What do we know about this topic?

Central venous access is a valuable tool for delivering medications or for intraoperative monitoring. Although the internal jugular approach is considered the first choice, it entails several risks. Despite several notable advantages of the subclavian vein over the jugular and femoral veins due to the lower risk of late complications such as infection and thrombosis, it is not considered a first choice due to its proximity to the pleura and the subclavian artery.

What new contribution does the study make?

The supraclavicular approach to the subclavian vein in central venous catheterization has been shown to have a lower risk of complications when performed under ultrasound guidance, improving needle visualization and reducing the risk of pleural puncture.

INTRODUCTION

Central venous access is often required in perioperative care and is a valuable tool for delivering medications or performing intraoperative monitoring ¹. Moreover, it is used long-term to administer antibiotic treatment, parenteral nutrition or chemotherapy ^2,3. The short pediatric neck limits maneuverability in ultrasound-guided approaches, while the tendency of the jugular vein to collapse and the proximity to the carotid artery hinder the insertion of a central line through this approach. With the introduction of ultrasound, it is now not only possible to reduce the number of failed cases and complications associated with central line insertion ⁴, but also to use other approaches with increased safety. The landmark-based supraclavicular approach to the subclavian vein was described by Yoffa in 1965 ⁵.

Despite notable advantages of the subclavian vein over the jugular and femoral veins because of a lower risk of late complications such as infection and thrombosis, this vessel is not considered a first choice because of its proximity to the pleura and the subclavian artery ⁶. More than a decade ago, Pirotte and Veyckemans ⁷ described the possibility of accessing the subclavian vein through the supraclavicular approach with the help of ultrasound. The establishment of the central venous access in order to use the subclavian vein from the supraclavicular approach during the procedure was reviewed in the institution where the study was first conducted ⁸ , with the finding that the technique was safe when ultrasound guidance was used. Prior observations showed that, with the adequate technique, arterial puncture and pneumothorax could be infrequent using this approach. This has been recently ratified in a clinical practice guideline ⁹ which suggests, with a GRADE 1 recommendation, the use of the subclavian vein in order to prevent central line-associated infection; additionally, the guideline indicates the use of ultrasound to access the brachiocephalic vein through the supraclavicular approach in children as the preferred approach in order to reduce the number of cannulation attempts and mechanical complications (GRADE 2). It is considered to be associated with a high success rate and a low incidence of arterial puncture and pneumothorax.

The objective of this study was to assess the sonoanatomical characteristics of the subclavian vein seen from the supraclavicular approach, seeking to analyze and describe the relationships between the right subclavian vein with the subclavian artery, the pleura and the skin from the supraclavicular fossa, using ultrasound. Additionally, it aims to quantify the superficiality of the subclavian vein from the window used for catheterization through a supraclavicular approach.

METHODS

Observational cross-sectional study in which data were collected during the intraoperative period. The population included ASA I, II and III children taken to non-emergent surgical procedures (NCEPOD 2, 3 or 4 classification) under general anesthesia, with tracheal intubation and with or without neuromuscular blockade at Fundación Hospital de la Misericordia in Bogotá, Colombia, during an 8-month period (June 2021 to March 2022).

The study was approved by the ethics committee of Fundación Hospital de la Misericordia, under number 342-20R, in May 2021. The informed consent process was carried out with each participant before anesthesia induction and the form was completed and signed by the legal guardian of each individual patient.

The exclusion criteria were patients with syndromes or disease conditions that altered the normal anatomy of the neck, the thorax, or the vascular structures found in those anatomical regions; neonates, premature infants; patients with cervical spine or neck conditions preventing extension; patients with malformation or genetic disease; obese patients; or teenage girls, in case they were pregnant.

The images were acquired by two trained ultrasonographers (Giraldo, DS; Bolívar, MA) with more than four years of experience with central line insertion through the supraclavicular approach in pediatric patients. The patients were divided into the following age groups ¹⁰: 1) Infants: less than 2 years of age; 2) pre-schoolers: between 2 and 5 years; 3) Schoolers between 5 and 10 years; 4) Adolescents: over 10 years of age. Age and anthropometric data were obtained from the clinical record.

Under general anesthesia with mechanical ventilation and orotracheal intubation, each patient was positioned in 30 grades Trendelemburg with a roll in the interscapular region to extend the neck and head, which was lateralized 45 grades to the left. Using a hockey stick probe (Sonosite SII, Fujifilm, 6-13 MHz linear HSL25x transducer) the internal jugular vein was followed on the short-axis view to the base of the neck and then the transducer was tilted and the ultrasound plane was taken caudally and anteriorly in order to identify the jugular-subclavian confluence. From the confluence, a long-axis view of the subclavian vein was acquired, trying to leave the pleural dome in the center of the image. The following characteristics were measured after freezing the image (Figure 1).

Source: Authors.

Figure 1 Sonoanatomical characteristics. 

Determination of whether the subclavian artery was visualized in the same ultrasound plane was also made. The images were then downloaded to a computer to calculate the following angles using the GeoGebra® software: 1) Minimum approach angle for vessel cannulation, formed by the skin surface and distance line D.; 2) Minimum approach angle for puncturing the pleura, formed by the surface of the skin and distance line E.

A different operator from the one performing the ultrasound scan (Velázquez, DA) used a 5-point Likert scale to rate the quality of the acquired window ¹¹, as follows:

STATISTICAL ANALYSIS

Non-probabilistic, consecutive sampling with patient inclusion in accordance with the surgical schedule of the institution. Data for each patient were entered in accordance with the protocol, using Microsoft-Excel 2019. Reported variables were: sex, age (years), weight (kg), height (cm), skin-to-vessel distance, skin-to-pleura distance, angle to the vessel (degrees), angle to the pleura (degrees), image quality (Likert scale), operator name. The STATA 18 software package was used for the statistical analysis of the database.

A descriptive analysis of the study variables was made. Continuous quantitative variables were reported as means and standard deviation (SD) or median and interquartile range (IQR), depending on distribution normality as determined by the Shapiro-Wilk test. On the other hand, categorical variables were reported with relative frequencies (percentages). For exploration purposes, age group differences for each variable were studied (Table 1) by means of hypothesis contrast, using the chi-square tests and Fisher's exact test for comparison of categorical variables, the ANOVA test for quantitative variables of normal distribution, and the Kruskal Wallis test as a non-parametric test for quantitative variables without a normal distribution. Statistical significance of the results was considered to exist with values p < 0.05.

RESULTS

Overall, 67 children were recruited during the study. The median age was 6 years (IQR: 2-12 years), with a minimum of 0.08 years and a maximum of 17, predominantly males (61%); median weight was 22 kg (IQR: 12.2-34 kg), and median height 115 cm (IQR: 88-142 cm). The sociodemographic variables and the study measurements are shown in Table 1.

Regarding vessel measurement, the mean skin-to-vessel distance was 0.70 cm (SD: 0,18 cm), as compared to the mean skin-to-pleura distance of 1.31 cm (SD: 0.28 cm). Mean vein diameter was 0.49 cm (IQR: 0.40-0.63 cm); and the mean hypothetical approach angle to the vessel was 22.09 degrees (SD: 4.37 degrees), while the mean hypothetical approach angle to the pleura was 39 degrees (SD: 5.31 degrees).

Finally, two ultrasonographers acquired the images, with CG acquiring a higher proportion (82%), with most of them being of good or excellent quality (76% and 18%, respectively). In none of the recorded sonoanatomical windows was simultaneous visualization of the artery and vein documented.

DISCUSSION

This study found that the use of the supraclavicular window to the subclavian vein in the pediatric population allows to find the vessel at a shallow depth (usually less than 10 mm), far from the subclavian artery (which is not visible in the sonoanatomical window), with good or excellent image quality in the vast majority of patients.

Although the subclavian vein is in close relationship with the pleura, it is feasible to perform in-plane cannulation with minimal vascular approach angles of close to 20 degrees, which in most cannulations direct the tip of the needle towards the mediastinum, in a course that avoids the pleural dome (Figure 2). The hypothetical cannulation angle considered in this study assumes that the entry point of the needle is just on the vertex or right upper corner of the ultrasound plane, which does not happen in real life cannulations. Usually, the puncture site moves away from the leading edge of the probe footprint at least a few millimeters, in such a way that a smaller cannulation angle is inevitable when the needle is forced to run more parallel to the skin surface. This has two very important advantages: improved sound reflection results in good needle visualization and allows the puncture to avoid the pleura as the tip of the needle is directed towards the jugular-subclavian confluence. This makes it possible to suggest a potential puncture angle of less than 20 degrees.

Safety margin enclosed between the two puncture lines. Source: Authors.

Figure 2 Vascular approach angle. 

For the sake of safety, the aim is to use a 15 degree angle or less in order to visualize the entire length of the needle in the subcutaneous tissue or in the muscle plane bound by the sternal head of the sternocleidomastoid muscle. The minimal depth required for accessing the vessel is then added. According to the authors' experience, this maneuver prevents the puncture from advancing towards the pleura. Moreover, given the small depth at which the vein is found, it is possible to perform the cannulation using a peripheral venous catheter (18-20G in adolescentes and 22G in younger children), thus limiting the reachable depth, as an additional safety factor.

The anatomy of the subclavian vein explains these results. The vein is located posterior to the clavicle and anterior to the scalene attachment on the first rib, arching over the latter at its most cephalad point, and the subclavian vein is separated from the subclavian artery by the anterior scalene muscle ¹². This anatomical configuration explains the shallowness of the vein documented in the patients, as well as the absence of the artery in the ultrasound views, considering that the latter is more cephalad and posterior, and is separated from the vein by the anterior scalene muscle.

Studies by other authors show a low risk of pneumothorax and arterial puncture. In a prospective sonoanatomy study, Stachura et al. document improved visualization of the subclavian vein from the supraclavicular fossa when compared to the infraclavicular approach ¹³. Attof et al. suggest that the supraclavicular approach to the subclavian vein poses a lower risk of failed catheterization, malposition, pneumothorax and arterial puncture when compared with the internal jugular vein and the infraclavicular approach to the subclavian vein ⁶. Rhondali et al., in an observational study of 37 children in whom the subclavian vein was cannulated through a supraclavicular approach, reported an 81% success rate on first cannulation and 100% with two attempts, without any major complications. ¹⁴ In their study, Byon et al. compared the supraclavicular vs. infraclavicular approach to the subclavian vein in a randomized study of 98 children under three years of age, comparing mean time to catheterization and number of attempts between the supraclavicular and infraclavicular approaches to gain central access to the subclavian vein, with a finding of shorter time and less needle passes when the supraclavicular approach was used ¹⁵.

Additionally, the risk of guidewire malposition was lower using the approach from the supraclavicular fossa, showing evidence of greater safety in pediatric patients when the insertion of a central catheter in the subclavian vein is planned using that approach +. In another observational study, Ye et al. described that it is possible to reduce the number of attempts and adverse effects when using a modified formula (based on the insertion point and external landmarks) to estimate the depth of insertion of the subclavian catheter through the supraclavicular approach ¹⁶. Finally, in 2016, a prospective study assessed the efficacy of using ultrasound for catheter insertion in children and neonates, and concluded that the procedure was easier and faster in both populations, when this method was used ¹⁷.

LIMITATIONS

As far as limitations of this study are concerned, it is important to say that in real-life catheterizations, the angle to approach the vessel can vary, considering that the needle does not always enter the ultrasound plane through the right upper corner. When the needle is first visualized at a greater depth, the real approach angle between the skin and the cannulation site will be smaller than the one reported in this study. Moreover, the sample size was small, making it difficult to extrapolate the data, and consecutive selection can introduce a potential selection bias. Finally, only two operators acquired the images and the majority were acquired by one of them. Given that ultrasound is operator-dependent, image quality will always depend on ultrasonographer skill in achieving optimal visualization.

CONCLUSION

The supraclavicular approach for subclavian vein catheterization in children is a potentially viable and safe technique. The mean skin-to-vessel distance is 0.70 cm, considerably shorter that the skin-to-pleura distance (1.31 cm), suggesting a lower pleural puncture risk. Additionally, ultrasound image quality was good or excellent in 94% of the patients included; and the possibility of cannulating with a minimal approach angle which avoids the pleura along the course of the needle under good needle visualization reduces the risk of puncturing the pleura. Further studies are needed to improve the current central venous access techniques in the pediatric population.

ETHICAL RESPONSIBILITIES

ACKNOWLEDGEMENTS