Central venous catheters are frequently placed in the operating rooms, intensive care units and emergency departments for various indications such as intravenous fluid, drug infusion, measurement of cardiac parameters and lack of vascular access. Ultrasound guidance has become a standard for central venous catheterization. The use of ultrasound has reduced the number of puncture attempts, increased success rate and reduced complications. While the central venous catheter is inserted by ultrasound, the vessels and the needle can be imaged in real-time. In plane and out-of-plane imaging techniques can be used during catheterization. The in-plane technique ensures the entire needle visualization in ultrasound images. With the linear ultrasound probe, the vessel and needle are imaged longitudinally in the in-plane technique. When an endocavity (micro-convex) ultrasound probe is used, three central vessels (jugular, subclavian and brachiocephalic veins) are displayed as Y-shape. The advantage of the endocavity (micro-convex) probe is that it can visualize deeper tissues and deep veins, and more tissues can be imaged in wider angle. Both techniques have been successfully applied in central catheter placement. In-plane technique also ensures syringe-free cannulation where blood aspiration with a syringe attached to the needle is not necessary.

The aim of this study is to compare two different ultrasound guided in-plane techniques for central venous catheterization. The investigators planned to compare jugular venous catheterization using a linear probe and lateral oblique approach to brachiocephalic catheterization using a micro-convex probe and Y-shape imaging.

The primary outcomes are number of puncture attempts, success rate at first attempt, overall success rate, procedure time, ultrasound scanning time and rate of complications. Secondary outcomes are visibility of the veins and the needle in ultrasound images.

The trial is a comparison of two different interventional technique and planned as prospective randomized and single-blind study. Patients aged between 18-85 years that are planned central venous catheter placement will be included in the study. Patients included in the study will be assigned into two groups by computer-assisted randomization. In the first group (Oblique visualization Group), central catheter will be placed to the jugular vein by using ultrasound-guided in-plane syringe-free technique. In the second group (Y-shape visualization Group), central catheter will be placed to the brachiocephalic vein by using ultrasound-guided in-plane syringe-free technique Linear ultrasound probe will be used in the first group, and endocavity (micro-convex) ultrasound probe will be used in the second group.

In both groups, the number of puncture attempts, the number of needle redirections, and the procedure time will be recorded. The time of preprocedural ultrasound scanning will be recorded in both groups. In addition, complications during the procedure such as bleeding, hemothorax, pneumothorax, hematoma and carotid vascular injury will be recorded. Overall success rates will be assessed in each group at the end of the study. A catheterization procedure will be considered as "unsuccessful" after third puncture attempt or more than 10 needle redirections are needed or requires a procedure time more than 3 minutes. At this moment, the catheter will be placed to a different region or the investigators will switch to a different approach. The ease of the catheterization process will be scored between 0 and 10 by the investigator performing the process (0: the hardest, 10: the easiest). The ultrasound visibility of the needle, vessels, guide wire and catheter will be scored between 0 and 4 (4: excellent view, 3: good view, 2: Medium, 1: difficult 0: impossible to image). The recorded data will be compared between the two groups.