As ultrasound machines have become more portable and easier to use, thus allows a rapid evaluation of an unstable patient, at the bedside. Ultrasound has a higher sensitivity than the traditional upright anteroposterior chest radiography for the detection of a pneumothorax. In this report which happened on November 2018 in Cipto Mangunkusumo Hospital would like to highlight the use of ultrasound to detect pneumothorax. A four-months old baby boy with tumor in palatum region was scheduled to undergo elective tumor excision. This patient also with history of code blue because of tracheostomy displacement. After surgery the patient’s oxygen saturation gradually decreased from 100% into the low 80s until bradycardia and cardiac arres. Using ultrasound, the right and left hemithoraces were examined. The ultrasound probe was placed on the anterior chest wall at multiple intercostal spaces. Lung sliding was demonstrated on the left lung after the exam, but not on the right lung. Because of the patient’s unstable condition, a 14-gauge intravenous catheter was placed superior to the rib at the second intercostal space along the midclavicular line. An immediate return of spontaneous circulation resulted. A chest tube was placed, and the patient’s oxygen saturation returned to 100%.