To the Editor,
We read with great interest the analysis by Boulet et al., which revisits long-term outcomes of central venous catheterization according to insertion site and suggests a preferential use of the subclavian approach [1]. We commend the authors for highlighting the clinical relevance of this topic and for drawing attention to the potential role of ultrasound guidance, particularly for subclavian/axillary access, which represents an important technical advance in contemporary critical care practice.
However, we believe that key methodological aspects of the original randomized trial substantially limit both the statistical interpretation and the generalizability of the conclusions drawn. In that trial, ultrasound guidance for subclavian/axillary catheterization was used in only approximately 5% of procedures (50/989) [1]. This very low exposure constrains the analysis to a context dominated by landmark-based techniques and limits the ability to robustly evaluate outcomes associated with ultrasound-guided access.
From a statistical perspective, such sparse utilization raises concerns regarding the stability of effect estimates. When exposure to the intervention of interest is rare, causal inference models—even when carefully adjusted—may yield estimates that are sensitive to model specification and small changes in event counts, particularly when the effective sample size (number of events) is below established thresholds for stable modeling [2, 3]. The absence or near absence of outcome events within the ultrasound-guided subclavian subgroup further restricts reliable estimation of hazard ratios for both infectious and mechanical complications [1].
In addition, the low rate of ultrasound-guided procedures likely reflects operator selection bias. Ultrasound-guided infraclavicular cannulation is technically demanding, and it is plausible that, within the trial, this approach was preferentially performed by a small group of highly experienced operators [4, 5]. Consequently, favorable outcomes may reflect operator expertise rather than intrinsic site safety, limiting extrapolation to broader ICU settings where operator skill and training vary considerably.
These limitations are accentuated by the evolution of technique over time. In current practice, what is often labeled “subclavian access” sometimes corresponds to an ultrasound-guided infraclavicular axillary vein puncture, a procedure that is anatomically and technically distinct from the landmark-based subclavian approach evaluated in the original study [1, 4–6]. Conflating anatomical site with procedural technique risks generating conclusions that are not directly applicable to modern, ultrasound-centered decision-making.
Moreover, site selection in clinical practice depends on multiple factors beyond anatomy alone, including catheter purpose (e.g., dialysis), patient-specific conditions such as coagulopathy or anatomical distortion, and operator proficiency [4–6]. Improving outcomes therefore requires not only choosing an appropriate site but also ensuring adequate training in ultrasound-guided technique, particularly longitudinal needle guidance and standardized procedural protocols. Structured training programs and competency-based progression have been shown to be essential for safely implementing these approaches [4, 6–8].
In conclusion, we believe that the study by Boulet et al. provides an important stimulus for discussion but should not be interpreted as a definitive recommendation favoring the subclavian site in contemporary practice. Future investigations should prioritize randomized comparisons of ultrasound-defined access techniques, performed under standardized conditions and with documented operator competency. Such efforts, combined with ongoing technological innovation, are essential to further improving the safety and quality of care for critically ill patients.
Acknowledgements
Not applicable.
Author contributions
All authors contributed equally to the conception, drafting, and critical revision of the manuscript, and approved the final version for submission.
Funding
Not applicable.
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
All authors consent to publication.
Competing interests
The authors declare no competing interests.
Footnotes
The original online version of this article was revised: the authors identified an error in the author name of Eric Maury.
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Change history
3/13/2026
A Correction to this paper has been published: 10.1186/s13054-026-05953-7
References
- 1.Boulet A, et al. Site-specific complications of central venous catheterization under systematic ultrasound guidance: a target trial emulation revisiting the 3SITES study. Crit Care. 2025;29:513. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Biondi-Zocai G, et al. Are propensity scores really superior to standard multivariable analysis? Contemp Clin Trials. 2011;32:731–40. [DOI] [PubMed] [Google Scholar]
- 3.Zampieri FG, et al. The Small Clinical Trial: Methods, Analysis, and Interpretation in Acute Care Cardiology. Can J Cardiol. 2025;41(4):656–68. [DOI] [PubMed] [Google Scholar]
- 4.Vegas A, et al. Guidelines for Performing Ultrasound-Guided Vascular Cannulation: Recommendations of the American Society of Echocardiography. J Am Soc Echocardiogr. 2025;38:57–91. [DOI] [PubMed] [Google Scholar]
- 5.Dawies TW, et al. Cannulation of the subclavian vein using real-time ultrasound guidance. J Intensive Care Soc. 2020;21(4):349–54. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Millington SJ, et al. Better With Ultrasound: Subclavian Central Venous Catheter Insertion. Chest. 2019;155(5):1041–8. [DOI] [PubMed] [Google Scholar]
- 7.Moureau N, et al. Evidence-based consensus on the insertion of central venous access devices: definition of minimal requirements for training. Br J Anaesth. 2013;110(3):347–56. [DOI] [PubMed] [Google Scholar]
- 8.Saugel B, et al. Ultrasound-guided central venous catheter placement: a structured review and recommendations for clinical practice. Crit Care. 2017;21:225. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
No datasets were generated or analysed during the current study.