Background: Ultrasound guidance is an important technique to improve the success rate of internal jugular vein catheterization (IJVC) at the first-attempt, however, both long-axis in-plane and short-axis out-of-plane techniques have their own disadvantages. The T-shaped ultrasonic probe invented by us combined with the help of laser positioning and 3D printing manipulator could realize real-time bi-plane guidance of the needle short-axis out-of-plane and long-axis in-plane. With the help of the Single-operator Laser-assisted T-shaped probe, the whole process of needle insertion, guide wire placement and catheter placement can be visualized, which is expected to improve the success rate on the first-attempt.

Objective: The primary outcome was the first-attempt success rate of initial RIJV catheterization without complications. The completion of the catheterization was defined as the presentation of the CVP waveform on the monitor. The secondary outcomes included first-attempt puncture success rate,first-attempt catheterisation success rate,overall catheterisation success rate,first-attempt needle tip location,first-attempt needle tip midline placement rate,number of needle direction adjustments,number of ultrasound probe repositionings, number of puncture attempts,first-attempt localisation time,first-attempt guidewire insertion success time,overall catheterisation success time.

Design, Setting, and Participants: This single-center, prospective, parallel-group, randomized controlled study enrolled surgical patients over 18 years and older (ASA grade Ⅰ-Ⅳ) who required IJVC ,fully understands the benefits and risks of the study, participates voluntarily, and signs the informed consent form in the First Hospital of Jilin University. The exclusion criteria were congenital abnormal development of the internal jugular vein; prior puncture at the same site last month; puncture site injury, infection, or hematoma; right neck surgery history and neck fixation due to surgery or injury. The participants were randomized into the traditional ultrasound-guidance group or the single-operator Laser-assisted T-shaped probe ultrasound-guidance group. After inducing general anesthesia, ultrasound-guided internal jugular vein catheterization was performed by the experienced operators.

Interventions: 352 patients were stratified into eight subgroups based on whether common carotid artery coverage exceeded 50% ,internal jugular vein depth exceeded 10mm , and internal jugular vein anteroposterior diameter exceeded 10mm . Each subgroup generated an independent randomisation sequence according to the block randomisation principle (T-mode ultrasound-guided group and 'long-axis plane' ultrasound-guided group). Upon enrolment, new subjects were assigned to corresponding subgroups based on stratification factors. Within each subgroup's dedicated random sequence, the allocation plan (T-shaped ultrasound guidance group or 'long-axis plane' ultrasound guidance group) was sequentially retrieved and marked. The next subject in that subgroup would receive the subsequent plan in the sequence. The operating team comprised six physicians (including two residents, two specialists, and two anaesthesiologists), who were not involved in other aspects of the study. Given the significant technical differences between the two approaches, the operators, equipment assistants, and research assistants were aware of the groupings. Conversely, participants' families were unaware of the groupings and could withdraw from the trial at any time. All data were collected and analysed by the same research assistant.

After the patient was admitted to the operating room, the vital signs of the patients were monitored，the thoraco-chin distance (the distance between the mandible and the upper edge of the sternostemma in cm when the patient's head was tilted back as far as possible) and neck circumference (the thinest neck, that is, the upper edge of the 7th cervical vertebra to the horizontal position below the Adam's apple in cm) were measured and recorded in the supine position. After the establishment of peripheral venous access, the patients received rapid induction of general anesthesia and tracheal intubation. Without special circumstances, the right internal jugular vein was selected by the operator after randomization. The probe frequency of 13 MHz and a depth of 4.0 cm were set for optimal image quality in both groups. The patient was placed in a supine position with the head 15 degrees lower and the head turned to the left to fully expose the right side of the neck, and a thin pillow was placed under the right shoulder if necessary.

T-type ultrasound guidance unit:

A 3D marking laser with laser emitter is mounted on the T-type ultrasound probe.The laser emitter is positioned directly above the Mark point on the short-axis plane of the T-shaped ultrasound probe. Due to the probe's hardware structure-where the long and short-axis probes are vertically and tightly fused, with the long-axis probe's centreline perpendicular to and passing through the short-axis probe's centreline-the emitted laser lies on the skin surface extension of the short-axis plane's centreline. Instruct the assistant to apply an appropriate amount ofcoupling agent evenly onto the ultrasound probe. The operator and assistant collaborate to cover the entire 3D-printed three-axis adjustable support arm and ultrasound probe with a sterile sleeve, evacuating any air between the probe and the sleeve. Coupling agent is then applied evenly to the outer layer of the sterile sleeve where it contacts the patient's skin,completing the equipment preparation. To commence positioning, the operator controls gently place the T-shaped ultrasound probe onto the patient's neck skin, positioning the short axis cephalad and the long axis caudally.Adjust the arm and rotation axis so the midline of the short-axis image centres the transverse section of the internal jugular vein. The laser direction now indicates the cutaneous pathway to the vein's centre point, coinciding with the long-axis probe's midline. Adjust the slide rail to align the midpoint of the short-axis probe with the marked point, then continue sliding 1 cm cephalad to ensure the needle tip approaches the maximum transverse plane level upon subcutaneous entry into the internal jugular vein. Positioning is complete. Secure the arm to stabilise the probe against the skin surface, establishing hands-free, stable, and continuously monitored ultrasound guidance. The operator's left hand stabilises the skin near the puncture site.

The right hand holds the puncture needle at a 45° angle to the skin, with the needle body aligned with the laser path and closely following the short-axis probe's MARK point during insertion, while simultaneously performing aspiration. Once the needle tip enters the subcutaneous tissue, if deviation is observed in the short-axis ultrasound image, adjust the insertion angle to penetrate the anterior wall directly above the internal jugular vein. Upon visualising needle entry into the vessel on both short-axis and long-axis ultrasound images, and observing uninterrupted, non-pulsatile venous blood return in the syringe, adjust the needle tip position to the centre of the longitudinal section of the internal jugular vein using the long-axis view. Subsequently, while maintaining the needle position with the left hand, slide the probe distally with the right hand and determine the needle tip position prior to guidewire placement using the 'dynamic needle tip method' via the short-axis plane image. Save a screenshot for the initial needle tip position assessment. During this attempt, the needle tip position remains fixed. Insert the guidewire 30 cm without resistance through the lumen at the rear end of the syringe connected to the tip of the puncture needle. Under guidewire guidance, place the guide catheter 12-15 cm into the internal jugular vein. If resistance persists, withdraw the guidewire and puncture needle from the internal jugular vein and apply pressure to the puncture site with sterile gauze for approximately 3 minutes. Subsequent attempts may proceed once no significant bleeding is observed at the puncture site. During this process, the timer shall not be paused, and the number of ultrasound probe repositionings and needle tip adjustments shall be recorded throughout.

Ultrasound-guided group within the longitudinal axis plane:

The assistant applies coupling agent to the surface of the ultrasound probe. The operator and assistant collaborate to cover the probe with a sterile sleeve, evacuating any air between the probe and sleeve. Coupling agent is then evenly applied to the outer layer of the sterile sleeve where it contacts the patient's skin, completing device preparation. To commence localisation, the operator holds the ultrasound probe with the left hand, aligning its longitudinal axis parallel to the course of the internal jugular vein. After superimposing the midpoint of the probe's longitudinal axis plane with the marked point, the probe is slid further along the longitudinal axis towards the cephalic direction by 1 cm. This ensures the needle tip approaches the most transverse plane. Stabilise the probe with the left hand to complete positioning.Hold the puncture needle at a 45° angle to the skin with the needle body aligned along the longitudinal axis.

Advance the needle closely alongside the midpoint of the probe's longitudinal axis while aspirating.Upon subcutaneous entry, if the needle trajectory deviates on the longitudinal ultrasound image, adjust the insertion angle or reposition the probe to ensure the needle tip penetrates directly above the internal jugular vein.

After confirming vascular entry on ultrasound and observing unobstructed venous blood return in the syringe, adjust the needle tip position to ensure the needle tip penetrates directly above the internal jugular vein. Upon visualising vascular entry in the ultrasound image and observing uninterrupted, pulsatile venous blood in the syringe, adjust the needle tip position to align it with the midpoint of the longitudinal axis plane of the internal jugular vein. At this stage, the right hand should stabilise the needle immovably, while the left hand manipulates the ultrasound probe to determine the needle tip position relative to the longitudinal axis plane using the the 'dynamic needle tip method' to determine the needle tip position prior to guidewire placement. Save a screenshot for the initial needle tip position assessment. During this attempt, the needle tip position remains unchanged. Insert the guidewire 30 cm without resistance through the lumen at the end of the syringe connected to the needle tip. Under guidewire guidance, place a 12-15 cm internal jugular vein catheter and secure it properly. Should significant resistance occur during guidewire insertion, withdraw the wire. After repositioning the ultrasound probe and adjusting the intravascular needle tip, reinsert the guidewire.If resistance persists, withdraw both the guidewire and puncture needle from the internal jugular vein. Apply pressure to the puncture site with sterile gauze for approximately 3 minutes.

The operation timer shall not be paused during this interval, and the number of ultrasound probe repositionings and needle tip adjustments shall be recorded throughout.

From patient admission to the operating theatre until completion of follow-up, the research assistant shall tick and record the following data in the CRF form: age, gender, height, weight, surgical scheduling (elective or emergency), surgical category, ASA classification, comorbidities, pre-procedural MAP, presence of coagulation, anticoagulant therapy status, antiplatelet therapy status,sternocleidomastoid distance, neck circumference, anterior/posterior jugular vein diameter and depth, common carotid artery coverage, initial catheterisation success, initial puncture success, initial needle tip position score, needle tip adjustment count, ultrasound probe repositioning count, total attempts, device preparation time, initial positioning time, initial guidewire Overall catheterisation success time, occurrence of complications (posterior jugular vein puncture, arterial puncture, haematoma, haemothorax, pneumothorax, nerve injury, jugular vein thrombosis), operator's assessment of the procedure (0-10 points, 0 being dissatisfied, 10 being highly satisfied).

Inclusion Criteria:

• The patient fully understood the benefits and risks of the study, voluntarily participated, and signed the informed consent form
• Require internal jugular vein catheterization
• ASA grade I~IV
• Over 18 years and older

Exclusion Criteria:

• Congenital malformation or abnormal development of the internal jugular vein;
• Prior internal jugular vein catheterization performed within the past month
• Puncture site injury, infection, or hematoma
• History of surgical intervention in the right neck region
• Restricted neck mobility due to prior surgery or traumatic injury