Internal jugular vein (IJV) cannulation is one of the commonly performed procedures, in both the peri-operative period and in intensive care unit. Use of Real-time Ultrasound guidance during IJV cannulation is considered to be relatively safe and is now recommended as a standard-of-care technique by the American Society of Anaesthesiologists practice guidelines for central venous access[1, 2]. Central venous catheterization is associated with various mechanical complications like accidental common carotid artery (CCA) puncture, haematoma, haemothorax, pneumothorax, etc.[3]. Carotid puncture is considered one of the most severe complication with the reported incidence as high as 10.6% with traditional landmark technique[4]. Although usually benign, accidental carotid artery puncture can sometimes be life-threatening when it results in accidental intra-arterial cannulation, haemothorax, acute cerebro-vascular  accident, IJV-carotid artery fistula or airway compromise secondary to a haematoma[5-7]. Real-time ultrasound reduces complications, yet CCA puncture rates remain 5.9%[8]. 

Although IJV is generally lateral and anterior to the CCA, there may be variations in the position and the degree of overlap of the IJV over CCA. Therefore, the risk of accidental CCA puncture is always there[9]. A safe and successful internal jugular vein cannulation depends on two main factors – larger diameter of IJV and minimum degree of overlap of IJV on CCA[8]. Several maneuvres which increase the size of IJV have been practiced, such as Trendelenburg tilt, head rotation, abdominal compression, passive leg elevation and providing positive end-expiratory pressure[10-12]. Traditionally, there has been a great temptation to rotate the head as far as possible to the opposite side to “open” the neck and visualize the anatomic landmarks. However, this rotation of the head changes the anatomical relationship between the IJV and the CCA. Ultrasound imaging has revealed that when the head is rotated to the contralateral side, the IJV tends to lie more anterior thereby overlapping the CCA. Several researches have studied relation of IJV and CCA with varying degrees of head rotation (0° to 80°), for optimal visualization of the vessels and to minimize the overlap and hence the risk for CCA puncture in normal patients[13]. Obesity exacerbates challenges due to obscured landmarks and deeper IJV placement hence USG guided IJV cannulation is a preferred technique in them. While studies in non-obese patients suggest ≤30° rotation minimizes overlap[14] data for obese populations are limited. This prospective observational study evaluates the optimal head rotation angle for IJV cannulation in obese patients (BMI ≥25 kg/m²) by measuring IJV-CCA overlap and vessel dimensions under US guidance. 

This Prospective Observational single centre study was conducted in a tertiary hospital. After obtaining approval from the Institutional Ethics Committee (IEC No: IEC/373/21), 60 consenting patients of age 18 years and above, with BMI ≥ 25 kg/m2, belonging to ASA physical status I – III were included in the study.  Patient with previous history of right IJV cannulation, or with evidence of mass/tumor/scar in the neck area, or with suspected/diagnosed cervical spine injury /disease in whom head rotation was contraindicated, patients with limited neck mobility due any reason and patients refusing to participate in the study were excluded from the study. 

The study was carried out in the Pre-operative holding area, Operation theatres and Intensive Care Units. Written informed consent was obtained from all patients. Before the procedure, patients were given supine position with 15° Trendelenburg position. All patients received a head ring of thickness 5 cm and a shoulder roll of thickness 5 cm. Real time ultrasound using standard high frequency (5- 12 MHz) linear probe was performed to visualize Right IJV and CCA, in the short axis view (transverse orientation) at the cricoid level with head in neutral position (0° head rotation). Neutral/0° head rotation was defined as having the patient’s sagittal plane perpendicular to the floor. Probe pressure was kept as low as possible to avoid compression of the vein. The head was then rotated to 15° and the diameter of the IJV was measured using calliper by drawing a line using electronic marker between the farthest two points of the vein wall in the Transverse and Anteroposterior (AP) planes, respectively ([Fig. 1]). The Overlap length - defined as the longest distance between the tangent of the outermost point of the CCA and the innermost point of the IJV ([Fig. 2]). The percentage of overlap between IJV and CCA as calculated by the formula % Overlap = (Overlap Length x 100) / CCA diameter. Each patient’s head was then be rotated in a stepwise manner to 30°, 45° and 60° based on the position of the tip of nose to neutral position (measured using a protractor). Similar sono-anatomical images of IJV and CCA were obtained and corresponding measurements were obtained and recorded for each head position. All sono-anatomical scans were performed under supervision of skilled anaesthesiologist, and all values were measured on the images after the patient is stabilized for at least 30 seconds in each of the measurement position. 

The following measurements were noted for each head position: 

Optimal Visualization of Right IJV by ultrasound was defined as the maximum diameter of the IJV with least degree of overlap of IJV over CCA.  The degree of head rotation which provides optimal visualization of right IJV was noted in each patient. In addition, the operators’ perception for the optimal view of IJV and the degree of head rotation was also noted.  The patients in whom there was inability to obtain the data in any of the four head rotations, were withdrawn from the study.

Sample size of the study was determined using SAS 9.2 package. Based on the study done by Izumi M et al. [9], to get the minimum difference of 20% in the mean overlap of IJV over CCA with the change in head rotation from 15° to 60°, calculated minimum sample size was 53 (Power of study 90% and alpha error of 0.05). Considering 10% dropout we decided to enroll 60 patients for this study.

Data was analysed using SPSS v26. Continuous variables are expressed as mean ± SD, and categorical variables as percentages. ANOVA and paired t-tests compared overlap across different head rotations (P<0.05 is considered as significant).

On the basis of body mass index (BMI), all 60 patients with BMI ≥ 25 kg/m2 were divided into 3 groups:

Group 1 - BMI 25 - 29.9 kg/m2 (n=10)

Group 2 - BMI 30.0 - 39.9 kg/m2 (n=44)

Group 3 - BMI > 40kg/m2 (n=6)

None of our cases were withdrawn from the study. The mean age of the study population was 43.40 ± 11.68 years, 33.3 % were male and 66.6% were female subjects with the mean BMI of 34.10 ± 4.18 Kg/m2 [Table. 1]. 

Transverse and Antero-posterior diameters of Internal Jugular Vein (IJV) and transverse diameter of Common Carotid Artery (CCA) and the overlap length of IJV over CCA at different degrees of head rotation are depicted in [Graph 1]. As the degree of head rotation was increased the overlap length of IJV over CCA also increased [Graph 2]. This overlap of IJV over CCA increased significantly from 34.9% at 15° head rotation to 47.79% at 45° (P=0.032) and to 55.3% at 60° head rotation (P<0.001) [Table. 2]. 

The effect of head rotation on the percentage overlap of IJV over CCA was more pronounced in patients with higher BMI i.e. Group 3 (BMI ≥40.0) > Group 2 (BMI = 30.0 - 39.9) > Group 1 (BMI = 25.0 - 29.9). This is depicted by a line diagram in [Graph 3].

Venous access is an important issue in the obese patients[1, 2]. A central venous catheter may be needed especially if there is difficulty finding a suitable peripheral venous access for the peri-operative period[2]. The right internal jugular vein (IJV) is the often preferred to place a central venous line. However, IJV catheterization may result in mechanical complications like accidental arterial puncture, haematoma, haemothorax, pneumothorax, arterial-venous fistula, venous air embolism, nerve injury, thoracic duct injury[4].

With landmark-guided IJV cannulation technique, the rate of mechanical complication is 10%–15% and unsuccessful insertion is up to 20%[1]. Although ultrasound guidance improves the insertion success rate upto 93.9%, first-attempt success rate is only 82% and carotid puncture rate is up to 5.9%[16]. Obscured landmarks, short neck and deeply placed IJV in obese patients, pose difficulty in IJV cannulation by landmark technique hence real time US guided IJV cannulation is preferred. Optimum conditions should be carried out before IJV cannulation particularly obese patients. Improving success rate and decreasing complications can be achieved by increasing the cross-sectional area (CSA) of IJV and minimizing the overlap of IJV on CCA respectively.

To increase the success rate, various landmark‑based techniques exist and measures such as head rotation and the Trendelenburg position are commonly used[17]. The degree of head rotation to the contra- lateral side is rarely specified[18]. There is a wide variation in the anatomical relationship of the IJV to the Common Carotid Artery (CCA). The IJV usually lies anterior and lateral to the CCA[13, 19]. As the head is rotated away from midline, the IJV becomes more directly anterior to the CCA. Extreme head rotation, to 80° or 90°, frequently causes the CCA to sit directly underneath the IJV, increasing the theoretical risk of CCA puncture[14, 15, 19]. Changes in the relationship between these two structures with head rotation may lead to accidental arterial puncture or failure to locate the IJV[3]. Most of the researchers have studied the effects of various degrees of head rotation on relationship of IJV to CCA in normal patients. Few studies have assessed the changes in relationship of IJV to CCA with head rotation in obese patients. Various degrees of head rotation for optimal IJV positioning have been studied. Woo et al.[4] studied at six positions: 0°, 30°, and 60° of head rotation to the contra-lateral side combined with 0° and 10° of Trendelenburg tilt in 102 subjects. Lamperti et al.[14] studied with head in neutral position (0°) and 45° head rotation in 932 patients. Purohit et al.[19] studied in neutral head position on both sides and also with the head rotated to the contra lateral side by 15° and 45° in 100 patients. Miki et al.[9] studied in 30 patients with head rotation at 0°, 15°, 30°, 45°, 60°, and 75° from the midline to the left, 2 and 4 cm above the clavicle. Lieberman et al.[18] studied in 49 patients with the head rotated to 0°, 15°, 30°, 45°, and 60°. 

In our study, we assessed with head rotated 15°, 30°, 45°, 60° like that of Lieberman et al.[18] and Miki et al.[9]. However, we did not include 0° (neutral head position) as it is technically difficult to perform IJV cannulation in neutral head position. Clearing the chin is needed for IJV cannulation, which is not possible without giving some degree of head rotation. Also, studies have shown that extreme head rotation, to 80° or 90°, frequently causes the CCA to sit directly underneath the IJV, increasing the theoretical risk of CCA puncture[14, 15]. Hence, head rotation for >60° was not included in our study.

In our study, we observed no significant difference (P>0.05) in the Transverse and AP Diameter of IJV, Transverse Diameter of CCA, during the head rotation at 15°,30°, 45°, 60°. Our findings correlated with Woo et al.[4] who observed that IJV diameter did not show any difference regardless of head rotation except for increase in IJV diameter by 10 to 20% with 10° Trendelenburg tilt. Trendelenburg position was given primarily to all our patients as a standard position for securing IJV, so this difference was not seen. 

Significant overlap length (of right IJV and CCA) was observed only during the head rotation from 15° to 60° (p=0.005; 95% CI of 0.06 - 0.18) in our study. Whereas, Miki et al.[9] observed this overlap (p<0.01) with head rotation ≥30°, 4 cms above clavicle in non-obese patients. This difference from our study could be attributed to their comparison between 0° to 30° as opposed to our comparison of 15° to 30°. They also observed flattening of IJV (IJV approximately to a perfect circle) ≥30°, 4 cm above the clavicle (P < 0.01) compared to neutral position. Woo et al.[4] observed significantly increased (p<0.05) overlap of the IJV and CCA in BMI ≥ 30 kg/m2 compared to BMI< 25 kg/m2. They had included subjects with BMI < 25 kg/m2 whereas our study included subjects only with BMI >25 kg/m2 which may the reason for this difference observed. Also, in their study, measurements were done with 0°, 30° and 60° head rotation whereas, in our study measurements were done with 15°,30°, 45° and 60° of head rotation (15° difference between the 2 positions). This difference of comparison may be reason for finding increased overlap at 30° between the two studies. Umana et al.[20] observed right IJV overlapped the CCA in 30.7% of patients in neutral head position compared to 37.3% with the head rotated to the opposite side. The degree of head rotation was not specified in their study for us to compare. 

Percent Overlap on head rotation from 15° to 45° and 15° to 60° was statistically significant (P=0.032;95%CI of 5.32-20.43) and (P<0.001;95% CI of13.13-27.64) respectively. Sulek et al.[13] observed that percent overlap of the CCA and IJV increased significantly at 40° head rotation on both right and left side (P < 0.05). Lieberman et al.[18] simulated catheter insertion of right IJV observed that the simulated needle did not hit the CCA until the head was rotated at least 30°. The CCA hit rate was higher at 45° compared to 30°(P<0.01). Purohit et al.[19] observed increase in overlap of CCA and IJV on both sides with 45° head rotation (99% on right and 97% on left, P<0.05). Miki et al.[9] observed that percent overlap at 2 cm and 4 cm above clavicle was significantly higher at 60° and 75° head rotation (p<0.01). Troianos et al.[3] observed that 53% of the patients exhibited >75% overlap of the CCA at 90° of head rotation.

On subgroup analysis between different BMI groups, percent overlap increased even with lesser degree of head rotation in higher BMI groups. On head rotation from 15° to 45°, Percent overlap was significant in Group II patients (BMI 30.0-39.9 kg/m2) (41.16%; P=0.003; 95% CI of 5.75 - 25.3) and Group III patients (BMI > 40kg/m2) (52.24%; P= 0.05) whereas on head rotation from 15° to 60°, it was significant in patients with BMI 25-29.9 kg/m2 (P=0.02; 95% CI of 5.29-48.73).

Percent overlap in Group II patients (BMI 30.0-39.9 kg/m2) was significant on head rotation from 15° to 45° (P=0.003; 95% CI of 5.75 - 25.3). On head rotation from 15° to 60°, it was significant even in patients with BMI 25-29.9 kg/m2 (P=0.02; 95%CI of 5.29-48.73) BMI 30.0-39.9 kg/m2 (P=0.003; 95% CI of 9.63 - 26.87).  However, subjects with BMI > 40kg/m2 there was no statistically significant difference (P=0.051) observed with this degree of head rotation. Our findings correlated with Woo et al.[4] who observed that the overlap of the IJV and CCA was significantly increased in patients with BMI ≥ 30 kg/m2 and with higher degrees of head rotation (0°, 30°, 60°) (p<0.05). Lamperti et al.[14] reported the risk of overall complications increased in patients with BMI ≥30 Kg/m2 (OR 3.42, P <0.0001, 95% CI 2.39 – 4.89).

Vessel overlap does not mean it will puncture CCA but there is an increased probability of CCA puncture. With the needle advancement to the IJV, the anterior wall of the IJV is compressed rather than penetrated immediately when the needle reaches the IJV. The IJV may partially or completely compress during needle advancement which could cause puncture of the anterior and posterior walls of IJV almost simultaneously[21]. So, with a smaller diameter of IJV and increasing percentage of overlap, the possibility of puncture of CCA, which positioned directly beneath the IJV, theoretically increases[4].

Based on our findings, we propose the following protocol for US-guided IJV cannulation in obese patients and we recommend that in obese patients, head rotation should be <45° and < 60° with BMI ≥ 30 kg/m2 and 25-29 kg/m2 respectively to minimize IJV – CCA overlap and to avoid accidental CCA puncture. Ultrasound is very helpful when the alignment of the IJV and CA is such that there is minimum overlap between the vessels and this can be achieved by optimum head rotation to optimize access and minimizes the risk of accidental CCA puncture.

There are several limitations in our study. First, we did ultrasound examination only at the cricoid level which is routinely used in our practice. Further studies are needed to evaluate the relationship between the IJV and CCA at various levels. Secondly, actual cannulation was not performed in our study which could guide if any altered needle approach angle under real-time ultrasound guidance is needed. Thirdly, the number of patients in our study was small (n=60); particularly patients with higher BMI i.e. > 40 kg/m2. Therefore, further studies are with larger sample size are necessary to confirm our findings, especially patients with higher BMI > 40 kg/m2. 

The effect of head rotation on relation between IJV and CCA placement is variable among patients. Therefore, it is unlikely to have one standard degree head rotation in all type of patients that would benefit ultrasound guided IJV canulation. Head rotation >45° in obese patients significantly increases CCA puncture risk. For Ultrasound-guided IJV cannulation in obese patients with BMI ≥30 kg/m², head rotation of ≤45° should be optimum to facilitate the ease of canulation and avoid complications.

Intensive Care Units, Operation theatres of L. T. M. Medical College & Hospital – for providing patients, equipment, & infrastructure.