A tourniquet is a flexible band used in venipuncture—the process of drawing blood—to temporarily modify blood flow in a patient’s limb. The device is wrapped around the arm to constrict the veins, making them visibly larger and easier to locate and access with a needle. Proper application and timely removal are important for ensuring accurate blood test results and patient safety.
Why Tourniquets are Necessary and Proper Placement
The underlying physiological reason for using a tourniquet is to achieve venous pooling, which is a temporary stagnation of venous blood flow. The tourniquet is applied with enough pressure to impede the return of deoxygenated blood through the veins, while simultaneously allowing arterial blood flow into the limb to continue. This imbalance causes the veins below the application site to engorge, or distend, which makes them more prominent and easier to enter.
Proper placement is critical to maximize this effect and avoid complications like nerve damage. The tourniquet should be positioned approximately three to four inches above the intended venipuncture site, such as the antecubital fossa, which is the inner elbow area. Placing the band too close to the site can interfere with the angle of needle insertion, while placing it too far away may not create sufficient venous distention. The band must lay flat against the skin and should never be placed over open wounds, bruises, or compromised skin.
The tension must be adequate to restrict venous return but not so tight that it stops the arterial pulse. Confirming a palpable pulse below the tourniquet ensures that blood is still flowing into the arm and that the constriction is not causing undue pressure or discomfort.
The Step-by-Step Application Technique
The physical application of the tourniquet must be performed using a method that allows for a rapid, single-handed release. Standard phlebotomy tourniquets are often elastic bands or specialized buckle-type cuffs.
To create a quick-release loop with an elastic band, the tourniquet is placed under the arm, pulled taut, and the two ends are crossed over the top to form an ‘X’ shape. One end is then looped under the crossed section and pulled through, creating a small tab that can be grasped for quick release. This securing method ensures that the band remains stable while the phlebotomist prepares the site and needle.
The tension should be checked by palpation, ensuring the veins are firm and prominent but that the radial pulse remains easily detectable. If the veins do not distend adequately, the patient may be asked to make a gentle fist, which temporarily increases venous pressure. Modern tourniquets often use a buckle or clip mechanism, which is applied by simply clipping the ends together and pressing a button for release. Regardless of the type, the tourniquet should not twist or pinch the skin, and any excess material should be directed away from the intended puncture area.
Safe Duration and Removal Procedures
Limiting the time a tourniquet remains on the arm is a safety measure to prevent complications and inaccurate lab results. Standard guidelines recommend that the tourniquet should not remain applied for longer than 60 seconds. Leaving the band on for an extended period can lead to hemoconcentration, where the concentration of blood components—like proteins and certain analytes—increases due to fluid leaking into the surrounding tissue.
Prolonged application can also cause pain, nerve compression, and the formation of petechiae, which are small red or purple spots caused by ruptured capillaries. To minimize these risks, the tourniquet should be released as soon as blood flow is established in the collection tubes. If the phlebotomist needs more time to locate a vein, the tourniquet must be removed after 60 seconds and reapplied only after the arm’s circulation has normalized.
The final step is the proper removal of the tourniquet, which must occur before the needle is withdrawn from the vein. This timing prevents a hematoma, or bruise, from forming as the pressure is released and blood rushes back into the vessel. The quick-release mechanism allows for a swift, single-handed action to release the tension while the other hand stabilizes the needle.