US technique
STERILE
A Philips (Philips Healthcare, Netherlands) CX50 system equipped with a L12-3 probe and an EPIQ system equipped with a XL14-3 probe were used for single-plane and x-plane CVCs, respectively. The CVCs were performed following previously recommended steps [The puncture site was prepared using antiseptic solution and protected with sterile drapes, whereas the probe was covered with a sterile sheath using sterile gel outside and inside the sheath. A real-time, single-operator, freehand technique was used. While introducing the needle, the operator held the probe with one hand, and the needle with the other hand, lidocaine 2% was used to anesthetize the puncture site, followed by needle puncture into the vein with the modified Seldinger technique.The single-plane approach was performed under the guidance of the long-axis view of the vein using in-plane method. The needle was held at 30°–45° angle, oriented in-plane with transducer. Vessel alignment was maintained during the procedure, and the entire length of the needle was visible during progression through the tissues.Using the x-plane approach, the vein was visualized simultaneously in transverse and longitudinal images. The probe was positioned as the single-plane approach, maintaining the vein in the middle of both the long- and short-axis views. During the procedure, the entire length of the needle was visible in-plane in the long-axis view, and the transient vessel deformation produced by the additional pressure when the tip abutted the venous wall was observed in the short-axis view. Once the vessel wall was penetrated, the deformation disappeared and a hyperechoic dot was displayed within the vein in the short-axis view.In both single- and x-plane approaches, the presence of the needle in the vein was confirmed by aspiration of blood into the syringe. When the needle tip was inserted into the vessel, the assistant advanced the guidewire. The needle was withdrawn, a dilator was used, and a catheter inserted as usual (Additional file Upper panels show 