This study is a double blinded randomized controlled trial evaluating the impact of tranexamic acid use on the transfusion rate in patients with complex kidney stones undergoing percutaneous nephrolithotomy.

Introduction: Kidney stone is a high incidence and prevalent disease affecting people around the world. Nearly 1 in 11 individuals in the United States will be affected at some point in their lives. Furthermore, stones are likely to recur with at least 50% of individuals experiencing another stone within 10 years of the first occurrence. Moreover, the disease mainly affects the economically active segment of the population with special social and economic implications in health.

Approximately 85% of stones are composed predominantly by calcium compounds and about 7% are attributed to urinary tract infections, named struvite stones, that usually develop as jagged structures called "staghorns" and can grow to be quite large, therefore becoming complex kidney stone. However, in HCFMUSP, as a Brazilian national reference center in urolithiasis treatment, this complex stones represents about 30 percent of all renal lithiasis treated.

This complex stones require individualized and specialized treatment, with percutaneous nephrolithotomy (PCNL) as the standard of care, with advantages of higher stone clearance and cost-effectiveness when compared with other treatment alternatives.

However, PCNL is associated with significant morbidity such as fever, urinary infections, septicemia and bleeding that may require blood transfusion. Of these complications bleeding is the most unpredictable and dreaded, and can lead to significant morbidity, beyond the potential risks of blood transfusions by itself.

In this way antifibrinolytic drugs, such as tranexamic acid, have been shown to reduce blood loss in a variety of surgical procedures, blood transfusion rate, morbidity and mortality related to bleeding.

Objectives: The main outcome measure of our study is to evaluate the impact of tranexamic acid use in blood transfusion rate in patients with complex kidney stones undergoing PCNL (number of patients receiving blood transfusions from surgery until hospital discharge). The secondary outcome is to evaluate blood loss by hemoglobin measure, surgical time, stone free rate and complications. Furthermore, we want to corroborate the drug safety, previously established in the medical literature.

Methods: After protocol approval by the hospital ethics committee, patients undergoing PCNL for complex renal stone (GUYS classification III and IV) and who provided written informed consent, will be eligible for the trial. After the patients' eligibility is confirmed, we will randomly allocate them to the intervention or placebo group by a computer program. Trial participants, care providers, surgeons, the anesthesiology team and data collectors will be blinded to group assignments. Patients will be managed with surgical standardized technique by Endourological HCFMUSP group and controlled care after surgery. Blood transfusion rate, hemoglobin drop and complications will be evaluated at 7, 30, 90 and 180 days after surgery. On postoperative day one, CT scan will be performed to assess stone free rate and complications.

Inclusion Criteria:

• Complex kidney stone (staghorn calculi GUYS III and IV)

Exclusion Criteria:

• Coronary artery disease - stent
• Severe chronic renal failure
• Congenital or acquired thrombophilia/thrombosis event
• Known or suspected allergy