Introduction and Background
Vascular Access Devices (VADs) are divided into two basic groupings, peripheral and central. The group delineation is determined, primarily, by the catheter tip termination position, rather that the insertion site. Peripheral catheter tips remain in the periphery, terminate distal to the subclavian or femoral vein, and are optimal for intravenous medications that are peripherally compatible.
Central venous catheters are intravenous catheters with tips terminating in a large central vein of the body, typically the lower superior vena cava or upper right atrium.
Infusates that have vesicant properties, have extremes of osmolarity or pH, or are irritant solutions (i.e., total parenteral nutrition and antineoplastics), can cause damage to the narrow, fragile peripheral vein walls, and therefore should be administered into the larger veins of the central system (Bodenham et al., 2016; Denton, 2016; Gorski, 2016).
The insertion of the traditional short peripheral intravenous catheter (PIVC) remains the most commonly performed procedure in healthcare (Rivera et al., 2005). PIVCs also known as cannulas, have been described as ‘indispensable to human health’ (Rivera et al., 2005). Globally, approximately 80% of patients will have at least one PVC inserted during their stay in hospital (Tjon and Ansani, 2000; Waitt, Waitt and Pirmohamed, 2004; Alexandrou et al., 2018). Once in situ, PIVCs have a failure rate as high as 69% and often fail or dislodge between days three and five, therefore peripheral IV therapies are not recommended when treatment extends beyond five days (Chopra et al., 2015; Helm et al., 2015; Denton, 2016; Gorski, 2016). To bridge the gap between PIVCs and central venous catheters such as peripherally inserted central caterers (PICC), midlines were introduced into practice in the 1980s. Subsequently, the midline catheter has continued to grow in popularity as a more appropriate alternative to the short PIVC or unnecessary central venous catheter placement (Figures 1 and 2).
Midline catheters are used for the administration of blood, fluid and medication when the therapy is expected to last between one and four weeks. They can be used where patients present with poor peripheral venous access and when the use of a central venous catheter is contraindicated. The midline catheter provides venous accessibility along with an easy, less hazardous insertion at the antecubital fossa (Gorski). As a new addition to the family of vascular access devices, variation and inconsistencies relating to terminology, insertion techniques and use is evident.
Terminology surrounding Midline Catheters
Within the literature, language defining midline catheters is varied and inconsistent (Qin, Nataraja and Pacilli, 2019). According to Gorski et al., (2021); Moureau and Chopra, (2016) and Adams et al., (2016), a midline catheter is a longer peripheral cannula, most commonly inserted into the upper arm via the basilic, cephalic or brachial veins, with the internal terminal tip located below the level of the axilla, distal to the shoulder. Similarly, Rosenthal, (2008) Denton, (2016) and define a midline catheter for adults as one that is between three and eight inches (7.5cm–20cm) in length. They are also often referred to as long peripheral catheters (Elia et al., 2012; Fabiani, Dreas and Sanson, 2017; Qin, Nataraja and Pacilli, 2019). Qin, Nataraja and Pacilli, (2019) describe a long peripheral catheter as one that is between six and fifteen centimetres. The insertion is either via a catheter – over – needle or direct Seldinger (catheter – over – guidewire) technique. When inserted in the upper extremity, the distal tip terminates before the axilla and typically no further than the mid – upper arm. Qin, Nataraja and Pacilli, (2019) then distinguishes the device from a midline catheter which they define as one inserted via a Modified Seldinger with the tip terminating at the axilla. Moureau and Alexandrou (2019, p.25) use the term extended dwell cannula (EDC) with this description: ‘a peripheral cannula is a catheter less than seven and a half centimetres (cm) in length, and an extended dwell peripheral catheter is less than eight centimetres but designed with a longer cannula between three to seven and a half centimetres to facilitate ultrasound-guided placement, deeper vein access and longer dwell’. The term extended dwell cannula is now evident in literature. Chenoweth, Guo and Chan, (2018) describe them as an extended dwell peripheral intravenous (EPIV) catheter and state that they are six-to-eight-centimetre silicone catheters for peripheral insertion in neonates. More recently, the term short or mini midlines has appeared in the literature (Scoppettuolo et al., 2016; Fabio, 2018; Qin, Nataraja and Pacilli, 2019; Gilardi et al., 2020; Brugioni et al, 2020). The authors describe them as peripheral cannulas of intermediate length between a short PIVC (3.5cms – 5.2cm) and a ‘standard’ midline (15 – 25cm). They further distinguish these devices by the insertion technique which is direct Seldinger rather than a Modified Seldinger Technique (MST). They also highlight the stability of the short or mini- midline as a variance to other midline catheters and PVCs. To add further confusion, Pittiruti and Scoppettuolo (2017) refer to long peripheral cannulas (or mini midlines) and “True” Midline Catheters as below:
Most recently, the updated Infusion Therapy Sandards of Practice (Gorski et al., 2021) redefined the category of peripheral intravenous catheter which now includes the term long peripheral intravenous catheter (LPIVC). Within this document, a LPIVC is defined as a device that is inserted in either the superficial or deep peripheral veins. They go on to suggest that this device offers an option when a short PIVC is not long enough to cannulate the target vein adequately. They indicate that a LPIVC can be inserted using a traditional over the needle approach, the Seldinger Technique (ST) or the Modified Seldinger Technique (MST). The standards define a midline catheter as a device inserted into a peripheral vein of the upper arm with the tip terminating at the level of the axilla.
Finally, within a new consensus paper, European recommendations on the proper indication and use of peripheral venous access devices: A WoCoVA project (Pittiruti et al., 2021), as well as proposing guidance on indications for central versus peripheral venous access, indications for different vascular access devices, proper insertion techniques and device maintenance. They also offered a suggestion for the classification of the current available peripheral access devices. These guidelines come from a European viewpoint and differ from the classification from the Infusion Therapy Sandards of Practice (Gorski et al., 2021). This recent paper acknowledged the differing terminology between North America and Europe in this area of vascular access and aimed to improve the standarisation of the terminology, bringing clarity of definition, and classification’ (Pittiruti et al., 2021). Within this paper the Midclavicular device is introduced.
Within this document the panel recommended that peripheral vascular access devices should be defined as catheters whose tips are located in the venous system but outside of the superior vena cava or the right atrium. They then go on to define these devices based on the length and classify them as follows:
- Short peripheral catheter: A device which is less than six centimetres. They expand on this classification further by identifying them as either simple or integrated. This is based on their design and material.
- Long peripheral catheter: A device which is six to fifteen centimetres in length
- Midline catheter or mid clavicular: A device which is fifteen centimetres or longer.
These devices remain undefined by the international nomenclature and therefore, until this occurs, terminology will remain inconsistent. Despite the terminology attributed to these devices there are some important factors that must be considered to ensure their safe use:
- Consideration should be given to the medications delivered through these devices. According to Gorski et al., (2021), midline catheters can be used for ‘medications and solutions such as antimicrobials, fluids replacement, and analgesics with characteristics that are well – tolerated by peripheral veins’. However, they are contraindicated for continuous vesicant therapy, parenteral nutrition (PN) or infusates with extremes of pH or osmolarity.
- If midlines have to be used for short term delivery of vesicant medications (less than six days), this should be restricted to the more superficial veins of the forearm rather than the deeper veins of the upper arm where the signs of complications such as phlebitis and extravasation might be masked and recognised late (Masters, Hickish and Cidon, 2014) .
- A 45% catheter to vein ratio is considered the optimal cut off with high sensitivity and specificity to reduce the risk of venous thromboembolism (VTE) (Sharp et al., 2021). To ensure an adequate catheter to vein ratio (CVR), ultrasound guidance should be used to measure the vein diameter. According to Gorski et al (2021) CVR is specifically for PICCs and cannot always be extrapolated to midlines. However, CVR is still often used to reduce the risk of VTE in midlines (Chopra et al. 2019; Bhal et al. 2019). If ultrasound is not available, inserted should consider placement of a single lumen catheter with a small diameter into a large vein to further reduce this risk.
- Typically, the tips of these devices terminate in the peripheral veins and do not extend beyond the axilla (Gorski et al., 2021). They can be inserted into the veins of the forearm: cephalic or basilic, or the veins of the mid upper arm: cephalic, basilic or brachial (Figure 2).
- If inserting a device into the mid clavicular area, the tip position should be confirmed with either ultrasound or x-ray (Elli et al., 2020).
- The length of these devices is important when considering vein purchase. To reduce the risk of dislodgement, it is important to ensure that at least two thirds of the catheter length resides within the vein (Bahl et al., 2019). Therefore, a longer device might be necessary when inserting them into the deeper veins of the upper arm. The veins of obese patients may also be deeper so the device length would have to accommodate this.
- The Zone Insertion Method (ZIM) should be used when inserting these devices both in the upper and forearm. To reduce the risk of mechanical phlebitis the devices should not be place in an area of flexion such as the antecubital fossa, nor should the insertion site be too close to the axilla. This position has been associated with an increased risk of infection (Dawson, 2011).
- To reduce the risk of device failure, it should be ensured that the device does not cross areas of flexion such as the antecubital fossa, wrist or shoulder.
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