Before the traditional subcutaneous injection, the air in the syringe needs to be discharged, but on the one hand, the amount of heparin sodium (authentic low molecular weight heparin) is less, after the injection, there is still some residual drug solution in the syringe, resulting in the drug quantity is insufficient, unable to play a better anticoagulation effect; On the other hand, the liquid discharged from the needle, once injected, will accidentally injure the epidermal capillaries, resulting in the formation of ecchymosis.

　　With the progress of science and technology, most of the heparin sodium (authentic low-molecular weight heparin) injected subcutaneously now USES pre-pot injection, leaving 0.1ml of air in the syringe. Do not exhaust before injection, can be down the needle, the air to the top, gently push injection, after the injection of a small amount of air will be with the push injection will remain in the needle in the handle of all the liquid into the skin, so that all injection, to ensure the accurate dose.