How the definition of ARDS has been adapted for use in children

A pediatric definition of ARDS is needed to deliver appropriate care and unify research.

The clinical syndrome we currently call Acute Respiratory Distress Syndrome (ARDS) has been described dating back to the 1940s, with a more clear description by Ashbaugh in 1967. Over the years, we have better understood the pathophysiology of ARDS, but unfortunately there is no single definitive diagnostic test to confirm a patient has ARDS. As such, our diagnostic criteria rely upon clinical signs and symptoms of the disease to reflect the pathophysiology of ARDS. Previous definitions have used clinical surrogates for this pathophysiology [i.e., PaO2/FiO2 ratio as surrogate for intrapulmonary shunt, bilateral infiltrates on chest imaging as surrogate for diffuse (non-lobar) disease.] However, these definitions need to be simple enough to apply at the bedside so that we can quickly recognize a patient has ARDS, and implement appropriate supportive care.

The Murray Lung Injury Score was initially proposed to define ARDS, although some found it too cumbersome for routine clinical care. The American-European Consensus Conference (AECC) Definition of ARDS was relatively simple to apply, and was used for nearly 20 years. However, there were many limitations to the AECC definition, most notably related to excluding patients with LV dysfunction, not controlling for ventilator support in the calculation of PF ratio, and inter-observer variability in the interpretation of bilateral infiltrates.

The Berlin definition has overcome some of these limitations for defining ARDS in adults, but pediatricians have not been involved in the process of creating consensus ARDS definitions. Because ARDS is a heterogeneous syndrome defined by clinical criteria, pediatric specific practice patterns, co-morbidities, and differences in outcome make adult-based ARDS definitions impractical for children. This prompted the Pediatric Acute Lung Injury Consensus Conference (PALICC) initiative, where a subgroup of pediatric ARDS (PARDS) investigators drafted a pediatric specific definition of ARDS based upon consensus opinion and supported by detailed literature review. They subsequently tested elements of the definition with patient data from previously published investigations on PARDS.

Several aspects of the PARDS definition align with the Berlin Definition of ARDS in adults: timing of ARDS after a known risk factor, the potential for ARDS to co-exist with left ventricular dysfunction, and the importance of identifying of a group of patients at risk to develop ARDS. Larger departures from the Berlin Definition include: 1) simplification of chest imaging criteria to eliminate bilateral infiltrates; 2) use of pulse oximetry based criteria when PaO2 is unavailable; 3) inclusion of Oxygenation Index and Oxygen Saturation Index instead of PaO2/FiO2 ratio with a minimum PEEP level for invasively ventilated patients; 4) and specific inclusion of children with pre-existing chronic lung disease or cyanotic congenital heart disease. Because clinical symptoms are used to define ARDS, and because these symptoms can be modified by the way care is delivered (e.g., the decision to obtain an arterial blood gas), a pediatric specific definition is necessary. This definition was meant to be a starting point, with the hope for external validation and continued iterative refinement.

References

PALICC Group. Pediatric Acute Respiratory Distress Syndrome. Pediatric Critical Care Medicine. 2015;16(5):428-439.

Khemani RG, Smith LS, Zimmerman JJ, Erickson S, PALICC Group. Pediatric Acute Respiratory Distress Syndrome: Definition, Incidence, and Epidemiology: Proceedings From the Pediatric Acute Lung Injury Consensus Conference. Pediatric Critical Care Medicine. 2015;16(5_suppl):S23-S40.

Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. Acute respiratory distress in adults. Lancet. 1967;2(7511):319-323.

ARDS Task Force, Ranieri VM, Rubenfeld GD, et al. Acute respiratory distress syndrome: the Berlin Definition. Consensus Development Conference presented at JAMA : the journal of the American Medical Association; Jun 20, 2012.