The concentration of lactic acid in blood can reflect the anaerobic metabolism of the body, and it is an important index to diagnose the effect of high lactic acid, lactic acidosis and observation of related drugs. If strict requirements, should draw arterial blood to measure, but the real face confirms that the blood lactic acid concentration between arterial blood and venous blood does not have significant difference. It has been proved that the blood concentration of blood lactic acid will not be affected by the bleeding of the tourniquet within 9Os. However, the blood lactic acid concentration increased obviously after the tourniquet was taken more than 120s. This is because the tightness of the tourniquet is good for the arterial movement, venous filling is obviously the degree, only blocked the venous reflux, but does not affect the arterial pulsation, the distal partial supply blood still maintains unobstructed, the short time venous pressure gradually rises away, the arterial average pressure level, the blood flow perfusion still maintains the high level, the organization does not appear the obvious hypoxia. Therefore, as long as the ligation of tourniquet is appropriate, after the tourniquet is the key to complete the blood extraction as soon as possible. According to the clinical face, after tourniquet, smooth blood pumping operation can be completed within 90s. Therefore, for the elderly, obesity, serious illness, dehydration, poor blood vessel conditions, low blood easily shock, and other patients, because of the difficulty of pumping blood, the high rate of low, blood lactic acid concentration detection can be tied tourniquet blood, in order to reduce the pain of patients, reduce the difficulty of operation.