Introduction

Blood collection is one of the most common procedures performed in hospitalized patients and is essential for diagnosis and monitoring the progress of medical interventions [1]. It allows for the assessment of organ function and the effectiveness of treatment in infectious, autoimmune, and oncological diseases [2]. Venous blood is typically obtained via single-use peripheral venipuncture, most often from the antecubital fossa. Although widely practiced, this method may lead to complications such as vessel damage, bleeding, pain, infection, phlebitis, and thrombosis [2–4]. While generally accepted by both patients and healthcare providers, repeated venipuncture can result in loss of venous access particularly in chronically ill patients, the elderly, obese patients and children leading to difficult intravenous access (DIVA) [2, 5, 6]. In patients with DIVA, unsuccessful blood draw attempts cause additional pain, discomfort, and reduce satisfaction with hospitalization [5]. Frequent and ineffective attempts are time-consuming, often unsuccessful, and increase the risk of pre-analytical errors [3, 7–9].
While venous blood drawn directly from a vessel is typically preferred for laboratory testing, in cases of DIVA, blood sampling may also be performed through previously inserted vascular access devices (VAD), such as midline catheters (MC), various types of central vascular access devices (CVAD), and, in exceptional cases, short peripheral catheters (SPC) [10–12].
The choice of vascular access depends on multiple factors, including the anticipated duration of intravenous therapy, the chemical properties of the administered medications, the need for frequent blood sampling, and the assessment of available peripheral veins [13].
Midline catheters are most commonly used in patients requiring intravenous therapy for more than five days, in whom CVAD is not recommended [14]. In other situations, where frequent blood sampling is necessary, peripherally inserted central catheters are the recommended option [15]. The duration of effective blood collection via SPC is limited, and their usefulness diminishes over time. After 24–48 hours, lumen occlusion, increased flow resistance, and endothelial irritation leading to phlebitis and/or venous thrombosis are frequently observed, compromising the safety and effectiveness of this method [16, 17]. For patients who do not require a CVAD but need frequent blood draws especially during multi-week therapy an MC represents a valuable option to reduce the number of peripheral venipunctures [17]. The aim of this study was to analyze and assess the effectiveness of using MC for laboratory blood sampling.

Material and methods

The analysis was based on documentation maintained by the vascular access team (VAT) (including the patient registry, cannulation records, and observation forms) at a university hospital in Warsaw. Records from the period between January 1, 2021, and December 31, 2024, were included.

Statistical analysis

Documentation from 1,903 patients was included in the study. The analysis covered: gender, age, indications for MC insertion, insertion site, catheter size and length, reason for removal, dwell time, and duration of blood aspiration. Variables subjected to statistical analysis included: time from hospital admission to MC insertion, duration of aspiration, and catheter dwell time. Selection of statistical tests was preceded by an assessment of variable types, distribution normality, and sample size. The Mann-Whitney U test, Kruskal-Wallis test, and χ² test were used for analysis. Results were considered statistically significant at a p-value < 0.05. Calculations were performed using IBM SPSS Statistics version 29.

Vascular access team

Midline catheters are inserted by an interdisciplinary VAT, consisting of 16 nurses and 3 physicians specialized in anesthesiology and intensive care.

Vascular access team’s scope of practice

The operation of the VAT is based on the Standards for Infusion Therapy Practice developed by the Infusion Nurses Society and involves assessing, diagnosing, and selecting the most appropriate vascular access for each patient, as well as managing the related complications [18]. Procedures are performed both electively and on an urgent basis. Vascular access team specialists not only insert VAD but also monitor their function and intervene in cases of vascular access-related complications [18].

Eligibility

After initial referral by the primary care unit, the VAT nurse is responsible for selecting the most appropriate type of intravenous access. The nurse conducts a patient interview and physical assessment, which includes the use of the A-DIVA scale [5]. If the planned intravenous therapy is expected to last fewer than five days, a long peripheral catheter or SPC is inserted under ultrasound guidance. Based on the collected data, the VAT specialist selects and inserts the optimal vascular access. If reassessment indicates the need for a CVAD, the procedure is performed by a VAT physician.

Procedure of midline catheters insertion

After obtaining patient consent, the MC is inserted using a linear ultrasound probe (8–13 MHz) and following the standard insertion procedure, with either the direct Seldinger technique or the modified Seldinger technique [19]. The procedure is performed in a dedicated procedure room using a surgical aseptic non touch technique (ANTT). The midline catheters are inserted at the mid-upper arm following the zone insertion method, targeting the basilic, cephalic, or brachial veins, while maintaining a catheter-to-vein ratio not exceeding 33% [18]. Upon completion, the operator confirms proper catheter function by blood aspiration and verifies tip location using ultrasound. The catheter is secured with a sutureless stabilization device and a transparent dressing; tissue adhesive is applied when necessary.

Blood sampling

Blood sampling through an existing VAD, such as an MC, allows the procedure to be performed without repeated venipuncture, significantly improving patient comfort and reducing the risk of complications typically associated with cannulation. Adherence to standard ANTT principles is essential. To avoid sample contamination, the initial blood volume equal to three times the catheter’s dead space must be discarded [20]. Blood should then be collected into tubes in the recommended order of draw, which ensures the reliability of laboratory results. Since the sample is drawn through an existing vascular access, the use of a tourniquet is unnecessary, simplifying the procedure and minimizing mechanical impact on the specimen.

Data collection

Data collection by the VAT is conducted through the systematic completion of cannulation and observation forms. After a VAD is inserted, the VAT nursing team responds to all requests from the primary care unit regarding issues with MC functionality. The vascular access team intervenes in person and documents each action taken in the patient’s medical record. Maintaining a detailed MC-specific record allows the VAT to perform thorough case analyses and draw conclusions regarding the effectiveness and safety of intravenous access devices, thereby supporting the implementation of improvements in clinical practice.

Results

A total of 1,903 MC observation records were analyzed. The most common indication for MC insertion was DIVA combined with an expected hospital stay exceeding five days (85.93%, n = 1637), followed by DIVA alone (4.99%, n = 95) or intravenous therapy planned for more than five days without documented DIVA (9.08%, n = 173) (Table 1).
Analysis of insertion sites showed that MC were more frequently placed in veins of the right upper extremity (55.04%, n = 1049) than the left one (44.96%, n = 857). The basilic vein was the most commonly selected vessel (69.84%, n = 1329) (Table 1).
Among catheter sizes used, the most common were 15 cm in length (63.48%) and 4 French (Fr) in diameter (51.03%) (Table 1).
In 58.61% of cases (n = 619), the indication for MC insertion was the need for frequent blood sampling. In most cases (75.82%, n = 1443), the catheter remained in place until the end of intravenous therapy, including hospital discharge with the catheter in situ, patient death, or switch to a CVAD (Table 1).
Catheter removal due to the presence of a fibroblastic sleeve (FS) was rarely reported (0.89%, n = 17). Fibroblastic sleeve involves the formation of a fibrous biofilm around the catheter, which can impede blood aspiration and, in some cases, lead to complete occlusion. Although FS represents a natural physiological response to a foreign body, its presence may negatively affect the long-term functionality of the catheter and increase the risk of unsuccessful blood draws [21].
The mean time from hospital admission to MC insertion was 6.16 days (min: 0; max: 96; SD = 10.92). The average catheter dwell time was 12.16 days (min: 0; max: 95; SD = 10.96), with a median of 9 days. The mean duration of successful blood aspiration from MC was 9.49 days (min: 0; max: 83; SD = 9.70). In 2022, the mean aspiration duration was 6.06 days (min: 1; max: 25; SD = 5.73). In 2023, it increased to 7.78 days (min: 0; max: 56; SD = 7.65), and in 2024, it reached 10.64 days (min: 0; max: 83; SD = 10.65) (Table 1). The proportion of MC in which the aspiration duration matched the catheter dwell time increased from 41.86% (n = 36) in 2022 to 58.94% (n = 712) in 2024 (Figure 1).

Discussion

The study results provide valuable insights into the use of MC in clinical practice, particularly in the context of blood sampling. The most common indication for MC insertion was the combination of DIVA and a planned hospital stay exceeding five days. This confirms the utility of the MC as an intermediate solution both literally and functionally between peripheral and central venous access. An indication directly related to the need for blood sampling occurred in 58.01% of cases, suggesting growing confidence among healthcare professionals in using MC for this purpose.
A tendency to insert MC into veins of the right upper limb (55.04%) and a predominance of basilic veins (69.84%) was also observed. This may be attributed to favorable anatomy and greater procedural comfort. The most frequently used catheters were 15 cm in length and 4 Fr in diameter, which may reflect their optimal performance in everyday clinical use. In a study conducted by Cichowlas et al. [22], 4 Fr MC demonstrated statistically longer dwell times. In this study, 50.89% of MC remained in place for a duration equal to the aspiration period, suggesting both the chemical compatibility of the infusates and the effectiveness of the insertion techniques. Proper MC placement and maintenance allow for their optimal use in clinical practice [23].
A particularly noteworthy finding is the increase in mean aspiration time from 6.06 days in 2022 to 10.64 days in 2024. This was accompanied by a rise in the proportion of cases where the aspiration duration matched the catheter dwell time – from 41.86 to 58.94%. These trends may indicate an appropriate level of nursing care and effective vascular access management, contributing to prolonged catheter patency and the continued ability to obtain blood samples [18].
The study findings are consistent with observations made by other authors who have also emphasized the benefits of using MC in patients with DIVA and in those requiring prolonged intravenous therapy [14]. Penoyer et al. [24] demonstrated high blood sampling success rates from MC with a low incidence of complications. However, the rates of occlusion (7.36%), accidental self-removal (6.62%), and suspected infection (2.84%) observed in this study highlight the need for continued monitoring of MC safety and ongoing staff education on proper device management.
It is also important to highlight the occurrence of FS as one of the reasons for catheter removal (0.89%). Although FS was not a frequent complication in this study, its presence may impair catheter function and increase the risk of limited or failed blood aspiration [24]. Fibroblastic sleeve may develop in up to 100% of VAD, but it does not always result in lumen occlusion or aspiration failure [24]. Therefore, early recognition of symptoms suggestive of FS confirmed or ruled out via ultrasound is essential, along with timely implementation of appropriate preventive and therapeutic measures [25].

Limitations

A limitation of this study was its retrospective design and the lack of comparison with other types of vascular access, such as central venous catheters or SPC. This aspect should be addressed in future research.

Conclusions

This study highlights the growing role of MC as an effective and safe method not only for medication administration but also for blood sampling. The increasing duration of successful aspiration and the stability of vascular access support their broader use in clinical practice. Future prospective studies should compare the effectiveness and safety of MC across different patient populations, with a focus on standardized blood sampling protocols and catheter patency maintenance techniques.

Disclosures

1. Institutional review board statement: This retrospective study (protocol number AKBE/80/2025) was approved by the Bioethics Committee.
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: None.

References