Review

REVIEW ARTICLE

Acute Respiratory Distress Syndrome
PRIYA PRABHAKARAN
From Division of Pediatric Critical Care, University of Alabama, Birmingham, AL ,USA. Correspondence to: Priya Prabhakaran, Suite 504, ACC Building, 1600, 7th Avenue S, Birmingham, AL 35233, USA. pprabhakaran@peds.uab.edu

Background: Acute respiratory distress syndrome (ARDS) is a common diagnosis among children admittedto pediatric intensive care units. This heterogeneous disorder has numerous pulmonary and non-pulmonary causes and is associated with a significant risk of mortality. Many supportive therapies exist for ARDS. Search: Literature search was performed by using the key words ARDS and related topics on the Pubmed search engine maintained by the National Heart, Lung, Blood Institute. Pediatricrandomized controlled trials that have been published in the last 10 years were included. Emphasis was placed on pediatric literature, although sentinel adult studies have been included. Most of the evidence presented is of levels I and II. Results: Low tidal volume is the only strategy that has consistently improved outcome in ARDS. A tidal volume of ≤6mL/kg predicted body weight should be used.Ventilator induced lung injury may result in systemic effects with multi-system organ failure, and all efforts should be made to minimize this. Positive end-expiratory pressure should be used to judiciously maintain lung recruitment. There is insufficient evidence to routinely use high frequency ventilation, prone positioning, or inhaled nitric oxide. Calfactant therapy is promising and may be consideredin children with direct lung injury and ARDS. Current literature does not support routine use of corticosteroids for non-resolving ARDS. Key words: Acute respiratory distress syndrome, Pediatric, Surfactant, Ventilation.

ince its description in 1967 by Ashbaugh(1), acute respiratory distress syndrome (ARDS) has been the subject of intense investigation. This heterogeneous disorder has anincidence of 8.5-16 cases/1,000 pediatric intensive care unit (PICU) admissions(2). While the outcome of pediatric ARDS has improved, the mortality rate remains high at about 22%(3). DEFINITION Based on the 1994 American European Consensus Criteria, ARDS is defined as (1) having acute onset (2) severe arterial hypoxemia (PaO2/FiO2 ≤200 torr) for ARDS and 7.2(18). Permissive hypercapnia iscontraindicated in patients with intracranial hypertension, pulmonary hypertension, and severe cardiac dysfunction. In adult patients without ARDS who were ventilated for over 48 hours, high TV and high peak inspiratory pressure (PIP) were both significantly associated with the development of ARDS(20).This highlights the importance of lung protective ventilation in all children, regardless of the presence orabsence of lung injury. Positive end-expiratory pressure (PEEP) is an essential component of ventilation in ARDS. PEEP keeps alveoli expanded, raises the lung volume towards functional residual capacity (FRC), improves lung compliance, and decreases ventilation -perfusion (V/Q) mismatch. The best PEEP and the strategy of choosing it remain unresolved. A RCT of high (mean 13.2 ± 3.5cm H20) versus low(mean 8.3 ± 3.2cm H20) PEEP in adults with ARDS, all of whom were ventilated with low TV, showed no benefit in mortality, organ failures, or duration of mechanical ventilation in the high PEEP group, although the patients who received higher PEEP had improved oxygenation. The concentrations of plasma inflammatory biomarkers in the two groups were not different(21). Two subsequent RCTs in adultsalso showed similar results(22,23). There are no pediatric RCTs on this subject. Titrating PEEP to the best static lung compliance compatible with a plateau pressure of ≤ 28-30 cm H2O with TV ≤ 6mL/ kg may be reasonable in children. High Frequency Oscillatory Ventilation (HFOV) HFOV is an alternative form of ventilation characterized by very high respiratory rates (3-12 Hz) and very small TV,...