Acute chest syndrome is a severe sickle cell disease complication in children requiring blood transfusion therapy to prevent acute respiratory failure and death. Nitric oxide is a potent vasodilator that could reverse pulmonary vascular occlusion and restore normal oxygenation. The randomized trial will test that hypothesis.

Acute chest syndrome is a severe sickle cell disease complication in children requiring blood transfusion therapy to prevent acute respiratory failure and death. Nitric oxide is a potent vasodilator that could reverse pulmonary vascular occlusion and restore normal oxygenation. The randomized trial will test that hypothesis in a prospective randomized double-blind placebo controlled study. 50 children in two years will be included: 25 in each arm.

Inclusion Criteria:

• child between 1 and 18 years old
• Sickle cell anemia or equivalent (sickle beta 0 thalassemia)whoe weight is between 10kg and 65kg
• presenting acute chest syndrome as defined a new radiological infiltrate with tachypnea, respiratory discomfort, cough, chest wall pain and fever more than 38.5°C
• hypoxaemia with transcutaneous oxygen saturation equal or less than 92%
• informed consent signed by parents and approved by the child able to express his consent
• insured by the National social security system or by the universal medical insurance
• previous medical physical examination

Exclusion Criteria:

• respiratory distress with hypoxaemia with transcutaneous oxygen saturation equal or less than 92% under more than 5l/min of oxygen or 40% oxygen inhaled, hypercapnia signs 'sweating, altered consciousness, paCO2 more than 60mmHg) with need of emergency exchange transfusion and/or tracheal intubation with mechanical ventilation
• Isolated acute asthmatic crisis
• stroke or priapism with emergency acute transfusion needed
• acute anemia with hemoglobin drop of more than 20% as compared to steady state hemoglobin
• chronic long term transfusion therapy
• nitric oxyde hypersensitivity
• patients with right-left extra-pulmonary cardiac shunt
• patient previously included in the protocol
• patient participating in another interventional protocol
• pregnancy or breast feeding