Tranexamic acid decreases external blood loss but not hidden blood loss in total knee replacement

Background. Total knee arthroplasty (TKA) is often carried outusing a tourniquet and shed blood is collected in drains. Tranexamicacid decreases the external blood loss. Some blood loss maybe concealed, and the overall effect of tranexamic acid on thehaemoglobin (Hb) balance is not known. Methods. Patients with osteoarthrosis had unilateral cementedTKA using spinal anaesthesia. In a double-blind fashion, theyreceived either placebo (n=24) or tranexamic acid 10 mg kg^–1(n=27) i.v. just before tourniquet release and 3 h later. Thedecrease in circulating Hb on the fifth day after surgery, aftercorrection for Hb transfused, was used to calculate the lossof Hb in grams. This value was then expressed as ml of bloodloss. Results. The groups had similar characteristics. The medianvolume of drainage fluid after placebo was 845 (interquartilerange 523–990) ml and after tranexamic acid was 385 (331–586)ml (P<0.001). Placebo patients received 2 (0–2) unitsand tranexamic acid patients 0 (0–0) units of packed redcells (P<0.001). The estimated blood loss was 1426 (1135–1977)ml and 1045 (792–1292) ml, respectively (P<0.001).The hidden loss of blood (calculated as loss minus drainagevolume) was 618 (330–1347) ml and 524 (330–9620)ml, respectively (P=0.41). Two patients in each group developeddeep vein thrombosis. Conclusions. Tranexamic acid decreased total blood loss by nearly30%, drainage volume by