When a tourniquet is left on too long, it can lead to hemoconcentration, which is a pooling of blood at the venipuncture site, according to MediaLab. A tourniquet is used to increase venous pressure so the phlebotomist or medical personnel can see and feel the patient's veins more easily.
Wrap a tourniquet, which is generally made out of a latex-type material, right above the elbow and just tight enough to prevent blood flow, notes MediaLab. This procedure allows for the medical personnel to see the patient's veins more easily and allows for easier access to take blood samples or create an IV port. However, never keep a tourniquet on a patient longer than one minute, maximum, without risk of hemoconcentration.
Hemoconcentration can cause a false increase in potassium levels, cholesterol levels and glucose levels for the patient; therefore, carefully time and monitor tourniquet use, explains MediaLab. If a tourniquet is used for vein selection, it is best to release the tourniquet once a vein is found. Then, gather the supplies needed to continue and reapply the tourniquet just before needle insertion. If drawing blood, release the tourniquet as the last sample is drawn, and remove the needle in a swift clean movement. Once the tourniquet is off, the medical assistant may ask the patient to make a fist to distend the arm veins further.