Nephron-Sparing Surgery (NSS) is a revolutionary advancement in renal surgery. It has been more than a century since Czerny performed the first partial nephrectomy for renal tumors in 1890, and was largely discarded by clinicians due to the high complications and mortality of the procedure. With the improvement of medical imaging technology, the improvement of surgical concept and technical level, the new understanding of biological characteristics of kidney cancer and the increase of early detection cases, the clinical application of NSS has gradually increased, and now it has been recognized by domestic and foreign colleagues that NSS can obtain the same efficacy as radical nephrectomy within its surgical indications and can significantly improve the quality of life of patients. Whether open NSS or laparoscopic NSS, there are some surgical concepts and ideas that are important for us to accomplish NSS. However, we can only obtain some common knowledge of NSS surgery from urological surgery or NSS-related papers, and it is difficult to find complete reference materials for complex NSS surgery with high difficulty at special sites. The authors propose ideas to deal with the problems commonly encountered in clinical practice in terms of renal anatomy, pathology, clinical diagnosis and surgical techniques, in order to improve the level of NSS surgery. Huang Yiran, Department of Urology, Shanghai Renji Hospital First of all, how do we understand the concept of NSS, which is the preservation of renal units to maintain the function of the kidney on the basis of renal tumor resection. There are two meanings here: what kind of tumor can be done NSS and how to preserve kidney function. In principle, kidney cancer with T1a (≤4cm) is suitable for NSS, and it has also been proposed that T1b (≤7cm) can also achieve the purpose of removing tumor and preserving kidney function. For patients with renal cancer of the sole kidney, renal cancer of bilateral kidneys, renal cancer of one kidney with renal insufficiency of the contralateral kidney, tumors >7cm but located at both poles of the kidney can also be considered for NSS surgery. In clinical preservation of renal function there are three situations: firstly, enough kidney tissue can be preserved to maintain normal renal function; secondly, a certain amount of kidney tissue can be preserved, and although renal insufficiency is present, long-term hemodialysis is not required; finally, for patients who already have renal insufficiency, preserving the remaining kidney tissue can maintain a certain amount of urine and facilitate the management of hemodialysis, such as reducing the amount of dehydration per hemodialysis and extending the hemodialysis gap time. Therefore, for patients with renal tumors with renal insufficiency, NSS surgery is also valuable to improve patients’ quality of life. Preservation of renal function should be considered not only for short-term postoperative renal function, but also for long-term renal function maintenance. Patients with kidney cancer with potentially damaging renal function diseases, such as healthy kidney combined with renal stone, chronic pyelonephritis, renal artery stenosis, ureteral reflux; systemic diseases, such as diabetes mellitus, nephrosclerosis, etc., try to do NSS surgery. NSS surgical methods mainly include: simple renal tumor enucleation, nephroureterectomy, nephron wedge resection, renal transection, which are commonly used clinically. We know from renal anatomy that superficial renal tumor and bipolar renal tumor NSS surgery is simpler, but the suprarenal pole tumor should avoid damaging the posterior branch of renal artery when performing suprarenal pole resection, because this vessel is closer to the funnel of suprarenal calyces, and the posterior branch of renal artery is responsible for 50% of renal parenchymal blood supply in some patients. Intraoperatively, the posterior branch of the renal artery should be carefully dissected through the renal sinus and ligated to avoid injury to the main trunk. When superficial renal tumors in the middle of the kidney are deeded for resection, attention should be paid to the collecting system, because about 2/3 of patients do not have middle calyces of the renal pelvis, and the collecting system in the middle of the kidney drains to the upper or lower calyces, so the surgery is prone to damage the upper or lower calyces and cause corresponding kidney tissue damage. There are special features on wedge resection of renal sinus tumor, firstly, whether the fatty tissue of renal sinus is infiltrated in the general view, and intraoperative pathological examination should be made if necessary. Tumor infiltration of renal sinus tissue has poor prognosis and loses the value of preserving renal unit surgery. When resecting the dorsal tumor of renal sinus, the base of the tumor should be separated in the plane of the avascular zone between the renal pelvis and the adipose tissue of the renal sinus, for one, it can find out whether the tumor is in the renal sinus, and for another, it can avoid damaging the renal pelvis when the tumor is fit. It is difficult to do NSS for tumors on the ventral side of the renal sinus, which has abundant venous branches and no clear anatomical level. The latter can prevent the inferior vena cava from backflowing into the renal vein, reduce bleeding, and ensure a clear surgical view. The renal sinus should be meticulously separated and ligated to cut off the venous branches to avoid damaging the main branches of the renal vein, while paying attention to tumor renal sinus infiltration or venous microscopic cancer emboli. For tumors located deep in the kidney with no pathological markings on the kidney surface, careful study of imaging data is required to determine the relationship between the tumor and blood vessels and collecting system, and intraoperative ultrasound localization to decide the surgical incision on the kidney surface. The incision is chosen parallel to the renal artery and incised from the dorsal side as far as possible. Renal tumor enucleation is simple to perform, and can better protect the residual kidney function and reduce bleeding. It is generally considered that renal tumor enucleation is used to treat patients with absolute indications such as hereditary renal cancer, or isolated renal kidney cancer, and is not used in patients with elective indications. The main reason is to worry about incomplete tumor resection and positive cutting edge. In recent years a research group from Florence, Italy published a study on renal tumor enucleation for patients with elective RCC in Eur-Urol, J-Urol, and concluded that this procedure can achieve the same treatment results as standard NSS. Whether this surgical approach can be replicated is to be verified in other medical centers. The route of surgery is generally chosen from a transumbilical incision, which is clearly visible and simple to perform for most renal tumors. For larger tumors located ventral to the renal sinus, the authors believe that a transabdominal approach is preferable. This is because the transabdominal approach is easier to reveal the renal vessels, especially the renal veins, and it is simpler to deal with the renal veins and branches within the sinus ventrally than the transumbilical approach. For NSS with renal tumor with a history of renal surgery, it is a very difficult surgery. The principle of choosing the incisional route is firstly to control the renal vessels and secondly to reveal the tumor easily. In addition to complete vascular blockage, it is very important to reveal the tumor site, effective use of surgical instruments and cooperation of assistants. Laparoscopic techniques are generally not advocated for difficult NSS surgery. Except for a few laparoscopic surgeons with particularly good surgical skills, laparoscopy is difficult to obtain the results of open surgery. Kidney cancer biologically becomes expansive growth with a pseudo-envelope outside the tumor, which is the basis of feasible NSS. How to remove the tumor outside the pseudo-envelope completely without leaving small satellite foci is the key to prevent local recurrence of the tumor. the surgical procedure of NSS ensures clear surgical field and careful removal of the mass under direct vision, while cutting too deep to damage too much normal kidney tissue and renal great vessels and collecting system. If there is tumor infiltration in the surgical wound, radical nephrectomy with NSS should be abandoned. The tumor envelope of the excised specimen is incomplete, and tissue is taken from the corresponding renal trauma for rapid pathological examination to prevent tumor remnants. The surgeon should identify the tissue type of kidney from the gross specimen. A few types of tumors in kidney cancer such as collecting duct cancer with infiltrative growth, high malignancy and poor prognosis, these types of tumors are not suitable for NSS. The vessels located in the medulla and the junction of medulla and cortex of the kidney must be sutured, while the vessels in the cortex can be left untreated. The collecting system must be completely closed with sutures. After the renal trauma is sutured, ask the anesthesiologist to give the patient positive pressure breathing to increase the venous pressure and observe the renal vein bleeding; if the patient’s blood pressure is low, he should wait for the blood pressure to stabilize before finishing the procedure so as not to miss the small renal artery bleeding. Kidney tissue is brittle, and cutting the renal parenchyma during trauma suturing can cause trauma bleeding, which is sometimes difficult to distinguish from deep renal vessels without complete control of bleeding. The former can be stopped by hot saline gauze compression, while the latter requires chaparral to create a new hemostasis. Bleeding is a common complication of NSS surgery, and intraoperative bleeding control is the key to renal unit preservation surgery, as described in detail earlier. Postoperative bleeding includes both perioperative bleeding and secondary postoperative bleeding. The former occurs mostly on the day of surgery and can be traumatic bleeding or/and hematuria. Traumatic hemorrhage can occur during surgery when the small renal artery is not tied, or during surgery when blood pressure is low and the small renal artery is in spasm, and after surgery when blood pressure rises and the vessel opens. Bleeding resulting in retroperitoneal hematoma or severe hematuria manifests with postoperative drainage of more bloody fluid, unstable vital signs, and sometimes bleeding leaking into the retroperitoneal space with little drainage. Therefore, it is necessary to be absolutely bedridden after surgery, closely observe the vital signs, hematocrit and hematocrit, and if it is found that the trauma bleeds a lot and blood transfusion is needed to maintain the vital signs, emergency renal arteriogram can be made to find the branch of the bleeding renal artery and embolize to stop the bleeding. If the vital signs are unstable after blood and fluid transfusion, emergency exploration should be performed to block the renal artery and suture the active bleeding point. Postoperative secondary hemorrhage often occurs 3-5 days after surgery and may be due to obstruction or infection of the collecting system or dislodgement of the sutures ligating the renal vessels and pressure bandaging the renal trauma and open bleeding of the arteries in the closed trauma. A limited retroperitoneal hematoma with pain may be a sarcoid hematuria if it is connected to the collecting system. Postoperative bleeding can usually be controlled with conservative treatment, but if it is severe a renal arteriogram or surgical exploration is required. Urinary leakage is another important complication, and persistent drainage of large amounts of fluid after surgery, with a creatinine measurement of the drainage fluid or an intravenous iodobenzyme (indigo carmine) drainage fluid that is blue in color can be diagnostic of a urinary fistula. There are two conditions of urinary leakage, mainly the collection system is not sutured tightly or there is obstruction in the distal collection system; secondly, there is blood supply to the renal tissue remaining in the cut surface, which secretes urine and leakage occurs. The amount of urine drained in this case is not large. Clinically most urinary fistulas heal on their own and the course of the disease may be longer, sometimes requiring drainage for more than three months. If there is an obstruction of the collecting system, the ureter can be drained with a double “J” tube; if it is not possible to insert a double “J” tube, a percutaneous nephrostomy can be performed. If there is no drainage of urine, a urinary cyst is formed locally and a perinephric abscess is formed by secondary infection. If secondary infection occurs, clinical management is more difficult, and the kidney may even be removed. The main reason for postoperative acute renal failure may be that the major renal vessels were caught during the surgical procedure to stop bleeding, or the renal collecting system, or the renal heat ischemia for a long time, and the renal tubular ischemia and necrosis, or the residual renal parenchyma is too little to maintain normal renal function. If oliguria or anuria occurs after kidney unit preservation surgery, hemodialysis is performed immediately, and most patients can recover their kidney function after short-term hemodialysis. NSS will develop towards minimally invasive with the development of medical technology, but the anatomical concept of kidney, the pathological basis of kidney cancer and the principles of clinical management during and after surgery must be mastered so that NSS can be performed well.