Buzz
Whether you're aiming to locate a vein on the skin's surface or preparing for a medical examination or ultrasound certification, distinguishing between arteries and veins is essential. Identifying veins is relatively straightforward: they appear blue and slightly raised on the skin's surface, whereas arteries typically lie deeper. Additionally, ultrasound machines can aid in isolating arteries based on their movement and blood flow direction. When examining images, variations in artery and vein size and wall structure become apparent.
Procedures
Spotting Veins Visually
Scan the arm, leg, or neck to locate a superficial vein. While veins are distributed throughout the body, identifying them can be challenging on thicker body surfaces. Begin by examining the neck or inspecting the arms or legs for visible veins. They are typically more prominent and observable in areas with less fatty tissue.
- While drawing blood from a vein is acceptable, it is crucial to avoid arterial puncture. Arteries transport blood to the heart, while veins carry it away. Puncturing an artery risks depriving the heart of blood returning to the ventricles and aortas.
- Unlike veins, arteries are not easily visible to the naked eye and do not protrude from the skin's surface. Arteries are deeper within the skin and do not exhibit the same raised appearance as veins.
Pro Tip: The median cubital vein, situated in the elbow crease, is commonly used for blood draws due to its size and accessibility.
Examine the skin's surface on the arm, leg, or neck for visible veins. Steadily hold the skin section under observation and scrutinize it closely. Look for bluish-green lines, approximately 1–2 millimeters in width, traversing the skin's surface. While many veins run longitudinally along the limbs and neck, smaller veins connecting to larger ones should be discernible in the arms, hands, legs, and neck.
- Locating veins on the dorsal aspect of the hands is often easier.
Palpate the skin's surface to confirm the presence of a vein. In individuals with leaner physiques or those who exercise regularly, veins may be palpable, slightly protruding from the skin. Gently glide your fingers over a vein; if you detect elevation, a vein is present. If difficulty arises in locating the vein, especially in the arms, apply a tourniquet above it to restrict blood flow and enhance visibility.
- A tourniquet, typically a rubber or fabric strip, is tightly tied above a vein to restrict blood flow, thereby increasing vein prominence.
- Never apply a tourniquet around the neck.
- Tourniquets also serve as a measure to control bleeding and are essential in emergency medical situations.
Performing Vascular Ultrasounds
Instruct the individual undergoing the test to remove any nearby jewelry or clothing. Vascular ultrasounds, also known as Doppler ultrasounds, can be conducted on any body part. Request the individual to remove clothing from the 6–12 inches of the body being examined. Additionally, ask them to remove any jewelry near the area, as it may interfere with the ultrasound.
- A vascular ultrasound employs sound waves to generate a two-dimensional image of arteries and veins within the body.
Pro Tip: While ultrasound can visualize veins, arteries are identifiable by their pulsating motion and blood flow direction, which can be observed upon activating the color box. Veins carry blood away from the heart, whereas arteries transport blood towards it. Arteries are more likely to be found beneath the skin's surface, exhibiting pulsatile movements.
Apply water-soluble gel to the transducer's surface. To facilitate smooth movement and obtain clear images, coat the transducer's sensor with ultrasound gel. This gel also enhances skin-transducer contact, enabling sound wave transmission. Don latex gloves and use the gel nozzle to apply the lubricant onto the sensor. Ensure thorough coverage by gently spreading the gel.
- The sensor refers to the flat portion at the transducer's end, opposite the cable.
- Prior to usage, ensure the transducer is adequately sterilized and cleaned.
- Apply sufficient gel to fully coat the transducer. While it may cause discomfort due to its cold temperature, excess gel does not pose practical issues.
Power on the ultrasound machine and adjust settings. Activate the ultrasound machine and navigate the menu to select the 'ultrasound' mode. Adjust the frequency to 5.0 MHz for vascular imaging, and set the intensity to the lowest level, gradually increasing if necessary.
- To ensure consistent imaging, set the ultrasound to 'continuous' mode.
- If the area is inflamed, deactivate head warming settings to maintain transducer coolness.
- Frequencies are adjusted based on the targeted anatomical structures. For example, 2.5 MHz is suitable for gynecological imaging, while 15 MHz is preferred for bone or muscle examination. Fine-tune the frequency according to the subject's characteristics.
Position the transducer on the examination site and identify an artery. Place the transducer on the skin surface over the intended artery location. Maneuver the transducer to distribute the gel evenly. Arteries typically appear as hollow tubes in black-and-white ultrasound images.
- Muscle tissue appears white or gray and fibrous, while arteries should exhibit no color. Adjust the frequency until the artery appears hollow.
- When viewed from an oblique angle, arteries or veins may appear as empty circles on the screen.
Activate the thermal imaging feature to assess blood flow. Blood, being warmer than surrounding tissues and in constant motion, enables visualization of blood flow status within arteries. Activate the thermal setting on the transducer to observe blood flow represented in the color box on the screen.
- An optimal blood flow range typically falls between positive 27 cm/s and negative 27 cm/s.
- If struggling to locate an artery, attempt to follow a horizontal empty space to identify a continuous length of hollow space.
- If blood flow is not visible on the screen despite multiple adjustments (excluding cadaver examination), an artery is likely not in view.
Differentiate arteries from veins by observing pulsation when flexed. While examining a live image and discerning between two lumens, instruct the patient to flex their muscles. Upon contraction, veins will smoothly open and close, whereas arteries will exhibit slight pulsation. Arteries also close at a slower pace compared to veins.
- Arterial pulsation resembles a subtle shiver, with the lumen repeatedly opening and closing as blood is propelled through.
- Applying additional pressure to the transducer can cause the vein to collapse while the artery remains open.
- A lumen refers to the tube-like structure present in veins and arteries.
- Some arteries may not close entirely, whereas veins always do.
Analyzing Arterial and Venous Images
Assess wall firmness and thickness for differentiation. When examining microscopic or thermal images of arteries and veins, focus on the luminal walls. Veins typically possess thinner walls with indentations around the opening, while arteries exhibit thicker, smoother walls.
- Arteries are generally slightly smaller than adjacent veins.
Identify arteries by observing the elastic lamina. Arteries feature elastic fibers arranged in an accordion-like pattern along the lumen's circumference, known as the elastic lamina. This characteristic is exclusive to arteries and serves as a definitive indicator of arterial presence.
Pro Tip: Arteries boast enhanced strength compared to veins, hence harboring an additional layer in their internal lining. This explains the presence of the elastic lamina solely in arteries, not veins.
Spot veins by examining the gap between the muscle and wall. When analyzing a thermal or microscopic image of a vein, observe the space between the vein's lumen edge and the adjacent muscle. Veins typically exhibit a smooth and thin space devoid of texture, distinguishing them from arteries.
- This region is referred to as the tunica media.
- In contrast, the corresponding area in an artery appears pointed and textured, resembling a distressed rug.
Helpful Tips
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Veins always appear blue, while arteries are not visible to the naked eye. Regardless of whether it's within a vein or artery, blood always appears red.
Warnings
- If you encounter difficulty locating a vein during blood draw, seek assistance from another phlebotomist. Repeatedly sticking the patient with a needle is unfair and a fresh perspective can be helpful.
- When using a tourniquet, avoid tying it into a knot. Instead, overlap the two ends as you would when starting to tie a shoe, then pull to tighten. Untying a knot in case of complications can be time-consuming.
- Only draw blood from an artery when necessary for specific tests such as arterial blood gases; otherwise, avoid arterial puncture.
