2013, adult PROSEVA trial:
• Improved survival in those with severe ARDS
• Prone positioning may be considered in severe ARDS, given available adult data

Curley MA, Hibberd PL, Fineman LD, Wypij D, Shih MC, Thompson JE, et al. Effect of prone positioning on clinical outcomes in children with acute lung injury: a randomized controlled trial. JAMA 2005;294(2):229-237.

Guerin C, Reignier J, Richard JC, Beuret P, Gacouin A, Boulain T, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013:368(23):2159-2168.

​

ADJUVANT THERAPIES

• Inhaled Nitric Oxide
• Despite expected short-term benefit, 3 RCTs in children have shown no improvement in outcome
• Can be helpful in patients with pulmonary hypertension, bridge to ECMO, or RV dysfunction
• Exogenous Surfactant
• Further study needed. May be beneficial in specific patient populations

​

​

• Neuromuscular Blockade
• Not adequately studied in pediatrics but has demonstrated survival benefit and vent free days in adults

​

EXTRACORPOREAL LIFE SUPPORT

• Optimal timing for cannulation remains controversial
• Survival rates >70% have been reported with V-V ECMO for viral induced ARDS
• Should be considered when unable to maintain clinical stability within recommended limits for safe mechanical ventilation management

Dalton HJ, Macrae DJ, Pediatric Acute Lung Injury Consensus Conference Group. Extracorporeal support in children with pediatric acute respiratory distress syndrome: proceedings from the pediatric acute lung injury consensus conference. Pediatr Crit Care Med 2015; 16(5 Suppl 1):S111-S117.

​

REVIEW

• On rounds in the PICU, you present a 10yo M with acute respiratory failure following an aspiration event. He weighs 30 kg, and he is intubated with a 6.0 cuffed ETT. Vitals: HR 125 beats/min, RR 15 breaths/min, BP 110/65 (55) mm Hg, and a saturation of 92% on 80% FiO₂. Exam reveals an intubated, sedated, and chemically paralyzed patient. The patient’s respiratory examination reveals symmetric chest wall expansion, and bilateral air entry with rhonchi.
• VC-SIMV with TV of 300 mL (10 mL/kg), PEEP 6, a rate of 15, inspiratory time of 0.7s, and an FiO₂ of 0.8. The patient's chest radiograph is shown. An arterial blood gas reveals a pH of 7.28, PCO₂ of 40 mm Hg, PaO₂ 62 mm Hg.
• The PICU fellow is concerned about the patient’s respiratory status, especially given that the peak pressures are in the mid-thirties and the mean airway pressure is 22.
• What’s his OI?
• How would you classify his ARDS?
• How can his ventilator be changed to protect the lungs from ventilator-induced lung injury?

​

CHECK FOR UNDERSTANDING

• What’s his OI?
• [(Mean Airway Pressure X Fractional Inspired Oxygen)/PaO₂] * 100
• [(22  * 0.8) / 62] * 100 = 28
• How would you classify his ARDS?
• An OI ≥ 16 is severe

​

• How can his ventilator be changed to protect the lungs from ventilator-induced lung injury?
• Tidal volume of 3-6 mL/kg in severe pediatric ARDS
• PEEP of 10-15 in severe pediatric ARDS

KEY POINTS

• Recognize pediatric acute respiratory distress syndrome has multiple potential causes
• Inflammatory response is a key feature in pathogenesis
• Mainstay of therapy is supportive care
• Mortality benefit demonstrated with an open lung approach (low tidal volume and high PEEP)
• Not all children will benefit from: steroids, proning, surfactant or iNO

​

​

THANK YOU!