An arterial puncture is a medical procedure that involves inserting a needle into an artery to obtain a blood sample or to place a catheter. This differs from a routine blood draw, known as venipuncture, which accesses a vein. Arteries carry oxygenated blood away from the heart, while veins carry deoxygenated blood back to the heart.
Reasons for Arterial Puncture
Arterial punctures are performed for specific diagnostic purposes when information about arterial blood is needed. The most frequent reason is to obtain an arterial blood gas (ABG) sample. ABG analysis measures the levels of oxygen, carbon dioxide, and the pH (acid-base balance) in the blood. This provides a precise assessment of a person’s respiratory and metabolic function, which is particularly useful in emergency and critical care settings.
Arterial blood is essential for ABG analysis because its composition directly reflects gas exchange in the lungs before the blood circulates through the body’s tissues. Venous blood, in contrast, has already delivered oxygen and picked up carbon dioxide from tissues, making it unsuitable for accurate assessment of lung function and systemic oxygenation.
An arterial line, a thin tube inserted into an artery, is also used for continuous, real-time blood pressure monitoring in critically ill patients, allowing for precise and immediate adjustments to medications.
How Arterial Puncture is Performed
The procedure begins with selecting an appropriate site. The radial artery in the wrist is the most common and preferred site due to its accessibility, proximity to the surface, and the presence of collateral circulation from the ulnar artery, which provides an alternative blood supply to the hand. Other potential sites include the brachial artery in the arm or the femoral artery in the groin, though these are typically less preferred due to deeper location or proximity to other structures.
Before puncturing the radial artery, a healthcare professional may perform an Allen test. This test temporarily compresses both the radial and ulnar arteries to check if the ulnar artery can adequately supply blood to the hand, ensuring sufficient collateral circulation. The skin at the chosen site is then thoroughly cleaned with an antiseptic solution to prevent infection. While not always used, a local anesthetic may be injected to numb the area.
With the site prepared, the healthcare professional carefully inserts a specialized needle, often at a 45-degree angle, directly into the artery. They typically use their fingers to palpate the artery and guide the needle. Once the needle enters the artery, blood will spontaneously flow into the collection syringe due to the artery’s higher pressure.
After collecting the required blood volume, the needle is quickly removed, and firm, direct pressure is applied to the puncture site for several minutes to prevent bleeding and hematoma formation. This pressure is maintained for a longer duration than after a venipuncture due to the higher arterial pressure. The procedure requires specialized training and a sterile technique to minimize complications.
What to Expect and Potential Outcomes
During an arterial puncture, individuals typically experience a sharp prick as the needle enters the skin, followed by a sensation of pressure or discomfort as it enters the artery. The sensation is usually brief, lasting only as long as the needle is in the artery.
Following the procedure, it is common to experience mild, localized effects at the puncture site. Bruising, soreness, or tenderness are frequent and generally resolve on their own over several days or weeks. Applying a cold pack and resting the affected limb can help manage these mild symptoms.
While arterial punctures are generally safe, seek medical attention if you notice excessive or persistent bleeding, swelling that increases in size, or signs of infection such as warmth, redness, or pus. Numbness, tingling, severe or worsening pain, or a cold or pale appearance of the limb distal to the puncture site are also signs that warrant immediate medical evaluation. These symptoms could indicate a more significant issue, such as nerve irritation, a large hematoma, or compromised blood flow.