ObjectiveTo describe the effects of inhaled nitric oxide on oxygenation and ventilation in patients with acute, hypoxic respiratory failure and to characterize those who respond to low doses with a significant improvement in PaO2.Designor=to15% improvement in PaO2were randomized to receive conventional mechanical ventilation with or without prolonged inhaled nitric oxide.SettingPediatric intensive care unit of a tertiary care children's hospital serving as a regional referral center for respiratory failure.PatientsPediatric patients with an acute parenchymal lung disease requiring mechanical ventilation, an FIO2or=to7 cm H2O, and whose PaO2/FIO2ratio was <or=to160.InterventionsPaO2, PaCO2, pH, heart rate, blood pressure, and methemoglobin were recorded at baseline and after inhaling 1, 5, 10, and 20 ppm of nitric oxide. Peak expiratory flow rate and mean airway resistance were measured while subjects received 0 and 20 ppm of inhaled nitric oxide. Patients were followed up until extubation or death.Measurements and Main ResultsTwenty-six patients (median age, 2.6 yrs [range, 1 mo-18.2 yrs]) were enrolled in the study. PaO2increased (p < .001) and PaCO (2or=to15% improvement in PaO2; 14 of these responses occurred at a dose of 1 or 5 ppm. Response to inhaled nitric oxide was not associated with age, length of intubation, presence of primary lung disease, chest radiograph, or illness severity. Among patients weighing <or=to20 kg, responders showed a greater fall in mean airway resistance (p < .05) than nonresponders. Mortality was not influenced by prolonged inhaled nitric oxide when analyzed by intention to treat. Patients receiving prolonged inhaled nitric oxide at doses of <or=to20 ppm maintained methemoglobin levels of <3.0% and circuit concentrations of NO2of <1 ppm.ConclusionsInhaled nitric oxide at doses of <or=to5 ppm improves the oxygenation and (to a lesser extent) ventilation of most children with acute, hypoxic respiratory failure. The unpredictable response of patients necessitates individualized dosing of inhaled nitric oxide, starting at concentrations of <or=to1 ppm. Inhaled nitric oxide at <or=to20 ppm may exert a small salutary effect on bronchial tone. The benefits of prolonged inhaled nitric oxide remain unknown. (Crit Care Med 1999; 27:989-996)