Intravenous cannulation is a technique in which a cannula is placed inside a vein to provide venous access. Venous access allows sampling of blood as well as administration of fluids, medications, parenteral nutrition, chemotherapy, and blood products. The decision to obtain peripheral rather than central venous access depends upon clinical circumstances. In general, peripheral catheters are preferred when IV access is required for shorter periods, when direct access to the central circulation is unnecessary, and when smaller gauge catheters suffice. Peripheral access is generally safer, easier to obtain, and less painful than central access. In patients taking anticoagulants, peripheral access allows for direct compression of puncture sites and fewer hematoma-related complications compared with the sites used for central venous catheters. There are few contraindications to the placement of peripheral venous catheters. Most concern problems with cannulation at a specific site. The sole absolute contraindication is when appropriate therapy can be provided by a less invasive route (eg, orally).
Many sites can be used for peripheral intravenous (IV) access, and they vary in their ease of cannulation and potential risks. Site selection varies according to clinical circumstances, expected duration of treatment, and the condition of the extremities. In general, distal extremity sites should be used first, saving more proximal sites for subsequent cannulation, if needed. Placing an IV in a vein distal to a site that was previously punctured can lead to extravasation of fluids and hematoma formation. Larger veins are generally more easily cannulated and are preferable to smaller veins in the same region. Veins of the upper extremity are preferred due to the increased risk of thrombosis and thrombophlebitis with venous cannulation of the lower extremities. Whenever possible, avoid using the dominant upper extremity. Contraindications to the use of a particular extremity include the presence of an arteriovenous fistula (catheter can alter venous blood flow or damage the fistula) and a history of mastectomy or lymph node dissection (catheter can exacerbate impaired lymphatic drainage). Venous catheter placement should be avoided at a site that may interfere with an anticipated procedure (eg, an injured extremity that requires surgery).
Veins that are firm to palpation may be sclerosed (eg, from IV drug abuse) and should be avoided as should veins with evidence of phlebitis or thrombosis. Venous puncture at sites where catheter placement was recently attempted should also be avoided, especially if a hematoma formed (ie, vein was "blown") following the previous attempt. Placement of an IV through infected tissue is not advised due to the risk of introducing a systemic infection. In addition, peripheral IV catheters should not be placed through burned tissue or in extremities with massive edema. Sites over joints (eg, cubital fossa) should be avoided if possible due to the increased risk of catheter dislodgement and kinking, and the need to then immobilize the joint to reduce these risks. Peripheral IV catheters used for trauma resuscitation are an exception to this rule and are routinely placed in the larger veins of the cubital fossa. The veins of the dorsum of the hand are often the most accessible sites for peripheral cannulation. As an example, the dorsal metacarpal veins are usually visible and palpable and make good sites for IV catheter placement. These veins merge into the dorsal venous network (or arch) and then form the cephalic vein, which runs along the lateral distal forearm.
The antecubital fossa, though not a primary choice for nonemergent IV access, contains several accessible veins, including the cephalic, median cubital, and basilic. These veins are usually large and easily cannulated and provide a useful option when emergent IV access is needed. Veins in the proximal arm are more safely cannulated using ultrasound guidance. If catheter placement is attempted in these proximal veins without ultrasound guidance, there is an increased risk of arterial puncture and nerve injury. In addition to the arm, leg and neck veins can be used to obtain peripheral IV access. The external jugular vein, which drains into the subclavian, is a large vein in the neck that is easily cannulated, even in patients with severe volume depletion or otherwise poor extremity access. Placing the patient's bed in a head-down (ie, Trendelenburg) position or having them perform a Valsalva maneuver often enlarges the vein making cannulation easier. Veins of the leg, including the greater saphenous vein at the level of the medial malleolus and the dorsal metatarsal veins on the dorsum of the foot, are often accessible. However, lower extremity sites should be used only if veins in the arm cannot be cannulated.
Keep the patient warm and relaxed; both excessive cold and anxiety stimulate the sympathetic nervous system and can cause vasoconstriction of superficial vessels, thus making cannulation more difficult. If a topical anesthetic is used, allow sufficient time for it to take effect. If possible, use the patient's nondominant extremity to reduce inconvenience and the effect of extravasation, should it occur. If possible, place patients in supine position to avoid lightheadedness from pain or the sight of blood. Placing the anticipated cannulation site below the level of the heart uses gravity to reduce venous return, which causes blood to pool and veins to distend. Lightly tapping or gently stroking the vein along its length in a proximal to distal direction causes venous distension.
Elevating skin temperatures to 39 to 42 C at the cannulation site causes venous dilation. This can be accomplished by placing the site in warm water or by applying a warm compress (eg, warm moist cloths, warming packs, heated carbon fiber mitts). Proximal compression, most often using a thin rubber tourniquet placed 5 to 10 cm proximal to the anticipated venipuncture site, impedes venous return and enhances venous dilation. Another simple, effective way to dilate veins consists of having the patient alternately clench and relax their fist. Nitroglycerin ointment applied to the venipuncture site and left for two minutes causes venous dilation and does not appear to cause deleterious changes in blood pressure, even in hypotensive patients.
*SWG (Standard Wire Gauge) *FG (French Gauge)