In this post, I'm covering cannula insertion. Like standard blood draw, IV insertion is one of those nursing tasks you'll have to master—the quicker the better. We all know the pressure, but the best way to get better is to maintain a clinical perspective. With that in mind, I’ll cover the basics and then offer a few best practices.
You will place cannulas most commonly in the cephalic, antecubital fossa, median cubital and basilic veins.
All veins are composed of three layers:
- Tunica intima. This is the elastic, outermost layer.
- Tunica media. This layer contains elastic tissue and muscle fibers.
- Tunica adventitia. This layer comprises connective tissue.
Most veins also contain valves. These structures are crucial for circulation because they prevent backflow. Valves are numerous in the limbs and you should avoid trying to run a catheter or cannula into them.
In the simplest terms, intravenous cannulation involves the insertion of a cannula into a vein. For those who are new to the game, a cannula is a thin, sturdy tube inserted into a vein or a body cavity to administer medicine, drain off fluid, or insert a surgical instrument. Cannulas come in four colors:
- Orange. 14G. Used in ERs or surgery theaters for rapid transfusion of plasma or other fluids.
- Grey. 16G. Heavy-duty version of the orange cannula. Used in the same circumstances.
- Green. 18G. Used for parenteral transfusion, stem cell harvesting and cell separation. Also used for rapid blood transfusion.
- Pink. 20G. Used for rapid intravenous infusions.
- Blue. 22G. Used in small veins, commonly in children.
Select the smallest gauge cannula that will do the job at hand.
There are two important steps in using a cannula. First, you must always open the “wings” on either side of cannula. These projections allow you to grip the cannula properly. Second, you must always point the bevel in the needle upward. Inserting the needle bevel-side down generates resistance, which can force the skin to bunch up. This results in unnecessary trauma. Inserting the bevel up also ensures smooth flow of liquid.
Naturally, you will also wash your hands, apply the tourniquet and clean the insertion site with two percent chlorhexadine and 70% alcohol solution as preparatory measures.
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Holding a Cannula in Three Steps
- Place your middle finger on the right “wing.”
- Place your index finger on the insertion port.
- Place your thumb at the end of the cannula.
Inserting the Cannula
- Insert the cannula into the vein at 30-degrees.
- Advance until you see blood at the base of the cannula. This is “flashback.”
- Hold the needle still while gently inserting the cannula into the vein.
- Without inserting the needle further, continue advancing the cannula. If you feel resistance, stop. Remove both the needle and the cannula. Try another insertion site.
- If you do not feel resistance, advance the cannula until the base meets the skin.
- Remove the tourniquet.
- Apply gentle pressure to the end of the cannula to stem blood loss. Use gauze to absorb any flowing blood while you withdraw the needle.
- Dispose of the needle into the sharps bin. Do not throw the bung away!
- Insert the bung into the cannula and apply the dressing.
- Insert 5 mls of flushing solution into the cannula—typically normal saline—noting residence or reports of discomfort from the patient. Either of these can indicate extravasation.
- Note the procedure and results in the patient’s notes.
Cannula Insertion Tips
The following tips can help you draw blood like a pro.
- Don’t rely on your eyes.
Veins close to the surface are typically more fragile than deeper veins, and they will blow more often—especially in children and the elderly. Deeper—but less visible—veins are sturdier. Consequently, practicing palpation is crucial. Palpate with your fingertips, feeling for a “springy” or “bouncy” vein, and always go with the biggest vein you find. Once you find a juicy vein, feel up and down an inch or two. You’re looking for consistency here. Finally, don’t palpate before applying the tourniquet. The tourniquet makes deep veins more visible.
- If your tourniquet is not helping, try a cuff.
Blood pressure cuffs put a lot of pressure on veins, so they can be a good alternative if your go-to tourniquet isn’t doing the job. To boot, cuffs are generally more comfortable for the patient. There is a procedure for this though. Once you apply the cuff, turn it upside down so the tubes are facing away from you. Then pump to the patient’s diastolic pressure. Release just a bit. The patient should report that the cuff is comfortable at this point. Do not exceed diastolic pressure!
- Manage your patient.
When looking for a vein, ask your patient to keep their hand below their heart and make a fist. This will help when palpating. However, when you go for the insertion, ask your patient to relax their hand and arm. This helps with rolling.
- Traction is your friend.
Once you’ve found a serviceable vein, place your thumb alternately to the left and right of it. The patient should report firm pressure on both sides. Pick a side. As you push the cannula into the vein, maintain this pressure.
- Avoid these areas.
If possible, avoid the elbow and wrist. These areas are very sensitive. Your patient will complain of pain, and you will lose time. The mid-arm and the hands are good options. Always start distal. Work toward the body only if you have to.
- A smoother insertion.
For a smoother insertion, insert the needle only 1/8th of an inch and lower your angle of attack to 0 degrees once you get your flash. This will allow you to slip the cannula into the vein with minimal fuss.
- Keep it shallow.
Make sure you use a shallow angle of between 30-40 degrees. The idea here is to mimic the angle of the vein itself. This can help you avoid bursts.
- Everyone makes mistakes; learn from yours.
Every profession has “grind.” Grind represents the tasks you must do repeatedly to gain proficiency. Learn from any mistakes you make along the way.
Ask yourself a few questions after every IV or blood draw:
- How did that go? Was there anything I could have done better?
- What, exactly, could I have done better?
- Was I rushed? Did I work faster than I needed to? Was I nervous?
- What can I do next time to optimize the process?
Acknowledging your mistakes can help you let go of them, which will help you stay anchored in the present moment.