Deciphering IV access devices
Intravenous (IV) access devices are a standard part of medical care for provision of fluids, medications, blood products, and parenteral nutrition. For the registered dietitian recommending parenteral nutrition, knowing the site and type of IV access devices can be beneficial.
To best understand IV access, an understanding of how blood flows through the body is important. Venous blood flow returns deoxygenated blood from the body to the heart. The size of these blood vessels varies and can impact medical care.
Veins located in the extremities are smaller, lie in the superficial fascia, and are visible and palpable. These peripheral veins in the arms and hands are a common site for IV access, with up to 80% of hospital patients requiring at least one peripheral venous catheter during admission. These vessels include the basilic, cephalic, antecubital, and antebrachial veins.
Larger vessels reside further up the torso. The superior vena cava (SVC) is the main vessel for venous return for the head, neck, arms, and chest. Smaller vessels, such as those listed above in the hand and arms, feed into the larger vessels of the upper chest including the subclavian, jugular, and brachiocephalic veins. These veins ultimately join to flow into the SVC followed by the right atrium of the heart. SVC blood flow is estimated at 2,000 mL/min, allowing for infusion of larger volumes or hypertonic solutions for rapid dilution.
Veins in the lower body can be used for IV access as well. The iliac veins constitute the main blood vessels of the legs. These veins flow upward to join at the fifth lumbar vertebra and into the inferior vena cava (IVC), the large vein that carries blood from the lower body, legs, and torso to the right atrium of the heart.
IV access is largely classified as peripheral or central. Access devices are not defined by the initial point of entry, but rather the position of the distal tip where the infusion will occur. Central access must terminate in the vena cava, whereas peripheral access terminates elsewhere.
Peripheral access devices
In a peripheral catheter, the tip position is located outside of the central vessels of the heart. Peripheral veins in the upper extremities of hands and arms can be accessed via peripheral catheters and are a standard practice in medical care.
Despite their commonality, they do have limitations. Smaller veins can be irritated easily, can’t accommodate large volumes of fluid, and do not have adequate blood flow to dilute hypertonic solutions. These are often used for a short duration, sometimes less than one week.
The leading complication in peripheral devices is thrombophlebitis, or inflammation of the vein. Replacement or rotation of the device may be necessary in these circumstances. However, rates of thrombophlebitis may vary depending on the length of the catheter, with short catheters carrying the highest risk. Midline catheters (8 to 10 cm) or long midline catheters (20 cm) may be preferential in these situations.
Central access devices
The other type of access device is the central venous access device (CVAD). In a central catheter, infusion occurs directly into the vena cava. Insertion sites usually include the cephalic, basilic, subclavian, jugular, or femoral veins. CVADs can be utilized for longer duration therapy but still carry risks, including vascular injury during placement, infection, and migration. Due to their placement into a larger blood vessel, infusion into these devices is not limited by osmolarity or volume like their peripheral counterparts.
CVADs can be further grouped into three categories – nontunneled, tunneled, and implanted. Tunneling is the practice of placing the access under the skin to separate the puncture and exit sites, and thus has been correlated with lower rates of infection. Implanted access devices, such as ports, can be implanted into a subcutaneous pocket and accessed when needed. Implanted devices are often more cosmetically appealing to patients as they are lower profile.
Defining features of access devices also include their lumens and presence of a cuff. Central venous devices often have multiple lumens. This allows for dual provision of multiple solutions or incompatible drugs. Cuffs are placed at the site of insertion and serve multiple roles – anchoring the device to prevent migration as well as providing a mechanical barrier.
Choosing an access device
Choosing the right access device is a multidisciplinary approach. Placement of IV access always comes with risks, and IV access teams are a crucial part of hospitals. Along with physicians, they can help manage IV access devices.
For the registered dietitian recommending parenteral nutrition, it is important to understand principles of blood flow, placement risks, and catheter features so that we can make informed parenteral nutrition recommendations.
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Neal AM, Drogan K.Parenteral Access Devices. In: The ASPEN Adult Nutrition Support Core Curriculum. 3rd ed.; 2017:321-344.
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