**3. Intraoperative tourniquet use**

#### **3.1. Blood loss**

Whether or not a tourniquet can reduce blood loss in total knee arthroplasty is still being debated in the literature. Although intraoperative blood loss was significantly less in the tourniquet group in the present study, there is often a substantial hidden or unmeasured blood loss in TKA. Some authors claimed that a tourniquet is effective for reducing blood loss [1, 2, 23], but others did not agree. Numerous studies reported no significant difference in the amount of blood loss with or without tourniquet use [24, 25], and others even suggested that the use of tourniquet induces more blood loss [26, 27].

There are some parameters commonly used to evaluate the blood loss of the surgery. Directly measured items include *the intraoperative blood loss* and *the transfusion rate. Measurable total blood loss*, the summation of intra- and postoperative blood loss, is determined by the increasing weight of soaked gauze added the amount of postoperative drainage. *Calculated total blood loss*, which is always regarded as true total blood loss, was measured by Hb and Hct levels before and after surgery.

In the research model of meta-analysis, some authors suggested that the use of tourniquet did not affect total blood loss [3, 5, 8, 28], which was opposed by Alcelik et al. [29]. However, Alcelik et al. [29] estimated total blood loss simply based on the measurable blood loss while overlooking the hidden blood loss. Thus, the evidence available indicates that tourniquet indeed significantly reduce the intraoperative blood loss rather than the total blood loss.
