Cannulation is the insertion of a cannula into a blood vessel to drain fluid or administer a substance such as a medication. In hemodialysis, cannulation is required to allow blood to be pulled out of the body by the blood pump. The pump will then force this blood through the dialyzer and back to the patient’s bloodstream. At any given time, the total amount of blood outside the body is approximately 300ml. Choosing the proper access placement for cannulation may be restricted to certain limits. This may be due to scarring from previous surgeries. In most cases, the non-dominant arm is the preferred access site. Access sites are normally situated on the distal portion of the arm. However, the definitive choice will be determined by the vascular surgeon based on blood flow tests and studies. Patients who have underlying cases of diabetes have more problems with peripheral vascular disease since this condition damages blood vessels. That’s why their choice of access placement areas are very limited. There are two basic types of vascular accesses a dialysis technician should know. While there will be advantages and disadvantages to both, the type of access used is dependent upon the patient.
The Basic Types of Vascular Accesses
- Internal – these accesses are usually permanent, and are ideal for patients who will be on long-term hemodialysis. An internal access is usually placed in the early stages of chronic renal failure, even before the patient needs it. This is done so it will be ready to use when the patient actually starts treatment. Internal accesses require that the dialysis technician knows how to care for them so they’ll last longer.
- External – these are temporary accesses placed while the internal access matures. An external access may come in the form of a straight hemodialysis catheter or a cuffed and tunneled hemodialysis catheter. This type of access is usually done when the patient only needs dialysis for a short while.
Internal Vascular Access
Getting a fistula or graft placed is part of preparing the patient for hemodialysis. A fistula or graft is the ideal access for dialysis. If your patient is right handed, the surgeon’s first choice is to place the access in the patient’s left arm. If he’s left handed, the right arm will be the surgeon’s first choice. However, there are instances when this will not be the case. The surgeon will always tell the patient which arm to protect. In this regard, the dialysis technician should be well aware that the designated arm should not be compromised by IV’s, needle sticks for lab work, or even checking the blood pressure. In some cases, patients may require additional studies to verify the size of their blood vessels before the placement of the access. Ultrasound mapping is typically the most effective tool a surgeon can use to plan for access. Normally, there are no needles involved when mapping is done. On the other hand, some patients may also need a venogram done. During this study, a small needle is used to inject sterile dye into the blood vessels. The surgeon and access team will decide which study is best for the patient. The placement of an internal vascular access requires a trip to the Outpatient Surgery Department. A fistula or graft will then be placed in the operating room.
The Types of Internal Vascular Accesses
- The Arterial-Venous (AV) Fistula – The AV fistula uses the patient’s native vein and artery to make a connection. A fistula is usually situated in the patient’s upper or lower arm. When the link is made, the artery’s higher pressure pushes blood into the vein. After a few months, the vein will become larger and its walls will become thicker. The blood from these vessels can then be used for dialysis. The fistula normally matures in about 4-6 weeks. When this happens, it will now be possible to insert two needles for treatment. One needle will be used to pull blood from the patient’s body through the dialysis tubing. The blood will then flow through the dialyzer, filtering it in the process. Clean blood will be returned to the patient’s body through the second needle. The AV fistula is the most popular type of internal vascular access for hemodialysis. Since it doesn’t utilize foreign material to make, it is less likely to become infected or clotted. It is also more flexible because it is made of native tissues. When well-cared for by the dialysis technician, the AV fistula will provide the patient with better dialysis, resulting to better results. Unfortunately, there are still risks involved. If a fistula does not develop successfully, a graft will then be utilized.
- The Graft – A graft is highly similar to an AV fistula. It still connects artery to a vein. It is also used for dialysis in the same way as a fistula. However, what differentiates the graft is the material it uses. Unlike a fistula, a graft utilizes a thin, hollow, semi-rigid tube of a man-made material. A graft is ideal for patients with veins that can’t or didn’t develop a fistula. Grafts are usually placed in the upper or lower arm, or the upper leg of the patient. This type of access can either be straight or looped, which are literally named after their design. Since grafts are larger and more rigid than a natural vein, a dialysis technician can cannulate them with less trouble than with a fistula. However, grafts can become infected or clotted more easily than a fistula since they are not naturally part of the patient’s body tissue. Grafts can be used in about 2 weeks after its first placement.
How a Dialysis Technician Should Initiate Dialysis with a Fistula or Graft
- Usually, a fistula is ready to use in 4-6 weeks, while a graft is ready 2–3 weeks after placement. Before initiating cannulation on a new patient, the dialysis technician should get clearance from the vascular surgeon. Is the fistula or graft ready to use?
- Assess for any signs of infection. Is there visible redness, itching, tenderness, pain, warmth, or swelling at the incision site? Vital signs should also be taken by the dialysis technician. Note that an oral temperature of above 100 degrees Fahrenheit may be an early symptom of an underlying infection. If there are any complications noted, immediately refer to the nurse or doctor for necessary treatment interventions. The dialysis technician should learn how to look at, listen to, and feel the access for any red flags. In some cases, scabs from needles, curves, flat spots, ballooning of the blood vessels and their width, height, and appearance, may be present. Immediately report them to your supervisors once verified. If you can feel some cold spots on or around the access, tell the nurse in charge so he or she can assess it before the needles are inserted. Cold spots can be a sign that the fistula or graft is clotted.
- The dialysis technician should always wash his hands before touching any dialysis access. Cleanliness is the key. Clean hands and clean gloves significantly help prevent the transmission of bacteria from the skin’s surface into the patient’s bloodstream by the needle. Never forget to change your gloves if they get contaminated. Touching your face or hair, the chair, or any other surface is totally unacceptable. The use of gloves, gown, eye protection, and face mask is compulsory and should be done to control the spread of infections.
- The dialysis technician may offer to place a local anesthetic (lidocaine) in the skin above the patient’s access where he will insert the needles. Some patients prefer its numbing effect. If the patient haven’t experience using topical anesthetic, the dialysis technician may try needle insertion both with and without it to see which is best for the patient.
- Confirm the direction of blood flow by palpating for the thrill, a vibration that you can feel. Feel the entire length of the access by compressing it lightly with your two middle fingers. Once you feel the pulse and/or thrill on both sides of the area being compressed, hold your position and observe. Always remember that you will feel the strongest pulse on the arterial side. The pulse of thrill will be gentle or can’t be felt at the venous end.
- Confirm your findings with the use of a stethoscope. The blood flowing through the access will create a sound, called bruit, which you can hear by placing your stethoscope over the access. The sound is normally strong and steady. But like the thrill, the bruit should decrease continuously over the venous side of the graft.
- Two needles will need to be inserted in the access at each treatment. Identify the arterial needle. It typically has a red clamp with a back eye. The sites can be rotated if the patient has a graft. If the patient has a fistula the sites may rotate. The buttonhole technique can also be used, where the same hole is used each time. Choose a site for cannulation. The site used should be at least half an inch away from any previous needle sites. Also, do not cannulate near the surgical connection of the vein and artery. New insertions should be made at least one inch from obstructions, or restrictions. Keep the distance between the arterial and venous needles to at least 2 inches apart.
- To have equal areas for cannulation, set the anastomosis, or surgical connection, as its middle. First, the dialysis technician should cannulate the arterial half of the graft by moving toward the arterial anastomosis. Next, cannulate the venous half by moving towards the venous anastomosis. The venous needle will normally have a blue clamp with no back eye.
- Attach heparin loading dose to venous needle tubing. Unclamp and carefully flush heparing back and forth for 3 to 5 times. Reclamp after.
- The dialysis technician should never initiate dialysis until 5 minutes have passed. This is done to allow the heparin to circulate systematically, preventing blood clots from occurring throughout the treatment.
- Remove heparin syringe from the venous needle tubing if applicable and secure connections
- Connect the needles to the their appropriate dialysis blood tubing. Blood lines are used for exchanging blood to and from the hemodialysis machine from the patient. Blood line sets are pre-labeled based on equipment compatibility. Most facilities make use of color coded tubes and can be confusing for a new dialysis technician. The arterial line typically has a red clamp with red connectors, while the venous line has blue. The arterial line withdraws blood from the patient and transports it to the dialysis machine. Meanwhile, the venous line carries blood back to the patient’s body after being filtered.
- Set the heparin infusion pump accordingly. It should deliver the prescribed hourly heparin infusion.
- During treatment, the patient may sit in a recliner chair or lie in a bed. The dialysis technician should ask the patient to stop moving the access arm or leg. The dialysis technician may offer the patient some ways to pass time in the form of watching TV, talking with others, sleeping, listening to tapes, and reading.
- When treatment is complete, the dialysis technician may then remove the needles, apply a bandage, gauze, and ask the patient to place with his fingers until the bleeding stops. Applying pressure can take from five to twenty minutes.
- Lastly, the dialysis technician should check to make sure the bleeding has stopped, before letting the patient leave.