The goals of infusion therapy are to preserve vascular health and safely deliver needed treatment. Achieving these goals is challenging in critical care because of the complexity of the treatment required. Daily justification of retaining an existing central venous catheter also creates urgency to change to a peripheral vascular access device. The midline catheter has had a resurgence in use because of the need for a long-term peripheral vascular access device not linked to central catheter–associated bloodstream infection risk.
To review the characteristics of midline catheters, the benefits and risks of midline catheters, and current evidence regarding midline catheter use in critical care.
Research related to midline catheters has greatly expanded the body of knowledge regarding vascular access device selection and midline catheter use.
Although the quality and results of research on vascular access devices vary widely, a more accurate safety profile is emerging to illustrate how midline catheter use can support the goals of infusion therapy.
Optimizing vascular access device selection requires recognition that every vascular access device can cause patient harm. Although the midline catheter appears to fill an important niche in infusion therapy, use of the midline catheter should be carefully evaluated. Midline catheters should not be used as a catheter-associated bloodstream infection prevention strategy, should be inserted to administer peripherally compatible solutions, and should be considered for short-term continuous vesicant therapy only in emergent situations until more definitive vascular access can be achieved.
Common vascular access challenges (as illustrated in Table 1) must be navigated wisely to achieve the critical and at times competing goals of vessel preservation and effective delivery of needed infusion therapy.2-5 Resources and algorithms are available to guide vascular access device (VAD) selection and placement, but the evolving nature of these situations, varied available resources, and conflicting or limited evidence-based recommendations create uncertainty.6-8 In addition, the process of daily justification of retaining an existing central venous catheter (CVC), an important strategy to prevent central line–associated bloodstream infections (CLABSIs), creates a sense of urgency to de-escalate infusions to a peripheral VAD. This process is often used in an effort to avoid reportable hospital-acquired infections.5,7-14 Use of the midline catheter (MC) has undergone a resurgence because of the need to provide a long-term peripheral vascular access option that is not associated with the risk of CLABSI.4,7-9,11-18 This article reviews the evolution and composition of MCs, the benefits and risks of current MC use patterns, and current evidence regarding the role of MCs when selecting the optimal VADs for critically ill patients.
Evolution and Composition of the MC
The MC was originally developed in the 1950s and was used as a peripheral vascular access option into the 1990s.14 Rigid catheter components and reported hypersensitivity reactions to specific catheter components caused a reduction in MC use.9,15,16 However, recent advancements in catheter design and characteristics have improved the safety profile of the MC, and several options are now on the market.15,18 The MC is generally composed of silicone or polyurethane. Midline catheters with single or dual lumens, a variety of sizes, and power injection options are available.9,14,15 Catheters with lengths ranging from 7.5 cm to 25 cm are identified as MCs in the literature,15,17,19-21 creating some confusion in nomenclature and product selection.2,3,18,22 Because of the various lengths, insertion locations, and expanding peripheral VAD options, the Infusion Nurses Society (INS) published standardized definitions for peripheral intravenous access catheters in 2021 (Table 2).23
An MC is inserted under sterile conditions into a deep vessel of the upper arm (eg, the basilic, cephalic, or brachial vein) by specially trained staff.2,14,17,24,25 Depending on the design of the catheter, a modified, accelerated, or traditional Seldinger technique is required.5,9,15,17,26,27 The optimal position for the MC distal tip is just inferior to or at the level of the axilla.18,21,23,28 A more proximal tip position (eg, midclavicular position, or proximal to the axillary-subclavian transition) is not recommended because this position has been associated with increased thrombotic risk.28-31 Ultrasonography guidance is strongly recommended to evaluate the length of the catheter in relation to the depth, width, and length of the selected vessel.5,8,23,32,33 Radiological imaging is not required to confirm tip placement.9,15,32,34 Because the distal tip of the MC is located in peripheral vasculature, most references recommend limiting MC use to infusions that are appropriate for peripheral vascular administration.7,8,19,23,25-27,35 Criteria for osmolarity and pH limits that are safe for peripheral vascular administration, however, are uncertain.14
Multiple factors fostered the push to improve the efficacy of the MC and the resultant acceleration in use. The high failure rate of the short peripheral intravenous catheter (PIVC) is an important impetus for MC use. Failure of the short PIVC, defined as a dwell time of less than the prescribed duration of treatment,32 is reported to be as high as 63%.36 In their systematic review of PIVC dwell times and complications, Hopkinson et al37 found an average dwell time of 3.5 days, with the presence of at least 1 complication significantly associated with dwell times of greater than 2 days (P < .01).37 Premature failure of the short PIVC, common in critical care, is associated with patient dissatisfaction, increased discomfort, and an increasing rate of failure with each subsequent insertion attempt.36,38 Inappropriate use of the peripherally inserted central catheter (PICC) and significant adverse events such as CLABSI and catheter-related thrombosis have also strengthened the push to identify a VAD option that would provide long-term, reliable access with fewer concomitant risks.6,12,14-16,39 Recognition of the impact of VAD placement on patient comfort and satisfaction is further incentive to explore options with a high first-insertion success rate, with the added potential for reduced procedural costs.3,4,7,9,15-17 Table 3 presents adverse events associated with peripheral intravenous therapy.
The MC can provide a valuable VAD option in patients in whom venous access is difficult, and a PICC may have been placed for a duration of therapy that a short PIVC cannot typically support.2-4,8,15 Although the expected dwell time of a VAD should not be used to dictate planned removal, the dwell time of the MC, 1 to 4 weeks, is certainly more favorable than that of other peripheral VADs.3,7,8,15 Another possible patient satisfier is the potential to collect blood specimens from the MC,9,42 although the 2021 INS standards indicate that no evidence is yet available to guide technique or validate the accuracy of blood specimen collection from the MC.23 The exponential increase in MC use, particularly in difficult venous access scenarios and as a CVC alternative,8,11,12,14,32,43 has stimulated expanded research into the benefits and risks of peripheral VAD use.
Failure of the short PIVC, defined as a dwell time of less than the prescribed duration of treatment, is reported to be as high as 63%.
Benefits of Current MC Use Patterns
The quest for the optimal VAD to safely reduce CVC use rates is daunting. The device would need to be a versatile peripheral VAD with a high rate of success on first insertion attempt, a low adverse event rate, and a predictable dwell time that would allow for long-term courses of treatment. The MC has been promoted as fulfilling all of these characteristics.9,15,16 Multiple studies have indicated support for the safety profile of the MC while acknowledging that further study is needed.4,5,12,13,34,39,43-45 The MC, with enhancements to catheter characteristics and design, would appear to fill a very important niche in infusion therapy.
Initially, 2 priority research questions for MC use were whether MCs were associated with higher complication rates than CVCs (particularly PICCs) and whether MCs could be safely used to administer vancomycin (pH < 5).7 The long-term administration of antibiotics that can cause vessel and tissue damage, such as vancomycin, is a notable challenge because a CVC has traditionally been recommended for their administration.7,46 This recommendation was made in part because of pH limitations included in early iterations of the INS standards. The 2011 iteration recommended that the peripheral route of intravenous administration be limited to infusates with a pH between 5 and 9 and/or an osmolality of less than 600 mOsm/L.47 Concerns that these parameters may have contributed to overuse of CVCs stimulated research to determine the safety of administering vancomycin through the MC.46 For example, in a small randomized controlled trial, Caparas and Hu48 found no significant difference in adverse events for vancomycin administration via an MC versus a PICC. These results and those of similar studies prompted challenges to the INS limitations for peripheral intravenous administration of infusates.46 After a thorough review of the evidence, the INS Standards of Practice Committee removed specific pH limitations from the 2016 infusion therapy standards of practice.49 The lack of conclusive evidence to substantiate limitation to a pH range between 5 and 9 and the vesicant designation of a number of infusates with pH levels within that range led to their conclusion that the pH of an infusion should not be the sole reason for evaluating peripheral compatibility.50 Rather, evaluation of the best route of delivery should include the full complement of characteristics of an infusate, the patient’s vascular health, and available VAD options.23
In a retrospective review of 1538 MC placements, Campagna et al4 evaluated the incidence of adverse events to determine which factors resulted in premature MC removal. The overall rate of adverse events was determined to be acceptably low at 2.49 per 1000 catheter-days, and the median dwell time was 26 days. In another retrospective review, Mushtaq et al13 found that the catheter-related bloodstream infection (BSI) rate was significantly lower for MCs than for CVCs and that the composite complication rate was also lower, indicating an acceptable safety profile. DeVries et al8 conducted a prospective study to determine the impact of a bundle of interventions on MC-related BSI. Using interventions such as chlorhexidine gluconate dressings and standardized insertion by a vascular access nurse–led MC program, they found no MC-related BSIs during their 2-year study, illustrating that standardization of insertion and management may improve outcomes.8
A crucial niche for MC use has been for patients with difficult intravenous access (DIVA).3,5-7,13-15 Although various definitions have been used to identify DIVA in the literature, the 2021 INS standards definition is as follows:
Difficult IntraVenous Access (DIVA). Refers to multiple, unsuccessful attempts to cannulate a vein; the need for special interventions to establish venous cannulation based on a known history of difficulty due to diseases, injury, and/or frequent unsuccessful venipuncture attempts; may be acute due to sudden illness (eg, fluid volume deficit) or chronic due to lengthy history of difficult intravenous access.23(pS205)
Scoppettuolo et al20 conducted a retrospective study to evaluate the use of an 8- to 10-cm MC (which they called a “short” MC) in patients with DIVA presenting to the emergency department. They found a high rate of success at insertion, with 73% of the MCs present for longer than 7 days.20 Fabiani et al3 conducted a study in patients with DIVA and acute cardiovascular disease. They compared outcomes for an 8- to 10-cm PIVC (which they called a “long” PIVC) with outcomes for an 18-cm MC and found a higher complication rate with use of the 8- to 10-cm catheter.3 These studies illustrate the variability in catheter characteristics and outcomes represented in MC-related research.
The rapid rise in popularity of the MC has led to the expansion of its use into areas that have traditionally been reserved for CVC administration. Sharp et al44 conducted a retrospective review to evaluate the use of the MC versus the PICC for long-term antibiotic administration in patients with cystic fibrosis, a population in whom vascular preservation is paramount. They found that adverse events of MCs were not statistically different from those of PICCs. They were, however, surprised to find that the premature removal rate of MCs was more than twice that of PICCs.44 Pathak el al43 conducted a retrospective cohort study to determine the impact of increased MC use on the CLABSI rate in a unit with ventilator-dependent patients. With a standardized approach to VAD selection and increased use of MCs, they found a significant reduction in the CLABSI rate.43
The rapid rise in popularity of the MC has led to the expansion of its use into areas that have traditionally been reserved for CVC administration.
The location of the MC distal tip in the axillary vein may contribute to lower reported MC-associated phlebitis rates because of the higher blood flow in this area as compared with more distal vessels.10,15,17 In their clinical review of the MC, Adams et al15 postulated that the tip location nearer to the central circulation may lead to use of the MC for some critical care scenarios. As facilities expanded the use of the MC, research continued to challenge conservative criteria for peripheral administration. In a prospective, observational case series, Spiegel et al51 described their experience with MC use in critically ill patients in the emergency department. They found a mean dwell time of 6.7 days, with a 99% placement success rate and a 2.5% insertion-related complication rate. They also reported that 29.5% of these MCs were successfully used to administer vasopressors, a criterion previously approved by their facility policy.51
The requirement to place a CVC for vasopressor administration has been challenged in PIVC-related research. A systematic review by Loubani and Green52 included 85 studies (primarily case reports) that evaluated peripheral administration of vasopressors. Administration using a PIVC was identified as use of a VAD that was not placed in the internal jugular, subclavian, or femoral vein. The authors stated that the degree of tissue injury from PIVC extravasation was likely related to infusion duration and to localized tissue hypoperfusion inherent in patients in unstable condition. They also stated that tissue injury was more likely to be noted in areas distal to the antecubital fossa.52 They recommended that peripheral administration of vasopressors be limited to a duration of less than 2 hours using a PIVC that is well placed in a proximal location (eg, antecubital fossa or external jugular vein).52 Prasanna et al17 conducted a retrospective review of vasopressor administration via the MC route. They found an average vasopressor administration duration of 7.8 days and a complication rate of 3.5%, with only 11.7% of patients in the study later requiring a CVC insertion.17
The lack of high-quality VAD-related randomized controlled trials reduces the applicability of research recommendations to guide VAD selection and management.
Potential Risks of MCs
Despite the benefits of MCs, there are growing concerns about the expanding use of the MC. The primary concern is the paucity of accurate and reliable MC-related outcomes by which to measure the impact of the MC on vascular health and the ability of the MC to effectively provide long-term infusion therapy needs.14,16,51 Unfortunately, MC-related research studies are often plagued with the limitations common to VAD-related research as a whole: retrospective analyses; single-site studies; small sample sizes; risk of bias; documentation gaps; and wide variability in research methods, VAD-related adverse event definitions, inclusion criteria, and VAD characteristics.14,18,37,40,53-55 The lack of high-quality VAD-related randomized controlled trials reduces the applicability of research recommendations to guide VAD selection and management.6 The following paragraphs include examples of recent MC-related studies suggesting that MCs may be associated with a higher risk of adverse events than previously thought. A more complete description of recent MC-related research is provided in Table 4.
In their retrospective review of adverse events associated with MC versus PICC use, Xu et al12 found a significantly higher total complication rate with MC use and no significant difference in serious complications between the 2 routes. They found a significantly higher 30-day readmission rate with MC use.12 Highlighting the potential risks of MC use in the outpatient setting, Underwood et al57 found in a retrospective review that use of an MC that was not placed under radiologic guidance was associated with a significantly higher incidence of extravasation, blockage, and displacement as compared with other PIVCs in outpatients.57
The role that peripheral venous access plays in the incidence of BSIs is also an area of expanding study. The PIVC may be implicated in BSIs much more often than is currently estimated.61 In their systematic review of MC practices and complications, Tripathi et al18 reviewed 31 MC-related studies that included placement of 18 972 MCs in 5 countries. They found that MCs appear to have a low rate of BSI but a higher rate of premature removal before therapy completion and a composite failure rate of 12.5%. They acknowledged, however, that MC-related BSI rates are likely inaccurate because of inadequate surveillance.18 In their prospective quality improvement program, Hankins et al58 implemented a VAD selection algorithm that included an MC option and then monitored VAD-related outcomes. Although the MC-associated BSI rate was lower than the CLABSI rate during this initiative, they found significant correlations between MC dwell times and rates of BSI and thrombophlebitis, with an apparent increase in risk in patients who required multiple concurrent VADs.58
Thrombotic risk is multifactorial and is generally attributed to or worsened by vessel trauma, patient comorbidities, catheter-to-vein ratio, VAD securement, infusate characteristics, and longer VAD dwell times.23,27,58 Because of the extended dwell time of the MC, the thrombotic risk has gained increasing attention. Thrombus related to VADs may delay delivery of needed therapy, increase costs, and lead to significant adverse events, such as BSI and pulmonary embolism.16 Lisova et al27 conducted a prospective observational study to evaluate the rate of upper limb venous thrombosis in a group of adult patients with MCs. They noted an upper limb venous thrombosis rate of 4.5% with first-time successful insertion, increasing to 9% with 3 or more insertion attempts. They recommended that thrombotic risk of the MC be considered when choosing the optimal VAD for a patient.27 Dickson et al32 conducted a retrospective analysis of a cluster of MC failures and also noted an increased thrombotic risk when MC use was extended beyond 14 days. The rate of thrombosis decreased once they limited MC use to 14 days or less. An important aspect of their study, however, was that the MC in use was a trimmed PICC.32 The abraded edges of the trimmed catheter may have contributed to thrombus development. Recommendations in the literature warn of the potential for vascular damage in the use of PICCs trimmed to MC length.8,32 In their retrospective comparison of PICC and MC insertion over a 13-month period, Bahl et al16 conducted a multivariate analysis and reported that the “MC is an independent predictor of increased odds for the development of CR [catheter-related] thrombosis.”16(p4) The study also coincidentally found isolated contralateral upper extremity thrombosis in 2.41% of patients with MCs.16
In a retrospective review of 165 MCs, Meyer2 found that 62.8% of MCs lasted to therapy completion, with a mean dwell time of 8.5 days. The overall complication rate was 15.8%, and 58% of complications occurred with dual-lumen catheters. The mean time to loss of blood return from the catheter was 3.89 days.2 Acknowledging the thrombotic risk of the MC, the study facility did not allow blood to be drawn from MCs and developed a blood return algorithm to determine if loss of blood return was due to mechanical issues or was thrombotic in nature. If blood return was not restored with a needleless connector change, the use of 3-mL syringe to withdraw blood, or repositioning of the extremity or MC, removal of the MC was indicated to prevent further vascular compromise (Figure 1).2
Ryder et al10 conducted a blinded randomized controlled trial with MCs placed in sheep to explore the impact of infusates on vascular integrity. Controlling for insertion technique and tip placement, they placed 2 separate catheters for interventional and control infusions in each of the sheep. In the interventional (test) catheter, infusates with low and high pH (pH of 2.12 and 11.06, respectively), osmolarity (675 and 930 mOs-m/L), and cytotoxicity were administered. In the control catheter, normal saline was infused. At the conclusion of the trial, the sheep were euthanized and histological examination was performed to determine the vessel injury score, which represents the combined extent of vascular damage and thrombosis. As the vessel injury score increases, the risk of irreversible damage to the vessel increases. The authors found clinically significant elevated vessel injury scores in all of the vessels in which test infusates were administered. They noted that symptoms of leaking, discomfort, and swelling should be considered probable indications of vascular damage and thrombosis. They postulated that PIVC failure may be a function of dwell time and duration of exposure to the test infusates.10
Clinical Summary of MC Use in Critical Care
How does the bedside clinician or the vascular expert sort through the mounting data and often inconclusive or conflicting guidelines to choose the best vascular access option for a particular patient? The first step is to realize that all VADs carry risk.7,46 The twin goals of vessel preservation and completion of therapy must be considered equally when choosing a VAD.6 Evidence-based VAD selection requires a clear understanding of the individual patient’s needs and risks, vascular health preservation concepts, urgency of needed therapy, skill of the inserter, available VAD options, and length and nature of the prescribed therapy.6,8,23,24,62 Once a VAD is placed either peripherally or centrally, it should be managed with the utmost care for prevention and early recognition and treatment of VAD-related complications.4,7,8,10,23,55 Table 5 provides a summary of evidence-based peripheral intravenous access management.
The Michigan Appropriateness Guide for Intravenous Catheters, published in 2015, provided a valuable summary of expert consensus on scenario-based VAD selection and placement according to patient need, duration of therapy, infusate, and duration of treatment.19 These guidelines recommended using the MC for peripherally compatible infusates for up to 14 days (possibly up to 4 weeks) of therapy, preferring the PICC for therapy durations of 15 days or more.19 As illustrated in the preceding paragraphs and in Table 4, MC-related research has greatly expanded the body of knowledge since the Michigan guidelines were released in 2015. The 2021 INS standards include updated guidance for VAD selection, identifying the MC as appropriate for peripherally compatible therapy with an expected duration of 5 to 14 days and recommending use of the smallest catheter that will deliver needed therapy. The INS standards also state that a PIVC may remain appropriate for 14 days or more according to the patient’s desires and vascular needs and clear quality outcomes that support patient safety.23 Both documents include multiple recommendations for further VAD-related research. Table 6 provides a summary of VAD guidelines related to MC placement and related research priorities, including information to guide the scenarios presented in Table 1.
Because of the complexity and variability in health care and a lack of well-defined and universally recognized limits for infusate pH and osmolarity, neither document lists infusates that require CVC placement or are considered peripherally compatible.2,7,19,23 Instead, facilities are encouraged to develop these resources on the basis of local practices and evidence-based references.23 In the study by Ryder et al,10 the extent of vascular damage in vessels with test catheters led to the conclusion that pH should be considered an independent risk factor for VAD-related adverse events. The authors concluded that a pH range of 5 to 9 and osmolarity level of less than 600 mOsm/L were appropriate for infusates used for peripheral intravenous therapy. They also recommended reducing the dwell time of the MC to 6 days or less to preserve vascular health.10
Manrique-Rodríguez et al63 conducted a 3-phase study to standardize the dilutions of intravenous drugs commonly administered to hospitalized adult patients and to provide guidance on PIVC and CVC selection. They categorized the infusates according to their pH, osmolarity, and cytotoxic nature, indicating a continuum of risk based on infusate characteristics. High-risk infusates that required a CVC were solutions that were considered vesicants, had an osmolarity of greater than 600 mOsm/L or a pH of less than 4 or greater than 9, or were required for patients with poor or limited vascular access options. Moderate risk factors were osmolarity of 450 to 600 mOsm/L and pH values of 4 to 5 or 7.5 to 9. Low-risk factors were osmolarity of less than 450 mOsm/L and pH values of 5 to 7.5. Their study, which drew on the INS article “Development of an Evidence-Based List of Noncytotoxic Vesicant Medications and Solutions,”64 has a detailed list of medication properties, including vesicant designation and VAD selection recommendations based on these limits.63 Tables 7 and 8 also provide examples of indications for CVC placement and infusates requiring CVC placement.
As research continues to explore MC risks and benefits, safe use of the MC will rely on a culture of safety that places the patient’s needs at the center of VAD selection rather than adhering to a “somewhat misguided philosophy that no central lines equal no CLABSI (and its associated penalties).”8(p1120) A question that contributes to this mistaken philosophy is asked at many daily patient care reviews or huddles: “Can the patient’s CVC be removed today?” That question should be amended because it is often prompted by fear of a negative quality metric and may actually cause negative outcomes by transitioning from a CVC that is generally well monitored to a PIVC that may not receive the same standard of care.7 The appropriate question for each patient in the patient care huddle is “What is/are the best VAD option(s) for this patient today?” Unless the individual patient’s needs are fully addressed and current standards of VAD management and monitoring are effectively in place, a transition from a CVC to an MC (or multiple MCs) is not in the patient’s best interest. Figure 2 provides an example of an MC audit form.
The MC provides a valuable VAD option for critical care patients, with 2 notable examples. If a patient requires emergency treatment, short PIVC or intraosseous needle placement is preferred when there is increased risk or delay with CVC placement. However, if other peripheral access is not available and the resources to safely place an MC are in place, MC placement may be a viable option. If continuous vesicant therapy (eg, vasopressors) is required, prompt transition to a more definitive VAD is indicated.15,23,35 Midline catheters are also valuable for patients with DIVA who require a relatively simple regimen of peripherally compatible infusates for an estimated 5 to 14 days, preferably with a single-lumen MC.2,6,7,14,16 Optimizing VAD selection and outcomes requires that clinicians recognize that every VAD carries the potential for a significant risk of patient harm. It is imperative that facilities use current guidelines and research to develop VAD-related expertise, resources, and workflow to provide evidence-based guidance on VAD selection, placement, and management.7,14,23,24,55,63,64 It is equally imperative that VAD-related outcomes are effectively monitored, analyzed, and disseminated to further optimize patient outcomes in the rapidly evolving environment of critical care.2,11,12,14,18
The author thanks Lisa Gorski, MS, RN, HHCNS-BC, CRNI, FAAN, chair of the Infusion Nurses Society Standards of Practice Committee, and Britt M. Meyer, PhD, RN, CRNI, VA-BC, NE-BC, member of the Infusion Nurses Society Standards of Practice Committee, for their substantive review of this manuscript.
To purchase electronic or print reprints, contact the American Association of Critical-Care Nurses, 27071 Aliso Creek Rd, Aliso Viejo, CA 92656. Phone, (800) 899-1712 or (949) 362-2050 (ext 532); fax, (949) 362-2049; email, email@example.com.
To learn more about using catheters in the critical care setting, read “Narrative History of the Swan-Ganz Catheter: Development, Education, Controversies, and Clinician Acumen” by Headley and Ahrens in AACN Advanced Critical Care, 2020;31(1):25-33. Available at www.aacnacconline.org.