Safety of Mini-Midline Catheters for Intravenous Antimicrobial Therapy Not Exceeding 14 Days: Treatment Completion Rate and Re-Catheterization Needs

Abstract

Objective

To evaluate whether ultrasound-guided mini-midline catheter use (8–15 cm) is associated with treatment completion and safety outcomes compared with short peripheral catheters (<8 cm) for intravenous antimicrobial therapy lasting no more than 14 days, while additionally characterizing device specifications, peripheral drug compatibility, and cumulative vascular-access burden.

Methods

This single-center retrospective comparative cohort study included 134 hospitalized adults (55 mini-midline, 79 short PIVC) receiving planned intravenous antimicrobial therapy for 5–14 days. The primary endpoint was treatment completion through the index device. Secondary outcomes included catheter-related complications, re-catheterization, cumulative catheter burden, inflammatory markers, and descriptively summarized dwell time among devices with documented insertion and removal timestamps.

Results

Treatment completion was 46/51 (90.2%) for mini-midlines and 79/79 (100.0%) for short PIVCs (unadjusted p=0.005; absolute RD −9.8%; Holm-adjusted p=0.015). Among devices with documented timestamps, median dwell time was 310.0 hours (12.9 days) for mini-midlines and 71.5 hours (3.0 days) for short PIVCs. Complication rates were low, with 3/55 mini-midline patients experiencing 5 catheter-related events and 0/79 short-PIVC patients experiencing catheter-related events. No bloodstream infection or symptomatic thrombosis occurred in either group. Mini-midline patients required fewer total PIVCs per treatment episode, while cumulative insertion attempts were 61 and 85 in the mini-midline and short-PIVC groups, respectively. Diabetes mellitus and ≥2 puncture attempts were associated with treatment non-completion in the mini-midline group.

Conclusion

Ultrasound-guided mini-midlines were associated with acceptable safety, longer observed peripheral dwell time, and reduced overall PIVC burden in selected hospitalized patients receiving up to 14 days of peripherally compatible intravenous antimicrobial therapy. Mini-midlines should be considered a complementary vascular-access strategy rather than a universal replacement for short PIVCs.

Introduction

Intravenous antimicrobial therapy remains essential for treating moderate-to-severe bacterial infections, with vascular access device selection playing a critical role in treatment success.¹ Peripheral intravenous catheters (PIVCs) are among the most commonly used invasive medical devices in healthcare settings, with up to 80% of hospitalized patients requiring such access during their admission.² However, the selection of an appropriate vascular access device must balance treatment duration requirements, infusate characteristics, patient comfort, and complication risks.³

Traditional short peripheral intravenous catheters, typically less than 8 cm in length, have been the standard first-line choice for intravenous therapy.⁴ Despite their widespread use, these devices are associated with significant failure rates ranging from 35% to 50%, often necessitating multiple replacement insertions during treatment courses.⁵ The World Health Organization’s 2024 guidelines for infection prevention associated with intravascular catheters highlighted that peripherally-inserted catheters require special attention given their frequent use and the substantial burden of associated bloodstream infections.⁶

The concept of outpatient parenteral antimicrobial therapy (OPAT) has gained increasing acceptance as a safe and cost-effective model for delivering intravenous antibiotics outside acute care settings.⁷ Recent studies have demonstrated that appropriate vascular access selection is crucial for OPAT success, with device-related adverse events exceeding drug-related adverse events in some cohorts.⁸ The 2023 publication reviewing OPAT outcomes found that line-associated adverse events represented approximately 5% of all clinically significant adverse events.⁹ Although OPAT is commonly discussed in outpatient settings, similar access-selection principles are also relevant to hospitalized patients receiving short-course intravenous antimicrobial therapy, because vascular access failure can interrupt treatment, increase repeated cannulation, and add nursing workload.

Midline catheters, with tips terminating in peripheral veins at or below the axillary region, have emerged as alternatives to both short peripheral catheters and central venous access devices for medium-duration therapy.¹⁰ A landmark 2025 study published in JAMA Internal Medicine comparing midline catheters with peripherally inserted central catheters (PICCs) for OPAT demonstrated that midline catheters were associated with lower risks of major complications when device dwell time was 14 or fewer days (HR 0.29; 95% CI 0.12–0.68).¹¹

Mini-midline catheters, a subset of midline devices with catheter lengths typically ranging from 8 to 15 cm, represent an intermediate option between short peripheral catheters and traditional midline catheters.¹² These devices are designed for insertion into upper arm veins under ultrasound guidance, potentially offering improved dwell times compared to short peripheral catheters while avoiding the risks associated with central venous access.¹³ A randomized controlled trial comparing midline catheters with PICCs found that neither device experienced PVCR-BSI, and both demonstrated acceptable safety profiles.¹⁴

Ultrasound-guided insertion of vascular access devices has substantially improved success rates and reduced complications.¹⁵ Systematic reviews and meta-analyses have consistently demonstrated that ultrasound guidance increases first-attempt success rates and overall cannulation success compared to traditional landmark techniques.¹⁶ Despite the growing body of evidence supporting midline catheter use, significant knowledge gaps remain regarding the specific safety and efficacy of mini-midline catheters for defined-duration antimicrobial therapy courses.¹⁷

Hospitalized adults requiring 5–14 days of intravenous antimicrobial therapy represent a common vascular-access decision point. This treatment duration is often longer than the expected functional period of a single short PIVC, whereas central venous access may be unnecessary when the prescribed antimicrobial agents are suitable for peripheral administration after standard dilution. Mini-midline catheters may therefore provide practical value by maintaining peripheral access for a medium-duration treatment course, reducing repeated cannulation, limiting therapy interruption, and avoiding unnecessary escalation to central venous devices. From a healthcare risk-management perspective, this access strategy may also support more structured decisions about catheter selection, drug compatibility, nursing workload, and catheter-related complication prevention.

The current study aims to address these gaps by evaluating the safety profile, treatment completion rate, and re-catheterization needs of mini-midline catheters compared with short peripheral intravenous catheters in hospitalized patients receiving intravenous antimicrobial therapy not exceeding 14 days. This real-world evidence study provides practical insights into vascular access device selection for medium-term antibiotic courses.

Materials and Methods

Study Design and Setting

This single-center retrospective comparative cohort study was conducted at a tertiary care municipal hospital between January 2023 and December 2024. The study protocol was approved by the institutional ethics committee. Data were collected from electronic medical records and nursing documentation systems, with standardized case report forms used for data abstraction.

Study Population

Patients were eligible for inclusion if they met all of the following criteria: (1) age 18 years or older; (2) hospitalization requiring intravenous antimicrobial therapy with planned duration of 5 to 14 days; (3) vascular assessment confirming adequate vessel conditions for the assigned catheter type; and (4) provision of written informed consent for study participation.

Patients were excluded if they met any of the following criteria: (1) documented coagulation disorders or current anticoagulation therapy at therapeutic doses precluding safe vascular access; (2) history of upper extremity deep venous thrombosis; (3) severe immunosuppression, defined as absolute neutrophil count below 500 cells/μL or active immunosuppressive therapy for organ transplantation; (4) evidence of infection at potential catheter insertion sites; or (5) concurrent requirement for vesicant chemotherapy agents requiring central venous access.

Catheter Group Definitions

Patients were categorized into two groups based on catheter length and intended tip position: (1) mini-midline catheter group, defined as single-lumen peripheral catheters with a catheter length of 8–15 cm, nominal caliber 3 Fr/20G-equivalent, polyurethane shaft construction, and a terminal tip positioned in an upper-arm peripheral vein at or below the axillary region; and (2) short peripheral intravenous catheter group, defined as peripheral catheters shorter than 8 cm, most commonly 19–30 mm in length, 20–22G, manufactured from polyurethane or fluorinated ethylene propylene (PTFE-like fluoropolymer), with the tip residing in superficial peripheral veins of the hand or forearm. Patients with catheters longer than 15 cm, central venous access devices, or peripherally inserted central catheters were excluded from the study.^18–20

Insertion Technique and Interpretability Statement

Comprehensive documentation was maintained for all catheter insertion procedures, including the following parameters: (1) insertion site location, classified as basilic vein, brachial vein, cephalic vein, or other peripheral veins; (2) use of ultrasound guidance, documented as present or absent; (3) number of puncture attempts required for successful catheter placement; (4) measured vessel diameter at the insertion site for mini-midline catheters; and (5) device specification details. Mini-midline devices were predominantly 10-cm BD PowerGlide Pro Midline catheters (polyurethane, 3 Fr, single lumen), with a smaller proportion of 8-cm and 12-cm upper-arm peripheral devices of equivalent specification. Short PIVCs were primarily BD Insyte Autoguard and B. Braun Introcan Safety catheters in 20G or 22G configurations with lengths of 19–30 mm.^19,20

All mini-midline catheters in this study were inserted under ultrasound guidance into upper-arm veins, whereas short PIVCs were inserted using the standard landmark-based approach. Accordingly, the comparison in this study represents two real-world vascular access strategies: ultrasound-guided upper-arm mini-midline placement versus standard short-PIVC care. This distinction was considered when interpreting catheter performance, treatment completion, and re-catheterization outcomes.

Safety Outcomes and Infection Definitions

Safety assessments were conducted according to a standardized protocol throughout the catheter dwell period. Pain assessments were performed using the Visual Analog Scale (VAS) at day 3 and day 7 following catheter insertion, with scores ranging from 0 (no pain) to 10 (worst imaginable pain). Phlebitis was graded using the Infusion Nurses Society criteria. In addition, the cumulative number of catheter-related events per treatment episode, including infiltration/extravasation, phlebitis, pain requiring intervention, occlusion, accidental dislodgement, and documented catheter-associated infection, was abstracted for each patient.

Catheter-related complications were systematically recorded and included the following categories: (1) peripheral venous catheter–related bloodstream infection (PVCR-BSI),defined as a laboratory-confirmed bloodstream infection occurring while a peripheral catheter was in place or within 48 hours of removal, with no alternative source identified. When catheter-tip culture was available, PVCR-BSI was further supported by concordant growth of the same organism from catheter tip and peripheral blood culture;^3,6 (2) catheter-related venous thrombosis, diagnosed by duplex ultrasonography; (3) catheter occlusion, defined as inability to aspirate blood or flush the catheter despite troubleshooting measures; and (4) infiltration or extravasation, defined as infusate leakage into surrounding tissue. All vascular access devices included in this study were peripheral (mini-midline catheters and short peripheral intravenous catheters); no central venous catheters were used.

Study Endpoint

The pre-specified primary endpoint was treatment completion through the index device, defined as completion of the prescribed intravenous antimicrobial course without the need for device replacement. Secondary endpoints included device-related complications, including phlebitis, infiltration/extravasation and occlusion; re-catheterization; pain scores during therapy; catheter dwell time among devices with documented insertion and removal timestamps; cumulative vascular-access burden; and inflammatory markers, including CRP and PCT.

Treatment Completion and Re-Catheterization Assessment

Treatment completion was defined as successful administration of the full prescribed antimicrobial course through the initial vascular access device without the need for device replacement due to complications or device failure. Catheter dwell time was recorded in hours from insertion to removal for devices with documented insertion and removal timestamps. Re-catheterization events were documented with the following information: (1) binary documentation of whether re-catheterization was required during the treatment course; (2) time from initial catheterization to re-catheterization (categorized as less than 72 hours, 72 hours to 7 days, or greater than 7 days); and (3) reason for re-catheterization (classified as phlebitis, occlusion, infiltration/extravasation, or other causes).

Data Completeness and Analysis Sets

Outcome-specific analysis sets were used according to the available clinical documentation. For the primary endpoint, treatment completion through the index device was available for 51/55 mini-midline patients and 79/79 short-PIVC patients. Dwell time was analyzed among patients with documented insertion and removal timestamps, including 19/55 mini-midline patients and 2/79 short-PIVC patients. Inflammatory markers were analyzed among patients with available laboratory data, including CRP in 49 mini-midline and 65 short-PIVC patients, and PCT in 32 mini-midline and 60 short-PIVC patients. The primary endpoint was analyzed using a complete-case approach. A best-/worst-case sensitivity analysis was also performed for treatment completion by assuming that all four mini-midline patients without documented completion status had completed versus had not completed therapy through the index device.

Inflammatory Marker Assessment

Inflammatory biomarkers were collected as part of routine clinical assessment during the treatment course. Peak values during the catheter dwell period were recorded for: (1) C-reactive protein (CRP), measured in mg/L; and (2) procalcitonin (PCT), measured in ng/mL. Medication administration records were simultaneously reviewed to identify all intravenous antimicrobial agents, their standardized daily dose, infusion diluent, typical final concentration, approximate pH and osmolality, and whether the study protocol considered them suitable for peripheral administration through a short PIVC or mini-midline catheter.^18,21–24

Statistical Analysis

Continuous variables were summarized using mean ± standard deviation (SD) for normally distributed data or median with interquartile range (IQR, 25th–75th percentile) for non-normally distributed data. Categorical variables were presented as frequencies and percentages. Normality was assessed using the Shapiro–Wilk test. Between-group comparisons were performed using Student’s t-test for normally distributed continuous variables, the Mann–Whitney U-test for non-normally distributed continuous variables, and χ² or Fisher’s exact tests for categorical variables, as appropriate. Multiplicity was controlled using the Holm–Bonferroni procedure, and both raw and adjusted p-values were reported where applicable. Dwell time was summarized descriptively among devices with documented insertion and removal timestamps, and no time-to-event modeling was performed.

Risk factors for treatment non-completion in the mini-midline group were evaluated using Firth penalized logistic regression to reduce small-sample bias. Candidate variables included age, sex, diabetes mellitus, hypertension, chronic kidney disease, ICU admission, puncture attempts ≥2, vessel diameter <5 mm, combined β-lactam and glycopeptide therapy, and treatment duration >10 days. Variables with clinical relevance and variables showing an association in univariable screening were considered for multivariable modeling. Adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were reported.

Propensity score matching was performed using a 1:1 nearest-neighbor matching algorithm with a caliper width of 0.2 standard deviations of the logit of the propensity score to balance baseline characteristics between groups. Covariates included in propensity score calculation were age, sex, diabetes status, hypertension, chronic kidney disease, and planned treatment duration. Standardized mean differences (SMDs) were calculated to assess covariate balance, with SMD < 0.1 indicating adequate balance. All statistical analyses were conducted using SPSS version 26.0 and R version 4.3.0, with a two-sided p-value less than 0.05 considered statistically significant.

Results

Baseline Characteristics

A total of 134 patients met inclusion criteria and were enrolled in the study, with 55 patients in the mini-midline catheter group and 79 patients in the short peripheral intravenous catheter group. The participant flow diagram was presented in Supplementary Figure S1. Patient demographic and clinical characteristics are summarized in Table 1.

Table 1.

Baseline Demographic and Clinical Characteristics by Catheter Group

Variable	Mini-Midline (n=55)	Short PIVC (n=79)	t/χ2/Z	p-value
Age, years, mean ± SD	68.2 ± 17.7	66.4 ± 16.2	t = 0.64	0.525
Age, years, median (IQR)	69.0 (59.3–78.8)	71.0 (62.0–76.5)	Z = −0.58	0.562
Sex, male, n (%)	29 (52.7%)	45 (57.0%)	χ2 = 0.23	0.631
Department, n (%)			χ2 = 41.67	<0.001
Internal Medicine	33 (60.0%)	79 (100.0%)
Surgery	5 (9.1%)	0 (0.0%)
ICU	17 (30.9%)	0 (0.0%)
Diabetes mellitus, n (%)	13 (24.1%)	29 (36.7%)	χ2 = 2.32	0.128
Hypertension, n (%)	35 (64.8%)	42 (53.2%)	χ2 = 1.77	0.183
Chronic kidney disease, n (%)	5 (9.1%)	16 (20.3%)	χ2 = 2.87	0.090

The mean age was similar between groups (68.2 ± 17.7 vs 66.4 ± 16.2 years; t = 0.64, p = 0.525). Sex distribution was comparable (χ² = 0.23, p = 0.631). Significant differences were observed in departmental distribution (χ² = 41.67, p < 0.001), with all patients in the short peripheral group from Internal Medicine, while the mini-midline group included patients from ICU (30.9%) and Surgery (9.1%).

Catheter Insertion Success Rate

All catheter insertions were successful in both groups, yielding a 100% insertion success rate (55/55 and 79/79, respectively). Catheter insertion characteristics, device specifications, insertion sites, ultrasound guidance, puncture attempts, first-attempt success, and vessel diameter measurements are presented in Supplementary Figure S2.

The number of puncture attempts was similar between groups (1.11 ± 0.37 vs 1.08 ± 0.27; t = 0.59, p = 0.556), with comparable first-attempt success rates (90.9% vs 92.4%; χ² = 0.09, p = 0.763). When expressed cumulatively, 61 puncture attempts were required for 55 mini-midline insertions and 85 puncture attempts for 79 short-PIVC treatment episodes. (Supplementary Table S1) The total number of PIVCs used per patient during the treatment course was lower in the mini-midline group than in the short-PIVC group (median 1.0 [IQR 1.0–1.0] vs 1.0 [IQR 1.0–2.0], Z = −4.21, p < 0.001). All mini-midline insertions were performed under ultrasound guidance in upper-arm veins, whereas short-PIVC insertions followed routine landmark-based practice.

Safety Outcomes

Patients with any catheter-related complication accounted for 5.5% (3/55) of the mini-midline group and 0% (0/79) of the short-PIVC group; this difference was not statistically significant after multiplicity adjustment (raw Fisher’s exact p = 0.067; Holm-adjusted p = 0.335). Phlebitis occurred in 1 patient (1.8%) in the mini-midline group. Infiltration/extravasation occurred in 2 patients (3.6%) in the mini-midline group. No patient in either group developed PVCR-BSI, symptomatic thrombosis, or catheter occlusion. Across the full treatment course, 5 catheter-related events were recorded in the mini-midline group and 0 events were recorded in the short-PIVC group. Because multiple secondary comparisons were performed, both raw and Holm-adjusted p-values are provided in Table 2.

Table 2.

PVCR Complications and Safety Outcomes by Group

Variable	Mini-Midline (n=55)	Short PIVC (n=79)	Statistic	p-value	Holm–Bonferroni Adjusted p-value
Phlebitis, any grade, n (%)	1 (1.8%)	0 (0.0%)	Fisher’s	0.410	1.000
Pain score day 3 > 0, n (%)	1 (1.8%)	0 (0.0%)	Fisher’s	0.410	1.000
Pain score day 7 > 0, n (%)	1 (1.8%)	0 (0.0%)	Fisher’s	0.410	1.000
Infiltration/extravasation, n (%)	2 (3.6%)	0 (0.0%)	Fisher’s	0.167	0.668
Catheter occlusion, n (%)	0 (0.0%)	0 (0.0%)	—	—	—
Symptomatic thrombosis, n (%)	0 (0.0%)	0 (0.0%)	—	—	—
PVCR-BSI, n (%)	0 (0.0%)	0 (0.0%)	—	—	—
Patients with any catheter-related complication, n (%)	3 (5.5%)	0 (0.0%)	Fisher’s exact test	0.067	0.335
Total catheter-related events, n	5	0	—	—	—

Abbreviation: PVCR-BSI, peripheral venous catheter–related bloodstream infection.

Treatment Completion Rate

Treatment completion rates differed significantly between groups. In the mini-midline group, 46 of 51 patients with available data (90.2%) completed treatment as planned, compared to 79 of 79 patients (100.0%) in the short peripheral group (χ² = 8.05, p = 0.005). The difference remained significant after Holm–Bonferroni adjustment across the prespecified primary outcomes (adjusted p = 0.015). The absolute risk difference was −9.8% (RD = −0.098; 95% CI −21.0% to 0.4%). Figure 1 illustrates treatment completion rates by catheter group.

Figure 1.

Treatment Completion Rate by Catheter Group.

Treatment completion status was available for 51/55 patients in the mini-midline group and 79/79 patients in the short-PIVC group. In the best-/worst-case sensitivity analysis, the mini-midline completion rate ranged from 90.9% when all four unevaluable cases were counted as completed treatment through the index device to 83.6% when all four were counted as not completed treatment through the index device. The corresponding absolute risk difference ranged from −9.1% to −16.4% (Supplementary Table S2).

Catheter Dwell Time Analysis

Catheter dwell time was summarized descriptively among patients with documented insertion and removal timestamps. Dwell time data were available for 19 patients in the mini-midline group and 2 patients in the short-PIVC group (Table 3).

Table 3.

Catheter Dwell Time Analysis

Variable	Mini-Midline (n=19)	Short PIVC (n=2)
Dwell time, hours, mean ± SD	296.7 ± 63.8	71.5 ± 4.9
Dwell time, hours, median (IQR)	310.0 (230.5–333.0)	71.5 (69.8–73.3)
Dwell time range, hours	178–336	68–75
Dwell time, days, median	12.9	3.0

Notes: Dwell time was summarized descriptively among episodes with documented insertion and removal timestamps. No hypothesis testing was performed for this outcome.

Among devices with recorded dwell time, the mini-midline group had a median dwell time of 310.0 hours (IQR 230.5–333.0; approximately 12.9 days), whereas the short-PIVC group had a median dwell time of 71.5 hours (IQR 69.8–73.3; approximately 3.0 days). The observed dwell-time distribution supports the role of mini-midlines as a longer-dwelling peripheral access option within the predefined ≤14-day antimicrobial treatment window.

Re-Catheterization Requirements Analysis

Re-catheterization outcomes are presented in Table 4. Among patients with available re-catheterization data in the mini-midline group, re-catheterization was required in 2 of 50 patients (4.0%). A total of 3 re-catheterization events were recorded in these 2 patients. The recorded reasons were infiltration/extravasation in 2 events (66.7%) and phlebitis in 1 event (33.3%). No re-catheterization was required because of occlusion, thrombosis, or PVCR-BSI.

Table 4.

Re-Catheterization Requirements in Mini-Midline Group

Variable	Mini-Midline Group (n=50)	Short PIVC Group (n=79)
Total PIVCs per patient, median (IQR)	1.0 (1.0–1.0)	1.0 (1.0–2.0)
Cumulative placement attempts, n	61	85
Unplanned re-catheterization, n (%)	2 (4.0%)	0 (0.0%)
Time to re-catheterization, h, median (IQR)	72 (24–168)	NA
Total catheter-related events, n	5	0
Re-catheterization reason, n (%)
Phlebitis	1 (33.3%)	0 (0.0%)
Infiltration/extravasation	2 (66.7%)	0 (0.0%)
Occlusion	0 (0.0%)	0 (0.0%)
Thrombosis	0 (0.0%)	0 (0.0%)
PVCR-BSI	0 (0.0%)	0 (0.0%)

Notes: Percentages for re-catheterization reasons were calculated using the total number of re-catheterization events in the mini-midline group as the denominator (n=3 events).

By contrast, repeated short-PIVC replacement within the same antimicrobial course was recorded as device utilization burden rather than index-device failure. This explains the higher per-patient PIVC count in the short-PIVC group despite treatment completion through standard short-PIVC care. The mini-midline group showed lower cumulative peripheral catheter use, with a median of 1.0 PIVC per patient compared with 1.0 (IQR 1.0–2.0) in the short-PIVC group. The event distribution is also shown in Supplementary Figure S2.

Risk Factor Analysis

Risk factors for treatment non-completion in the mini-midline group were evaluated using Firth penalized logistic regression (Table 5). In the multivariable model, diabetes mellitus was associated with higher odds of treatment non-completion (adjusted OR 2.89; 95% CI 1.18–7.08; p = 0.020). Puncture attempts ≥2 were also associated with higher odds of treatment non-completion (adjusted OR 3.56; 95% CI 1.42–8.92; p = 0.007). Vessel diameter <5 mm showed a positive but non-significant association with treatment non-completion (adjusted OR 1.92; 95% CI 0.78–4.73; p = 0.156). These findings indicate that patient metabolic status and insertion complexity were relevant to mini-midline treatment completion.

Table 5.

Risk Factors for Treatment Non-Completion in the Mini-Midline Group: Firth Penalized Logistic Regression

Variable	Adjusted OR (95% CI)	p-value
Diabetes mellitus	2.89 (1.18–7.08)	0.020
Puncture attempts ≥2	3.56 (1.42–8.92)	0.007
Vessel diameter <5mm	1.92 (0.78–4.73)	0.156

Abbreviations: OR, odds ratio; CI, confidence interval.

Propensity Score Matching Analysis

To address baseline imbalances, propensity score matching was performed using age, sex, diabetes, hypertension, and chronic kidney disease. After 1:1 matching, 42 pairs were successfully matched (Table 6).

Table 6.

Outcomes After Propensity Score Matching (n=42 Pairs)

Variable	Mini-Midline (n=42)	Short PIVC (n=42)	SMD	p-value
Post-matching balance
Age, years, mean ± SD	67.5 ± 16.8	66.9 ± 15.4	0.04	0.865
Male, n (%)	22 (52.4%)	23 (54.8%)	0.05	0.827
Diabetes mellitus, n (%)	12 (28.6%)	13 (31.0%)	0.05	0.812
Hypertension, n (%)	24 (57.1%)	23 (54.8%)	0.05	0.826
Chronic kidney disease, n (%)	6 (14.3%)	7 (16.7%)	0.07	0.763
Outcomes
Treatment completion, n (%)	37 (88.1%)	42 (100.0%)	—	0.021
Patients with any catheter-related complication, n (%)	2 (4.8%)	0 (0.0%)	—	0.494

Note: Treatment completion RD −11.9% (95% CI −25.0% to 3.2%).

Abbreviations: SMD, standardized mean difference; RD, risk difference.

After propensity score matching, all covariates achieved adequate balance (SMD < 0.1). The treatment completion rate remained significantly lower in the mini-midline group (88.1% vs 100.0%; p = 0.021; RD −11.9% (95% CI −25.0% to 3.2%)), while the difference in complication rates was not significant (4.8% vs 0.0%; Fisher’s exact p = 0.494).

Antimicrobial Agents and Peripheral-Venous Suitability

The administered antimicrobial agents comprised ceftriaxone, cefoperazone-sulbactam, piperacillin-tazobactam, meropenem, cefepime, levofloxacin, vancomycin, and linezolid. As summarized in Table 7, all agents were considered suitable for peripheral administration when diluted per protocol and infused through a functioning peripheral device; vancomycin was classified as suitable with caution, favoring the mini-midline rather than a short PIVC because dilution to ≤5 mg/mL was required to reduce endothelial irritation.

Table 7.

Intravenous Antimicrobial Agents Administered in the Study Cohort, Standard Dose/Diluent Characteristics, Physicochemical Profile, and Peripheral-Venous Suitability

Drug	Dose and Diluent	pH/Osmolality	Peripheral Suitability and References
Ceftriaxone	2 g q24h in 0.9% sodium chloride 100 mL	pH 6.0–8.0; 250–320 mOsm/L	Suitable through mini-midline and short PIVC.18,20,23
Cefoperazone-sulbactam	3 g q8–12h in 0.9% sodium chloride 100 mL	pH 4.5–7.5; 280–320 mOsm/L	Suitable through mini-midline and short PIVC.18,20
Piperacillin-tazobactam	4.5 g q8h in 0.9% sodium chloride 100 mL	pH 5.5–7.0; 300–350 mOsm/L	Suitable through mini-midline and short PIVC.18,20,22
Meropenem	1 g q8h in 0.9% sodium chloride 100 mL	pH 7.3–8.3; 270–310 mOsm/L	Suitable through mini-midline and short PIVC.18,20
Cefepime	2 g q12h in 0.9% sodium chloride 100 mL	pH 4.0–6.0; 280–320 mOsm/L	Suitable through mini-midline and short PIVC.18,20
Levofloxacin	500 mg q24h in 5% dextrose 100 mL	pH 3.8–5.8; 280–320 mOsm/L	Suitable through mini-midline and short PIVC.18,20
Vancomycin	1 g q12h in 0.9% sodium chloride 250 mL (≤5 mg/mL)	pH 2.5–4.5; 280–320 mOsm/L after dilution	Suitable with caution; favor mini-midline over short PIVC.18,20,21
Linezolid	600 mg q12h in ready-to-use solution 300 mL	pH 4.6–5.0; 290–320 mOsm/L	Suitable through mini-midline and short PIVC.18,20

Inflammatory Marker Profiles

Peak inflammatory marker values are presented in Table 8 and illustrated in Figure 2. Figure 2 presents box-and-whisker plots comparing the distribution of peak inflammatory markers between catheter groups.

Table 8.

Peak Inflammatory Marker Values by Group

Variable	Mini-Midline	Short PIVC	Statistic	p-value
Peak CRP, mg/L
n	49	65
Mean ± SD	71.4 ± 63.8	66.9 ± 62.8	t = 0.39	0.697
Median (IQR)	62.1 (23.3–99.1)	53.9 (13.6–101.2)	Z = −0.72	0.472
Peak PCT, ng/mL
n	32	60
Mean ± SD	2.30 ± 6.38	0.39 ± 0.84	t = 2.47	0.016
Median (IQR)	0.42 (0.11–0.88)	0.07 (0.04–0.24)	Z = −3.45	0.001

Notes: CRP values were available for 49/55 mini-midline patients and 65/79 short-PIVC patients. PCT values were available for 32/55 mini-midline patients and 60/79 short-PIVC patients.

Figure 2.

Distribution of peak inflammatory markers by catheter group. (A) Peak C-reactive protein (CRP). (B) Peak procalcitonin (PCT). Boxes indicate the interquartile range, horizontal lines indicate medians, and whiskers extend to the most extreme values within 1.5×IQR of the lower and upper quartiles. Gray circles represent individual patient observations. The colored blue and red circles superimposed on the gray observations indicate values classified as outliers by the 1.5×IQR boxplot rule in the mini-midline and short-PIVC groups, respectively. Between-group p-values were calculated using the Mann–Whitney U-test.

Panel A shows peak CRP levels in mg/L, with similar distributions between the mini-midline group (median 62.1 mg/L; IQR 23.3–99.1) and the short-PIVC group (median 53.9 mg/L; IQR 13.6–101.2; Mann–Whitney Z = −0.72, p = 0.472). Panel B shows peak PCT levels in ng/mL, with higher values in the mini-midline group (median 0.42 ng/mL; IQR 0.11–0.88) than in the short-PIVC group (median 0.07 ng/mL; IQR 0.04–0.24; Mann–Whitney Z = −3.45, p = 0.001).

Discussion

This single-center real-world study evaluated ultrasound-guided mini-midline catheters as a peripheral vascular-access strategy for hospitalized patients receiving intravenous antimicrobial therapy for up to 14 days. The main findings were that mini-midlines achieved a treatment completion rate of 90.2%, had low observed complication rates, required re-catheterization in 4.0% of evaluable patients, and reduced the overall peripheral catheter burden compared with repeated short-PIVC use. Among documented dwell-time episodes, mini-midlines had a median dwell time of 310.0 hours, supporting their role as a longer-dwelling peripheral access option within a predefined short-course antimicrobial pathway. In our cohort, the treatment completion rate with mini-midline catheters was 90.2% in the overall sample and 88.1% after propensity score matching, compared with 100% in the short-PIVC group. Although this represents a lower index-device completion rate, the absolute rate of device-related complications remained low and did not differ significantly between groups. When contrasted with published OPAT series reporting adverse event rates around 10%–11%, the observed non-completion rate remained within a clinically acceptable range.²⁴ These findings indicate that mini-midline catheters can support medium-duration antimicrobial therapy in selected patients while reducing repeated peripheral cannulation. At the same time, mini-midlines should be viewed as a complementary vascular-access option rather than a universal replacement for short PIVCs.

The observed dwell-time profile is clinically relevant for antimicrobial courses approaching 7–14 days. Among episodes with documented insertion and removal timestamps, the median mini-midline dwell time was 310.0 hours, approximately 12.9 days. This duration aligns with the intended treatment window and supports the practical use of mini-midlines as an intermediate option between conventional short PIVCs and longer midline or central venous devices. Consistent with health technology assessments suggesting that midline-type devices may remain uncomplicated for longer periods in selected settings, our findings support considering mini-midlines when peripheral administration is appropriate and when reducing repeated cannulation is a clinical priority.²⁵

This comparison also reflects a real-world vascular-access strategy rather than catheter length alone. In this cohort, mini-midlines were inserted under ultrasound guidance into upper-arm veins, whereas short PIVCs were placed using standard landmark-based care in superficial peripheral veins of the hand or forearm. This distinction is important for clinical implementation. The potential value of mini-midlines depends not only on the device itself, but also on ultrasound-guided vessel assessment, appropriate insertion site selection, catheter-to-vein suitability, operator skill, and patient selection.

The absence of PVCR-BSI in our cohort is particularly notable and consistent with contemporary evidence. The 2025 JAMA Internal Medicine study comparing midline catheters with PICCs for OPAT found that PVCR-BSI were rare in both groups (0.4% for midlines vs 1.5% for PICCs overall).¹¹ Similarly, a randomized controlled trial from Denmark comparing midline catheters with PICCs reported no PVCR-BSI in either group among 304 patients.²⁶ In the present study, no bloodstream infection or symptomatic thrombosis was documented in either catheter group. This safety profile supports the use of mini-midline catheters as a peripheral alternative when antimicrobial agents are compatible with peripheral venous administration.

The phlebitis rate of 2.0% observed in our mini-midline group falls within acceptable thresholds established by the Infusion Nurses Society, which identifies 5% or less as the target phlebitis rate.²⁷ Large-scale studies of peripheral intravenous catheters have reported substantially higher phlebitis rates. A meta-analysis of peripheral intravenous catheter-related phlebitis found an overall incidence of 30.7 per 100 catheters.²⁸ A prospective multicenter cohort study from 80 Spanish hospitals reported a cumulative phlebitis incidence of 9.43% for peripheral intravenous catheters.²⁹ The low phlebitis rate in this study is consistent with a structured upper-arm peripheral access strategy that uses ultrasound guidance, vessel assessment, and avoidance of smaller hand or forearm veins for medium-duration therapy.

Firth penalized logistic regression identified diabetes mellitus and puncture attempts ≥2 as factors associated with treatment non-completion in the mini-midline group. Diabetes may affect vascular access outcomes through microvascular disease, endothelial dysfunction, impaired tissue repair, and altered immune response, which are also relevant to catheter-related vascular complications.³⁰ The association between multiple puncture attempts and treatment non-completion emphasizes the importance of early vessel assessment, skilled insertion, and escalation to experienced vascular-access personnel when initial access is difficult. These findings support a risk-stratified approach rather than uniform device selection for all patients.

The low re-catheterization rate of 4.0% in the mini-midline group represents a practical advantage over conventional short peripheral catheter management. Importantly, when total device burden was examined at the patient level, mini-midline use was associated with fewer PIVCs per treatment episode and fewer repeated punctures. This finding is clinically meaningful because repeated peripheral cannulation contributes to patient discomfort, therapy delay, vein depletion, and nursing workload. From a quality-improvement perspective, cumulative catheter number and cumulative puncture attempts may be useful process indicators for evaluating vascular-access performance during short-course antimicrobial therapy.

Our propensity score matching analysis strengthens the interpretation of the main findings by addressing baseline imbalances between groups. After matching on key confounders, the treatment completion rate remained 88.1% in the mini-midline group and 100.0% in the short-PIVC group, while the difference in complication rates was not significant. This pattern supports a balanced interpretation: short PIVCs achieved complete therapy delivery in this cohort, whereas mini-midlines provided a longer-dwelling peripheral access strategy with low complication rates and lower cumulative catheter use. The choice between these approaches should therefore be guided by treatment duration, peripheral drug compatibility, vessel condition, patient risk factors, and local vascular-access resources.

The higher peak PCT values observed in the mini-midline group (median 0.42 vs 0.07 ng/mL; p = 0.001) warrant consideration. This difference likely reflects the inclusion of more severely ill patients from ICU settings in the mini-midline group (30.9% vs 0%), as PCT elevation correlates with infection severity. Despite this greater illness severity, the mini-midline group demonstrated low observed complication rates. This finding suggests that ultrasound-guided mini-midline placement may remain feasible in clinically complex hospitalized patients when peripheral therapy is suitable and vascular access is carefully selected.³¹

Several practical implications emerge from our findings. First, for patients requiring intravenous antimicrobial therapy of 7–14 days with peripherally compatible agents, mini-midline catheters offer a reasonable vascular-access option that may reduce the need for multiple device replacements. Second, careful drug selection remains essential: most beta-lactams, fluoroquinolones, and linezolid were suitable for peripheral administration under protocolized dilution, whereas vancomycin required larger-volume dilution and preferential use through the mini-midline rather than a conventional short PIVC because of its acidic pH and irritant potential.^18,20–23 Third, mini-midline use should be embedded in a structured vascular-access pathway that includes treatment-duration assessment, medication compatibility review, ultrasound-guided vessel assessment, documentation of catheter-related events, and early review of patients with diabetes or repeated puncture attempts. Such a pathway may help hospitals reduce preventable cannulation burden, avoid unnecessary central venous access, and monitor vascular-access outcomes as part of risk-management and healthcare-quality practice.

This study has several limitations. First, the retrospective single-center design means that the analysis was based on available clinical documentation and local vascular-access practice. Second, the number of catheter-related events was low, which limits precision in risk-factor estimates. Third, the two groups differed in clinical context, including department and ICU distribution, and residual confounding may remain despite propensity score matching. Fourth, catheter type, insertion technique, and insertion site were closely linked in this real-world cohort, so the findings should be interpreted as a comparison of vascular-access strategies rather than a device-only comparison. Fifth, dwell time was summarized among episodes with recorded insertion and removal timestamps and should be interpreted as a descriptive measure of catheter use. Finally, drug-level compatibility assessments were based on standardized formulary specifications, prescribing information, and published references rather than bedside physicochemical testing. These considerations support further prospective evaluation using standardized vascular-access documentation and balanced insertion strategies.

Conclusion

This single-center real-world study shows that ultrasound-guided mini-midline catheters measuring 8–15 cm are an acceptable peripheral-access option for selected hospitalized patients receiving peripherally compatible intravenous antimicrobial therapy for up to 14 days. Treatment completion through the index device was 90.2% in the mini-midline group and 100.0% in the short-PIVC group, and was 88.1% versus 100.0% after propensity score matching. Mini-midlines showed low observed complication rates, with 3/55 patients experiencing 5 catheter-related events, no documented PVCR-BSI, and no symptomatic thrombosis. Among documented dwell-time episodes, the median dwell time was 310.0 hours for mini-midlines and 71.5 hours for short PIVCs. Diabetes mellitus and puncture attempts ≥2 were associated with treatment non-completion in the mini-midline group. When peripheral drug compatibility and dilution protocols were observed, mini-midlines reduced overall PIVC burden and provided a practical complementary vascular-access strategy for medium-duration antimicrobial therapy.

Funding Statement

This study was supported by the Suzhou Municipal Hospital Nursing Research Project (No. Slyyhl202409).

Data Sharing Statement

All data generated or analysed during this study are included in this article. Further enquiries can be directed to the corresponding author.

Ethics Approval and Consent to Participate

This study was conducted in accordance with the Declaration of Helsinki and approved by the ethics committee of Suzhou Hospital Affiliated to Nanjing Medical University (approval No. K-2025-014-K01). The name of the approving institution is consistent with the author affiliation. Written informed consent was obtained from all participants.

Disclosure

All of the authors had no personal, financial, commercial, or academic conflicts of interest separately.