++
There are four main techniques of vein cannulation.6–8 The first is the needle-only technique using a butterfly-type needle. This is seldom used today. The catheter-over-the-needle technique is the one most commonly used for peripheral venous cannulation. The catheter-through-the-needle technique is occasionally used but not very popular. The Seldinger wire-guided technique is most commonly used for central venous access. The major advantages and disadvantages of each technique are summarized in Table 47-1.
++
Identify the vein to be cannulated and the site of the skin puncture. Clean the area of any dirt and debris. Cleanse the skin with isopropyl alcohol, chlorhexidine solution, or povidone iodine solution and allow it to dry. Apply a tourniquet to the extremity, proximal to the venous cannulation site, to engorge the vein. Additional engorgement of the vein or the use of a device to locate a vein, both described previously, can aid in the identification of a peripheral vein. Do not attempt cannulation if the vein cannot be seen, palpated, or otherwise visualized (e.g., ultrasound) in the engorged state. Place a small subcutaneous wheal of local anesthetic solution, or some other previously mentioned alternative, at the skin puncture site to provide some comfort to the patient. The next step is to cannulate the vein by one of the methods described below.
+++
Needle-Only Technique
++
This technique is used occasionally for short-term venous access in young children and elderly patients with fragile veins. This system is prone to malposition and infiltration. The tip of the needle can easily lacerate the vein if the needle is not secure and allowed to move.
++
Grasp and fold the wings of the butterfly needle with the dominant index finger and thumb (Figure 47-6B). Briskly insert the needle, with the bevel facing upward, through the skin and into the vein.14 A flash of blood will be seen in the tubing when the tip of the needle enters the vein. Carefully advance the needle an additional 3 to 5 mm into the vein. Attach a 5 mL syringe to the extension tubing and aspirate blood. The flow of blood into the syringe confirms proper intravascular placement of the needle. Remove the tourniquet from the extremity. Securely tape the wings of the butterfly needle to the patient's skin. Remove the 5 mL syringe, attach intravenous tubing to the catheter, and begin the intravenous infusion.
+++
Catheter‐over‐the-Needle Technique
++
The catheter-over-the-needle systems are the ones most commonly used for venous access. The infusion catheter fits closely over a hypodermic needle. The needle and the catheter are advanced as a unit into the vein. These devices are inexpensive (about $1-4 each), come in a variety of diameters (12- to 24-gauge) and lengths, and are widely available. Versions designed to minimize accidental needlestick injuries are available and their use is encouraged (Figure 47-7B).9
++
Insert the catheter-over-the-needle, with the bevel facing upward, through the skin and into the vein (Figure 47-9A).14 A flash of blood in the hub of the needle confirms that the tip of the needle is within the vein. Advance the unit an additional 2 to 3 mm to ensure that the catheter is within the vein. Hold the hub of the needle securely. Advance the catheter over the needle until its hub is against the skin (Figure 47-9B). Apply pressure, with the nondominant index finger, over the skin above the catheter to prevent blood from exiting the catheter. Remove the tourniquet from the extremity. Securely hold the hub of the catheter against the skin. Withdraw the needle (Figure 47-9C). Attach intravenous tubing to the hub of the catheter and begin the infusion (Figure 47-9D). Secure the catheter to the skin with tape.
++
++
Placement of these catheters is usually quick and simple. Several considerations should always be kept in mind when using the catheter-over-the-needle technique. Intravascular placement of the system is indicated by a flash of blood in the hub of the needle. If the patient's venous pressure is very low or if the needle is long and narrow, both sides of the vessel may be traversed (i.e., through-and-through) before the practitioner realizes that the needle was within the vein (Figure 47-10A). If the tip of the needle has withdrawn from the vein, the catheter will not advance. If the catheter is advanced when the tip of the needle but not the catheter is within the vein, the catheter will not advance. The catheter will push the vein off the needle (Figure 47-10B). Place a finger just distal to the puncture site. Depress the skin and pull it distally to prevent the vein from “rolling” as the catheter-over-the-needle is inserted into the vein (Figures 47-10C & D).
++
+++
Catheter‐Through‐the-Needle Technique
++
As opposed to the over-the-needle approach, this technique eliminates the need for a needle that is as long as the catheter and eliminates the possibility of pushing the vein off the end of the needle when the catheter is advanced.10 This system is used most commonly for central, rather than peripheral, venous access. Catheters up to 61 cm (24 in) long are available and allow central venous access from the antecubital vein or the femoral vein. Select a catheter size that is appropriate for the patient and the site of entry. Packaged with each catheter are a needle and a needle guard. The needle will have an inner diameter that is slightly larger than the outer diameter of the catheter. The needle guard has a beveled channel in which the needle can reside. The needle guard hinges closed over the needle to hold it securely and prevent the needle from shearing the catheter. Holes in the corners of the needle guard allow it to be sewn to the patient's skin.
++
Place the needle on a tuberculin syringe. Insert the needle, with the bevel facing upward, through the skin and into the vein while applying negative pressure to the syringe (Figure 47-11A).14 A flash of blood in the syringe confirms that the tip of the needle is within the vein. Advance the needle an additional 2 mm to ensure that the tip of the needle is completely within the vein. Grasp and hold the needle securely with the nondominant hand. Remove the syringe with the dominant hand. Immediately place the nondominant thumb over the needle hub to prevent air from entering the vein. Remove the tourniquet from the extremity.
++
++
Insert the catheter through the hub of the needle (Figure 47-11B). Advance the catheter through the needle until the desired length of catheter is within the vein. If the catheter will not advance, remove the catheter and needle as a unit. Never withdraw the catheter through the needle. The sharp bevel of the needle may cut the catheter as it is being withdrawn and result in a catheter embolism in the central venous circulation.
++
Withdraw the needle over the catheter (Figure 47-11C). Do not allow the catheter to be withdrawn through the needle. Continue to withdraw the needle until the tip is completely outside the skin. Apply the needle guard over the needle (Figure 47-11D). Attach intravenous tubing to the hub of the catheter and begin infusing fluids through the catheter. Secure the catheter and needle guard to the skin with tape and/or sutures.
++
The main disadvantage of this technique is the possibility of the needle tip shearing off the catheter, causing a catheter embolism in the venous circulation. This can be prevented by not withdrawing the catheter through the needle and applying the needle guard immediately after the needle is withdrawn from the skin. The contaminated needle must be handled to some extent, creating a potential risk for a needlestick injury. The needle used for the venipuncture must be larger in diameter than the catheter. This limits the practical diameter of the catheter. The needle punctures a hole in the vessel larger than the catheter and increases the risk of hematoma formation.
++
First described by Seldinger in 1953, this technique allows for the placement of a catheter over a wire rather than directly over a needle.11,12 The wire used must be longer than the catheter. The needle used to insert the wire can be short and of a smaller gauge than the catheter. If desired, the catheter type may be changed later without the need for a new venous puncture. Materials needed for catheter insertion are commercially available in a prefabricated kit (Teleflex Medical, Cleveland, OH; Cook Medical Inc., Bloomington, IN).
++
The Seldinger technique is most commonly used for central venous catheter insertion. It can be used for peripheral venous access if a short, thin guidewire is available. Ultrasound may be a useful adjunct with this technique.13 Please refer to Chapter 50 regarding ultrasound-guided vascular access for a complete discussion. All-in-one arterial line kits are commercially available. They are intended for peripheral arterial line placement but can also be used to place catheters in peripheral veins, the brachial veins, and the external jugular veins.
++
The Seldinger technique for venous catheter insertion is described briefly here. Refer to Chapter 49 (central venous access techniques) for a more complete discussion. Choose the puncture site. Prepare the patient for the procedure. Clean and prepare the puncture site as previously described. The vein may first be located with a small “finder” needle if there is doubt about its exact location. Insert a 25 or 27 gauge needle attached to a 5 mL syringe, with the bevel facing upward, through the skin. Advance the needle while applying negative pressure to the syringe. A flash of blood signifies that the tip of the needle is within the vein. Note the depth and location of the vein based on the depth and direction of the “finder” needle.
++
Insert the thin-walled introducer needle while applying negative pressure to the syringe. The introducer needle has a tapered hub on the proximal end to guide the wire into the needle lumen. Avoid using a standard hypodermic needle, as it does not allow for the passage of the guidewire. A flash of blood in the needle hub signifies that the tip of the needle is within the vein (Figure 47-12A). Advance the needle an additional 1 to 2 mm into the vein. Hold the needle securely in place and remove the syringe.
++
++
Occlude the needle hub with a sterile gloved finger. This will prevent air from entering the venous system. Insert the guidewire through the hub of the needle (Figure 47-12B). Advance it to the desired depth, ensuring that it is at least several centimeters beyond the beveled end of the needle. To prevent loss of the wire into the venous circulation, never let go of the guidewire with both hands at the same time. Hold the guidewire securely in place. Remove the needle over the guidewire (Figure 47-12C). Make a small nick in the skin adjacent to the guidewire with a #11 scalpel blade (Figure 47-12D). Direct the sharp edge of the scalpel blade away from the guidewire to prevent nicking the guidewire.
++
Place the dilator over the guidewire. Advance the dilator over the guidewire to enlarge the subcutaneous passage for the catheter. Continue to advance the dilator until its hub is against the skin. Withdraw the dilator over the guidewire while leaving the guidewire in place. Advance the catheter over the guidewire until its hub is against the skin (Figure 47-12E). A twisting motion of the catheter may aid in its advancement through the subcutaneous tissues and into the vein. Securely hold the hub of the catheter. Remove the guidewire through the catheter (Figure 47-12F).
++
Aspirate blood from the catheter with a syringe to confirm intravenous placement. Flush the catheter with sterile saline or begin an infusion. Secure the catheter to the skin with sutures and tape. While this technique seems complicated at first glance, it is easy to learn and can be performed in a few minutes by an experienced Emergency Physician.