Laparoscopic and minimally-invasive robotic access has transformed the delivery of urological surgery. While associated with numerous desirable outcomes including shorter post-operative stay and faster return to preoperative function, these techniques have also been associated with morbidity such as reduced renal blood flow and post-operative renal dysfunction. The mechanisms leading to these renal effects complex are multifactorial, and have not been fully elucidated. However they are likely to include direct effects from raised intra-abdominal pressure, and indirect effects secondary to carbon dioxide absorption, neuroendocrine factors and tissue damage from oxidative stress. It is well documented that pneumoperitoneum places profound stress on the cardiovascular, respiratory and gastrointestinal systems; it also places strain on the renal system.

During robotic surgery, continuous pneumoperitoneum and continuous rising of intra-abdominal pressure causes transient oliguria. Moreover, kidney function, estimated by the GFR, deteriorates during elevated intra abdominal pressure (IAP), and most of the studies identified decrease in renal blood flow (RBF) and renal cortical perfusion.

Studies conducted to assess the contribution of the nitric oxide (NO) system to the renal hemodynamic/function alterations during pneumoperitoneum, concluded that these adverse effects are probably related to interference with the NO system, and could be partially ameliorated by pretreatment with nitroglycerine.

Mannitol is an osmotic diuretic and a renal vasodilator that promotes tubular flow, prevents intratubular cast formation, decreases postischemic cellular swelling, and might serve as a free radical scavenger. Mannitol has traditionally been administered before renal surgeries to minimize perioperative renal dysfunction according to preclinical animal studies and clinical experience with renal transplantation. However, high-level clinical data in support of this belief are not available.

The aim of this study is to characterize the effects of increased intra-abdominal pressure on renal perfusion and function in cases undergoing robotic lower tract urologic surgeries, and to assess the contribution of either mannitol or nitroglycerin infusion to the renal hemodynamic/function alterations during pneumoperitoneum.

Inclusion Criteria:

• ASA class I - III
• Normal renal functions or Mild renal disease (GFR < 60 ml/min &/or presence of albuminuria > 30 mg/dl)

Exclusion Criteria:

• BMI > 40
• Previous renal surgery
• Moderate (GFR 30 - 59 mg/dl) & severe (GFR 15 - 29 mg/dl) renal impairment
• Decompensated cardiac disease: New York Heart Association (NYHA) class 3 or 4
• Allergy to mannitol or nitroglycerin