Dynamic contrast-enhanced MRI and MRA is rapidly increasing in popularity and creating new skill requirements for MR technologists. For MR Angiography, as well as MR of the liver, breast, and other applications it is increasingly necessary to inject gadolinium contrast agents dynamically during scanning while the patient is inside the magnet. This requires starting an intravenous line and attaching a long length of tubing that reaches outside the magnet.
It is important to point out that starting an iv is an art-form which is learned with experience accumulated after performing hundreds of ivís. Some patients are easy but many are difficult.
Preparation: An ounce of prevention
Before even getting started with the iv, first accumulate all the necessary supplies. You will need:
Introduce yourself "Hello, I am ________. I will be starting the iv for your MR examination. Have you ever had an iv before?"
When you introduce yourself, it is important to ask if the patient has had an iv before so you will know how much of the procedure needs to be explained to them. It is also useful to ask how much difficulty there has been in starting ivís in the past and if there is a preferred location. Often patients know more about the iv process and the best sites than anybody else.
Often the antecubital fossa is chosen because there is a large antecubital vein easily accessible there. For dynamic MR contrast injections generally 20 gauge is a good compromise. It is sufficient caliber for fast injections but still small enough to be easy to insert. In a pinch, a 22-gauge angio-catheter is probably also acceptable especially if you warm the gadolinium contrast to body temperature to lower its viscosity.
Prepare the Intravenous Tubing:
It is important to use intravenous tubing that allows simultaneous attachment of separate syringes for the gadolinium contrast injection and a subsequent saline flush. The Smart Set (TopSpins, Inc., Tel: 734-623-6400. Ann Arbor- www.topspins.com) was developed at The University of Michigan specifically for performing dynamic contrast injections for MR Angiography, liver MRI, breast MRI, and pelvic MRI. It has one-way valves that allow switching between the contrast injection and saline flush. In this way it is easy to have one continuous bolus without any gaps. By using the same tubing for all patients receiving dynamic gadolinium injections, the operator will become familiar with performing the injections and the resistance to the injection. It will then be easier to concentrate on bolus timing and instructing the patient in breath holding.
Prepare the tubing by filling it with normal saline and making sure there are no large air-bubbles. If using off the shelf iv tubing, be sure to clamp it so that the saline doesnít drip out onto the floor. When using the Smart Set this is not a problem, because the valves have a normally closed position.
Preparing the arm:
Apply a tourniquet high on the upper arm. It should be tight enough to visibly indent the skin without causing patient discomfort. In order to maximize venous engorgement, have the patient squeeze his hand into a fist several times.
Now start the search for suitable distended subcutaneous veins. If you cannot see any veins popping up from the distention caused by the tourniquet, you can sometimes feel them by palpating the arm. If you still cannot find any veins, then it might be useful to cover the arm in a warm compress to help with peripheral vasodilation. If after a meticulous search no veins are found; release the tourniquet from above the elbow, place it around the forearm and search in the distal forearm, wrist and hand. If no suitable veins are found, then you will have to move to the other arm. Be careful to stay away from arteries which are pulsatile.
Once a suitable vein is found, then it is necessary to clean and disinfect the area by swiping it several times with two alcohol wipes. If the arm is particularly hairy in this spot it may be necessary to use a disposable razor to shave the hair partially too make a region that will be clean.
Usually a 20 or 22 gauge angiocatheter is suitable. Take it apart and put it back together to get a sense of how it works and how much force is required to slide the plastic catheter over the metal stylet.
Use one hand to apply counter tension against the skin. This hand, generally the left hand, will be pulling the skin distally towards the wrist in the opposite direction to the needle will be advancing. When applying counter tension be careful not to compress inflow to the vein which may cause the vein to collapse. Advance the angiocatheter through the skin over top of the vein or adjacent to the vein. Use a quick, jab motion to minimize patient discomfort. Slow pokes through the skin will maximize the sensation of pain. Then advance the angio catheter well into the vein and look for the dark red flashback of blood at the angio catheter hub indicating that the angio catheter is within the vein.
If this first pass is unsuccessful in entering the vein and there is no flashback then slowly withdraw the angio catheter, without pulling all the way out, and carefully watch for the flashback to occur. If you are still not within the vein, then advance it again in a 2nd attempt to enter the vein. While withdrawing always stop before pulling all the way out to avoid repeating the painful initial skin puncture. If after several manipulations the vein is never entered and the attempt is considered a failure; release the tourniquet, place a gauze over the skin puncture site, withdraw the angiocatheter and tape down the gauze. Now it is time to move onto the other arm.
Advance Plastic Catheter
Once the angiocatheter is well seated within the vein, slide the plastic angio catheter forward deeper into the vein over top of the needle. The hub of the angio catheter should be all the way to the skin puncture site. The plastic catheter should slide forward easily. Do not force!!
Once the angio catheter is advanced in the vein up to the hub, release the tourniquet, apply gentle pressure over the vein to collapse it, so that blood will not pour out of the angio catheter when the stylet (needle) is removed. Once you remove the stylet (needle) set it aside to be disposed of in a Sharps container.
Attach the male end of the Smart Set to the female hub of the angio catheter. This is a press fit.
Lock Tubing Connection
Lock the iv tubing to the angio catheter by advancing and rotating the luer locking mechanism. It requires a clockwise twist to fully lock. At this point, quickly test the iv with a small injection of saline to make sure it is working properly. The saline should flush easily. If the saline does not flush easily, check to be sure the tourniquet is released. Also try straightening the arm because sometimes bending the elbow can kink a vein and prevent the iv from functioning. If it still does not flush easily, try aspirating. Sometimes an iv will begin to work if it is withdrawn slightly so the tip of the iv seats in a better position within the vein.
Secure with Tape
Tape the iv in place using three or four strips of tape to prevent accidental removal. Place one or two pieces over the actual skin puncture site. Place additional pieces over loops of tubing so that there is some strain relief. Consider taping to be one of the most important tasks because it prevents you from having to repeat the iv insertion in the event of an inadvertent tug on the iv tubing.
To test the iv inject saline. There should be no resistance. If necessary you may also test the iv by removing the Smart Prep MR Adaptor and aspirating until blood is seen entering the iv tubing. Alternatively you can test by engaging the clamp and injecting the side port or aspirating by the side port.