Prone Positioning in Pediatric Acute Lung Injury

Inclusion Criteria: * Age \>42 weeks post-conceptual age and \<18 years of age * On mechanical ventilation (defined as presence of an endotracheal/tracheostomy tube and currently using ventilator support) * All of the following in the same 48 hour period: * acute pulmonary parenchymal disease (i.e., chest radiograph report of diffuse bilateral pulmonary alveolar infiltrates) * mechanical ventilation for at least 1 hour and anticipated need to continue mechanical ventilation for at least 24 hours * at least one PaO2/FiO2 ratio \<300 (adjusted for barometric pressure: if altitude \> 1000m, then PaO2/FiO2 \<= 300x(B.P./760), regardless of mean airway pressure) * functional arterial catheter for blood gas analysis Exclusion Criteria: * Persistent hypotension (defined as systolic blood pressure of 70mmHg+(2x age in years)); i.e. patients requiring either intravenous fluids and/or increases of additional cardiotonic medications every 2 hours * Active bleeding that requires ongoing blood/fluid volume replacement * Currently on extracorporeal membrane oxygenation (ECMO) * Severe chronic lung disease (cystic fibrosis or bronchopulmonary dysplasia) * Respiratory failure presumed to be the result of cardiac disease * History of symptomatic or uncorrected congenital heart disease or a right to left intracardiac shunt * Bone marrow or lung transplant * Current known diagnosis of any of the following: * upper airway disease (i.e., tracheitis, tracheomalacia) * reactive airway disease (receiving beta agonists or acute doses of systemic corticosteroids) * refractory cerebral hypertension (intracranial pressure \[ICP\] \>20mmHg for 1 hr) * neuromuscular respiratory failure (chronic assisted ventilation) * spinal instability (uncleared cervical spine) * unstable long bone fractures * Nonpulmonary condition that may be exacerbated by the prone position (for example, osteogenesis imperfecta, craniofacial surgery in the past week) * Draining abdominal surgical wound * Pregnancy * Subject's family/medical team have decided not to provide full support (patient treatment considered futile) * Enrollment in any other clinical trial within the last 30 days