What happens when a tourniquet is left on too long during venepuncture?

Leaving a tourniquet on for too long during venepuncture can cause several complications:

1. Hemoconcentration: When the tourniquet is applied, it restricts the venous return to the heart, causing the blood to pool in the veins distal to the tourniquet. This leads to an increased concentration of red blood cells (hemoconcentration) in the blood sample. Hemoconcentration can affect the accuracy of laboratory test results, particularly those that measure the concentration of substances in the blood.

2. Hemolysis: Prolonged tourniquet application can cause damage to the red blood cells (hemolysis). Hemolysis occurs when the red blood cells rupture, releasing hemoglobin into the plasma. This can interfere with certain laboratory tests, such as blood counts and coagulation studies.

3. Tissue damage: Leaving the tourniquet on for an extended period can compress the surrounding tissues, leading to discomfort, pain, and potential tissue damage. Prolonged compression can cause nerve damage and skin breakdown.

4. Extravasation: When the tourniquet is released, the sudden rush of blood back into the veins can cause the blood to leak out of the vein into the surrounding tissues (extravasation). This can result in bruising and pain at the venipuncture site.

5. Venous thrombosis: In rare cases, prolonged tourniquet application can increase the risk of venous thrombosis, which is a blood clot that forms in a vein. This complication is more likely in individuals with underlying risk factors for thrombosis.

It's important for healthcare professionals to follow proper venipuncture procedures, including using a tourniquet only for a brief period to minimize the risk of these complications. The tourniquet should be removed as soon as the blood sample is collected, and the patient should be observed for any adverse reactions.