eMedicine Specialties > Emergency Medicine > Pediatric

Pediatrics, Respiratory Distress Syndrome

Author: Andrew K Feng, MD, Attending Physician, Division of Pediatric Critical Care, Kapiolani Medical Center for Women and Children, Honolulu
Coauthor(s): Dale Steele, MD, Division of Pediatric Emergency Medicine, Assistant Professor, Department of Emergency Medicine, Brown University School of Medicine and Hasbro Children's Hospital
Contributor Information and Disclosures

Updated: Sep 18, 2009

Introduction

Background

Although originally described in adults, acute respiratory distress syndrome (ARDS) occurs in children of all ages; hence, the change from "adult" to "acute" respiratory distress syndrome. The syndromes of acute lung injury (ALI) and ARDS usually do not manifest in the typical time frame for emergency department (ED) treatment. However, effective early recognition and treatment of bacteremia, shock, and respiratory failure may prevent or ameliorate the cascade of host responses that result in ARDS as well as comorbidities.

Recognizing that patients who have been resuscitated from circulatory failure may have a period of relative stability followed by deterioration secondary to ARDS or other components of the multiple organ failure syndrome (MOFS) is important. This recognition should allow informed decision making of the need for transport or ongoing critical care.

Pathophysiology

ALI and ARDS are characterized by progressive hypoxemia. According to the 1994 American-European Consensus Conference on ARDS, ALI is defined by the following:

• Acute onset
• Arterial oxygen tension/fractional concentration of inspired oxygen ratio (PaO₂/FiO₂) of <300 (regardless of positive end-expiratory pressure [PEEP] levels)
• Acute-onset bilateral infiltrates on chest radiograph
• Noncardiogenic pulmonary edema

ARDS is defined by all of the above and PaO₂/FiO₂ of <200.

The syndrome follows a direct pulmonary or systemic insult resulting in injury to the alveolar-capillary unit. Several diseases can cause ALI/ARDS, more commonly following pneumonia, aspiration, and sepsis.

The course of ARDS can be divided into 3 pathologic stages as follows: exudative, proliferative, and fibrotic.

• Exudative: Injury to lung endothelial cells and alveolar epithelial cells occurs and results in air spaces filled with exudate and fluid and the development of microvascular thrombi leading to capillary occlusion.
• Proliferative: This stage occurs between the first and third week after the initial insult. Type II pneumocytes, fibroblasts, and myofibroblasts proliferate, resulting in widening of the alveolar septa and conversion of intra-alveolar hemorrhagic exudate into cellular granulation tissue.
• Fibrotic: If the patient survives for 3 weeks, the lungs exhibit remodeling and fibrosis.

Patients presenting in the ED will typically be confined to the exudative stage.

Pulmonary mechanics

Involvement is nonhomogeneous, with patchy and transient airway collapse occurring primarily in dependent portions of the lung. In these areas, functional residual capacity (FRC) is reduced and the closing capacity is above FRC. Thus, airway closure occurs during normal tidal breathing, leading to alveolar collapse, ventilation/perfusion (V/Q) mismatch, and progressive hypoxemia. During early stages, pulmonary resistance is near normal, as is anatomic dead space; thus, the initial problem usually is one of oxygenation rather than ventilation.

Effectively, the lung may be conceptualized as small rather than stiff. Although the total lung compliance is reduced, as little as 25% of the lung may be participating in gas exchange. Those areas that remain viable for gas exchange are normally compliant and subject to overdistension when subject to excessive inflating pressures.

Frequency

United States

Approximately 1-4% of patients admitted to pediatric intensive care units (PICU) have established ARDS.

International

ARDS is observed in all locations where medical care allows patients to survive acute insults of a primary pulmonary or systemic nature.

Mortality/Morbidity

• Mortality rates have varied between 20-75% among several studies, but they are difficult to interpret because of inconsistent diagnostic criteria. In a recent prospective multicenter study, Flori et al examined the epidemiology and risk factors associated with ALI/ARDS; the following findings were noted:¹
  • Of patients admitted to the PICU, 72% required intubation at the onset of ALI.
  • The mortality rate was 22%.
  • Poor prognostic indicators were associated independently with (1) the initial severity of hypoxemia, measured by the PaO₂/FiO₂ ratio; (2) the presence of nonpulmonary organ system failure, especially with 2 or more organ systems; and (3) the presence of central nervous system dysfunction.
  • Higher mortality rates occurred in patients with near-drowning, heart disease, and sepsis.

Age

In one series, the ages of children with ARDS ranged from 2 months to 21 years, similar to the overall distribution of the PICU population.

Clinical

History

Histories at the time of initial presentation offer little with regards to diagnosis of ALI/ARDS except for alerting the clinician to risks for development of lung injury such as exposure to gaseous fumes or hydrocarbon ingestion and potential aspiration. The time to develop hypoxemia severe enough for ALI/ARDS criteria is also dependent on the time of onset of the triggering disease or injury. ALI/ARDS may further be masked by preexisting medical problems including reactive airway disease and bronchopulmonary dysplasia. Exacerbation of such underlying chronic lung diseases can lead to severe wheezing as the chief complaint.

• Establishing ALI/ARDS criteria is highly variable and is dependent of the onset of illness/insult.
• In most patients, ARDS developed within 72 hours after the onset of the associated acute disease and many (42%) within 24 hours.
• In those with infectious pneumonia, the onset is often gradual.

Physical

Patients who present with a short history of symptoms are unlikely to meet ALI/ARDS criteria. As their lungs undergo changes during the first exudative stage of the disease, patients may become hypoxic out of proportion to the underlying disease. They may also become tachypneic but not significantly dyspneic, ie, comfortably tachypneic.

• The evolution of clinical signs depends on the type, acuity, and severity of the initial insult. However, often a latent period occurs in which the patient exhibits little respiratory distress, except for hyperventilation and hypoxia, with normal auscultation and normal or mildly abnormal chest radiograph findings.
• Over a period of hours to days, hypoxemia worsens, and the patient appears dyspneic and more tachypneic.
• Chest examination reveals diffuse rales.
• Supplemental oxygen may maintain adequate oxygenation, but often fails to improve the clinical appearance.

Causes

• ARDS is a clinical syndrome for which no specific marker exists. However, several have been identified to be associated with ARDS including tumor necrosis factor-a (TNF-a), interleukin-b (IL-b), interleukin 10 (IL-10), and more recently, soluble intercellular adhesion molecule 1 (sICAM-1). One of the most common diseases associated with ARDS is sepsis and/or septic shock. Other more common etiologies include infectious pneumonia, aspiration pneumonia, aspiration of gastric contents and other noxious substances (eg, hydrocarbons), inhalational injury (eg, thermal injury, noxious gases), and barotrauma/volutrauma secondary to mechanical ventilation.
• Failure of other organ systems commonly results in ARDS.
• Most near-drowning victims aspirate at least some water. Both fresh and saltwater aspiration results in pulmonary edema. If near-drowning occurs in stagnant or contaminated water, the risk of bacterial pneumonia is high. However, neither corticosteroids nor prophylactic antibiotics are beneficial.

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