Fig. 1

Normal three-vessel and tracheal view. a Schematic drawing. b Ultrasound images. The vena cava is located on the right side of the trachea. The pulmonary artery is connected to the descending aorta through the ductus arteriosus or ductal ligament, forming a symmetrical “V” sign with the aorta (the inner diameter of the aorta and the pulmonary artery is similar), both of which are located on the left side of the trachea. AO: aorta; E: esophagus; PA: pulmonary artery; T: trachea; SVC: superior venae cava