A number of different types of peripheral cannula are available. It has been shown that the incidence of vascular complications increases as the ratio of the external diameter of the cannula to vessel lumen increases. The placement of large PIVCs is known to increase the incidence of malfunction that leads to failure (Alexandrou et al. [6]). Therefore, most of the literature recommends using the smallest, shortest gauge cannula possible in any given situation (Bitmead and Oliver [39], Frank [157], Gorski et al. [181], Macklin and Chernecky [287], RCN [381]). The measurement used for needles and cannulas is standard wire gauge (swg), which measures the internal diameter; the smaller the gauge size, the larger the diameter. Standard wire gauge measurement is determined by how many cannulas fit into a tube with an inner diameter of 1 inch (25.4 mm) and uses consecutive numbers from 13 to 24. The diameter, for example 1.2 mm, may be expressed as a gauge, for example 18 G (Nauth‐Misir [344]). Needles use odd numbers, for example 19 G or 21 G, while cannulas use even numbers, for example 18 G or 20 G (Weinstein and Hagle [465]). Therefore, a smaller gauge cannula will minimize trauma to the vein and increase blood flow around the device, promoting dilution and minimizing the risk of mechanical phlebitis (Bitmead and Oliver [39], McGowan [306]) (Figures 17.13, 17.14 and 17.15).

The walls of the device should therefore be thin to provide the largest possible internal diameter without increasing the external diameter. This is to ensure that maximum flow rates may be achieved while reducing complications such as mechanical irritation. Flow rates vary with equipment from different manufacturers. Flow rate through a cannula is related to its internal diameter and is inversely proportional to its length (Table 17.2). However, as the length of the cannula increases, so does the likelihood of vascular complications. For example, a large‐gauge device of longer length (1.6–2.0 cm) will fill the vessel, preventing blood flow around it, which could result in mechanical trauma to the vessel and encourage the development of phlebitis (Dougherty [124], Tagalakis et al. [434]).

The most suitable material is one that is non‐irritant and does not increase the risk of thrombus formation (Dougherty [124]). The material should also be radio‐opaque or contain a stripe of radio‐opaque material for radiographic visualization in the event of catheter embolus (Dougherty [124], Perucca [369]). Types of material can vary and include PVC (polyvinyl chloride), Teflon, Vialon, and various polyurethane and elastomeric hydrogel materials (Bitmead and Oliver [39], Dojcinovska [121]). Studies have compared the different types of material available to ascertain which is associated with the lowest potential risk of phlebitis (Karadag and Gorgulu [236]). When considering the results of these studies, however, it must be noted that investigators often use different phlebitis scales and calculations to create a total score for each device. Other inconsistencies relate to differences in catheter size, skin preparation, the use of dressings and the type of solution being infused. This makes it difficult to interpret research comparing catheter materials.

The ‘over the needle’ type of cannula is the most commonly used device for peripheral venous access and is available with various gauge sizes, lengths, compositions and design features (Dougherty [124]). The cannula is mounted on the needle (known as the stylet) and once the device has been pushed off the needle into the vein, the stylet is removed. A sharp‐tipped stylet facilitates penetration into the vein and the type of graduation from the cannula to the needle can affect the degree of trauma to the vessel and the cannula tip (Dougherty [124]). A thin, smooth‐walled cannula tapering to a scalloped end causes less damage than one that is abruptly cut off (Dougherty [124], Macklin and Chernecky [287]).

Some peripheral cannulas have wings, which help with securing the device to the skin in order to prevent a piston‐like movement within the vein and accidental removal (Dougherty [124]). Some devices have small ports on the top (these are favoured more in Europe than in the US) (Figure 17.13). The advantage of a ported device is the ability to administer drugs without interfering with a continuous infusion. However, the caps are often not replaced correctly, which leaves the system exposed to contamination and the risk of air entering, so where ported devices are used they should be capped off using a needle‐free injection connector (Easterlow et al. [136]). It has also been found that the ports cannot be adequately sterilized with a swab, as there is no flat surface, so these devices are associated with an increased risk of infection (Easterlow et al. [136]).

Safety cannulas are now available and have either active or passive mechanisms. In the active devices the practitioner has to push a button in order to activate the safety feature, while in the passive devices the stylet has a blunting or shielding facility, which is automatically activated on removal from the cannula (Dojcinovska [121], Dougherty [124], Gorski et al. [181], HSE [217], RCN [381]) (Figure 17.14). New closed system safety cannulas (Figure 17.15) can also reduce the healthcare professional's exposure to blood by introducing an integrated catheter tubing that prevents blood spillage (Bitmead and Oliver [39]). There is evidence that these integrated closed‐cannula systems can reduce the risks of needle stick injury, blood leakage and exposure, as well as increase dwell time and patient comfort (Shaw [411]), making them safer, more convenient and more economical (Barton [20], Bitmead and Oliver [39]).

Proactive patient assessment and intentional device selection are fundamental to the successful placement and preservation of the PIVC (Bitmead and Oliver [39]). There are various models, for example:

These all provide guidance on the selection and insertion of intravenous devices by offering a standardized pathway approach (Bitmead and Oliver [39]) and give guidance on how to select an intravenous device, based on the type and duration of therapy, vein health and the patient's medical condition. Using a care bundle for insertion helps to promote best practice and includes hand hygiene and ensuring the practitioner has the appropriate equipment (e.g. gloves, tourniquet, skin preparation, cannulas, dressings and sharps bins) (Burnett et al. [58]). Many PIVC infusion phlebitis scales and definitions are used internationally, for example the Visual Infusion Phlebitis (VIP) scale (Figure 17.17). The scale was developed by Jackson ([226]) and measures the signs and symptoms of phlebitis, matching them to the appropriate management. Each stage has a numbered score; this is recorded by nursing staff at regular intervals and, where necessary, the corresponding action is taken (Groll et al. [186], Morris [325]). However, there is now debate as to the lack of inter‐rater agreement between these phlebitis assessment scales and the need for new approaches to evaluate vein irritation that demonstrate comprehensive reliability and validity (Marsh et al. [296], Ray‐Barruel et al. [380], [379]).

As the most common cause of VAD infection is the patient's own skin flora, it is important to clean the skin adequately prior to cannulation (Figure 17.18). The patient's skin should be washed with soap and water if visibly dirty, which will remove most transient flora (Perucca [369]). Then an antiseptic solution, such as 2% chlorhexidine solution in 70% alcohol, should be applied with repeated up‐and‐down, back‐and‐forth strokes with friction for 30–60 seconds over an area of 4–5 cm diameter (Bitmead and Oliver [39], Bodenham et al. [43], DH [117], Perucca [369]). A quick wipe fails to reduce bacteria count (Weinstein and Hagle [465]). The skin should then be allowed to air dry for up to 1 minute to ensure coagulation of the organism and to prevent stinging as the needle pierces the skin (Gorski et al. [181], RCN [381], Weinstein and Hagle [465]). Fanning, blowing on and blotting the prepared area are contraindicated (Perucca [369]). Once the skin has been cleaned, it must not be touched or repalpated (Dougherty [124]). If it is necessary to repalpate, then the cleaning regimen should be repeated. The principles of aseptic non‐touch technique must be adhered to at all times (Bitmead and Oliver [39]).

Shaving the skin prior to cannulation is not recommended (Gorski et al. [181], RCN [381], Weinstein and Hagle [465]) as the supposed need to remove hair has not been substantiated by scientific evidence (Weinstein and Hagle [465]). Shaving with a razor should not be performed because of the potential to cause microabrasions, which increase the risk of infection (Gorski et al. [181], Perucca [369], RCN [381]). Depilatories should not be used because of the potential for allergic reaction or irritation (Perucca [369], RCN [381]). If hair removal is felt to be necessary then this can be accomplished by clipping with scissors or clippers (Perucca [369], RCN [381]). These should be cleaned between patient use or only used once to prevent cross‐infection (RCN [381]).

The influence of a bad experience can be overwhelming for a patient, and any practitioner performing venepuncture or cannulation must never underestimate either the impact for the patient of undergoing the procedure or how they may view these procedures in the future (Dougherty [125]). It has been found that 20% of adults experience mild to intense fear of injections and blood, with 10% having a profound fear of needles; this may be expressed as feelings of anxiety and/or a vasovagal episode with symptoms of bradycardia and hypotension (Dougherty [124], Jenkins [231]). Anxiety can be caused by previous bad experiences, a degree of needle phobia or dislike of needle procedures (Andrews [12], Andrews and Shaw [13], Jenkins [231], Lavery and Ingram [264]). Many patients will be apprehensive and this anxiety may cause vasoconstriction, making cannulation more difficult as well as more painful for the patient. How nurses approach the patient, and their manner and attitude, may have a direct bearing on the patient's response to the procedure (Dougherty [125], McGowan [306]).

If the patient's history includes complications associated with any procedure, venepuncture or cannulation may be very difficult (Jenkins [231], Weinstein and Hagle [465]). However, when a procedure is performed by an experienced practitioner and it is a positive experience for the patient, they may feel comfortable and relaxed. The nurse should ask patients about their past experiences and acknowledge their feelings and fears (Dougherty [125], McGowan [306]). Provision of clear and comprehensive information on the procedure should reduce the patient's anxiety and pain (Dougherty [125], Lüker and Stahlheber‐Dilg [279], Weinstein and Hagle [465]).