**2.3.1 Renal function deterioration after NSS vs. RN**

Acute reduction in functional renal mass leads the remnant glomeruli to maintain the renal function by several mechanisms: adaptive glomerular hypertrophy, hyperperfusion, hypertension and hyperfiltration. These phenomena result in proteinuria.

NSS aims to achieve two goals: a complete excision of the tumour but at the same time guarantee an optimal preservation of renal function. With less excision of healthy renal tissue with NSS, we can expect less glomerulosclerosis and renal failure (Van Poppel et al., 2003). Therefore, NSS seems to be the best way to prevent Chronic Kidney Disease (CKD).

In one of our studies on OPN for T1b renal tumours (Joniau et al., 2009), 10% of patients developed de novo renal insufficiency. Six of those seven patients had imperative indication. Serum creatinin levels dropped significantly in imperative indication, while this was not seen in elective and relative indications.

In our last study of 98 open partial nephrectomies for T1b, estimated Glomerular Filtration Rate (eGFR) deteriorated postoperatively on average by 1.74 ml/min/1.73m².

10.2% of patients developed CKD post-operatively, but 20.4% patients had an improved CKD stage after surgery.

In his study, Roos (Roos & Brenner, 2010) also observed a significant difference in eGFR at last follow up and in e GFR difference (calculated as e GFR preoperative – eGFR at last follow up). After NSS, 14.5% of patients (10) had reached an eGRF < 60ml/min/1.73m² versus 44.7% (42) after RN.

In a retrospective study (Lane et al., 2010) Lane studied 2402 patients with a normal preoperative kidney function (serum creatinin less or equal to 1.4 mg/dl) and compared: 1833 PN versus 569 RN. Tumour stage was pT1b or more in 31% of PN and 64% of RN. NSS even - with a warm ischemia time of longer than 31 minutes - demonstrated better renal outcomes, however patients in the RN group were older, had more co-morbidities and were affected by larger and more aggressive tumours.

A solitary kidney is not a contra-indication for NSS. Lee (Lee 2010) reports 38 patients with solitary kidney who underwent partial nephrectomy: 53. 1% of them had a tumour larger than 4 cm and 76.3 % had post operatively a GFR more than 30 ml/min/1.73m². He noticed an acceptable complication rate: 7.9% Clavien I, 18.4% for Clavien II and 5.3% Clavien III. One patient required immediate post-operative haemodialysis and another one long term haemodialysis for a mean follow up of 20 months.

Partial nephrectomy offers minimal reduction of renal function, but on the other hand unfortunately exposes the patient to higher peri-operative risk.

#### **2.3.2 Surgical aspects influencing renal function preservation**

For small tumours, clamping the renal artery is sometimes not necessary. Resection without clamping can provide adequate oncologic surgery with a lower peri-operative complication rate and limited renal function deterioration. In the case of larger renal tumours, surgery requires in most cases an interruption of renal blood flow through pedicle clamping. Clamping is necessary to resect the tumour in a bloodless field, to minimise intra-operative blood loss, to contribute to a better vision during dissection and to facilitate renorraphy. Ischemia induces endothelial lesions which lead via multi-inflammatory response to vasoconstriction and vasospasms and thus ischemia. The low renal blood flow induces renal cell lesions and subsequent release of angiotensin II and eicosanoids. During ischemia, there is a failure of oxidative phosphorylation and depletion in adenosine triphosphate (ATP). It causes cellular swelling by passive diffusion of water into cells. Cell swelling prevents reperfusion when unclamping (no reflow phenomenon) and ATP degradation produces free radicals which cause further cell damage (reperfusion injury).
