An observational study in Internal Jugular Vein Anatomy, Common Carotid Artery Anatomy and Cardiac Surgery, sponsored by Ankara City Hospital Bilkent. Not yet recruiting at 1 site in Turkey (Türkiye). Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-23.
Sponsored by Ankara City Hospital Bilkent · Observational
This prospective observational study will describe the anatomical relationship between two major blood vessels on the right side of the neck: the internal jugular vein and the common carotid artery. These vessels lie close together, and their relative positions are relevant when placing a central venous catheter.
The study will enroll 200 adults undergoing elective cardiac surgery at Ankara Bilkent City Hospital who require right internal jugular vein catheterization as part of their routine care. A single ultrasound image will be recorded for each participant under standardized conditions after general anesthesia and before catheter placement.
Computer-assisted image analysis will determine the angular position of the artery around the center of the vein on a 0°-360° scale. The study will describe the distribution of these angles and their frequencies within eight anatomical sectors. The findings may provide a more detailed quantitative description of neck vascular anatomy and support future research on ultrasound-guided central venous access. Participation will not alter routine anesthesia or catheterization management.
This single-center, prospective, cross-sectional, descriptive observational study will characterize the angular relationship between the right internal jugular vein (IJV) and the right common carotid artery (CCA) using standardized transverse ultrasound images.
The primary objective is to quantify the angular position of the CCA center relative to the IJV center on a continuous 0°-360° scale and describe its circular distribution. Secondary objectives are to determine the distribution across eight 45° anatomical sectors, calculate circular descriptive statistics, assess whether the angular distribution deviates from uniformity, and explore associations between angular distribution and basic patient characteristics, including age, sex, and body mass index.
The study will consecutively enroll 200 consenting adults aged 18 years or older undergoing elective cardiac surgery at Ankara Bilkent City Hospital who are scheduled for right IJV catheterization under general anesthesia as part of routine clinical care. There will be no control group.
The sample size calculation was based on a preliminary anatomical analysis previously conducted by the research team in 68 patients, with one ultrasound image evaluated per patient. In this preliminary dataset, the right CCA center was located in the medial sector relative to the right IJV center in 24 patients and in the posteromedial sector in 41 patients. The combined proportion of these two positions was therefore 65/68 (95.6%).
The sample size was calculated to estimate the combined proportion of medial and posteromedial positions with approximately ±3 percentage points of absolute precision at a 95% confidence level. The formula for estimating a single proportion, n = Z² × p × (1-p) / d², was used. With Z = 1.96, a rounded anticipated proportion of p = 0.956, and d = 0.03, the required sample size was approximately 180 patients. Allowing for approximately 10% missing or non-evaluable images, the target enrollment was set at 200 patients. This calculation addresses the precision of estimating the combined proportion of medial and posteromedial positions; it does not establish separate precision or statistical power targets for each of the eight anatomical sectors, the continuous angular distribution, or exploratory association analyses.
Ultrasound imaging will be performed after induction of general anesthesia and endotracheal intubation, during mechanical ventilation with a positive end-expiratory pressure of 5 cmH2O. Participants will be positioned in 15° Trendelenburg with the head rotated approximately 30° to the left. A high-frequency linear ultrasound transducer will be used to visualize the right IJV and CCA in the transverse plane at the level of the cricoid cartilage. The transducer marker will face the patient's left, toward the cricoid cartilage and trachea. Minimal transducer pressure will be applied to limit venous compression.
One ultrasound image meeting the predefined standardization and image-quality criteria will be digitally recorded for each participant. Routine central venous catheterization will then proceed according to clinical practice. Research measurements will not influence the indication, site, or technique of catheterization.
De-identified images will be analyzed using custom computer-based image annotation software. The center of each vessel will be manually identified at the intersection of its anteroposterior and transverse diameters. The software will record the pixel coordinates of both centers and automatically calculate the angle of the CCA center relative to the IJV center using a two-argument arctangent function, with correction for the downward-increasing image y-axis. No manual angle measurement will be performed.
The IJV center will serve as the origin of the angular coordinate system and the center of an imaginary clock face. The position of the CCA center relative to the IJV center will be expressed as follows: 0°/360° corresponds to lateral (3 o'clock), 90° to anterior (12 o'clock), 180° to medial (9 o'clock), and 270° to posterior (6 o'clock). Angles will increase counterclockwise from the lateral direction. Each calculated angle will also be assigned to one of eight 45° anatomical sectors: lateral, anterolateral, anterior, anteromedial, medial, posteromedial, posterior, or posterolateral.
Recorded variables will include age, sex, height, weight, body mass index, planned cardiac surgical procedure, calculated angular position, and the corresponding anatomical sector. Vessel diameters, inter-center distance, and CCA-IJV overlap percentage will not be included as study variables or analyzed.
Angular data will be evaluated using circular statistical methods. Analyses will include the circular mean direction, mean resultant vector length (R), circular standard deviation, and 95% confidence interval for the mean direction. The Rayleigh test will assess deviation from circular uniformity. The number and percentage of participants in each anatomical sector will be reported. Angular distributions will be illustrated using rose diagrams and two-dimensional vessel-center distribution plots. Exploratory analyses will examine associations of age and body mass index with angular position using appropriate circular-linear methods. Directional differences between sex groups will be evaluated using appropriate circular group comparison methods.
The study involves no additional invasive procedures, medication administration, blood sampling, or ionizing radiation. Routine anesthesia and central venous catheterization management will remain under the responsibility of the clinical team.
Ankara City Hospital Bilkent is the lead sponsor of 437 studies on the registry; 109 are open to participants now.
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Adult patients aged 18 years or older scheduled for elective cardiac surgery at Ankara Bilkent City Hospital who require ultrasound-guided right internal jugular vein catheterization under general anesthesia as part of routine perioperative care. Eligible patients will be recruited consecutively after providing written informed consent. A single standardized transverse ultrasound image of the right internal jugular vein and common carotid artery will be recorded after induction of general anesthesia and endotracheal intubation, before catheterization, for computer-assisted angular mapping.
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Exclusion Criteria:
Adults aged 18 years or older undergoing elective cardiac surgery who are scheduled for right internal jugular vein catheterization under general anesthesia as part of routine clinical care. Each participant will undergo a single standardized ultrasound image recording before catheter placement to determine the angular position of the right common carotid artery center relative to the right internal jugular vein center.
Other: Standardized Ultrasound Imaging and Computer-Assisted Angular Mapping
A single transverse ultrasound image of the right internal jugular vein and common carotid artery will be recorded at the cricoid cartilage level after induction of general anesthesia and endotracheal intubation, before routine central venous catheterization. Imaging will be performed in 15° Trendelenburg with approximately 30° leftward head rotation and a positive end-expiratory pressure of 5 cmH2O, using minimal transducer pressure. Vessel centers will be manually marked on de-identified images using custom software, which will automatically calculate the angular position of the artery center relative to the vein center on a 0°-360° scale. This is an observational imaging and analysis procedure; routine anesthesia and catheterization management will not be altered.
Angular Position of the Right Common Carotid Artery Center Relative to the Right Internal Jugular Vein Center
The angular position of the right common carotid artery center relative to the right internal jugular vein center will be determined from standardized transverse ultrasound images. The internal jugular vein center will serve as the reference point, and the angular position will be calculated automatically using image-based coordinate analysis. Each participant will have one angular measurement expressed in degrees (0°-360°). The angular distribution across participants will be characterized using circular statistical methods.
Time frame: After anesthesia induction and before catheterization
Distribution of the Right Common Carotid Artery Center Across Eight Anatomical Sectors
The number and percentage of participants whose right common carotid artery center falls within each of eight 45° anatomical sectors relative to the right internal jugular vein center: lateral, anterolateral, anterior, anteromedial, medial, posteromedial, posterior, and posterolateral.
Time frame: After anesthesia induction and before catheterization
Circular Descriptive Statistics of the Angular Distribution
The angular distribution will be characterized by the circular mean direction in degrees, mean resultant vector length (R; dimensionless, ranging from 0 to 1), circular standard deviation in degrees, and 95% confidence interval for the circular mean direction.
Time frame: After anesthesia induction and before catheterization
Deviation of the Angular Distribution From Circular Uniformity
Deviation of the angular distribution of the right common carotid artery center around the right internal jugular vein center from circular uniformity will be evaluated using the Rayleigh test of uniformity.
Time frame: After anesthesia induction and before catheterization
Exploratory Associations Between Patient Characteristics and Angular Distribution
Exploratory analyses will assess associations of age and body mass index with the angular position of the right common carotid artery center relative to the right internal jugular vein center using appropriate circular-linear statistical methods. Differences in angular distribution between sex groups will be evaluated using appropriate circular group comparison methods.
Time frame: After anesthesia induction and before catheterization
Plan to share: No — This is a single-center academic observational study. Individual participant data (IPD) will not be shared publicly. Only de-identified aggregate study results will be reported in scientific publications.
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