Venipuncture, commonly known as a blood draw, is a routine medical procedure involving the puncture of a vein to collect a blood sample. A frequent complication is the formation of a hematoma, which is a localized collection of blood outside the blood vessels. This pooling of blood under the skin results in the familiar bruise that occurs when blood leaks from the puncture site into surrounding tissues. Understanding the factors that lead to this leakage and implementing preventative measures minimizes the risk of this common complication.
Identifying Key Contributing Factors
Hematoma formation is caused by either mechanical issues during the procedure or underlying physiological factors in the patient. Mechanically, a hematoma occurs if the needle passes completely through the vein, allowing blood to escape into the tissue. Positioning the needle so the bevel is only partially inside the vein can also cause blood to leak into the subcutaneous tissue.
Physiological elements increase a person’s susceptibility to bruising. Patients taking anticoagulant or antiplatelet drugs have a reduced ability to form a clot quickly, delaying the sealing of the vein puncture. The elderly often possess fragile or sclerosed veins that are more prone to damage and subsequent blood leakage.
Technique Adjustments During Blood Draw
Proper technique begins with careful site selection and equipment preparation. Choosing a vein that is palpable and well-anchored, typically in the median cubital area, reduces the likelihood of the vein “rolling” or being perforated. The needle gauge should be appropriately sized for the target vein; using a needle that is too large can cause trauma to the vessel wall.
Firmly anchoring the vein from below the puncture site is necessary to secure the vessel and prevent movement during insertion. This stabilization helps ensure the needle enters and remains within the vein’s lumen without passing entirely through the back wall. The insertion angle should be shallow, generally between 15 and 30 degrees, sufficient to penetrate only the uppermost wall of the vein. Moving the needle while it is seated in the vein, such as during tube changes, can lacerate the vein wall and must be avoided.
A key sequence adjustment is releasing the tourniquet before the needle is withdrawn. Keeping the tourniquet in place maintains pressure within the vein, and removing the needle while the vein is engorged increases the force of blood leaking out. By removing the tourniquet first, the internal venous pressure is reduced, minimizing the initial leakage. The needle should be removed swiftly and gently to prevent further trauma.
Critical Steps Immediately Following Needle Removal
The most immediate and effective preventative action after the needle is removed is the application of firm, direct pressure to the puncture site. This pressure must be applied instantly and directed over the wound in the vein wall, not merely on the skin surface. The patient should be instructed to hold this pressure without rubbing or checking the site, as disturbing the forming platelet plug can restart the bleeding.
Sustained pressure is required to allow for primary hemostasis, the formation of a stable platelet plug over the puncture site. For individuals with normal clotting function, this pressure should be held for a minimum of two to three minutes. Patients on anticoagulants or with known bleeding disorders require a longer duration, often three to five minutes or more, to ensure the vein is properly sealed.
The positioning of the arm following the draw also plays a role in prevention; the arm should be kept straight or slightly elevated above the heart. Bending the arm at the elbow is counterproductive, as flexion causes the skin and muscle to pull away from the vein puncture site, allowing blood to pool. Patients should also avoid heavy lifting or strenuous exercise for several hours after the procedure to prevent reopening the newly formed clot.