The review, registered prospectively on the Open Science Framework and reported according to the PRISMA-ScR checklist, casts a wide net across eleven databases including PubMed, EMBASE, Scopus, CINAHL and the major Chinese literature platforms. From 762 initial records, the research team screened down to 41 eligible publications representing 39 unique studies conducted between 2015 and 2026. Nearly three-quarters of the studies appeared after 2020, a signal of how quickly clinical interest in midlines has accelerated. But the geographic picture was strikingly lopsided: 30 of the 39 studies came from China, seven from Italy, and just one each from the United States and India, a concentration the authors acknowledge limits the generalizability of any conclusions to other healthcare systems.

At the heart of the confusion is anatomy. The 2024 Infusion Therapy Standards of Practice from the Infusion Nurses Society define a midline catheter as a peripheral device inserted into the basilic, cephalic or brachial vein of the upper arm, with its tip terminating at the level of the axilla—strictly outside the central circulation. The Michigan Appropriateness Guide for Intravenous Catheters from 2015 went further still, describing tips ending in the basilic or cephalic vein themselves. European experts disagree. The 2023 ERPIUP consensus and the 2025 position statement from GloVANet and the World Congress of Vascular Access both endorse placing the tip deeper, in the thoracic tract of the axillary vein or even the subclavian vein. A 2020 Chinese expert consensus declined to recommend any specific position at all, calling instead for individualized assessment. The review’s evidence map traces this evolution year by year, showing a field that has split into two philosophical camps: one guarding the peripheral boundary, the other pushing deliberately closer to the central veins.

The stakes of this definitional brawl are not academic. Three recent meta-analyses have suggested that more proximal tip positions may be safer. Zhang and colleagues found that subclavian placement was associated with lower overall complication rates and reduced catheter-related thrombosis compared with axillary placement, while Sheng’s team reported broader advantages including longer dwell times and fewer episodes of phlebitis, bleeding, occlusion and dislodgement. A Bayesian network meta-analysis by Yang and colleagues likewise ranked subclavian placement favourably for thrombosis, occlusion, phlebitis and overall complications. But the new scoping review urges caution: these pooled analyses were built on studies that used wildly different anatomical categories, confirmation techniques and outcome definitions, and some carried wide credible intervals reflecting small sample sizes. The signal is real, the authors conclude, but it is a signal—not a standard.

How clinicians actually verify where a tip has landed turns out to be equally fragmented. The review identified three broad families of confirmation methods. The simplest is external body measurement: estimating insertion depth from surface landmarks, such as measuring from the puncture site to the sternoclavicular joint and subtracting two centimetres for a subclavian target, or to the midclavicular line minus three to four centimetres for the thoracic axillary vein. One study of 125 patients found that confirmatory ultrasound showed only 88.1 percent of tips measured this way actually landed at the expected site. The method is fast and equipment-free, but it is an indirect guess that cannot account for tortuous vessels, obesity, edema or joint contractures.

Ultrasound has emerged as the dominant alternative, described in 63.41 percent of the included publications. Real-time imaging allows operators to watch the catheter advance, identify the axillary vein where the cephalic vein drains into it, and track the tip as a double echogenic line. When the tip cannot be directly seen, clinicians can flush saline to generate a transient microbubble signal that reveals its location. The technique proved feasible in 98.9 percent of patients in one Italian study, and a retrospective Chinese analysis found ultrasound-guided localization cut complications from 20 percent to 6 percent compared with external measurement alone. Yet ultrasound has its own ceiling: the clavicle obscures the subclavian vein in most supine patients, morbid obesity defeated sonographic identification of the tip in roughly 1.1 percent of cases, and success rates for confirming axillary placement have dipped as low as 75 percent in some hands. Everything depends on the operator, and no objective, quantifiable benchmark yet exists.

Chest radiography, long the gold standard for central lines, fared worst in the review. Only about a quarter of studies used it, and for good reason. In one American cohort, X-ray failed to visualize the catheter tip at all in 28.14 percent of patients. Routine imaging of a non-central device also collides with the ALARA principle of minimizing radiation exposure, and the delay inherent in radiologist reporting forfeits the possibility of immediate bedside correction. On X-ray, the lateral border of the scapula serves as the anatomical boundary of the axillary vein, but the review shows even this landmark is applied inconsistently. The authors argue for multimodal confirmation pathways that reserve radiography for genuinely uncertain cases rather than reflexive routine use.

Beyond the tip itself, the review maps a thicket of variables that shape placement accuracy and complication risk. The catheter-to-vein ratio at the tip level has emerged as a particularly powerful predictor: one retrospective study identified a ratio above 45 percent as an independent risk factor for catheter failure, and a subsequent prospective cohort found that even a ratio above 33 percent correlated with elevated failure risk, aligning with ultrasound screening thresholds for peripheral access. Insertion site matters too—a few centimetres’ difference in puncture height within the mid-upper arm’s so-called green zone can shift a fixed-length catheter’s tip from the distal axillary vein all the way to the brachiocephalic vein. Catheter tip configuration adds another wrinkle, with database evidence suggesting open-tipped devices trigger more complications and removals than closed or valved designs, though inconsistent reporting makes the independent effect of material—silicon versus polyurethane—impossible to pin down. A randomized trial of antithrombogenic and antimicrobial coatings, for instance, found no significant difference in thrombosis rates.

The complication data compiled in the review’s evidence map span dizzying ranges. Reported overall complication rates ranged from under 1 percent to 60 percent depending on tip position and study, catheter-related thrombosis from 0.085 percent to 41.5 percent, and dwell times from five days to more than 150 days. Some findings cut against the proximal-placement trend: one pilot study of 27 patients found no significant association between tip position and fibroblastic sleeve formation or thrombosis, while another study comparing superficial with deeper tip placement found complication rates of 23.81 percent versus 7.55 percent. The review’s authors stress that these unweighted ranges describe the spread of the literature, not comparative effect estimates, and that dwell time in particular is an ambiguous metric—long indwelling may reflect success or simply prolonged exposure to endothelial irritation and biofilm.

What the review ultimately delivers is less an answer than an agenda. The authors call for professional societies to agree on standardized anatomical terminology, for prospective cohort studies and randomized trials using precise positioning techniques to clarify the relationship between tip location, catheter lifespan and patient comfort, and for clinical pathways built on multimodal confirmation that spares patients unnecessary X-rays. They are candid about their own limitations: the exclusion of mini-midlines shorter than 15 centimetres, the restriction to English and Chinese publications, the absence of formal quality appraisal, and the overwhelming Chinese dominance of the evidence base. But the core message stands. Midline catheters have earned their place in modern infusion therapy, and their popularity will only grow as care migrates out of hospitals. Until the field settles where the line should end—and how to prove it—a device praised for its simplicity will keep carrying a hidden burden of uncertainty that only coordinated, multinational research can lift.

Subject of Research: Midline catheter tip location, tip confirmation methods and associated clinical characteristics

Article Title: Mapping the Evidence on Midline Catheter Tip Location, Confirmation Methods and Associated Characteristics: A Scoping Review

Article References: Mapping the Evidence on Midline Catheter Tip Location, Confirmation Methods and Associated Characteristics: A Scoping Review. (n.d.). https://doi.org/10.1002/nop2.70876

Image Credits: AI Generated

DOI: 10.1002/nop2.70876

Keywords: midline catheter, vascular access, catheter tip location, ultrasound guidance, chest radiography, catheter-related thrombosis, scoping review, infusion therapy standards, catheter-to-vein ratio, nursing practice, peripheral intravenous therapy, evidence mapping