Overview of Ultrasound Intravascular Access
For over 20 years, ultrasound technology has been widely employed to establish intravenous access, which is the process of inserting a needle into a vein. Nowadays, it is regularly used in many places for non-urgent central line placements and situations where it’s tough to insert a needle into a vein. Past studies have confirmed the safety and high success rate of this procedure, leading to its common use in emergency departments.
An ultrasound can also help access and insert a needle into arteries, though this is not as commonly done. Once a medical professional has learned the procedure, it’s straightforward, effective, and safe, with very little increased risk. However, the availability of ultrasound machines and the need for proper training can limit the use of ultrasound for this purpose.
When planning to do this procedure, it’s important to consider other options as well. These include the traditional way of using anatomy landmarks to guide needle placement, or using alternate methods of gaining access to the body’s circulation such as intraosseous (inside the bone), intramuscular (in the muscle), and oral routes, which bypass the need for intravenous access. There are also devices designed to aid intravenous access by making veins easier to see.
Anatomy and Physiology of Ultrasound Intravascular Access
Before inserting a needle into a blood vessel (a process called cannulation), it’s crucial to know the difference between an artery and a vein. This can be done by understanding their structure and how they appear on ultrasound scans. Veins can be easily squished or compressed when pressure is applied using the ultrasound device, whereas arteries typically cannot. If you press on an artery, you might notice a rhythmic throbbing or pulsating movement – this is caused by the blood being pumped by the heart (you can see an example of this in an online video titled “Ultrasound Assessment for Intravenous Placement”). Arteries also usually have slightly thicker and brighter-looking (or more ‘hyperechoic’) walls compared to veins.
It might be trickier to tell arteries and veins apart when a person has low blood pressure or when their blood vessels have hardened due to calcium deposits – in these situations, an ultrasound feature called color flow mode can help, or a specialized ultrasound called a Doppler. Be careful though, when using these features – the colours used in the scan don’t inherently represent arteries or veins, but rather they show the direction of blood flow – towards or away from the ultrasound probe. As such, you must be cautious about how you are holding or angling the probe. Usually, arteries show a much greater change in blood flow speed compared to veins when using a Doppler ultrasound.
After you’ve identified the correct blood vessel, it’s import to track the path of the vessel to check for any branching or twisting that could make cannulation difficult. Looking at the vessel in different orientations (longitudinally and transversely) can help here. It’s also helpful to check the location of nearby structures like nerves to avoid potential issues should the needle be accidentally placed incorrectly. Using an ultrasound to scan the blood vessels can greatly help in finding the safest and most successful site for cannulation.
Why do People Need Ultrasound Intravascular Access
Ultrasound technology can be used to help doctors find and access the veins more easily when they need to insert a needle for a test or treatment. This is generally used for patients who are known to have ‘difficult access’ – meaning their veins are hard to find or get into. This could be the case for patients who have previously had issues with drug injections, have had treatments that involve regularly getting a needle into a vein (like dialysis), or have certain health conditions that make it hard to find a vein (like low blood pressure, dehydration, bleeding disorders, obesity, or swelling). It is also particularly useful for very young children, who can be harder to treat this way than adults.
Doctors might want to use ‘ultrasound-guided access’ for several different reasons. For example, they might need to put dye into a patient’s veins to help them see the inside of the body more clearly on an imaging scan. Alternatively, they could need to give medication, fluids, or blood through a vein. Sometimes, they might need to take a blood sample or monitor a person’s blood pressure during a procedure, and using ultrasound technology can help them do those things more effectively and with less discomfort for the person being treated.
When a Person Should Avoid Ultrasound Intravascular Access
There are no strict rules stopping doctors from using ultrasound to guide the placement of an intravenous line (a tube into your vein for giving medicines or fluids). However, if the doctor hasn’t been trained correctly or doesn’t have enough experience, they could misidentify parts of your body and unintentionally cause harm. Sometimes, doctors may opt for other methods to access your veins when previous attempts didn’t work, or when time is of essence. This could involve reaching the vein through a bone (intraosseous access) or spotting the vein through visible landmarks.
It may be best to stick with the traditional method (without ultrasound) under certain circumstances, like if the area where the IV is to be placed has a burn, infection, or injury, or if the patient has a removed breast (mastectomy), a condition causing clots in veins (deep vein thrombosis), or a connection between an artery and a vein (arteriovenous fistula). Doctors need to make a well-informed decision considering these factors.
As more doctors get trained in this procedure, situations where lack of training or experience causing problems will likely become less common. In fact, many medical schools are already teaching ultrasound to students and many training programs are being taught by doctors well-versed in the technique.
Equipment used for Ultrasound Intravascular Access
Aside from the tools needed to access blood vessels, the main equipment needed is a type of scanner called an ultrasound machine that comes with a high-frequency probe. This machine is important as it lets the doctor see inside your body in real-time. If the procedure involves accessing the body’s central vessels, strict cleanliness standards are also maintained to prevent infections.
Different clinics or hospitals use different designs of ultrasound machines, so doctors become familiar with the ones available at their own institutions. The ultrasound probe, the part of the machine that is moved over the skin, has an indicator or mark, like a small bump, on one side. This corresponds with a marker on one side of the ultrasound screen (usually the left side) to help doctors know where they are looking.
In order for the movements of the probe to match the image on the screen, the probe’s marker should be lined up with the screen’s marker. Normally, this is achieved by pointing the probe marker towards the patient’s right side. The ultrasound screen also features vertical markers which allow the doctor to judge the depth of the structures being viewed. This depth view can be tweaked based on how deep the targeted vessel is.
For veins that are located deep within the body, long tubes called angiocatheters are used to access them.
Who is needed to perform Ultrasound Intravascular Access?
In many cases, the person who is going to perform a medical procedure using ultrasound doesn’t need another medical professional there with them. Who carries out this kind of medical procedure can change depending on the medical center and the specific part of the body where the procedure will be done. This could be a technician, a nurse, an advanced practice clinician (a highly trained healthcare professional), or even a doctor.
Preparing for Ultrasound Intravascular Access
When a doctor plans to give you medicine through your veins using ultrasound technology, it’s important they prepare properly. This could involve putting medicine into your arm (peripheral) or closer to the heart (central). Doctors always use safety measures to prevent infection, and they explain the process to you to ease any nervous feelings. If there’s enough time, they will ask for your permission before doing the procedure.
The tools used in this procedure are typically:
– An intravenous (IV) kit, which includes a band (like what you’d see in a blood pressure cuff), a tube for the medicine to flow through, and a cleanser to clean the skin.
– Fluids for the IV, which could include salt water (saline).
– A cap to keep the IV clean when not in use (saline lock).
– The ultrasound machine and its scanner tool.
– Special germ-free gel and scanner cover.
For an IV in your arm, the doctor might use a sticky patch, like a Band-Aid, to cover the scanner. They often look for veins in the back of your hand, the fold of your arm, the side of your neck, or the upper part of your arm. They usually use the inside part of your arm to find the larger veins. For central IVs, the doctor locates veins in your leg, below your collarbone, or inside your neck.
How is Ultrasound Intravascular Access performed
There are four main ways to use an ultrasound to help guide a needle into a vein (a process known as intravenous access): static, real-time, longitudinal, and transverse methods.
In the static method, the vein is located using the ultrasound, and then marks are made on the skin to show where the needle should enter. After marking, the ultrasound is put aside, the area is cleaned, and, the needle is inserted into the vein. This way, there’s no need for the ultrasound to stay on the patient during the process or to have a special sterile cover for the ultrasound. However, the chances of being successful with this method are generally lower compared to the real-time approach.
In the real-time method, the ultrasound is used continuously to guide the needle into the vein throughout the whole process. For this to work, the ultrasound needs to have a sterile cover. Since the needle is guided visually using the ultrasound, the success rate is higher. This method usually makes for a smoother experience for the patient and requires fewer tries.
During a longitudinal approach, the vein looks like a long tube on the ultrasound image. This way, you can see the entire needle as it’s being pointed towards the vein. However, this approach requires the ultrasound, needle, and vein to be precisely aligned and can be tricky with veins that curve or twist.
In the transverse approach, the vein appears more like a circle on the ultrasound image. The needle must be inserted so that its pointed end can be clearly seen on the ultrasound, ideally with the needle’s groove facing the ultrasound. It’s very important not to lose sight of the needle as it’s going into the vein because if the needle isn’t clearly visible, it could unintentionally poke other nearby structures or even poke all the way through the back wall of the vein.
Once the needle is inside the vein, it should stay there until the catheter (a small tube) can be put in. In the longitudinal approach, it’s usually easier to see when the needle goes into the vein because both the needle and the length of the vein can be seen at the same time. With the transverse approach, the needle can be seen going into the vein one little bit at a time by looking at it from different angles while slowly moving the ultrasound back and forth. These two methods can be used separately or together, depending on what the person performing the procedure prefers and what the situation requires.
Regardless of the method, the procedure to be followed is roughly the same. First, the procedure is explained to the patient, outlining the steps involved, what’s expected to happen, any risks or potential benefits, and possible alternatives. It might also be necessary to obtain the patient’s permission to perform the procedure. All necessary supplies and materials are collected.
Next, a high-frequency ultrasound probe is used to scan the desired area and identify the best spot to insert the needle into the vein. Considerations include the relative depth, width, and contours of the vein, as well as the presence of other structures like nerves or other veins in the pathway of the needle. The comfort of the patient and their ability to move freely also need to be taken into account.
The area is then prepared and cleaned. A tourniquet (a device used for controlling venous and arterial circulation) is placed 3 to 4 centimeters (about 1 to 1.5 inches) away from the insertion site. Depending on the situation and the person, local anesthesia, warming, or both may be applied to the site to lessen pain and improve blood flow. The needle is also prepared and attached to a pre-flushed syringe.
Once the procedure starts, the needle is guided into the vein using the ultrasound. Real-time guidance from the ultrasound is crucial to make sure the needle and vessel are properly positioned. When the needle enters the vein, the syringe will typically fill up with a small amount of blood; this is also called “flash”. The needle is then advanced further to make sure the catheter is well placed within the vein.
The catheter is then introduced into the vein through the needle, which is then withdrawn and discarded. If needed, blood can be collected at this time for diagnosing. Once the catheter is properly placed and secured, the tourniquet is removed and a saline fluid is injected to confirm the smooth flow of fluid and to verify that the catheter is placed correctly. At this point, the ultrasound may also be used again to observe the target vessel and confirm proper placement of the catheter by looking at the subtle dilation (expansion) of the vein.
Finally, the catheter is secured in place and covered with a bio-occlusive dressing (a dressing that prevents liquid, bacteria, and viruses from reaching the insertion site). The site must be reassessed daily to ensure there’s no infection or infiltration (leakage of fluid into surrounding tissue).
Possible Complications of Ultrasound Intravascular Access
Using ultrasound to guide placing an intravenous catheter (a thin tube put into a vein to give fluids or medication) does not have particular complications compared to the usual method. However, research indicates that these catheters might stop working sooner than expected, lasting on average about 26 hours. This might not be due to the procedure itself but could be related to the specific patient’s condition or the person placing the catheter.
What Else Should I Know About Ultrasound Intravascular Access?
Ultrasound-guided intravenous access, or using ultrasound to help insert an IV, has shown benefits in both adults and children. One of the main advantages is that it increases the chance of getting it right the first time. This fact has been proven in various complicated cases and with patients who come for outpatient services.
Using ultrasound to guide the IV insertion process reduces the need for centrally placed IVs, which are typically more complex to insert. The use of ultrasound not only makes the process faster but also increases the chance of success on the first try. This leads to a faster process of administering the required treatment via the IV and makes the overall experience better for patients.
