Pediatric Acute Respiratory Distress Syndrome (pARDS)
Acute respiratory distress syndrome (ARDS) is a form of hypoxemic respiratory failure secondary to increased pulmonary vascular permeability and diffuse alveolar damage from a variety of risk factors and etiologies.
Background and Diagnosis
The most common causes of pediatric ARDS (pARDS) include sepsis, aspiration, and pneumonia. Other etiologies include trauma, transfusion-related causes, drugs, and alcohol. As no reliable biomarkers have been developed, the diagnosis is primarily based on clinical grounds.
Much of what is known about ARDS in pediatrics is extrapolated from adult data; however, the following important differences must be considered for the diagnosis and stratification of pARDS:
- Use of invasive arterial oxygen monitoring is less frequent; thus, stratification of disease severity may be done with the oxygenation saturation index rather than the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2).
- pARDS is more commonly managed with noninvasive ventilation as compared to ARDS in adults.
The Berlin ARDS definition is used to classify ARDS in adults, and pediatric criteria have been developed from consensus meetings to define pediatric ARDS (pARDS), taking into account the differences noted above.
Pediatric Acute Respiratory Distress Syndrome Definition (pARDS)*
ARDS is characterized by hypoxemic lung injury from a dysregulated immune response incited by some predisposing factor. Alveolar injury causes an immune response leading to diffuse alveolar damage. This response also leads to increased capillary permeability from release of proinflammatory cytokines and, in the process, further damage to the capillary and alveolar endothelium. Alveolar “leakiness” leads to accumulation of bloody and proteinaceous edema fluid, with loss of functional surfactant, leading to alveolar collapse. The resultant hypoxemia is secondary to severe ventilation–perfusion mismatch.
The Healthy Lung and the Exudative Phase of ARDS
Management of pARDs involves the following:
1. Treat underlying condition (e.g., sepsis, trauma).
2. Provide respiratory support through ventilation.
- low-tidal-volume ventilation (targeting 4–6 mL/kg predicted body weight)
- open-lung ventilation
- combine low-tidal-volume ventilation with recruitment maneuvers and titrated positive end-expiratory pressure (PEEP) to optimize recruitment of collapsed alveoli
- use of relatively high PEEP to maintain adequate oxygenation
- use of recruitment maneuvers in which high amounts of PEEP are applied for short amounts of time to open collapsed alveoli (some evidence of harm has been reported from this approach, but ongoing studies are evaluating the risks versus benefits)
- maintain plateau pressure <28 cm H20
- tolerate permissive hypercapnia (pH 7.15–7.3) to facilitate lower tidal volumes
- maintain low driving pressure (plateau pressure minus PEEP)
- lower oxygenation goals to saturations of 88%–92% rather than normoxemia
3. Consider neuromuscular blockade in severe pARDS.
4. Use goal-directed fluid management with diuretics as necessary to maintain intravascular volume and perfusion while preventing positive fluid balance.
5. Consider prone positioning (although shown to improve outcomes in adults with ARDS, evidence of benefit has not yet been demonstrated in children).